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The main STI-healthcare providers in the Netherlands are GPs and sexual health clinics (SHCs). SHCs offer free-of-charge STI-care for key-populations. At the same time, Internet-based STI-test and home-sampling offers increase, offering new opportunities for a blended, more efficient, low threshold service. Currently, SHCs and national partners are reshaping sexual healthcare for young people and other key-populations, using a stepped-care model (SCM). The SCM is based on the principal that not all individuals need the same level of STI-care: some may be helped by online self-assessment tools (sense.info, Advies.chat) and a home sampling-kit and others need support by a professional. NoMoreC and Limburg4zero are regional e-STI services for MSM, developed by SHCs, and co-created with MSM communities, healthcare professionals and other stakeholders, based on a scientific/theoretical framework. NoMoreC targets high-risk MSM for HCV-prevention and offers anonymous, low cost, home-sampled HCV-testing. Limburg4zero provides home-sampling for HIV/STI testing as an extension of regular STI-care including peer-to-peer sharing, and e-counselling on e.g. chemsex and PrEP. Opportunities Community involvement is essential to reach the right target groups Personalized e-STI advice and test-options provide a viable alternative for those preferring autonomic testing, and can saves costs The HCV-test service appeared especially suitable for MSM using PrEP who arrange their own STI-care e-STI should deliver prevention messages for those who tested negative Challenges Quality assurance of test procedures (e.g. quality of the test, which test is offered) is a topic that should be high on the agenda Implementation is only effective when based on a clear theoretical/scientific framework Sustainability of regional e-STI initiatives is challenging; most are financed by research grants and broader/sustainable expansion may need governmental funding Tracking linkage-to-care is challenging in interventions with anonymous participation Return rates of home-sampling kits may be improved through digital innovations

Background The COVID-19 pandemic and associated lockdowns have impacted MSM’s sexual activity and access to HIV/STI-related services. This study among MSM in the Netherlands assesses COVID-19-induced changes in numbers of sex partners, condomless anal intercourse (CAI), PrEP use, and HIV/STI testing. Methods From July 20th to September 11th 2020, MSM were recruited via social media to complete an online survey. 2182 respondents (Mage=40 years) provided data on their sexual activity in 3 bimesters before the first lockdown (T1 Jan.–Feb.), during the lockdown (T2 mid-March-mid-May) and after the lockdown (T3 June–July). PrEP use and HIV/STI testing were reported per semester. Results The mean number of sex partners decreased by 39% between T1 and T2 and remained 12% lower at T3 than at T1. The number of CAI partners decreased by 36% between T1 and T2, and at T3 was similar to T1. A majority (62%) of PrEP users stopped using PrEP at some point because of COVID-19, of which 73% subsequently resumed PrEP. A fifth (20%) of respondents postponed/missed appointments for STI testing and 16% postponed/missed appointments for HIV testing. Only 39% of these respondents caught up on missed testing. Self-sampling/testing accounted for 1% of HIV testing and 1.2% of STI testing in the last semester before COVID-19 (past 7–12 months), and 5.5% and 2.7% respectively in the first semester with COVID-19 (past 0–6 months). Conclusion Sexual behaviours that put MSM at risk of STI or HIV acquisition were significantly reduced during the first lockdown. However, reengagement in sexual activity and CAI was rapid in the two months after the lockdown. Resumption of PrEP use after an interruption was more frequent than catching up on HIV/STI testing. Further promoting self-sampling/testing may contribute to mitigating the adverse impact of a succession of lockdowns and periods of easing of restrictions.

Background Since its formal introduction in 2019, PrEP uptake in the Netherlands is growing, but remains at suboptimal levels. Hence, the analysis of determinants is paramount. Given the initial focus of PrEP provision among men-who-have-sex-with-men (MSM) via a demonstration project, AmPrEP in Amsterdam, and pharmacies in the main urban areas (so called ‘Randstad’, entailing Amsterdam, Utrecht, Leiden, The Hague and Rotterdam), investigating regional discrepancies is necessary. We seek to unravel regional differences jointly with known predictors of PrEP use, intention and awareness. Method This cross-sectional study included 3,232 HIV-negative Dutch MSM recruited via the EMIS survey in late 2017. Prevalence and standardized prevalence ratio (SPR) of PrEP use, awareness and intention were measured on a regional level (Randstad vs. the rest of the country). Multi-level logistic modeling was conducted to identify the association of PrEP use with PrEP awareness and intention, sociodemographic, behavioral, psychological/cognitive determinants, and random effects from regional differences. Results MSM from Randstad used more PrEP (SPR=1.4 vs. 0.7) compared to the rest of the country, but there were minor differences for awareness and intention. The regional distinction was estimated to explain 4.6% of the PrEP use variance (adjusted ICC=0.046). Greater influence from intention to use (OR=4.5, 95%CI 2.0–10.1) and knowledge of PrEP (OR=7.0, 95%CI 4.1–12.0), while limited influence from the awareness of PrEP was observed (OR=0.4, 95%CI 0.04–4.4). Lower education (OR=0.4, 95%CI 0.2–0.9) was negatively associated with PrEP use, however, no significant difference was found between middle and high education (OR=1.2, 95%CI 0.7- 2.0). Conclusion We showed that regional differences – MSM in non-urban regions – and with a low educational background account for lower PrEP use and intention. Based on these findings more fine-tuned PrEP access with a focus on non-urban regions can be implemented, and tailored campaigns increasing intention/use can be conducted among target populations.

Background Fear of COVID-19 infection and the response measures have affected sexual behaviours of men who have sex with men (MSM) and access to care for sexually transmitted infections (STI). We investigated whether these changes resulted in increased or decreased STI transmission among MSM. Methods We developed a mathematical transmission model for chlamydia and gonorrhoea among MSM. We accounted for 15–35% reduction in the number of casual partners and 50–80% reduction in STI testing during lockdowns (March-May 2020; October 2020 to February 2021); these reductions were 0–10% and 20–35%, respectively, in periods with less restrictive COVID-19 measures (June-September 2020, March-August 2021). Reductions until August 2020 were estimated from Dutch data; other reductions were based on expert opinion. We assumed no changes after August 2021. Two scenarios were examined: with home-testing (in 25% of cases not tested at healthcare facilities) and without home-testing. We calculated the percentage change in prevalence due to COVID-19 associated changes, compared to prevalence in the same year without changes due to COVID-19. Results From the model, we estimated an increase of 8.4% (interquartile range (IQR), 7.6–9.4%) in chlamydia prevalence and an increase of 7.5% (IQR, 6.0–8.9%) in gonorrhoea prevalence at the end of 2020 without home-testing, compared to the prevalence without COVID-19 associated changes. The increase subsided in 2021, but chlamydia and gonorrhoea prevalence remained higher than without COVID-19 until 2025. With home-testing, the percentage increase in 2020, compared to the scenario without COVID-19, was 5.3% (IQR, 4.6–5.9%) for chlamydia and 3.5% (IQR, 2.6–4.4%) for gonorrhoea prevalence. Conclusion The COVID-19 pandemic may have resulted in an increase in chlamydia and gonorrhoea prevalence in 2020. The increase can be smaller after 2020, if STI testing at healthcare facilities and/or at home increases. The findings emphasize the importance of facilitating STI (self) care in times of crisis.

Background On a national level, the Netherlands is closing in on the ambitious 95–95–95 HIV targets set by UNAIDS for 2025. Here, we investigated to what extent this is also the case on a regional level. Methods From the ATHENA national HIV cohort, we retrieved data about all individuals with an HIV-1 infection living in each of the eight sexually transmitted infection (STI) public health surveillance regions in the Netherlands. Based on those newly-diagnosed during 2002–2019 data, we estimated the number of people remaining undiagnosed by the end of 2019, using ECDC’s HIV Modelling Tool, a CD4 count-based back-calculation method. We subsequently estimated a four-stage HIV care continuum: (i) living with HIV, including those undiagnosed, (ii) diagnosed, (iii) in care and on antiretroviral treatment (ART), and (iv) with viral suppression (HIV RNA Results The estimated number living with HIV nationwide by the end of 2019 was 23,560 (95% confidence interval [CI] 23,370–23,820), or 135 (134–137) per 100,000 population; approximately 1,770 (1,570–2,030) were still undiagnosed. Numbers living with HIV per 100,000 population were highest in Noord-Holland/Flevoland (273, 95%CI 270–276), Zuid-Holland Noord (164, 159–171), and Zuid-Holland Zuid (144, 142–149), which include the three largest cities Amsterdam, The Hague, and Rotterdam. Across the eight regions, 90%-95% had been diagnosed, 92%-96% of those diagnosed were on ART, and 95%-98% of those on ART had a suppressed viral load. Conclusion All STI surveillance regions are on track of achieving UNAIDS’ 95–95–95 2025 targets. Increased efforts are necessary to reduce the undiagnosed population and the number of individuals not retained in care and on treatment.

Improving testing uptake among men who have sex with men with a non-western migration background (MSM-NW) is a public health priority, as people who are unaware of their HIV infection are at higher risk of transmitting HIV and are unable to benefit from HIV treatment. Formative semi-structured interviews with 13 MSM-NW assessed key factors for the successful implementation of social network testing with HIV self-tests (SNT-HIVST). Interviews were thematically analysed. Participants mentioned that SNT-HIVST might overcome barriers to regular HIV testing including; being seen while testing, disclosure of sexual identity, and stigma related to HIV and sexual practices. Trust between the HIVST distributer and receiver was important. Finally, SNT-HIVST requires tailored peer support to address practical, informational, and emotional needs. MSM-NW distributing HIVST can have an important role in reducing health disparities in testing uptake among MSM-NW. Provided sufficient trust among MSM-NW; key factors found for successful implementation were education through an e-tool, and establishing quality support by a peer-coordinator for unanticipated questions. In conclusion, HIVST distribution has the potential to reduce health disparities in testing uptake, in particular, if adjusted to MSM-NWs individual preferences and the needs and preferences of the person they are inviting to test.

To map regions of the Netherlands with high HIV prevalence for surveillance and prevention purposes.Information on numbers of HIV patients receiving clinical care on 31 December 2014 per postcode region was requested from the HIV monitoring foundation (SHM). These details were related to data from Statistics Netherlands on the number of residents per municipal area or district with the aid of a geographic information system (GIS).Distribution mapping showed that ten municipal areas in the Netherlands have an HIV prevalence of 2 or more per 1000 residents aged 15-60 years. We discovered the highest prevalence in Amsterdam (8.1) and suburbs, Rotterdam (3.4), The Hague (2.7) and Arnhem (2.5). Large differences were seen between districts, particularly in Amsterdam where HIV was concentrated within two districts: Central Amsterdam (9-28) and Amsterdam Southeast (5-20). In Rotterdam and The Hague, HIV prevalence rates are lower and differences between districts are smaller.Geographical analyses show differences in HIV prevalence for municipal areas and districts in big cities in the Netherlands. These data can be used for new interventions, to better focus HIV detection.

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are usually asymptomatic for decades, thus targeted screening can prevent liver disease by timely diagnosis and linkage to care. More robust estimates of chronic HBV and HCV infections in the general population and risk groups are needed. Using a modified workbook method, the total number of ever chronically infected individuals in the Netherlands in 2016 was determined using population size and prevalence estimates from studies in the general and high-risk population. The estimated 2016 chronic HBV infection prevalence is 0.34% (low 0.22%, high 0.47%), corresponding to approximately 49 000 (low 31 000, high 66 000) HBV-infected individuals aged 15 years and older. The estimated ever-chronic HCV infection prevalence is 0.16% (low 0.06%, high 0.27%), corresponding to approximately 23 000 (low 8000, high 38 000) ever-chronic HCV-infected individuals. The prevalence of chronic HBV and HCV infections in the Netherlands is low. First-generation migrants account for most infections with 81% and 60% of chronic HBV and HCV infections, respectively. However, about one-fifth of HCV infections is found in the general population at low risk. This method can serve as an example for countries in need of more accurate prevalence estimates, to help the design and evaluation of prevention and control policies.

Contains fulltext : 170977.pdf (Publisher’s version ) (Open Access) OBJECTIVES: Prior research has shown that Dutch general practitioners (GPs) do not always offer HIV testing and the number of undiagnosed HIV patients remains high. We aimed to further investigate the frequency and reasons for (not) testing for HIV and the contribution of GPs to the diagnosis of HIV infections in the Netherlands. DESIGN: Observational study. SETTING: (1) Dutch primary care network of 42-45 sentinel practices where report forms during sexually transmitted infection (STI)-related consultations were routinely collected, 2008-2013. (2) Dutch observational cohort with medical data of HIV-positive patients in HIV care, 2008-2013. OUTCOME MEASURES: The proportion of STI-related consultations in patients from high-risk groups tested for HIV, with additional information requested from GPs on HIV testing preconsultation or postconsultation for whom HIV testing was indicated, but not performed. Next, information was collected on the profile of HIV-positive patients entering specialised HIV care following diagnosis by GPs. RESULTS: Initially, an HIV test was reported (360/907) in 40% of STI-related consultations in high-risk groups. Additionally, in 26% of consultations an HIV test had been performed in previous or follow-up consultations or at different STI-care facilities. The main reasons for not testing were perceived insignificant risk; 'too' recent risk according to GPs or the reluctance of patients. The initiative of the patient was a strong determinant for HIV testing. GPs diagnosed about one third of all newly found cases of HIV. Compared with STI clinics, HIV-positive patients diagnosed in general practice were more likely to be older, female, heterosexual male or sub-Saharan African. CONCLUSIONS: In one-third of the STI-related consultations of persons from high-risk groups, no HIV test was performed in primary care, which is lower than previously reported. Risk-based testing has intrinsic limitations and implementation of new additional strategies in primary care is warranted.

To gain insight into the transmission of HIV and sexually transmitted infection (STI) among large migrant groups in The Netherlands, we studied the associations between their demographic and sexual characteristics, in particular condom use, and their sexual mixing patterns with other ethnic groups. In 2002-2005, cross-sectional surveys were conducted among migrants from Surinam (Afro- and Hindo-), the Netherlands Antilles, Cape Verde, and Ghana at social venues in three large cities. A questionnaire was administrated and a saliva sample was collected for HIV antibody testing. Of 2105 migrants recruited, 1680 reported sexual contacts, of whom 41% mixed sexually with other ethnicities, including the indigenous Dutch population. Such disassortative mixing was associated with being second-generation migrant, having several sexual partners, and having a steady and concurrent casual partner. Less disassortative mixing occurred in participants reporting visiting the country of origin. The association between condom use and sexual mixing differed by gender, with men using condoms inconsistently being most likely to be mixing with the Dutch indigenous population. HIV infection and recent STI treatment were not associated with disassortative mixing. This study shows substantial sexual mixing among migrant groups. Since disassortative mixing is more prevalent in second-generation migrants, it might increase in the upcoming years. The mixing patterns in relation to concurrency and the reported condom use in this study suggest a possibly increased level of HIV/STI transmission not only within migrant groups but also between migrant groups, especially via men who mix with the indigenous population and via migrant women who mix with non-Dutch casual partners. Although the observed HIV prevalence in migrants (0.6%) is probably too low to lead to much HIV transmission between ethnicity groups, targeted prevention measures are needed to prevent transmission of other STI.

Gedragssurveillance zou een integraal onderdeel moeten zijn van de reguliere soa- en hiv-surveillance. Het verzamelen van gegevens over seksueel gedrag geeft inzicht in de mate waarin soa- en hiv-trends worden beinvloed door gedragsveranderingen. Deskundigen op het gebied van gedragssurveillance in Nederland hebben een set van kernindicatoren samengesteld voor het monitoren van seksueel gedrag binnen de bestaande soa- en hiv-surveillancesystemen. Door dezelfde set kernindicatoren in verschillende surveillancesystemen mee te laten lopen, worden gedragsgegevens op gelijke wijze verzameld en kunnen gegevens van verschillende risicogroepen met elkaar worden vergeleken.

In November 2002, the Netherlands adopted a vaccination program targeted at behavioural risk groups. Between January 2003 and December 2007, 1386 patients acutely infected with HBV were reported. Reported cases declined from 326 in 2003 to 220 in 2007. Sexual intercourse was the most frequently reported mode of transmission (65%), especially among men having sex with men. Genotypes A and D remained predominant. In total, 40,600 participants were fully vaccinated, the overall compliance was 62%, and the estimated overall program coverage was 12% of the at-risk population. With more effort, more susceptibles may be reached, but the program will not be sufficient to substantially reduce HBV in the Netherlands. Therefore, universal vaccination should be considered. (C) 2009 Elsevier Ltd. All rights reserved.

To gain insight into hepatitis B virus (HBV) transmission in the Netherlands, epidemiological data and sera were collected from reported cases of acute HBV infections in the Netherlands in 2004. Cases were classified according to mode of transmission. A fragment of the S-gene of HBV (648 bp) was amplified, sequenced, and subjected to phylogenetic analysis. Of the 291 acute HBV cases reported in 2004, 158 (54%) were available for genotyping. Phylogenetic analysis identified 6 genotypes: A (64%), B (3%), C (3%), D (21%), E (5%) and F (5%). Of HBV infected men having sex with men, 86% were infected with genotype A, accounting for 43% of all patients infected with this genotype. There were only three reported cases of injecting drug use of which one was available for sequencing (genotype A). Unlike the genotype A cluster, sequences within the genotype B-E clusters were heterogenic. Within genotype F, several isolates had identical sequences, but patients could not be epidemiologically linked. Sexual transmission, particularly by men having sex with men was the most important transmission route for HBV. Injecting drug use plays a minor role. Genotype A is predominant in the Netherlands, especially among men having sex with men. In addition to imported strains, there seems to be a pool of related but non-identical strains circulating among chronic carriers in the migrant population, from which occasionally new patients are infected, primarily by heterosexual transmission.

To gain insight into the spread of hepatitis B among various risk groups in Amsterdam a 6-year (1992‐1997) retrospective DNA sequencing study was carried out on isolates from stored sera from reported primary cases of acute hepatitis B infection. Cases were classified according to risk behavior, as determined in interviews. Of the available serum, a selected region of hepatitis B-virus-DNA was amplified and sequenced. The nucleotide alignments were subjected to phylogenetic tree analysis. When nucleotide alignments were subjected to phylogenetic analysis, the strains of 54 isolates, 26% of the 204 reported primary cases, clustered in five genotypes: A, C, D, E, and F. In genotype A, a cluster related to men having sex with men was identified. In genotype D, two subclusters could be identified: one was related to injecting drug use and another was related to the Moroccan population in Amsterdam. The remaining strains showed a high genetic variability within three different genotypes: F, E, and C. Of the 14 identical isolates in the ‘‘homosexual men cluster,’’ one was isolated from a female heterosexual. Of the 14 identical strains in the ‘‘drug users strain,’’ six were from non-drug using heterosexual active individuals. In the cluster of twelve isolates related to hepatitis B-endemic areas, probable modes of transmission were varied. Sequence analysis provides important insight into the spread of hepatitis B among various highrisk groups. The analysis indicates that the prevention strategy in The Netherlands fails to stop transmission of hepatitis B from persistently infected individuals originating from hepatitis Bendemic countries. J. Med. Virol. 66:159‐

Objective To reconstruct the epidemiological relationships of the HIV epidemics among injecting drug users (IDU) in western Europe. Methods HIV env V3 sequences of and epidemiological data were obtained from 145 IDU who seroconverted in three sequential periods: 1984-1988, 1989-1992 and 1993-1997. The sequences were phylogenetically analysed and examined for signature patterns characteristic of northern European IDU, including the conserved GGC codon in the V3 loop. Results Subpopulations of genetically related HIV strains were observed in Italy, France, Scotland and Spain, in contrast to the Netherlands, Austria and Switzerland. This difference between the two groups of countries suggests that the HIV epidemics amongst IDU in the latter group was caused by multiple virus introductions. In Edinburgh and the surrounding area, most IDU were infected with the same GGC strain over the 12-year study period. The epidemic among IDU in north-western Europe started with GGC viruses, whereas in south-western Europe non-GGC viruses predominated. This geographical separation has faded during the course of the epidemic, most likely because of virus exchange among IDU populations.

SUMMARYA population-based anti-hepatitis C virus (HCV) prevalence is important for surveillance purposes and it provides insight into the burden of disease. The outcomes of recent studies in the general Dutch population as well as recent HCV data from specific risk groups including migrants, men who have sex with men (MSM) and injecting drug users (IDUs), were implemented in a modified version of the Workbook Method (a spreadsheet originally designed for HIV estimations), to estimate Dutch HCV seroprevalence. The estimated national seroprevalence of HCV was 0·22% (min 0·07%, max 0·37%), corresponding to 28 100 (min n = 9600, max n = 48 000) HCV-infected individuals in The Netherlands. Of these, first-generation migrants from HCV-endemic countries (HCV prevalence ⩾2%) accounted for the largest HCV-infected group, followed by IDUs and HIV-positive MSM.

SUMMARYEthnic disparities in chlamydia infections in The Netherlands were assessed, in order to compare two definitions of ethnicity: ethnicity based on country of birth and self-defined ethnicity. Chlamydia positivity in persons aged 16–29 years was investigated using data from the first round of the Chlamydia Screening Implementation (CSI, 2008–2009) and surveillance data from STI centres (2009). Logistic regression modelling showed that being an immigrant was associated with chlamydia positivity in both CSI [adjusted odds ratio (aOR) 2·3, 95% confidence interval (CI) 2·0–2·6] and STI centres (aOR 1·4, 95% CI 1·3–1·5). In both settings, 60% of immigrants defined themselves as Dutch. Despite the difference, classification by self-defined ethnicity resulted in similar associations between (non-Dutch) ethnicity and chlamydia positivity. However, ethnicity based on country of birth explained variation in chlamydia positivity better, and is objective and constant over time and therefore more useful for identifying young persons at higher risk for chlamydia infection.

Background & Aims Little is known about the HCV prevalence in non-Western migrant populations. To determine whether targeted HCV screening and prevention programs for migrants are needed, we examined HCV prevalence and determinants among non-Western, Western migrants, and the native Dutch population in the Netherlands. Methods Data were obtained from four surveys: (1) 3895 heterosexual visitors recruited during biannual surveys at the STI-clinic Amsterdam, 2007–2009; (2) random sample of 4563 pregnant women in Amsterdam, 2003; (3) population-based random sample of 1309 inhabitants of Amsterdam, 2004; (4) population-based random sample of 4428 people living in the Netherlands, 2006–2007. Characteristics associated with HCV-positivity were examined and phylogenetic analysis was used to obtain insight in the geographical origin of HCV strains. Results HCV seroprevalence in the four surveys was low (0.3–0.6%). In total 4860/14,195 (34%) were non-Western and 9329/14,195 (66%) Western participants (including Dutch). First-generation non-Western migrants were more likely to be HCV-positive (0.7–2.3%) than Western participants (0.1–0.4%). Except for survey 3, second-generation non-Western migrants had a lower HCV prevalence than first-generation migrants, comparable to Western migrants and the Dutch population. Phylogenetic analysis showed that the majority of the HCV-positive, first-generation non-Western non-European migrants were infected with endemic strains which are rarely observed in Europe. Conclusions First-generation non-Western migrants are at increased risk for HCV. Phylogenetic analysis suggests that transmission likely took place in the country of origin, causing introduction but no further transmission of endemic HCV strains in the Netherlands. HCV screening and prevention programs should target first-generation, but not second-generation, non-Western migrants.

To gain insight into hepatitis B virus (HBV) transmission in the Netherlands.Descriptive.During 2004, epidemiological data and blood samples (if available) were collected for all reported cases of acute HBV infections in the Netherlands. Following DNA isolation and amplification a 648 base pairs fragment of the HBV S gene was sequenced and subjected to phylogenetic analysis. The sequencing details were also linked to epidemiological information.In 2004, 291 cases ofacute HBV infections were reported. Blood samples were received from 171 patients (59%), and the genotype could be determined for 158 patients (54%). 6 genotypes were identified: A (64%), B (3%), C (3%), D (21%), E (5%) and F (4%). Of all patients with genotype A, 52% had been infected via homosexual or bisexual contact and 16% via heterosexual contact. Of all patients with genotype D, 42% had been infected via heterosexual contact and 15% via homosexual or bisexual contact. The genotype A cluster was extremely homogeneous with many identical sequences, while genotype B-E clusters were more heterogeneous. 4 identical sequences were found within genotype F, but the patients could not be epidemiologically linked.Sexual transmission, particularly via homosexual or bisexual contact in men, formed the most important risk factor for acquiring an acute HBV infection. Genotype A was predominant in the Netherlands, especially among homosexual or bisexual men. Most infections within genotype D occurred as a result of heterosexual contact. The results show that there was ongoing transmission of HBV in homosexual or bisexual men, while in heterosexuals more cases of new introduction were seen, possibly via chronic carriers from areas where HBV is endemic.

Background: By having unprotected heterosexual contact in both The Netherlands and their homeland, migrants who travel to their homeland might form a bridge population for HIV and sexually transmitted infection (STI) transmission. We studied the determinants for such a population in two large migrant communities in The Netherlands. Methods: From 2003 to 2005, 1938 people of Surinamese and Antillean origin were recruited at social venues in two large cities, interviewed and their saliva samples tested for HIV antibodies. We used multivariate multinomial logistic regression to explore characteristics of groups with four risk levels (no, low, moderate and high) for cross-border transmission. Results: 1159/1938 (60%) participants had travelled from The Netherlands to their homeland in the previous 5 years and 1092 (94%) of them reported partnerships and condom use in both countries. Of these 9.2% reported having unprotected sex with partners in both countries. People in this high-risk or bridge population group were more likely to be male, frequent travellers and older compared with people who had no sex or had sexual contact solely in one country in the past 5 years. Conclusions: Older male travellers of Surinamese and Antillean origin are at high risk for cross-border heterosexual transmission of HIV/STIs. They should be targeted by prevention programmes, which are focused on sexual health education and HIV/STI testing, to raise their risk awareness and prevent transmission.

Introduction Women attending termination of pregnancy (TOP) clinics are a risk group for STIs, and those with STIs are at increased risk of developing postabortal complications. We explored what STI care is provided in Dutch TOP clinics, and we compared these results with the United Kingdom (UK). Methods A qualitative study including 14 semi-structured interviews with health care professionals (HCPs) in TOP clinics (Netherlands: 9, UK: 5). Interviews were recorded, transcribed, and analysed by thematic content analysis. Results In the Netherlands, azithromycin prophylaxis is routinely prescribed after a surgical TOP, but not routinely after a medical TOP. STI tests are only offered by Dutch clinics if clients are considered at high STI risk based on the intake questionnaire. High costs of STI testing form the main barrier for clients not accepting STI testing, as costs are not covered by all health insurances. Alternatively, some clinics refer women to the Public Health Service (PHS), where STI testing is free for high-risk groups. This also involves barriers as not all women go for testing. HCPs in TOP clinics that collaborate with PHSs in the Sense program (sexual and reproductive health care) experience less barriers, as free STI testing is then offered on location of the TOP clinic. Sexual health counselling in TOP clinics is often limited to birth control conversations, also in the UK. The major difference between Dutch and UK TOP clinics is that UK clinics (who are not privately owned) offer free STI testing to all clients. Conclusion HCPs in Dutch TOP clinics consider STI testing an important part of their service, but financial barriers prevent STI testing on location. In the UK, free STI care is broadly implemented in TOP clinics. Collaboration with PHSs (in Sense program) could improve STI testing and sexual health counselling in Dutch TOP clinics. Disclosure of interest statement The study is funded by the RIVM. No pharmaceutical grants were received in the development of this study.

Introduction The proportion of MSM unaware of their HIV infection is 31% in the Netherlands. People who are unaware of HIV are more likely to transmit HIV to others and are unable to benefit from (early) treatment. To improve HIV testing, it is crucial to identify characteristics of MSM who were never tested. Methods We analysed HIV testing behaviour in the Dutch sample (n = 3,787) of the European MSM Internet Survey (EMIS) in relation to socio-demographic and behavioural factors by logistic regression. Results Of the MSM, 20.5% reported to be ‘never tested for HIV’. The adjusted model showed that MSM of younger age ( 40 yrs), with lower education (2.1 CI 1.8–2.4 vs high), with lower HIV knowledge (5.5 CI 3.8–8.0 vs higher) had higher odds on ‘never tested for HIV’. Further, MSM with lower sexual risks were more likely to be never tested for HIV; MSM with no UAI Conclusion MSM with lower sexual risks were more likely to be never tested for HIV, suggesting that MSM make risk assessments to inform their choices about HIV testing. Nevertheless, MSM who never tested for HIV also showed sexual behaviour that put them at HIV risk, and are therefore important to target for HIV interventions. Disclosure of interest statement The study is funded by the RIVM. No pharmaceutical grants were received in the development of this study.

In 2004, numbers of sexually transmitted infections (STIs) increased in the Netherlands compared with 2003

To gain insight into the prevalence of HIV infection, the determinants thereof and the risk behaviour in injecting drug users (IDUs) in Rotterdam, The Netherlands, in 2002 in comparison to the HIV survey data from 1994 and 1997.Questionnaire study.In 1994-2002, three periodic HIV surveys were conducted in Rotterdam among IDUs using semi-structured questionnaires on risk behaviour and saliva samples for HIV-antibody determination. In the present study, the data for 2002 were analysed and compared with those from 1994 and 1997.The number of participants recruited was 494, 470 and 452, respectively. HIV prevalence did not change over time: 1994: 11.4%, 1997: 9.4% and 2002: 10.2%. In the 2002 survey, independent risk factors for HIV were homelessness and onset of injecting drug use at an early age. The percentage of IDUs that had recently shared needles declined from 18% in 1994 to 8% in 2002. Risky sexual behaviour remained prevalent: inconsistent condom use was reported by 85% with steady partners, 43% with casual partners and 31% with clients. The IDUs who knew that they were HIV positive used condoms consistently more often.The combination of a relatively high HIV prevalence among IDUs in Rotterdam and the high level of unsafe sexual behaviour results in a serious risk of further spread of HIV among both IDUs and the general population.

The increasing trend in sexually transmitted infections (STIs) in the Netherlands observed over the past few years, appeared to stabilise in 2003. The number of genital chlamydial cases remained stable and the number of gonorrhoea cases decreased

The HIV epidemic in the Netherlands is changing as a result of increasing life expectancy due to the introduction of highly active antiretroviral therapy (HAART) since 1996, and a shift from homosexual to heterosexual transmission that is associated with rising numbers of HIV infected immigrants.

The National Institute of Public Health and the Environment (RIVM) in the Netherlands has begun surveillance of Staphylococcus aureus (MRSA) strains with the Panton-Valentine Leukocidin (PVL) gene in the Netherlands. This PVL gene is known to produce a potent toxin causing severe skin infections and necrotising pneumonia in both immunocompromised and immunocompetent individuals. About 60% of PVL positive isolates in the Netherlands belonged to ‘cluster 28’, which is an epidemic strain in the European mainland, but which has not yet caused large outbreaks in the Netherlands.

Background The Chlamydia Screening Implementation (CSI) is a Dutch large-scale pilot of an internet-based self-sampling Chlamydia trachomatis (Ct) screening program for 16–29-year-old men and women. The effectiveness of CSI can be estimated from changes in the positivity rate of the sampled individuals, but shifts in health-care use and CSI participation rates makes modelling a valuable alternative approach for estimating screening effectiveness. Methods We simulated the spread of Ct in a heterosexual population of age 13–65, using sexual survey data to parametrise a dynamic sexual contact network. A screening program was implemented in the model by constructing “participation trees”, which capture the likelihood to participate given an individuals participation history, as observed in the CSI program. Currently available health-care options to test for and treat Ct were also implemented in the model as a baseline (including trends in their usage), against which the effect of screening could be compared. In order to estimate the long-term effects of screening on the Ct prevalence in the Netherlands, future participation rates were estimated from trends in the yearly number of new participants, and by extrapolation of the participation trees. Results Compared to a baseline scenario, there is a moderate additional effect of 3 years of screening: the estimated Ct prevalence for the target population (16–29) dropped from 2.8% to 1.7% in large cities, and from 1.9% to 1.2% in more rural regions. As repeated invitees were likely not to participate, the largest effect of screening occurred in its first year when everyone in the target population was invited for the first time. After 3 years, the largest effect of screening on the Ct prevalence had been reached. Due to the anticipated further decrease in participation rates the long-term decrease in Ct prevalence is estimated to be in the range of 0.5–0.7 and 0.4–0.6 per cent-points in urban and rural regions, respectively. Conclusions A continued population based screening program has a permanent additional effect on lowering the Ct prevalence in the Netherlands, but the size of this effect is strongly tied to the participation rate in the targeted population. Therefore, the accuracy of long-term predictions of screening effectiveness depends on a good model implementation of the available data on participation behaviour.

Background Chlamydia infections are frequently found in young persons and ethnic minorities. Ethnicity can be defined in different ways. In this study, ethnic disparities in Chlamydia trachomatis positivity in the Netherlands were assessed comparing two definitions of ethnicity. The study objective was to determine which definition is most useful to discriminate persons at risk for Chlamydia infection. Methods Chlamydia positivity rates in persons aged 16−29 years, were investigated using data from the first round of the Chlamydia Screening Implementation (CSI, 2008−2009) and surveillance data from specialised at STI centres in the Netherlands (2009), comparing self-defined ethnicity and ethnicity based on the country of birth of a person and his parents (first and second generation immigrants). The relation between ethnicity and Chlamydia positivity rates were evaluated using logistic regression, adjusting for age, sex and SES, in both data sets. Results Overall, the Chlamydia positivity rate was 13 % in the STI centres, and 5% in CSI. Being a young (first or second generation) immigrant was associated with Chlamydia positivity in both CSI (adjusted OR 2.3 [95% CI 2.0 to 2.6]) and the STI centres (adjusted OR 1.4 [95% CI 1.3 to 1.5]). Classifying the population by self-defined ethnicity resulted in a considerable group labelling themselves as Dutch (57% of the immigrants in CSI and 60% of those in the STI centres), especially second generation immigrants (72% in CSI and 80% in the STI centres). Self-defined non-Dutch ethnicity showed similar associations with testing positive in CSI (OR 2.4 [95% CI 2.1 to 2.7]) and the STI centres (OR 1.2 [95% CI 1.0 to 1.3]), but the model basing ethnicity on country of birth of a person and his parents had a better fit (higher likelihood). Self-defined ethnicity may allow for more personal input, this however also makes it a dynamic variable: in the second round of CSI, 15% of the immigrants identified themselves by a different ethnicity than in the first round see Abstract P1-S4.02 Figure 1. Conclusions Both self-defined ethnicity and ethnicity based on the country of birth of a person and his parents, can be used to detect young persons at a higher risk of Chlamydia infection. However the definition of ethnicity based on the country of birth explains variation in the Chlamydia data better and is objective and constant, whereas self-defined ethnicity would disregard a large part of the young population at higher risk for Chlamydia infection.

Background A register- and Internet-based chlamydia screening started in 2008 among 16–29 year olds in Amsterdam, Rotterdam and South-Limburg, aiming to reduce population prevalence of chlamydia infections. Automated respondent reminders by letter, email and SMS were used to encourage and optimise participation. The contribution of reminders on package request and sample return was examined in relation to characteristics of the target population. Methods On average, 280 000 persons were annually invited by means of a personal letter. Individuals who did not respond to the invitation letter received a reminder letter after 1 month. Email- and SMS reminders were sent to individuals who requested a test kit and did not return a sample or did not check their test results online. We evaluated the effect of reminders on response and participation rates in two screening rounds. Logistic regression analyses were conducted to identify determinants of providing a GSM number, late response (requesting a test package after a reminder letter), and late participation (returning a sample after email/SMS reminders). Results The overall package request rate in the first round increased from 12% to 20% (see Abstract P2-S8.06 Figure 1) after the reminder letter (in round 2 from 8% to 14%). The proportion of individuals returning a sample increased from 10% to 16% after email/SMS reminders (in round 2 from 7% to 11%). Of all respondents, 99% provided an email address and 72% a GSM number. Factors associated with providing a GSM number were younger age (16–24 yrs), non-Dutch background, lower educational level, symptoms of an STI, and sexual risk behaviour in the past 6 months (p Conclusions Respondents’ willingness to provide an email address or GSM number for communication during the screening procedure was high. Factors associated with providing a GSM number were also related to chlamydia positivity. Automated respondents reminders by letter influenced response rates (package request) and resulted in reaching more people at higher risk. Email- and SMS reminders contributed substantially to participation rates (sample return).

Background The impact of a Chlamydia screening programme can be measured by the incremental amount of Chlamydia tests performed and cases detected as compared to the throughput in regular care. In the Netherlands, regular STI care is provided by specialised STI-centres (aimed at high-risk groups) and General Practitioners (GP9s, basic opportunistic screening and care for symptomatic cases). An annual register-based Chlamydia screening programme is implemented in three regions since 2008. Methods The number of persons tested and cases detected in the Chlamydia Screening among 16–29 year olds in Amsterdam, Rotterdam and South Limburg, 2008–2010, were compared to consultations and diagnoses in this age group reported in surveillance data from STI centres in the regions and estimates of STI care in general practices in these regions, 2007–2010. Round 3 data are based on the first 6 months of the year. Results The baseline testing rates (at STI centers and by GP9s in year pre-screening) were 10% in Rotterdam, 13% in Amsterdam and 6% in South-Limburg. CSI increased testing rates steeply in the first year to 26–30% in the cities and 17% in Limburg; this decreased to 20–21% and 13% in round 3, still doubling testing rates as compared to baseline. Positivity rates at regular STI-care facilities are higher than in CSI: 12–15% in regular care vs 4–5% in CSI; therefore the addition of CSI to case-finding in the three regions was lower than that to testing: the screening programme added about 41% on top of the cases found in regular care in round 1, but this decreased to 20% in round 3 due to lower participation and positivity rates in consecutive rounds. Conclusions By comparison to regular testing at STI centers and in general practice, the Chlamydia Screening had a major contribution towards the number of young people tested for Chlamydia in the three regions. The addition towards case-finding was lower, because the case-detection rate of the screening programme was lower than that in regular care. The Screening programme did not seem to affect the number of patients seen in regular care, but double “consumers” cannot be excluded.

Background Reinfections remain challenging in the control of Chlamydia trachomatis (Ct). In a systematic internet-based Ct Screening programme (CSI) in the Netherlands, all Ct-positive participants automatically received a test kit after 6 months to facilitate discovery of reinfections. Determinants for reinfection for two screening rounds, treatment and partner notification are discussed. Methods CSI-home-based testkits can be requested online after register based postal invitation. Infected participants get a referral letter for their health provider to get treatment for themselves and their current partner; expartners can be alerted by the participant and request a test kit via the website. Participants fill in a questionnaire on sexual behaviour voluntarily. Ct-positives answer questions about treatment and partner notification 10 days after checking their results. Infected participants who do not check their result online receive it by postal letter. After 6 months retest kits are automatically sent to previously infected participants. Results Overall, 3185 participants (4.1%) tested positive; 7% of Ct-positives did not check their result online and received a postal letter. The majority (86%) of Ct-positive participants who answered the treatment questionnaire (response 43%) was treated within 2 weeks after checking their result online; 80% of those with a current relationship reported their partner had also been treated and 16% of those with past relationships notified ex-partners via the website. One third of the ex-partners participated, 28% of whom were Ct-positive. After 6 months, 3055 participants received a retest kit and 66% responded. The reinfection rate was 8.8%. Results of the questionnaire revealed 75% of retest-positives had been treated for the initial infection and 70% had had their partner treated, while these proportions were 87% and 80% among retest-negatives. At higher risk for reinfections were young people ( Conclusions The uptake of retesting was successful counting two third with automatically sent testkits 6 months after screening. Reinfection rates were high, especially among known risk-groups. Questionnaire results show that follow-up of (partner) treatment after Chlamydia infections could be improved.

Background Partner notification (PN) is crucial for STI control. We developed SuggestATest.nl (SAT), an internet-based notification system for verified diagnoses of STI/HIV, that uses an index-chosen method per partner (email, text messaging, postal letter or a gay dating site; anonymous or non-anonymous). SAT was piloted at the Public Health STI clinics in Amsterdam and Rotterdam, the Netherlands. It was offered additional to counselling by the nurse. Method We evaluated SAT use and effectiveness from March-July 2012. Numbers/method of sent SAT notifications were extracted from the SAT database, and epidemiological data from electronic patient records. Determinants for SAT use (age, sex, ethnicity, partners, STI) were assessed using logistic regression analysis. Results Of 1184 index-clients receiving a SAT code, 160 (14%) notified through SAT. They sent 588 notifications (median 2), 82% by text messaging and 16% by email; 86% was non-anonymous. Univariate analysis of SAT use in heterosexuals showed that people with only 1 partner used SAT less often than others; this was the only significant predictor. In MSM, the STI diagnosed was the only significant univariate factor, with MSM with syphilis using SAT more often than MSM having other STI. Among all 67 SAT users in Rotterdam, 56% (225/402) of their eligible partners were notifiable, and 95% (213/225) of those were notified using SAT. In 17 MSM, 36% (87/239) of eligible partners were notifiable, and 97 (111% of 87) were notified in SAT. Of all notified partners, 56% entered SAT to see the STI they were notified for, and 20% visited the STI clinic in Amsterdam/Rotterdam. STI positivity in partners was lower in those notified by SAT (28%, n = 116) than in those with contact cards (45%, n = 152; p Conclusion SAT is a valuable addition for supporting partner notification and management, although challenges as non-notifiable partners are not solved by SAT.

Background The number of newly diagnosed HIV infections among men who have sex with men (MSM) has gradually increased in the Netherlands during the past decade. However, the current HIV surveillance system cannot differentiate recent HIV infections from longstanding HIV infections. We determined the proportion of recent HIV infections (RI) and estimated HIV incidence using Recent Infection Testing Algorithm (RITA) among newly diagnosed HIV infections among MSM in Amsterdam and Rotterdam. Methods Plasma samples (n = 251) collected from newly HIV-diagnosed MSM during 2009–2011 at the STI clinics in Amsterdam and Rotterdam were analysed in the study. To test for recent infections, anti-HIV avidity index (AI) was measured in plasma with Architect HIV Ag/Ab Combo immunoassay. Samples were classified as recent if the AI was ≤ 0.80. Data on viral load, CD4 count and previous HIV testing were incorporated in the RITA algorithm to minimise false recent infections. HIV incidence and 95% confidence intervals (CI) were estimated using previously described methods. Results Of the 251 samples from MSM, 83 were classified as recent by the avidity index. Five cases were reclassified as non-recent based on low CD4 count (n = 2) and viral load (n = 2) and history of HIV infection (n = 1) and thus, 78/251 (31%) infections were determined as recent on RITA. Proportions of RIs in 2009, 2010 and 2011 were 32%, 28% and 33%, respectively. The estimate for combined incidence was 1.5% per year (95% CI 1.17–1.83). No significant changes over time were observed. Conclusions This study estimated the proportion of RIs and HIV incidence among MSM in the Netherlands using the RITA algorithm for the first time. The proportion of RIs was comparable to similar studies in other European countries such as the UK, which however used different methodology.

Background Prediction of Chlamydia trachomatis (Ct) infection is important to identify subjects at high risk. We aimed to develop Ct prediction rules with different levels of detail in information, i.e. with readily available registries only and with additional detailed questionnaires. Methods In the Chlamydia Screening Implementation (CSI) study all inhabitants of Rotterdam and Amsterdam aged 16–29 were invited yearly from 2008 until 2011 for home based urine testing. This resulted in 80,385 unique participants of whom 3,440 were infected. In addition to registry data (gender, age, ethnicity, neighbourhood level socioeconomic status [SES]) participants were asked to fill in a questionnaire on education, STI history, symptoms, partner information and sexual behaviour. We developed prediction rules based on registry risk factors only and with additional questionnaire risk factors by multilevel logistic regression to account for clustering within neighbourhoods. We assessed the discriminative ability by the area under the receiver operating characteristic curve (AUC). The models were internally validated with a bootstrap procedure. Results Strong registry based predictors for Ct infection were young age (especially for women) and either Surinamese, Antillean or Sub-Sahara-African ethnicity. SES was of minor importance especially when questionnaire predictors were added. From the questionnaire, low to intermediate education level, ethnicity of the partner (non-Dutch) and having sex with casual partners showed strong associations with Ct infection. The AUC at internal validation was 0.67 based on registry risk factors only and 0.75 when questionnaire risk factors were added. To find 80% of the Chlamydia infections approximately 50% of the population needed to be screened when using the prediction rule including questionnaire risk factors. Conclusion The registry based prediction rule can potentially facilitate selective Ct screening at population level, with further refinement at the individual level by including questionnaire risk factors.

Background Partner notification (PN) is seen as a vital tool to break HIV/STI transmission chains. In the Netherlands, studies assessing PN effectiveness were lacking. Here, we evaluated effectiveness of current PN practises in STI clinics to provide recommendations to further enhance PN. Methods PN outcomes were collected through a newly developed registration system from index patients with HIV, syphilis, and gonorrhoea visiting five STI centres in 2010–2011. PN outcomes for men who have sex with men (MSM) and heterosexuals included partners: at risk, notifiable, notified, tested and diagnosed with STI/HIV. Results Of all index patients newly diagnosed with HIV/STI (N = 388) for whom PN was indicated, 312 MSM, 35 heterosexual men and 41 women reported respectively 2042, 126 and 82 partners at risk (6.5, 3.6 and 2.0 partners per index). Proportions of notifiable partners differed significantly by sexual preference (MSM: 46%, heterosexual men: 63%, women: 87%, p Conclusions The major challenge in PN among MSM remains the large proportion of unnotifiable (anonymous) partners, whereas among heterosexuals a higher percentage partners were lost during the actual notification process. Therefore, newly developed interventions, e.g.anonymous internet-based PN or PN training, should be tailored to specific risk-groups.

Objective To assess the association between chlamydia (CT)-test results and subsequent sexual risk behaviour change in a register based Chlamydia Screening (CSI) programme consisting of four screening rounds. Methods All participants in the CSI programme, who had completed questionnaires and corresponding CT-test results in ≥ 2 rounds, were included. Measurements in round four were excluded, because of low participation rates. Sexual risk behaviour parameters contained the use of condoms, number of partners and having casual, concurrent or new partners. Generalised estimating equations (GEE) were used to assess the influence of the test result on the change in sexual risk behaviour in the subsequent round. Analysis were adjusted for sexual preference, having a steady or casual partner, age and number of rounds participated. Results Of 9360 included participants, 80.5% (n = 7536) and 19.5% (n = 1824) completed CT-testing and questionnaires in respectively two and three rounds. Across all rounds, a significant difference in change of sexual risk behaviour could be found: participants who tested CT-positive in the previous round more often reported reduced risk behaviour (more use of condoms with a casual partner (32.1% vs 24.1%, p = 0.018), less having sex with a casual partner (21.7% vs 15.3%, p = 0.001), lower number of sex partners (38.5% vs 24.7%, p Conclusion Sexual risk behaviour change was associated with previous CT-test results. Participants who tested CT-positive more often positively changed their sexual risk behaviour compared to participants with a negative test result in the previous round.

Background In cervical cancer screening, uptake of screening is approximately 10% higher if a woman is invited by her General Practitioner (GP) compared to invitation by Municipal Public Health Service (PHS). A large register-based selective Chlamydia Screening Programme is implemented in Amsterdam (Netherlands) since 2008 by the PHS. We wanted to evaluate whether response rates in Chlamydia screening where higher if invitational letters are sent by a persons9 GP and not by PHS. Methods Based on the municipal registers, annually all 140 000 persons in Amsterdam aged 16–29 yr are invited with a postal letter to participate. Further procedures are internet-based: requesting test-packages, obtaining results, even partner-referral, can be realised via the internet and the unique identifier provided in the personal letter. In one part of the city, the Southeast inner-city area, GP-registers of six health centre are matched with the list of invitees extracted from the municipal register. In the invitational letter these matched eligible9s are personally addressed by their GP and not by the physician of the PHS. Participation rates from invitees of GP and PHS in the same geographical town area are compared in three screenings-rounds (r 3 not yet fully completed). Results In these four town area9s in each screening round annually 13 500 persons are invited, of which 35% by the GP and 65% by PHS. In screenings-round 1, the response to invitations by the GP was slightly higher than the response to invitations sent by the PHS in 3 out of 4 neighbourhoods where this was piloted (overall GPs: 16.2% [range: 15.3%–29.1%]; overall PHS: 14.9% [14.4%–21.6%], p=0.023). In round 2 and 3 the difference was not significant (GP vs MHS: r2 10.3%–10.2%; r3 9.5% vs 9.4%). (Abstract O5-S4.01 figure 1). Conclusions In the first screening-round uptake was slightly higher among GP-invited, but this effect was lost in subsequent screening-rounds. Inviting universally via the PHS is logistically easier and yields the same response rate.

Background Chlamydia screening programmes can only work when they motivate sufficient persons at risk to get tested regularly. The outcomes of the Chlamydia Screening Implementation (CSI) in the Netherlands are novel and valuable because of the large scale of the programme (315 000 young persons targeted), its systematic nature (invitations based on municipal registers) and its multiple screening rounds (annual invitations in three consecutive years). Methods From April 2008 to March 2010, Chlamydia Screening was offered annually to municipal-registered 16–29 year olds in three regions of the Netherlands. A phased implementation was applied by grouping clusters in three random, risk-stratified blocks. Participation and positivity rates were compared between blocks submitted to 1, 2 or 3 screening rounds (3rd round only partially completed). The effect of the repeated screening rounds on the prevalence of Chlamydia in the whole target group was estimated by weighting procedures comparing demographic characteristics of participants and target group. Results The participation rate in the first round was 16% among all invitees and 20% among the sexually active target population (M13%, F 25%). The participation fell down to 11% in blocks invited two times and 9% in the block invited three times, whereas it was 13% in the control block invited in round two only. The positivity rate in round one was 4.2% among all participants. Positivity rates decreased significantly to 4.0% in blocks screened twice and to 3.5% in the block screened thrice (p=0.04); in the control block 4.3% tested positive. The population prevalence was estimated at 2.6% in Amsterdam, 3.8% in Rotterdam and 2.4% in South Limburg. The prevalence declined over the three screening rounds, but declines were not significant (see Abstract O1-S09.03 figure 1). Conclusions The participation in the CSI project was lower than expected and declined with repeated invitation. Chlamydia positivity rates were reduced by 17% in clusters screened three times, whereas these stayed high in control groups. Only a small and non-significant impact on population prevalence was measured. Further extrapolation of the findings in a simulation model suggest a limited impact on Chlamydia prevalence after 10 years of screening and estimates of cost-effectiveness do not support a nationwide roll-out of this programme in the Netherlands.