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Objectives: Chlamydia trachomatis (chlamydia) is one of the most reported bacterial sexually transmitted infections (STI) worldwide. Chlamydia can cause long term complications such as pelvic inflammatory disease (PID), ectopic pregnancy (EP) and tubal factor infertility (TFI). Changing testing strategies, for example reduced asymptomatic testing, influence chlamydia surveillance, highlighting the need for exploring alternative ways of monitoring chlamydia. We investigated the possibility of introducing routine surveillance of chlamydia related long term complications., Methods: A qualitative study including 15 in-depth interviews with a purposive sample of gynaecologists, general practitioners (GP), sexual health and emergency doctors was conducted in the Netherlands in 2021-2022. A semi-structured interview guide focused on experiences with diagnosis and registration of PID, EP and TFI and how a change in asymptomatic chlamydia testing strategy might influence this. Interviews were transcribed and analysed using a thematic approach., Results: Analysis showed that gynaecologists most frequently reported diagnosing PID, EP and TFI. Other professions rarely diagnose these complications, with emergency doctors only diagnosing EP. Most respondents reported unique registration codes for PID and EP, but the coding for TFI is more ambiguous. They reflected that diagnosis and registration of PID, EP and TFI are handled differently within their professions. Most respondents acknowledged registration in diagnostic codes as a useful surveillance tool. They expressed concerns in representativeness (e.g. differences in interpretation of diagnosis criteria) and data quality for surveillance., Conclusions: Patient files of gynaecologists are likely to be most complete for monitoring trends of diagnosed chlamydia related long term complications in the Netherlands. However, when establishing a chlamydia complication surveillance system, professionals should be engaged in further standardizing diagnosis and registration practices. This will improve the quality and interpretability of complication surveillance and facilitate comparison between countries., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Boogert et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: Control of Neisseria gonorrhoeae infection (gonorrhoea) depends on effective testing strategies. Anorectal testing in women is often done on indication of anal sex; however, anorectal infections are seen with and without anal exposure, possibly caused by autoinoculation. This study aims to enhance understanding of anorectal infections in women, by identifying risk factors for anorectal diagnosis., Methods: In this retrospective cohort study we used national surveillance data from Dutch sexual health centres from Jan 1, 2016, to Dec 31, 2021. We included cisgender women having sex with men who were tested urogenitally and anorectally for gonorrhoea. Due to different testing policies, we identified three groups: women who had not reported recent anal sex (in the past 6 months), women who had reported recent anal sex, and sex workers. Extracted data for analyses included demographics, sexual behaviour, and diagnosis of a sexually transmitted infection (STI). Per group, multivariable models using Firth's penalised maximum likelihood logistic regression were constructed, identifying determinants of anorectal gonorrhoea among all women and among gonorrhoea-positive women only. Variables included in model construction were age, education level, migration background, number of partners, condom use, partner notification, STI symptoms, having a partner who has sex with men (MSM) or a migrant partner, previous STI test, anal sex, and chlamydia and gonorrhoea diagnoses per anatomical location., Findings: In total, 117 693 women were included: 43 757 women without reported recent anal sex, 51 728 women with reported recent anal sex, and 22 208 sex workers. In all three groups, around 2% of women were gonorrhoea positive, and 70% or more of women had an anorectal infection. The strongest determinant of anorectal gonorrhoea was a concurrent urogenital gonorrhoea diagnosis (adjusted odds ratios [aOR] 782 [95% CI 605-1018]) among women without reported recent anal sex (612 [490-768] among women with reported recent anal sex, and 464 [335-652] among sex workers). Among gonorrhoea-positive women, determinants of anorectal gonorrhoea were urogenital and anorectal chlamydia co-infection (aOR 2·03 [95% CI 1·38-3·02], for women without reported anal sex) and migration background (1·44 [1·02-2·06], for women with reported anal sex). Determinants among sex workers were condomless sex (2·43 [1·55-3·82]), anal sex (1·71 [1·10-2·66]), MSM or migrant partner (1·78 [1·13-2·79]), and urogenital and anorectal chlamydia co-infection (2·28 [1·11-5·14])., Interpretation: These findings support the possibility of an autoinoculation process from the urogenital to the anorectal location due to the very strong correlation between urogenital and anorectal gonorrhoea, and due to the similarity of results across all three groups. Current testing strategies could miss anorectal infections, which should be considered when developing gonorrhoea prevention and control guidelines., Funding: None., Competing Interests: Declaration of interests We declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Objectives: To report sex and age-specific Chlamydia trachomatis (Ct) seroprevalence estimates in the general population of the Netherlands between 1996 and 2017 and identify risk factors associated with Ct seropositivity., Methods: Participants (n=5158, aged 15-59 years) were included from three independent nationwide population-based serosurveillance studies in 1996, 2007 and 2017. Participants completed a questionnaire on demographics and sexual behaviour. Serum antibodies were analysed using Medac Ct IgG ELISA test. Census weights were assigned to achieve seroprevalence estimates representative of the general Dutch population. Weighted seroprevalence estimates were stratified by gender, age and birth cohort. Trends and risk factors in men and women were identified using multivariable logistic regression., Results: Weighted overall Ct seroprevalence was 10.5% (95% CI: 9.2% to 12.0%) in women and 5.8% (95% CI: 4.7% to 7.0%) in men. Among women <25 years, there was a non-significant increase in seroprevalence from 5.9% (95% CI 3.7% to 9.2%) in 1996, to 7.6% (95% CI 5.1% to 11.1%) in 2007 and 8.8% (95% CI 5.5% to 13.9%) in 2017. Among women ≥25 years, the seroprevalence significantly decreased from 15.6% (95% CI: 12.2% to 19.7%) in 1996 to 9.5% (95% CI: 7.2% to 12.4%) in 2007 but did not further drop (11.2% (95% CI 8.1% to 15.3%) in 2017). In men, we did not observe trends between study rounds. In both men and women, having a non-Western migration background was a risk factor for seropositivity. In women, having had a prior sexually transmitted infection and ≥2 recent sex partners were risk factors for seropositivity as well., Conclusions: We have not found evidence for a decrease in population seroprevalence in those under 25 years old despite decades of intensified testing-and-treatment efforts in the Netherlands. This suggests further monitoring of Ct burden in the general population is needed. If serum banks are used for this, specifically individuals <25 years old and with diverse migration backgrounds should be included., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Pharyngeal Chlamydia trachomatis (CT) was diagnosed in 1.2% and pharyngeal-only CT in 0.5% of routinely universally tested men who have sex with men (MSM). In these 3-anatomic-site tested MSM, pharyngeal-only CT comprised 4.8% of all CT. The low positivity of pharyngeal-only CT indicates low public health impact of pharyngeal CT., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America.)

Background: Pharyngeal Chlamydia trachomatis in women might contribute to autoinoculation and transmission to sexual partners. Data for effectiveness of different testing practices for pharyngeal C trachomatis are scarce. We therefore aimed to assess the prevalence of pharyngeal C trachomatis, determinants, and effectiveness of different testing practices in women., Methods: We did a retrospective cohort study, in which surveillance data for all women visiting sexually transmitted infection clinics in all regions in the Netherlands between Jan 1, 2008, and Dec 31, 2017, were used. We collected consultation-level data and individual-level data from 2016 onwards for sociodemographic characteristics, sexual behaviour in the past 6 months, self-reported symptoms, and STI diagnoses. The primary outcome was the positivity rate of pharyngeal C trachomatis infection compared between routine universal testing (>85% tested pharyngeally per clinic year), selective testing (5-85% tested pharyngeally per clinic year), and incidental testing (<5% pharyngeally tested per clinic year). We calculated the number of missed infections by extrapolating the positivity rate assessed by routine universal testing to all selectively tested women. We used multivariable generalised estimating equations logistic regression analyses to assess independent risk factors for pharyngeal C trachomatis and used the assessed risk factors as testing indicators for comparing alternative testing scenarios., Findings: Between Jan 1, 2008, and Dec 31, 2017, a total of 550 615 consultations with at least one C trachomatis test was recorded, of which 541 945 (98·4%) consultations (including repeat visits) were included in this analysis. Pharyngeal C trachomatis positivity was lower in the routine universal testing group than in the selective testing group (1081 [2·4%; 95% CI 2·2-2·5] of 45 774 vs 3473 [2·9%; 2·8-3·0] of 121 262; p<0·0001). The positivity rate was also higher among consultations done in the incidental testing group (44 [4·1%; 95% CI 3·1-5·5] of 1073; p<0·0001) than in the routine universal testing group. Based on extrapolation, selective testing would have hypothetically missed 64·4% (95% CI 63·5-65·3; 6363 of 9879) of the estimated total of C trachomatis infections. The proportion of pharyngeal-only C trachomatis was comparable between routinely universally tested women (22·9%) and selectively tested women (20·4%), resulting in a difference of 2·5% (95% CI -0·3 to 5·3; p=0·07). When using risk factors for pharyngeal C trachomatis as testing indicators, 15 484 (79·6%) of 19 459 women would be tested to detect 398 (80·6%) of 494 infections., Interpretation: No optimal testing scenario was available for pharyngeal C trachomatis, in which only a selection of high-risk women needs to be tested to find most pharyngeal C trachomatis infections. The relative low prevalence of pharyngeal-only C trachomatis (0·5%) and probably limited clinical and public health effect do not provide support for routine universal testing., Funding: Public Health Service South Limburg., Competing Interests: Declaration of interests We declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: During the COVID-19 pandemic, the disruption in care for sexually transmitted infections (STIs) and the social distancing measures have led to reductions in STI testing and sexual behavior. We assessed the impact of these COVID-19-related changes on transmission of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) among men who have sex with men (MSM) in The Netherlands., Methods: We developed a mathematical model for CT and NG transmission among MSM, accounting for COVID-19-related changes in sexual behavior and testing in 2020 to 2021. Changes in 2020 were estimated from data from the Dutch COVID-19, Sex, and Intimacy Survey among MSM and the National Database of STI Clinics. Because of the lack of data for 2021, we examined several scenarios covering a range of changes., Results: A reduction of 10% and 40% in STI testing of symptomatic and asymptomatic, respectively, individuals with a 10% to 20% reduction in numbers of casual partners (according to partner status and activity level) during the second lockdown, resulted in a 2.4% increase in CT prevalence, but a 2.8% decline in NG prevalence in 2021. A 5% and 30% reduction in STI testing of symptomatic and asymptomatic, respectively, individuals with the same reduction in casual partners resulted in a 0.6% increase in CT prevalence and a 4.9% decrease in NG prevalence in 2021., Conclusions: The disruption in STI care due to COVID-19 might have resulted in a small increase in CT prevalence, but a decrease in NG prevalence. Scaling up STI care is imperative to prevent increases in STI transmission., Competing Interests: Conflicts of Interest and Sources of Funding: None declared., (Copyright © 2021 American Sexually Transmitted Diseases Association. All rights reserved.)

Objectives: Pre-exposure prophylaxis (PrEP) users are routinely tested four times a year (3 monthly) for asymptomatic Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) infections on three anatomical locations. Given the high costs of this testing to the PrEP programme, we assessed the impact of 3 monthly screening(current practice), compared with 6 monthly on the disease burden. We quantified the difference in impact of these two testing frequencies on the prevalence of CT and NG among all men who have sex with men (MSM) who are at risk of an STI, and explored the cost-effectiveness of 3-monthly screening compared with a baseline scenario of 6-monthly screening., Methods: A dynamic infection model was developed to simulate the transmission of CT and NG among sexually active MSM (6500 MSM on PrEP and 29 531 MSM not on PrEP), and the impact of two different test frequencies over a 10-year period. The difference in number of averted infections was used to calculate incremental costs and quality-adjusted life-years (QALY) as well as an incremental cost-effectiveness ratio (ICER) from a societal perspective., Results: Compared with 6-monthly screening, 3-monthly screening of PrEP users for CT and NG cost an additional €46.8 million over a period of 10 years. Both screening frequencies would significantly reduce the prevalence of CT and NG, but 3-monthly screening would avert and extra ~18 250 CT and NG infections compared with 6-monthly screening, resulting in a gain of ~81 QALYs. The corresponding ICER was ~€430 000 per QALY gained, which exceeded the cost-effectiveness threshold of €20 000 per QALY., Conclusions: Three-monthly screening for CT and NG among MSM on PrEP is not cost-effective compared with 6-monthly screening. The ICER becomes more favourable when a smaller fraction of all MSM at risk for an STI are screened. Reducing the screening frequency could be considered when the PrEP programme is established and the prevalence of CT and NG decline., Competing Interests: Competing interests: EH obtained advisory board fees and a research grant from Gilead Sciences; both of which were paid to her institute., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Antenatal screening for HIV, syphilis and HBV has been successfully implemented in The Netherlands, but data on other STI among pregnant women or male partners are limited. Our objectives: (i) to assess the prevalence of Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG) and Trichomonas vaginalis (TV) among pregnant women and male partners, (ii) to identify risk factors for these STI during pregnancy, and (iii) to identify adverse perinatal outcomes (APO) associated with STI., Methods: Cross-sectional study. Pregnant women aged ≤ 30 years (n = 548) and male partners (n = 425) were included at 30 midwifery practices during 2012-2016. Participants provided a self-collected vaginal swab (women) or urine sample (men) and completed a questionnaire. Perinatal data were derived from pregnancy cards. APO was defined as premature rupture of membranes, preterm delivery, low birthweight, stillbirth, neonatal conjunctival and respiratory infections. Data were analysed by logistic regression., Results: STI were present in 2.4% of pregnant women (CT 1.8%, NG 0.4%, TV 0.4%), and in 2.2% of male partners (CT 2.2%, NG 0.2%, TV 0%). Of young women (≤ 20 years), 12.5% had a CT infection. Prevalent STI during pregnancy was associated with female young age (≤ 20 years vs ≥ 21 years) (adjusted OR 6.52, CI 95%: 1.11-38.33), male non-Western vs Western background (aOR 9.34, CI 2.34-37.21), and female with ≥ 2 sex partners < 12 months vs 0-1 (aOR 9.88, CI 2.08-46.91). APO was not associated with STI, but was associated with female low education (aOR 3.36, CI 1.12-10.09), complications with previous newborn (aOR 10.49, CI 3.21-34.25 vs no complications) and short duration (0-4 years) of relationship (aOR 2.75, CI 1.41-5.39 vs ≥ 5 years). Small-for-gestational-age was not associated with STI, but was associated with female low education (aOR 7.81, 2.01-30.27), female non-Western background (aOR 4.41, 1.74-11.17), and both parents smoking during pregnancy (aOR 2.94, 1.01-8.84 vs both non-smoking)., Conclusions: Prevalence of STI was low among pregnant women and male partners in midwifery practices, except for CT among young women. The study could not confirm previously observed associations between STI and APO, which is probably due to low prevalence of STI, small study sample, and presumed treatment for STI.

Objectives: Although ethnic minority clients (EMs) from STI endemic countries have a higher risk for STI, little is known about their STI clinic consultation rate proportionality. The aim of this study was to assess consultation and chlamydia positivity rates among different EMs visiting STI clinics in the Netherlands., Methods: We calculated consultation rates in EM groups by dividing the number of STI consultations by the total number of inhabitants in the region belonging to an EM, then compared the EM rates to native Dutch rates. Factors associated with chlamydia positivity were analysed using multivariate regression analysis., Results: A total of 23,841 clients visiting an eastern Netherlands STI clinic between 2011 and 2013 were included in the analysis, of which 7% were EMs. The consultation rate of native Dutch clients was 22.5 per 1000, compared to 8.5 per 1000 among EMs. Consultation rates in all EMs were lower than in Dutch clients, except for Antillean or Aruban EMs and Latin American EMs. The chlamydia positivity rate among all clients was 15.5%, and Antillean or Aruban ethnicity (27.1%) EMs had the highest rates. Multivariate analysis identified the following factors associated with chlamydia positivity: Eastern or Northern European EM, African EM, Antillean or Aruban EM, STI related symptoms, heterosexual preference, partner in a risk group, receiving a partner notification, and having had three or more partners in the past six months., Conclusion: On a population level, most EMs visit STI clinics less often than native Dutch clients, but they have a higher rate of positive chlamydia diagnoses. STI clinics should increase outreach activities for EM clients because they are insufficiently reached by current practices, but contribute substantially to chlamydia incidence rates., Competing Interests: The authors have declared that no competing interests exist.

Background: A Chlamydia trachomatis infection (chlamydia) can result in tubal factor infertility in women. To assess if this association results in fewer pregnant women, we aimed to assess pregnancy incidences and time to pregnancy among women with a previous chlamydia infection compared with women without one and who were participating in the Netherlands Chlamydia Cohort Study (NECCST)., Methods: The NECCST is a cohort of women of reproductive age tested for chlamydia in a chlamydia screening trial between 2008 and 2011 and reinvited for NECCST in 2015 to 2016. Chlamydia status (positive/negative) was defined using chlamydia screening trial-nucleic acid amplification test results, chlamydia immunoglobulin G presence in serum, or self-reported chlamydia infections. Data on pregnancies were collected via questionnaires in 2015-2016 and 2017-2018. Overall pregnancies (i.e., planned and unplanned) and time to pregnancy (among women with a pregnancy intention) were compared between chlamydia-positive and chlamydia-negative women using Cox regressions., Results: Of 5704 women enrolled, 1717 (30.1%; 95% confidence interval [CI], 28.9-31.3) women was chlamydia positive. Overall pregnancy proportions were similar in chlamydia-positive and chlamydia-negative women (49.0% [95% CI, 46.5-51.4] versus 50.5% [95% CI, 48.9-52.0]). Pregnancies per 1000 person-years were 53.2 (95% CI, 51.5-55.0) for chlamydia negatives and 83.0 (95% CI, 78.5-87.9) for chlamydia positives. Among women with a pregnancy intention, 12% of chlamydia-positive women had a time to pregnancy of >12 months compared with 8% of chlamydia negatives (P < 0.01)., Conclusions: Overall pregnancy rates were not lower in chlamydia-positive women compared with chlamydia-negative women, but among women with a pregnancy intention, time to pregnancy was longer and pregnancy rates were lower in chlamydia-positive women., Trial Registration Number: Dutch Trial Register NTR-5597.

Objectives: Spontaneous clearance of Chlamydia trachomatis (CT) infections can occur between diagnosis and treatment. We followed CT patients to assess clearance using a conventional definition (no total CT-DNA, assessed by routine quantitative PCR methods) and a definition accounting for viability, assessed by viability PCR testing., Methods: Three outpatient STI clinics included CT-diagnosed women (The Netherlands, 2016-2017, FemCure study); participants had vaginal CT (vCT) and rectal CT (rCT) (group A: n=155), vCT and were rectally untested (group B: n=351), single vCT (group C: n=25) or single rCT (group D: n=29). Follow-up (median interval 9 days) vaginal and rectal samples underwent quantitative PCR testing (detecting total CT-DNA). When PCR positive, samples underwent V-PCR testing to detect 'viable CT' (CT-DNA from intact CT organisms; V-PCR positive). 'Clearance' was the proportion PCR-negative patients and 'clearance of viable CT' was the proportion of patients testing PCR negative or PCR positive but V-PCR negative. We used multivariable logistic regression analyses to assess diagnosis group (A-D), age, days since initial CT test (diagnosis) and study site (STI clinic) in relation to clearance and clearance of viable CT., Results: Clearance and clearance of viable CT at both anatomic sites were for (A) 0.6% and 3.9%; (B) 5.4% and 9.4%; (C) 32.0% and 52.0% and (D) 27.6% and 41.4%, respectively. In multivariate analyses, women with single infections (groups C and D) had higher likelihood of clearance than women concurrently infected with vCT and rCT (p<0.001).Of rectally untested women (group B), 76.9% had total CT-DNA and 46.7% had viable CT (V-PCR positive) at the rectal site., Conclusions: Of untreated female vCT patients who had CT also at the rectal site, or who were rectally untested, only a small proportion cleared CT (in fact many had viable CT) at their follow-up visit (median 9 days). Among single site infected women clearance was much higher., Trial Registration Number: NCT02694497., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Repeat Chlamydia trachomatis (CT) infections are common. To better understand the characteristics of patients frequently infected with CT at our sexually transmitted infection (STI) care services, we assessed the differences between patients repeatedly infected with CT and those who repeatedly tested negative., Methods: In this cross-sectional analysis of cohort data, we assessed individuals tested for CT at different STI care providers between 2011 and mid-2018 in Southwest Limburg, the Netherlands (n = 17,616). Patients with ≥2 repeat CT infections in the study period were categorized as "patients with repeat CT infections." Multivariable logistic regression analyses were performed for the binary outcome measure: patients with repeat CT infections versus patients who repeatedly tested negative (reference group). Additional analyses were performed for only the STI clinic population., Results: Patients aged < 25 years (OR: 1.83; 95%CI:1.38-2.43), co-infected with HIV (OR: 2.07; 95%CI: 1.02-4.22) or co-infected with Neisseria gonorrhoeae (NG) (OR: 5.04; 95%CI: 3.33-7.63) had more repeat CT infections. In additional analyses among exclusively STI clinic visitors, patients with urogenital symptoms (OR: 2.17; 95%CI: 1.41-3.35), and patients notified for STIs (OR: 4.55; 95%CI: 3.17-6.54) had more frequent repeat CT infections., Conclusions: Patients aged < 25 years and patients coinfected with HIV or NG had more frequent repeat CT infections, accounting for ~ 20% of the diagnosed CT infections. These patients are likely at the highest risk for transmitting and acquiring CT. Therefore, testing and retesting this group remains important to enhance CT control.

Background Female sex workers (FSW) are at risk for sexually transmissible infections (STI). This study aimed to investigate whether the risk for chlamydia and gonorrhoea differs by work location among FSW in Amsterdam. Additionally, trends in STI positivity rates between 2011 and 2016 were assessed., Methods: This was a retrospective analysis of routinely collected clinical data during STI consultations of FSW by the Prostitution and Healthcare Centre (P&G292). Work location was categorised as window prostitution, escorts/homeworkers, clubs/brothels/private houses/massage salons and other., Results: In total, 7558 STI consultations of 2529 FSW in the period 2011-16 were included. Positivity rates for chlamydia and gonorrhoea were 6.6% and 2.0%, respectively. Infectious hepatitis B virus, syphilis and HIV were diagnosed in <0.2% of consultations. Positivity rates of chlamydia and rectal gonorrhoea differed significantly by work location (P < 0.001). Genital and rectal chlamydia and rectal gonorrhoea were significantly less likely among women working in window prostitution, except for the other-group. Risk factors for STI did not vary by work location. Among women working in window prostitution, positivity rates for oropharyngeal and genital chlamydia and genital gonorrhoea were significantly decreasing between 2011 and 2016 (P trend <0.05)., Conclusions: The higher STI positivity among escorts/homeworkers and FSW in clubs/brothels/private houses/massage salons emphasises the need for extra attention to improve condom use and STI testing in this group. Factors associated with STI did not vary by work location, thus interventions, including those used by P&G292, to reduce STI risk, can be used for women at all work locations.

Background: On 1 January 2014, the minimum age to buy alcohol increased (16-18 years), accompanied by a public awareness campaign (NIX18). Decreases in alcohol consumption are associated with less risky sexual behaviour. This study analyzed the association between the health reforms andChlamydia trachomatis infections (chlamydia) among young heterosexual people., Methods: Chlamydia positivity rates, age, and gender from all STI-clinic attendees between 16 and 19 years old in the Netherlands of 2010 to 2016 were obtained. Interrupted time-series assessed immediate and gradual trends in chlamydia rates., Results: Among the control group (18-19 year olds) chlamydia rates increased 0.5% each post-ban month (95% Confidence Interval [CI] 1.002-1.008, p = .001). Among 16-17 year olds there was no monthly increase post-ban (Rate Ratio 1.000, 95% CI 0.993-1.007, p = .948). In terms of confounders, only controlling for partner notification dissolved these time trends., Conclusions: We found that chlamydia rates after the alcohol ban differed between 16-17 year olds and 18-19 year olds. This demonstrates that the health reforms might have affected this secondary outcome, but obtaining certainty using national surveillance data is difficult. Specific studies should be designed, as now changes in chlamydia over time could be explained by STI-clinic policy changes, by changes on an individual level including reduced alcohol consumption or most likely by the combination of these factors., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Prevention of infectious diseases depends on health-related behavior, which is often influenced by psychological characteristics. However, few studies assessing health-related behavior have examined psychological characteristics to identify risk groups, and this multidimensional approach might improve disease risk assessment. We aimed to characterize subgroups based on psychological characteristics and examine their influence on behavior and disease risk, using chlamydia as a case study. Selected participants (heterosexuals aged 18-24 years and females aged 18-24 years who had sex with both men and women) in a Dutch longitudinal cohort study (the Mathematical Models Incorporating Psychological Determinants: Control of Chlamydia Transmission (iMPaCT) Study) filled out a questionnaire and were tested for chlamydia (2016-2017). Latent class analysis was performed to identify risk classes using psychological predictors of chlamydia diagnosis. Two classes were identified: class 1 (n = 488; 9% chlamydia diagnosis) and class 2 (n = 325; 13% chlamydia diagnosis). The proportion of participants with high shame, high impulsiveness, and lower perceived importance of health was higher in class 2 than in class 1. Furthermore, persons in class 2 were more likely to be male and to report condomless sex compared with class 1, but the number of recent partners was comparable. Thus, risk classes might be distinguished from each other by psychological characteristics beyond sexual behavior. Therefore, the impact of the same intervention could differ, and tailoring interventions based on psychological characteristics might be necessary to reduce chlamydia prevalence most effectively., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health.)

Objectives: Online testing for STIs might complement regular care provided by general practitioners or STI clinics. Two types of online testing can be distinguished, self-testing and self-sampling (sending sample to a laboratory for diagnosis). Online testing can occur without consultation with a healthcare professional, therefore information given by providers is essential for informed decision-making. We aimed to enumerate online test providers in the Netherlands focusing on chlamydia tests, to evaluate information using quality indicators and to gain insight on the proportion of online testing in the STI testing arena., Methods: We performed a systematic internet search to identify online STI test providers. Twenty quality indicators were evaluated on their websites; indicator scores were weighted by level of importance (expert opinion). High scoring providers were recommended, on the condition that the sensitivity and specificity of the test were above 95% and providers included a follow-up procedure in case of a positive result. Finally, providers were contacted to inquire about the number of sold tests, positivity rates and demographic characteristics of testers., Results: Five out of 12 identified self-sample test providers could be recommended, versus zero out of eight self-test providers. Self-sample test providers gave complete and correct information on more indicators (67%) compared with self-test providers (38%). In 2015, an estimated 30 000-40 000 self-sample tests were purchased, and 12 000-25 000 self-tests, which is roughly 10%-15% of the total number of STI tests., Conclusion: This evaluation shows that some online self-sample test providers could be put forward as way of STI testing complementing regular testing options. None of the self-test providers were recommended. Regularly evaluating online test providers is advised to improve quality of the information on the websites. Finally, self-testing might not be suited for all populations as most information is provided in written format only., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Introduction: Response rates in health research are declining, and low response rates could result in biased outcomes when population characteristics of participants systematically differ from the non-respondents. Few studies have examined key factors of non-response beyond demographic characteristics, such as behavioral and psychological factors. The aim of the current study was to identify predictors of non-response and loss to follow-up in a longitudinal sexual health study., Materials and Methods: A longitudinal cohort study (iMPaCT) was conducted from November 2016 to July 2018 among heterosexual STI clinic visitors aged 18-24 years. At four different time points in one year, data was collected on sexual behavior, psychological determinants and chlamydia infections. The national STI surveillance database provided data on demographic, behavioral and sexual health-related characteristics for non-respondents. Predictors of non-response at baseline and of loss to follow-up were identified using multivariable logistic regression analyses., Results: In total, 13,658 STI clinic visitors were eligible to participate, of which 1,063 (8%) participated. Male gender, low/medium education level, young age (≤ 20 years) and having a non-Dutch migration background were significant predictors of non-response at baseline. Furthermore, non-respondents at baseline were more likely to report STI-related symptoms, to have been notified by a partner, to have had condomless sex, and to have had ≤ 2 partners in the past six months, compared to participants. Psychological predictors of loss to follow-up differed between STI clinic regions, but low perceived importance of health at baseline was associated with loss to follow-up in all regions. The baseline chlamydia positivity rate was significantly higher in the non-respondents (17%) compared to the participants (14%), but was not a predictor of loss to follow-up., Discussion: Targeted recruitment aimed at underrepresented groups in the population based on demographic, behavioral and psychological characteristics, might be necessary to decrease loss to follow-up, and to prevent non-response bias in health research., Competing Interests: The authors have declared that no competing interests exist.

Objectives: A better understanding of Chlamydia trachomatis infection (chlamydia)-related sequelae can provide a framework for effective chlamydia control strategies. The objective of this study was to estimate risks and risk factors of pelvic inflammatory disease (PID), ectopic pregnancy and tubal factor infertility (TFI) with a follow-up time of up until 8 years in women previously tested for chlamydia in the Chlamydia Screening Implementation study (CSI) and participating in the Netherlands Chlamydia Cohort Study (NECCST)., Methods: Women who participated in the CSI 2008-2011 (n=13 498) were invited in 2015-2016 for NECCST. Chlamydia positive was defined as a positive CSI-PCR test, positive chlamydia serology and/or self-reported infection (time dependent). Data on PID, ectopic pregnancy and TFI were collected by self-completed questionnaires. Incidence rates and HRs were compared between chlamydia-positive and chlamydia-negative women corrected for confounders., Results: Of 5704 women included, 29.5% (95% CI 28.3 to 30.7) were chlamydia positive. The incidence rate of PID was 1.8 per 1000 person-years (py) (1.6 to 2.2) overall, 4.4 per 1000 py (3.3 to 5.7) among chlamydia positives compared with 1.4 per 1000 py (1.1 to 1.7) for chlamydia negatives. For TFI, this was 0.4 per 1000 py (0.3 to 0.5) overall, 1.3 per 1000 py (0.8 to 2.1) and 0.2 per 1000 py (0.1 to 0.4) among chlamydia positives and negatives, respectively. And for ectopic pregnancy, this was 0.6 per 1000 py (0.5 to 0.8) overall, 0.8 per 1000 py (0.4 to 1.5) and 0.6 per 1000 py (0.4 to 0.8) for chlamydia negatives. Among chlamydia-positive women, the strongest risk factor for PID was symptomatic versus asymptomatic infection (adjusted HR 2.88, 1.4 to 4.5) and for TFI age <20 versus >24 years at first infection (HR 4.35, 1.1 to 16.8)., Conclusion: We found a considerably higher risk for PID and TFI in chlamydia-positive women, but the incidence for ectopic pregnancy was comparable between chlamydia-positive and chlamydia-negative women. Overall, the incidence rates of sequelae remained low., Trial Registration: NTR-5597., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Host immunogenetic factors can affect late complications of urogenital infections with Chlamydia trachomatis . These findings are creating new avenues for updating existing risk prediction models for C. trachomatis -associated tubal factor infertility (TFI). Research into host factors and its utilization may therefore have future implications for diagnosing C. trachomatis -induced infertility. We outline the epidemiological situation regarding C. trachomatis and TFI in high-income countries. Thereupon, we review the main characteristics of the population undergoing fertility work-up and identify screening and diagnostic strategies for TFI currently in place. The Netherlands is an exemplary model for the state of the art in high-income countries. Within the framework of existing clinical approaches, we propose a scenario for the translation of relevant genome-based information into triage of infertile women, with the objective of implementing genetic profiling in the routine investigation of TFI. Furthermore, we describe the state of the art in relevant gene- and single nucleotide polymorphism (SNP) based clinical prediction models and place our perspectives in the context of these applications. We conclude that the introduction of a genetic test of proven validity into the assessment of TFI should help reduce patient burden from invasive and costly examinations by achieving a more precise risk stratification.

Objectives: National prevalence estimates of Chlamydia trachomatis (chlamydia) and Neisseria gonorrhoeae (gonorrhoea) are important for providing insights in the occurrence and control of these STIs. The aim was to obtain national prevalence estimates for chlamydia and gonorrhoea and to investigate risk factors associated with infection., Methods: Between November 2016 and January 2017, we performed a national population-based cross-sectional probability sample survey among men and women aged 18-34 years in the Netherlands. Individuals were invited to complete a questionnaire about sexual health. At the end of the questionnaire, sexually active individuals could request a home-based sampling kit. Samples were tested for chlamydia and gonorrhoea using nucleic acid amplification test (NAAT). Logistic regression analyses were performed for predictors of participation and chlamydia infection., Results: Of the 17 222 invited individuals, 4447 (26%) participated. Of these, 3255 were eligible for prevalence survey participation and 550 (17%) returned a sample. Participation in the prevalence survey was associated with age (20+) and risk factors for STI. We did not detect any gonorrhoea. The overall weighted prevalence of chlamydia was 2.8% (95% CI 1.5% to 5.2%); 1.1% (0.1% to 7.2%) in men and 5.6% (3.3% to 9.5%) in women. Risk factors for chlamydia infections in women aged 18-24 years were low/medium education level, not having a relationship with the person you had most recent sex with and age at first sex older than 16., Conclusions: Chlamydia and gonorrhoea prevalence were low in the general Dutch population, as was the participation rate. Repeated prevalence surveys are needed to analyse trends in STI prevalences and to evaluate control policies., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2019. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Objectives: To assess to what extent triage criteria, client and regional characteristics explain regional differences in Chlamydia trachomatis (Ct) and Neisseria gonorrhoeae (Ng) positivity in sexually transmitted infection (STI) clinics., Design: Retrospective cross-sectional study on the Dutch STI surveillance database of all 24 STI clinics., Participants: STI clinic visits of heterosexual persons in 2015 with a Ct (n=101 495) and/or Ng test (n=101 081)., Primary Outcome Measure: Ct and Ng positivity and 95% CI was assessed for each STI clinic. Two-level logistic regression analyses were performed to calculate the percentage change in regional variance (PCV) after adding triage criteria (model 1), other client characteristics (model 2) and regional characteristics (model 3) to the empty model. The contribution of single characteristics was determined after removing them from model 3., Results: Ct positivity was 14.9% and ranged from 12.6% to 20.0% regionally. Ng positivity was 1.7% and ranged from 0.8% to 3.8% regionally. For Ct, the PCV was 11.7% in model 1, 32.2% in model 2% and 59.3% in model 3. Age, notified for Ct (triage), level of education (other characteristics) and regional degree of urbanisation (region) explained variance most. For Ng, the PCV was 38.7% in model 1, 61.2% in model 2% and 69.1% in model 3. Ethnicity (triage), partner in risk group, level of education and neighbourhood (other characteristics) and regional socioeconomic status (SES) explained variance most. A significant part of regional variance remained unexplained., Conclusions: Regional variance was explained by differences in client characteristics, indicating that triage and self-selection influence positivity rates in the surveillance data.Clustering of Ng in low SES regions additionally explained regional variance in Ng; targeted interventions in low SES regions may assist Ng control. Including educational level as triage criterion is recommended. Studies incorporating prevalence data are needed to assess whether regional clustering underlies unexplained regional variance., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Although anorectal Chlamydia trachomatis (CT) infections are frequently diagnosed in men who have sex with men (MSM) and women, the reason for this infection often remains unexplained, as anal sex is not always reported. Oropharyngeal infections inoculating the gastrointestinal (GI) tract may contribute to anorectal-CT infections, as evidence in animals suggests that chlamydia bacteria undergo GI passage; however, no evidence exists in humans. Longitudinal patient clinic-registry data from MSM (n = 17 125) and women (n = 4120) from two Dutch sexually transmitted infection clinics were analysed. When adjusting for confounding socio-demographics, co-infections and risk behaviour, previous (from 3 weeks up to 24 months) oropharyngeal CT was not a risk factor for subsequent anorectal CT in women (odds ratio (OR) 0.46; 95% confidence interval (CI) 0.18-1.18; P = 0.11) and MSM (OR 1.33; 95% CI 0.86-2.07; P = 0.204). Despite the large dataset, the numbers did not allow for the estimation of risk in specific subgroups of interest. The role of the GI tract cannot be excluded with this epidemiological study, but the impact of preceding oropharyngeal CT on anorectal-CT infection is likely limited.

Background: In the Netherlands, there are strong disparities in Chlamydia trachomatis (CT) prevalence between ethnic groups. The current study aims to identify whether socioeconomic status, sexual risk behavior and sexual healthcare seeking behavior may explain differences in CT seroprevalence between ethnic groups., Methods: We used 2011-2014 baseline data of the HELIUS (HEalthy LIfe in an Urban Setting) study, a multi-ethnic population-based cohort study in Amsterdam, the Netherlands, including participants from Dutch, African Surinamese, South-Asian Surinamese, Ghanaian, Moroccan and Turkish origin. For this analysis, we selected sexually active, heterosexual participants aged 18-34 years old. CT seroprevalence was determined using a multiplex serology assay. The CT seroprevalence ratios between different ethnicities are calculated and adjusted for potential indicators of socioeconomic status, sexual risk behavior and sexual healthcare seeking behavior., Results: The study population consisted of 2001 individuals (52.8% female) with a median age of 28 years (IQR 24-31). CT seropositivity differed by ethnicities and ranged from 71.6% (African Surinamese), and 67.9% (Ghanaian) to 31.1% (Turkish). The CT seroprevalence ratio of African Surinamese was 1.72 (95% CI 1.43-2.06) and 1.52 (95% CI 1.16-1.99) of Ghanaian as compared to the Dutch reference group, after adjustment for socioeconomic status, sexual risk behavior and sexual healthcare seeking behavior., Conclusions: Indicators of socioeconomic status, sexual risk behavior, and sexual health seeking behavior could not explain the higher CT seroprevalence among African Surinamese and Ghanaian residents of Amsterdam.

Objectives: Expedited partner therapy (EPT) may reduce chlamydia reinfection rates. However, the disadvantages of EPT for chlamydia include missing the opportunity to test for other STIs and unnecessary use of antibiotics among non-infected partners. As part of a larger study that investigated the feasibility of EPT in the Netherlands, we explored the frequency of STI among a potential EPT target population of chlamydia-notified heterosexual men and women attending STI clinics for testing., Methods: Cross-sectional national STI/HIV surveillance data, which contain information on all consultations at STI clinics, were used to calculate STI positivity rates stratified by chlamydia notification and gender, and proportions of STI that were attributable to clients notified for chlamydia., Results: Of all consultations in 2015 (n=101 710), 14 445 (14.4%) clients reported to be notified exclusively for chlamydia. Among chlamydia-notified clients, the chlamydia positivity rate was 34.2% (n=4947), and consequently 65.8% (n=9488) of them tested negative for chlamydia. Chlamydia-notified clients contributed to 10.2% of all gonorrhoea infections (n=174/1702) and 10.9% of all infectious syphilis, HIV and/or infectious hepatitis B infections (n=15/173)., Conclusion: Implementing EPT without additional STI testing for all partners of chlamydia-infected index patients implies that STIs other than chlamydia will be missed. Although the chlamydia positivity rate was high among chlamydia-notified partners, two-thirds would unnecessarily use azithromycin. An evaluation of EPT against the current partner treatment strategy is needed to carefully weigh the potential health gains against the potential health losses and to explore the characteristics of EPT-eligible partners., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Background: Chlamydia trachomatis (chlamydia), the most commonly reported sexually transmitted infection (STI) in the Netherlands, can lead to severe reproductive complications. Reasons for the sustained chlamydia prevalence in young individuals, even in countries with chlamydia screening programs, might be the asymptomatic nature of chlamydia infections, and high reinfection rates after treatment. When individuals are unaware of their infection, preventive behaviour or health-care seeking behaviour mostly depends on psychological determinants, such as risk perception. Furthermore, behaviour change after a diagnosis might be vital to reduce reinfection rates. This makes the incorporation of psychological determinants and behaviour change in mathematical models estimating the impact of interventions on chlamydia transmission especially important. Therefore, quantitative real-life data to inform these models is needed., Methods: A longitudinal cohort study will be conducted to explore the link between psychological and behavioural determinants and chlamydia (re)infection among heterosexual STI clinic visitors aged 18-24 years. Participants will be recruited at the STI clinics of the public health services of Amsterdam, Hollands Noorden, Kennemerland, and Twente. Participants are enrolled for a year, and questionnaires are administrated at four time points: baseline (before an STI consultation), three-week, six-month and at one-year follow-up. To be able to link psychological and behavioural determinants to (re)infections, participants will be tested for chlamydia at enrolment and at six-month follow-up. Data from the longitudinal cohort study will be used to develop mathematical models for curable STI incorporating these determinants to be able to better estimate the impact of interventions., Discussion: This study will provide insights into the link between psychological and behavioural determinants, including short-term and long-term changes after diagnosis, and chlamydia (re)infections. Our mathematical model, informed by data from the longitudinal cohort study, will be able to estimate the impact of interventions on chlamydia prevalence, and identify and prioritise successful interventions for the future. These interventions could be implemented at STI clinics tailored to psychological and behavioural characteristics of individuals., Trial Registration: Dutch Trial Register NTR-6307 . Retrospectively registered 11-nov-2016.

Background: Victims could become infected with sexually transmitted infections (STIs) during a sexual assault. Several guidelines recommend presumptive antimicrobial therapy for sexual assault victims (SAVs). We assessed the STI positivity rate and treatment uptake of female and male SAVs at the Amsterdam STI clinic., Methods: Sexual assault victims answered assault-related questions and were tested for bacterial STI (chlamydia, gonorrhea, and syphilis), hepatitis B, and HIV during their initial visits. Sexual assault victim characteristics were compared with non-SAV clients. Backward multivariable logistic regression analysis was conducted to assess whether being an SAV was associated with a bacterial STI. The proportion of those returning for treatment was calculated., Results: From January 2005 to September 2016, 1066 (0.6%) of 168,915 and 135 (0.07%) of 196,184 consultations involved female and male SAVs, respectively. Among female SAVs, the STI positivity rate was 11.2% versus 11.6% among non-SAVs (P = 0.65). Among male SAVs, the STI positivity rate was 12.6% versus 17.7% among non-SAVs (P = 0.12). In multivariable analysis, female SAVs did not have increased odds for an STI (odds ratio 0.94; 95% confidence interval, 0.77-1.13), and male SAVs had significantly lower odds for an STI (odds ratio, 0.60; 95% confidence interval, 0.36-0.98). Of SAVs requiring treatment, 89.0% (female) and 92.0% (male) returned., Conclusions: The STI positivity rate among female SAVs was comparable with female non-SAVs, but male SAVs had lower odds for having a bacterial STI than did male non-SAVs, when adjusting for confounders. The return rate of SAV for treatment was high and therefore does not support the recommendations for presumptive therapy.

Objectives: Chemsex (i.e., drug use during sex) is practiced by some men who have sex with men (MSM) and is associated with high-risk behavior. In a cross-sectional study at the sexually transmitted infection (STI) clinic of Amsterdam, we explored chemsex practices, risk behavior, and STI prevalence., Method: A survey on chemsex (γ-hydroxybutyrate, crystal methamphetamine, and/or mephedrone) was offered to clinic clients during routine STI screening and to Amsterdam users of a gay online dating app. Associations were assed using χ test and multivariable regression., Results: Chemsex in the past 6 months was practiced by 866 (17.6%) of 4925 MSM clients and by 159 (1.5%) of 10857 non-MSM clients. Among gay dating app users, the proportion that reported chemsex engagement was higher than among MSM visiting the STI clinic (29.3% [537/1832] vs. 17.6%; P < 0.001). Chemsex was a significant risk factor for bacterial STI in HIV-negative MSM visiting the STI clinic (adjusted odd ratio, 1.5; 95% confidence interval, 1.2-1.8), but not in HIV-positive MSM. A majority practiced chemsex once a month or less, and 87.0% reported sex without drug use in the past month., Conclusions: In Amsterdam, chemsex is frequently practiced and significantly associated with bacterial STI in HIV-negative MSM but not in HIV-positive MSM. Future prevention strategies to reduce STI incidence should especially target HIV-negative MSM engaging in chemsex.

Introduction: This prospective study aimed to study the composition and structure of the vaginal microbiota prior to Chlamydia trachomatis infection., Methods: A nested case-control study was performed in 122 women, half of which acquired C. trachomatis within a year after their first visit. At the first visit, the composition and structure of vaginal microbial communities were analysed using 16S rRNA sequencing in the context of the sociodemographic and sexual risk behaviour information using logistic regression., Results: Five vaginal community state types (CSTs) were identified. Four CSTs were dominated by Lactobacillus spp., of which L. crispatus (37%) and L. iners (33%) were the most common. One CST was characterised by the absence of Lactobacillus spp. (25%) and the presence of an array of strict and facultative anaerobes. Multivariate logistic regression analysis revealed that women with a L. iners- dominated CST had an increased risk of C. trachomatis infection (p=0.04; OR: 2.6, 95% CI 1.0 to 6.6)., Conclusions: The distribution of CSTs dominated by Lactobacillus spp. agreed with previous studies. However, the frequency of dysbiosis among Caucasian women was relatively high (24%). Having vaginal microbiota dominated by L. iners was associated with an increased risk for C. trachomatis infection. Therefore, we hypothesise that specific signatures of vaginal microbiota are indicative of increased host predisposition to acquiring STIs., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Objectives: To develop prediction models for Chlamydia trachomatis (Ct) infection with different levels of detail in information, that is, from readily available data in registries and from additional questionnaires., Methods: All inhabitants of Rotterdam and Amsterdam aged 16-29 were invited yearly from 2008 until 2011 for home-based testing. Their registry data included gender, age, ethnicity and neighbourhood-level socioeconomic status (SES). Participants were asked to fill in a questionnaire on education, sexually transmitted infection history, symptoms, partner information and sexual behaviour. We developed prediction models for Ct infection using first-time participant data-including registry variables only and with additional questionnaire variables-by multilevel logistic regression analysis to account for clustering within neighbourhoods. We assessed the discriminative ability by the area under the receiver operating characteristic curve (AUC)., Results: Four per cent (3540/80 385) of the participants was infected. The strongest registry predictors for Ct infection were young age (especially for women) and Surinamese, Antillean or sub-Saharan African ethnicity. Neighbourhood-level SES was of minor importance. Strong questionnaire predictors were low to intermediate education level, ethnicity of the partner (non-Dutch) and having sex with casual partners. When using a prediction model including questionnaire risk factors (AUC 0.74, 95% CI 0.736 to 0.752) for selective screening, 48% of the participating population needed to be screened to find 80% (95% CI 78.4% to 81.0%) of Ct infections. The model with registry risk factors only (AUC 0.67, 95% CI 0.656 to 0.675) required 60% to be screened to find 78% (95% CI 76.6% to 79.4%) of Ct infections., Conclusions: A registry-based prediction model can facilitate selective Ct screening at population level, with further refinement at the individual level by including questionnaire risk factors., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Objectives: The objective of this study is to assess the effect of reminder text messages 6 months after the initial treatment on retest and chlamydia reinfection rates in young heterosexuals compared with a historical control group and to assess factors associated with both outcomes., Methods: Heterosexual people (aged 16-23 years), testing positive for urogenital chlamydia, were offered a retest after 6 months. Participants received a text message reminder at 6 months after the initial chlamydia diagnosis. Rates of retest uptake and the result of the retest were analysed using Cox regression. Prevalence ratios (PRs) were calculated to identify factors associated with these outcomes. Furthermore, the retest rate was compared with the retest rate of a historical control group., Results: 30.6% (253/838) of the study group returned within 5-8 months compared with 9.2% (140/1530) in the historical control group. Women and persons who were not notified for a sexually transmitted infection (STI) at inclusion were more likely to return for a retest. 20.4% (56/275) of participants had a chlamydia reinfection upon retesting. Reinfection was higher in participants reporting STI-related symptoms (PR 3.2, 95% CI 1.8 to 5.6) and in participants who were notified for an STI at retest (PR 5.3, 95% CI 2.4 to 11.5)., Conclusions: A text message reminder appeared to have a clear, positive impact on the resulting retest rate. These results also indicate that retesting is necessary to identify chlamydia reinfections., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Objectives: Recently, we reported a high prevalence (16%) of urogenital Chlamydia trachomatis infections among women in a rural setting in South Africa. Molecular epidemiological studies on C. trachomatis infections could provide insights into the characteristics of this epidemic, yet such data are not available. The objective of this study was therefore to assess the distribution of C. trachomatis strains among women from a South African rural community, the Mopani district, and to compare it with strains from Amsterdam, the Netherlands., Methods: High-resolution multilocus sequence typing (hr-MLST) was used to study urogenital C. trachomatis infections in women visiting primary healthcare facilities across rural Mopani District in Limpopo Province, South Africa. Sequence types (STs) were compared with 100 strains from women visiting the sexually transmitted infection clinic in Amsterdam, the Netherlands., Results: Full hr-MLST data were obtained for C. trachomatis infection in 43 women from Mopani district. Using the complete hr-MLST profile of all 43 women from Mopani district, 26 STs could be identified, of which 18 (69%) were novel to the hr-MLST database. The remaining STs clustered together with strains from Amsterdam., Conclusions: Hr-MLST data revealed a diverse molecular epidemiology with novel STs and a specific cluster for the Mopani district. Also C. trachomatis types that occur worldwide were detected., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Background: Both anorectal Chlamydia trachomatis (CT) and Neisseria gonorrhoea (NG) can occur as a rectal-only infection or concurrently with simultaneous urogenital infection with the same pathogen. Characterising the target groups in which rectal-only infections occur may improve the efficacy of screening practices., Methods: We analysed data from two Dutch outpatient sexually transmitted infection (STI) clinics between 2011 and 2012. We included all men who have sex with men (MSM) (n = 9549) and women (n = 11113), ≥18 years, who had been tested for anorectal and urogenital CT and/or NG (either as a result of reporting anal sex/symptoms or via routine universal testing). Factors associated with rectal-only CT and NG infections were assessed using univariable and multivariable logistic regression., Results: In MSM, anorectal CT prevalence was 9.8% (693/7094), anorectal NG prevalence was 4.2% (397/9534). In women this was 9.5% overall (439/4597) and 0.9% (96/10972) respectively. Anorectal CT prevalence among women who were routinely universally tested was 10.4% (20/192), for selective testing this was 9.5% (419/4405) (p = 0.68). Anorectal NG infections were not detected among women who were routinely universally tested (p = 0.19). Among CT or NG positive MSM, rectal-only CT infections were found in 85.9% (595/693), for NG this was 85.6% (340/397) respectively. In positive women these figures were 22.1% (97/439)for CT and 20.8% (20/96) for NG, respectively. In MSM, independent factors associated with rectal-only CT were: being a sex worker (OR0.4,CI0.2-1.0), exclusively having sex with men (OR3.4,CI1.7-6.8), and absence of urogenital symptoms (OR0.2,CI0.2-0.4). In women, these factors were: older age (OR2.3, CI1.3-4.0) and non-Western nationality (OR1.8, CI1.0-3.5). Factors associated with rectal-only NG in MSM were: having been warned for STIs by an (ex) partner (OR2.9,CI1.1-7.5), oropharyngeal NG infection (OR2.4,CI1.0-5.3), and absence of urogenital symptoms (OR0.02,CI0.01-0.04), while in women no significant factors were identified., Conclusions: The prevalence of anorectal CT and NG was substantial in MSM and prevalence of anorectal CT was also substantial in women. Anorectal infections occurred mostly as rectal-only infections in MSM and mostly concurrent with other infections in women. Given the lack of useful indicators for rectal-only infections, selective screening based on a priori patient characteristics will have low discriminatory power both in relation to MSM and women.

We assessed whether infection with chlamydia increases the incidence of carcinogenic human papillomavirus (HPV) infections and if HPV persistence is affected by chlamydia co-infection. For 1982 women (16-29 years-old) participating in two consecutive rounds of a chlamydia screening implementation trial, swabs were polymerase chain reaction tested to detect chlamydia and 14 carcinogenic HPV genotypes. HPV type-specific incidence and persistence rates were stratified for chlamydia positivity at follow-up. Associations were assessed by multilevel logistic regression analyses with correction for sexual risk factors. HPV type-specific incidence ranged from 1.4% to 8.9% and persistence from 22.7% to 59.4% after a median follow-up of 11 months (interquartile range: 11-12). Differences in 1-year HPV persistence rates between chlamydia -infected and noninfected women were less distinct than differences in HPV incidence rates (pooled adjusted odds ratios of 1.17 [95% CI: 0.69-1.96] and 1.84 [95% CI: 1.36-2.47], respectively). The effect of chlamydia co-infection on HPV-infection risk did not significantly differ by HPV genotype. In conclusion, infection with chlamydia increases the risk of infection by carcinogenic HPV types and may enhance persistence of some HPV types. Although these findings could reflect residual confounding through unobserved risk factors, our results do give reason to explore more fully the association between chlamydia and HPV type-specific acquisition and persistence., (© 2015 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Introduction: Previous studies found conflicting results regarding associations between urogenital Chlamydia trachomatis infections and ethnicity or urogenital symptoms among at-risk populations using either ompA-based genotyping or high-resolution multilocus sequence typing (MLST). This study applied high-resolution MLST on samples of individuals from a selected young urban screening population to assess the relationship of C. trachomatis strain types with ethnicity and self-reported urogenital symptoms. Demographic and sexual risk behaviour characteristics of the identified clusters were also analysed., Methods: We selected C. trachomatis-positive samples from the Dutch Chlamydia Screening Implementation study among young individuals in Amsterdam, the Netherlands. All samples were typed using high-resolution MLST. Clusters were assigned using minimum spanning tree analysis and were combined with epidemiological data of the participants., Results: We obtained full MLST data for C. trachomatis-positive samples from 439 participants and detected nine ompA genovars. MLST analysis identified 175 sequence types and six large clusters; in one cluster, participants with Surinamese/Antillean ethnicity were over-represented (58.8%) and this cluster predominantly consisted of genovar I. In addition, we found one cluster with an over-representation of participants with Dutch ethnicity (90.0%) and which solely consisted of genovar G. No association was observed between C. trachomatis clusters and urogenital symptoms., Conclusions: We found an association between urogenital C. trachomatis clusters and ethnicity among young screening participants in Amsterdam, the Netherlands. However, no association was found between C. trachomatis clusters and self-reported urogenital symptoms., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Objectives: Chlamydia trachomatis (CT) reporting rates from sexually transmitted infection clinics and general practitioners have shown a rising trend in the Netherlands. It is unknown to what extent this reflects increased CT transmission or improved case finding. To achieve more insight into the CT epidemic, we explored the CT IgG seroprevalence (a marker of past CT infection) in the general population of the Netherlands in 1996 and in 2007., Methods: From two population-based studies in 1996 and 2007, serum samples, demographic and sexual behaviour outcomes were examined, including 1246 men and 1930 women aged 15-39 years. Serum CT IgG antibodies were analysed using the Medac CT IgG ELISA test. Multivariate logistic regression analyses explored the seroprevalence and determinants over time., Results: The CT IgG seroprevalence was higher in women than in men (10% vs 6%). Among women aged 25-39 years the seroprevalence was lower in 2007 (9%) than in 1996 (14%; adjusted OR (aOR) 0.6, 95% CI 0.4 to 0.8). There was no statistical evidence of a difference in seroprevalence within birth cohorts. Factors associated with seropositivity were male gender (aOR 0.4, 95% CI 0.3 to 0.7), a self-reported history of CT infection (aOR 5.1, 95% CI 2.6 to 10.0), age 25-39 years (aOR 1.7, 95% CI 1.1 to 2.7), non-Western ethnicity (aOR 2.2, 95% CI 1.4 to 3.3) and ≥ 2 recent sexual partners (aOR 2.2, 95% CI 1.3 to 3.5)., Conclusions: Between 1996 and 2007 the proportion of individuals in the general population with CT IgG antibodies was lower among women aged 25-39 years, but remained similar among younger women and men., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Background: Symptom- and sexual history-based testing i.e., testing on indication, for anorectal sexually transmitted infections (STIs) in women is common. Yet, it is unknown whether this strategy is effective. Moreover, little is known about alternative transmission routes i.e. by fingers/toys. This study assesses anorectal STI prevalence and infections missed by current testing practice, thereby informing the optimal control strategy for anorectal STIs in women., Methods: Women (n = 663) attending our STI-clinic between May 2012-July 2013 were offered routine testing for anorectal and urogenital Chlamydia trachomatis and Neisseria gonorrhoeae. Data were collected on demographics, sexual behaviour and symptoms. Women were assigned to one of the categories: indication (reported anal sex/symptoms), fingers/toys (only reported use of fingers/toys), or without indication., Results: Of women, 92% (n = 654) participated. There were 203 reports (31.0%) of anal sex and/or symptoms (indication), 48 reports (7.3%) of only using fingers/toys (fingers/toys), and 403 reports (61.6%) of no anal symptoms, no anal sex and no anal use of fingers/toys (without indication). The overall prevalence was 11.2% (73/654) for urogenital chlamydia and 8.4% (55/654) for anorectal chlamydia. Gonorrhoea infections were not observed. Prevalence of anorectal chlamydia was 7.9% (16/203) for women with indication and 8.6% (39/451) for all other women (P = 0.74). Two-thirds (39/55) of anorectal infections were diagnosed in women without indication. Isolated anorectal chlamydia was rare (n = 3): of all women with an anorectal infection, 94.5% (52/55) also had co-occurrence of urogenital chlamydia. Of all women with urogenital chlamydia, 71.2% (52/73) also had anorectal chlamydia., Conclusions: Current selective testing on indication of symptoms and sexual history is not an appropriate control strategy for anorectal chlamydia in women visiting an STI clinic. Routine universal anorectal testing is feasible and may be a possible control strategy in women. Yet costs may be a problem. When more restricted control measures are preferred, possible alternatives include (1) anorectal testing only in women with urogenital chlamydia (problem: treatment delay or loss to follow up), and (2) direct treatment for urogenital chlamydia that is effective for anorectal chlamydia as well.

Objectives: Current strategies for controlling non-urogenital chlamydia and gonorrhoea are not uniform. It is assumed that present anorectal/oropharyngeal infections are coincidentally treated with urogenital infections. However, it is not clear whether this control strategy is effective. To inform current debate, we evaluated the anatomical site distribution of chlamydia and gonorrhoea by routine testing in men who have sex with men (hereafter men) and in high-risk women (prostitutes and swingers, hereafter women)., Methods: Between January 2010 and November 2012, all men (n=2436) and women (n=1321) attending our sexually transmitted infection clinic were routinely tested for anorectal, oropharyngeal and urogenital Chlamydia trachomatis and Neisseria gonorrhoeae. Data were collected on demographics and sexual behaviour., Results: Overall chlamydia positivity was 10.4% (254/2436) in men and 7.0% (92/1321) in women, for gonorrhoea this was 6.3% (154/2436) and 3.1% (41/1321), respectively. Isolated non-urogenital infections amounted to 76% of all infections in men and for up to 59% of all infections in women. For combined urogenital and anorectal infections, this amounted to 14% for men and up to 54% for women., Conclusions: Testing only for non-urogenital infections is insufficient, as it overlooks many infections. The use of coincidental treatment is therefore a suboptimal control strategy in high-risk groups for halting complications and transmission. There is an urgent need to optimise the testing guidelines for chlamydia and gonorrhoea at different anatomical sites.

The prevalence of Chlamydia trachomatis varies between ethnic groups in The Netherlands. It is, however, unknown whether this is associated with specific serogroups. The objective of this study was to determine whether serogroup distribution is associated with ethnic origin in the region of The Hague, The Netherlands. Serogroups of 370 microbiologically confirmed C. trachomatis-positive samples were analysed. The samples were obtained from 247 women and 123 men between January and October 2008, of self-reported Dutch Caucasian, Dutch Antillean, Surinamese, N. African/Turkish or other descent. We observed a difference in serogroup distribution comparing Dutch Caucasian women to Dutch Antillean women (χ2 for distribution P = 0·035). Serogroup C was more common in Dutch Antillean women, whereas serogroup B was less common (P = 0·03). This difference was not observed for Dutch Antillean men. The observed difference in distribution of C. trachomatis serogroups between ethnic groups is relevant for further transmission studies.

Background: Chlamydia trachomatis infection in pregnancy may lead to adverse pregnancy outcomes. In the Netherlands, testing for C. trachomatis is based on risk assessment. We assessed midwives' knowledge, test practices, assessment of risk behavior, and attitudes regarding testing for C. trachomatis infection during pregnancy. We evaluated the association between midwives' characteristics and their knowledge of C. trachomatis infection in terms of symptomatology and outcomes., Methods: This was a cross-sectional study among primary care midwives in the Netherlands. Between September and November 2011, midwives from all Dutch primary care midwifery practices were invited to complete a questionnaire about C. trachomatis infection., Results: Of the 518 midwives invited to participate in this study, 331 (63.9%) responded. The overall median knowledge score for questions about symptomatology and outcomes was 10 out of a maximum score of 15. The median knowledge score was higher among midwives in urban areas. In total, 239 (72.2%) midwives reported testing pregnant women for C. trachomatis. The primary reason for testing was a request by the woman herself (96.2%), followed by symptoms of infection (89.1%), risk behavior (59.3%), and risk factors for infection (7.3%). Almost 25% of midwives showed positive attitudes towards universal screening for C. trachomatis., Conclusions: Midwives were knowledgeable about symptoms of infection, but less about outcomes. Midwives test pregnant women for C. trachomatis mainly on the women's request. Otherwise, testing is based on symptoms of infection rather than on known risk factors. This may contribute to under-diagnosis and under-treatment, leading to maternal, perinatal, and neonatal morbidity.

Background: In The Netherlands, a national chlamydia screening program started in 2008, but the participation was low and the screening was not cost-effective. This study aimed to explore unconscious and conscious associations with chlamydia screening (16-29 year-olds). In addition, we examined whether information presented in chlamydia screening invitation letters had an effect on the evaluation of these determinants compared to a no-letter group., Methods: An Internet survey was conducted that included self-report measures of attitude, susceptibility, severity, unrealistic optimism, subjective, moral, and descriptive norm, perceived behavioral control, outcome expectations, barriers, intention, and a response time measure to assess unconscious associations of chlamydia screening with annoyance, threat and reassurance., Results: On the unconscious level, participants (N = 713) who received no information letter associated testing for chlamydia with annoyance and threat, but also with reassurance (all p's < .001). On the self-report measures, participants showed a low intention towards chlamydia screening (M = 1.42, range 1-5). Subjective norm, moral norm, perceived susceptibility and attitude were the most important predictors of the intention to screen (R2 = .56). Participants who rated their susceptibility as high also reported more risky behaviors (p < .001).In the groups that received a letter (N = 735), a weaker unconscious association of chlamydia screening with annoyance was found compared with the no-letter group (p < .001), but no differences were found in reassurance or threat. Furthermore, the letters caused a higher intention (p < .001), but intention remained low (M = 1.74). On a conscious level, giving information caused a more positive attitude, higher susceptibility, a higher subjective and moral norm, and more positive outcome expectations (all p's < .001)., Conclusion: Subjective norm, moral norm, susceptibility, and attitude towards chlamydia might be crucial targets to increase chlamydia screening behavior among sexually active young people. This study shows that informational invitation letters increase the intention and the intention-predicting variables. More evidence is needed on whether screening behavior can be increased by the use of an alternative information letter adapted to the specific unconscious and conscious determinants revealed in this study, or that we need other, more interactive behavior change methods.

The large Surinamese migrant population in the Netherlands is a major risk group for urogenital Chlamydia trachomatis infection. Suriname, a former Dutch colony, also has a high prevalence of C. trachomatis. Surinamese migrants travel extensively between the Netherlands and Suriname. Our objective was to assess whether the Surinamese migrants in the Netherlands form a bridge population facilitating transmission of C. trachomatis between Suriname and the Netherlands. If so, joint prevention campaigns involving both countries might be required. Between March 2008 and July 2010, participants were recruited at clinics in Paramaribo, Suriname and in Amsterdam, the Netherlands. Participants were grouped as native Surinamese, native Dutch, Surinamese migrant, Dutch migrant, or Other, based on country of residence and country of birth of the participant and of their parents. Risk behavior, such as sexual mixing between ethnic groups, was recorded and C. trachomatis positive samples were typed through multilocus sequence typing (MLST). A minimum spanning tree of samples from 426 participants showed four MLST clusters. The MLST strain distribution of Surinamese migrants differed significantly from both the native Surinamese and Dutch populations, but was not an intermediate state between these two populations. Sexual mixing between the Surinamese migrants and the Dutch and Surinamese natives occurred frequently. Yet, the MLST cluster distribution did not differ significantly between participants who mixed and those who did not. Sexual mixing occurred between Surinamese migrants in Amsterdam and the native populations of Suriname and the Netherlands. These migrants, however, did not seem to form an effective bridge population for C. trachomatis transmission between the native populations. Although our data do not seem to justify the need for joint campaigns to reduce the transmission of C. trachomatis strains between both countries, intensified preventive campaigns to decrease the C. trachomatis burden are required, both in Suriname and in the Netherlands.

We investigated Chlamydia trachomatis strains from Nanjing, China, and whether these strains differed from Amsterdam, the Netherlands. C. trachomatis type was determined with multilocus sequence typing. Most strains were specific to Nanjing, but some clustered with strains from Amsterdam. This demonstrates a geographical variation in C. trachomatis previously left undetected.

Background: In affluent countries, the prevalence of Chlamydia trachomatis (CT) is often higher in certain ethnic minorities than in the majority population. In The Netherlands, we examined why CT prevalence is higher in Surinamese/Antilleans, the largest minority in the country., Methods: Heterosexuals were recruited for a cross-sectional survey from May through August 2010 at the sexually transmitted infections (STI) clinic in Amsterdam. Participants completed a questionnaire and were tested for STI. A causal directed acyclic graph was assumed to investigate whether the association between ethnicity and CT could be explained by differences in sexual risk behaviour and socio-economic status., Results: Subjects included 1044 with Dutch background and 335 with Surinamese/Antillean background. Median age for the combined population was 25 (IQR 22-30) years, and 55.4% was female. Sexual risk behaviour did not differ significantly between the two groups. CT was diagnosed in 17.9% of Surinamese/Antilleans and in 11.4% of Dutch. Surinamese/Antilleans were significantly more likely to have CT (OR 1.70; 95% CI 1.21-2.38). The association between ethnicity and CT remained statistically significant after adjusting for sexual risk behaviour, age, sex, and ethnic mixing (aOR 1.48; 95% CI 1.00-2.18), but not after adjusting for education and neighbourhood, markers of socio-economic status (aOR 1.08; 95% CI 0.71-1.64)., Conclusion: The difference in CT prevalence between the minority and majority groups was not explained by differences in sexual risk behaviour. The higher CT prevalence found among Surinamese/Antilleans appeared to reflect their lower educational level and neighbourhood, two markers of lower socio-economic status. We hypothesise that the effect results from lower health-seeking behaviour.

Background: A large trial to investigate the effectiveness of population based screening for chlamydia infections was conducted in the Netherlands in 2008-2012. The trial was register based and consisted of four rounds of screening of women and men in the age groups 16-29 years in three regions in the Netherlands. Data were collected on participation rates and positivity rates per round. A modeling study was conducted to project screening effects for various screening strategies into the future., Methods and Findings: We used a stochastic network simulation model incorporating partnership formation and dissolution, aging and a sexual life course perspective. Trends in baseline rates of chlamydia testing and treatment were used to describe the epidemiological situation before the start of the screening program. Data on participation rates was used to describe screening uptake in rural and urban areas. Simulations were used to project the effectiveness of screening on chlamydia prevalence for a time period of 10 years. In addition, we tested alternative screening strategies, such as including only women, targeting different age groups, and biennial screening. Screening reduced prevalence by about 1% in the first two screening rounds and leveled off after that. Extrapolating observed participation rates into the future indicated very low participation in the long run. Alternative strategies only marginally changed the effectiveness of screening. Higher participation rates as originally foreseen in the program would have succeeded in reducing chlamydia prevalence to very low levels in the long run., Conclusions: Decreasing participation rates over time profoundly impact the effectiveness of population based screening for chlamydia infections. Using data from several consecutive rounds of screening in a simulation model enabled us to assess the future effectiveness of screening on prevalence. If participation rates cannot be kept at a sufficient level, the effectiveness of screening on prevalence will remain limited.

Background: Genovar distributions of Chlamydia trachomatis based on ompA typing differ between men who have sex with men (MSM) and heterosexuals. We investigated clonal relationships using a high resolution typing method to characterize C. trachomatis types in these two risk groups., Methods: C. trachomatis positive samples were collected at the STI outpatient clinic in Amsterdam between 2008 and 2010 and genotyped by multilocus sequence typing. Clusters were assigned using minimum spanning trees and these were combined with epidemiological data of the hosts., Results: We typed 526 C. trachomatis positive samples: 270 from MSM and 256 from heterosexuals. Eight clusters, containing 10-128 samples were identified of which 4 consisted of samples from MSM (90%-100%), with genovars D, G, J, and L2b. The other 4 clusters consisted mainly of samples from heterosexuals (87%-100%) with genovars D, E, F, I, and J. Genetic diversity was much lower in the MSM clusters than in heterosexual clusters. Significant differences in number of sexual partners and HIV-serostatus were observed for MSM-associated clusters., Conclusions: C. trachomatis transmission patterns among MSM and heterosexuals were largely distinct. We hypothesize that these differences are due to sexual host behavior, but bacterial factors may play a role as well.

National surveillance data from 2006 to 2010 of the Dutch sexually transmitted infection (STI) centres were used to analyse current practices on testing extragenital sites for chlamydia and gonorrhoea in men who have sex with men (MSM) and women. In MSM, 76.0% and 88.9% were tested at least at one extragenital site (pharyngeal and/or anorectal) for chlamydia and gonorrhoea, respectively; for women this was 20.5% and 30.2%. Testing more than one anatomic site differed by STI centre, ranging from 2% to 100%. In MSM tested at multiple sites, 63.0% and 66.5% of chlamydia and gonorrhoea diagnoses, respectively, would have been missed if screened at the urogenital site only, mainly anorectal infections. For women tested at multiple sites, the proportions of missed chlamydia and gonorrhoea diagnoses would have been 12.9% and 30.0%, respectively. Testing extragenital sites appears warranted, due to the numerous infections that would have been missed. Adding anorectal screening to urogenital screening for all MSM visiting an STI centre should be recommended. Since actual testing practices differ by centre, there is a need for clearer guidelines. Routine gonorrhoea and chlamydia screening at multiple sites in STI centres should be investigated further as this might be a more effective approach to reduce transmission than current practice.

Objective: To evaluate the effectiveness of register based, yearly chlamydia screening., Design: Controlled trial with randomised stepped wedge implementation in three blocks., Setting: Three regions of the Netherlands: Amsterdam, Rotterdam, and South Limburg., Participants: 317 304 women and men aged 16-29 years listed on municipal registers at start of trial., Intervention: From March 2008 to February 2011, the Chlamydia Screening Implementation programme offered yearly chlamydia screening tests. Postal invitations asked people to use an internet site to request a kit for self collection of samples, which would then be sent to regional laboratories for testing. Treatment and partner notification were done by the general practitioner or at a sexually transmitted infection clinic., Main Outcome Measures: Primary outcomes were the percentage of chlamydia tests positive (positivity), percentage of invitees returning a specimen (uptake), and estimated chlamydia prevalence. Secondary outcomes were positivity according to sex, age, region, and sociodemographic factors; adherence to screening invitations; and incidence of self reported pelvic inflammatory disease., Results: The participation rate was 16.1% (43 358/269 273) after the first invitation, 10.8% after the second, and 9.5% after the third, compared with 13.0% (6223/48 031) in the control block invited at the end of round two of the intervention. Chlamydia positivity in the intervention blocks at the first invitation was the same as in the control block (4.3%) and 0.2% lower at the third invitation (odds ratio 0.96 (95% confidence interval 0.83 to 1.10)). No substantial decreases in positivity were seen after three screening rounds in any region or sociodemographic group. Among the people who participated three times (2.8% of all invitees), positivity fell from 5.9% to 2.9% (odds ratio 0.49 (0.47 to 0.50))., Conclusions: There was no statistical evidence of an impact on chlamydia positivity rates or estimated population prevalence from the Chlamydia Screening Implementation programme after three years at the participation levels obtained. The current evidence does not support a national roll out of this register based chlamydia screening programme., Trial Registration: NTR 3071 (Netherlands Trial Register, www.trialregister.nl).

Research into the diagnostic accuracy of clinical tests is often hampered by single or double partial verification mechanisms, that is, not all patients have their disease status verified by a reference test, neither do all patients receive all tests under evaluation (index tests). We show methods that reduce verification bias introduced when omitting data from partially tested patients. Adjustment techniques are well established when there are no missing index tests and when the reference test is 'missing at random'. However, in practice, index tests tend to be omitted, and the choice of applying a reference test may depend on unobserved variables related to disease status, that is, verification may be missing not at random (MNAR). We study double partial verification in a clinical example from reproductive medicine in which we analyse the diagnostic values of the chlamydia antibody test and the hysterosalpingography in relation to a diagnostic laparoscopy. First, we plot all possible combinations of sensitivity and specificity of both index tests in two test ignorance regions. Then, we construct models in which we impose different assumptions for the verification process. We allow for missing index tests, study the influence of patient characteristics and study the accuracy estimates if an MNAR mechanism would operate. It is shown that data on tests used in the diagnostic process of the same population are preferably studied jointly and that the influence of an MNAR verification process was limited in a clinical study where more than half of the patients did not have the reference test., (Copyright © 2011 John Wiley & Sons, Ltd.)