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During the last 20 years we have seen the re-emergence of diseases; emergence of new diseases in new locations and witnessed outbreaks of varying intensity and duration. Spatial epidemiology plays an important role in understanding the patterns of disease and how they change over time and across space.The aim of this paper is to bring together a public health and geospatial data science perspective to provide a framework that will facilitate the integration of geographic information and spatial analyses at different stages of public health response so that these data and methods can be effectively used to enhance surveillance and monitoring, intervention strategies (planning and implementation of a response) and facilitate both short- and long-term forecasting.To demonstrate elements of this framework and how it can be utilized, we selected three case studies ranging from the current the global COVID-19 Coronavirus pandemic of 2020 to more historical examples such as the John Snow Cholera outbreak of 1854 and the Ebola outbreak of 2014 in West Africa.A variety of methods including spatial descriptive statistics, as well as methods for analysing patterns were used. The examples we provide can reveal sources of infection, connectivity between locations, delineate zones of containment and show the spread of an outbreak globally and locally across space and time.

Background West Nile Virus (WNV) is a mosquito-borne pathogen that has become established in North America. Risk for human infection varies geographically in accordance with climate and population factors. Though often asymptomatic, human WNV infection can cause febrile illness or, rarely, neurologic disease. WNV has become a public health concern in Canada since its introduction in 2001. Methods To identify predictors of human WNV incidence at the public health unit (PHU) level in Ontario, Canada, we combined data on environmental and population characteristics of PHUs with historical mosquito and human surveillance records from 2002 to 2013. We examined the associations between annual WNV incidence and monthly climate indices (e.g. minimum and maximum temperature, average precipitation), land cover (e.g. deciduous forest, water), population structure (e.g. age and sex composition) and the annual percentage of WNV-positive mosquito pools from 2002 to 2013. We then developed a generalized linear mixed model with a Poisson distribution adjusting for spatial autocorrelation and repeat measures. Further to this, to examine potential ‘early season’ predictors of WNV incidence in a given year, we developed a model based on winter and spring monthly climate indices. Results Several climate indices, including mean minimum temperature (o C) in February (RR = 1.58, CI: [1.42, 1.75]), and the annual percentage of WNV-positive mosquito pools (RR = 1.07, CI: [1.04, 1.11]) were significantly associated with human WNV incidence at the PHU level. Higher winter minimum temperatures were also strongly associated with annual WNV incidence in the ‘early season’ model (e.g. February minimum temperature (RR = 1.91, CI: [1.73, 2.12]). Conclusions Our study demonstrates that early season temperature and precipitation indices, in addition to the percentage of WNV-positive mosquito pools in a given area, may assist in predicting the likelihood of a more severe human WNV season in southern regions of Ontario, where WNV epidemics occur sporadically. Electronic supplementary material The online version of this article (10.1186/s12879-018-3052-6) contains supplementary material, which is available to authorized users.

ObjectivesRepeat positive tests for chlamydia (CR) may help explain current high rates of chlamydia despite years of screening, partner notification and treatment to reduce sequelae. We wanted to determine the numbers of CRs over time as a proportion of all chlamydia cases, and define the differences in demographic, clinical, behavioural, and public health management indicators, between individuals who have experienced a CR and individuals who experienced a single infection in Brant County, Ontario.MethodsA retrospective cohort was developed using notifiable disease data extracted from the integrated public health system. Cases were laboratory confirmed chlamydia and gonorrhea infections in Brant County between January 1st, 2006 and December 31st, 2015. During the study period, 3,499 chlamydia cases and 475 gonorrhea cases were diagnosed. The total number of individuals with chlamydia in that period was 3,060, including 157 coinfections with gonorrhea. Differences between those with reinfection and those with single infection were evaluated using univariate and multivariate (Cox proportional hazards model) methods.ResultsFour hundred and ninety-nine (16.30%) individuals experienced CR 28 days from initial infection; of which 328 (65.73%) occurred within 2 years and 211 (42.28%) within 1 year. The median time to CR was 276 days, consistent with existing Canadian literature. Independent risk factors for CR included being male, 25 years old or younger, and not receiving recommended treatment for initial and/or subsequent infection.ConclusionsThese findings suggest that inadequate treatment play a significant role in CR, while accounting for young age and male gender, likely due to untreated sex partners.Key MessagesSixteen percent of people experienced a second positive chlamydia test more than 28 days after their initial positive test in a cohort of 3,499 patientsThose who had a second positive test were more likely to be male, younger than 25 and had not received recommended antimicrobialsConfirmation of any kind of partner notification was missing in 88% of records

Background Despite increased awareness of infection control precautions, methicillin-resistant Staphylococcus aureus (MRSA) still spreads through patients and contaminated objects, causing a substantial burden of illness and cost. Our objective was to define risk factors for contracting MRSA in a tertiary health care facility using a historic case-control study and to validate health care network changes during pre-outbreak and outbreak periods. Methods We conducted a case-control study using secondary data on hospitalizations where infected or colonized cases were compared with matched controls who tested negative by age, sex, and campus over 1 year. Social networks of all cases and controls were built from links joining patients to rooms, roommates, and health care providers over time. Results Matched controls were similar to cases in comorbidity, lengths of stay, mortality, and number of roommates, rooms, and health care providers. As expected, the number of rooms and roommates increased in the outbreak by more than 50%. A timed animation of the network at one campus identified potential source patients linked to 2 rooms and many roommates, after which cases connected to those same rooms proliferated. Conclusions Only the network animation over time revealed possible transmission of MRSA through the network, rather than attributes measured in the traditional case control study.

We utilized public health data and a geographic information system (ArcGIS) to study long-distance sexual partnerships (opposite and same sex partnerships) among chlamydia, gonorrhea, and coinfected STI (sexually transmitted infection) cases. The top 10% of relationships among chlamydia and gonorrhea cases and their contacts equaled or exceeded 198 km and 237 km respectively; the top 15% of partnerships among coinfected cases equaled or exceeded 207 km. This research also detected proportionately more long-distance partnerships among gonorrhea cases than among chlamydia cases. Wasserheit and Aral's four-phase model for understanding the impact of control programs on STI incidence over time offers one framework for interpreting these results: as chlamydia was in an early decline phase during the period under study, while gonorrhea had reached a phase of low endemicity, our results could suggest that in later phases of an STI control program, the overall proportion of long-distance relationships among cases and contacts may increase.

Secondary syringe exchange (SSE) refers to the exchange of sterile syringes between injection drug users (IDUs). To date there has been limited examination of SSE in relation to the social networks of IDUs. This study aimed to identify characteristics of drug injecting networks associated with the receipt of syringes through SSE. Active IDUs were recruited from syringe exchange and methadone treatment programs in Montreal, Canada, between April 2004 and January 2005. Information on each participant and on their drug-injecting networks was elicited using a structured, interviewer-administered questionnaire. Subjects’ network characteristics were examined in relation to SSE using regression models with generalized estimating equations. Of 218 participants, 126 were SSE recipients with 186 IDUs in their injecting networks. The 92 non-recipients reported 188 network IDUs. Networks of SSE recipients and non-recipients were similar with regard to network size and demographics of network members. In multivariate analyses adjusted for age and gender, SSE recipients were more likely than non-recipients to self-report being HIV-positive (OR = 3.56 [1.54–8.23]); require or provide help with injecting (OR = 3.74 [2.01–6.95]); have a social network member who is a sexual partner (OR = 1.90 [1.11–3.24]), who currently attends a syringe exchange or methadone program (OR = 2.33 [1.16–4.70]), injects daily (OR = 1.77 [1.11–2.84]), and shares syringes with the subject (OR = 2.24 [1.13–4.46]). SSE is associated with several injection-related risk factors that could be used to help focus public health interventions for risk reduction. Since SSE offers an opportunity for the dissemination of important prevention messages, SSE-based networks should be used to improve public health interventions. This approach can optimize the benefits of SSE while minimizing the potential risks associated with the practice of secondary exchange.

Aim To examine the scientific evidence regarding the association between characteristics of social networks of injection drug users (IDUs) and the sharing of drug injection equipment. Methods A search was performed on MEDLINE, EMBASE, BIOSIS, Current Contents, PsycINFO databases and other sources to identify published studies on social networks of IDUs. Papers were selected based on their examination of social network factors in relation to the sharing of syringes and drug preparation equipment (e.g. containers, filters, water). Additional relevant papers were found from the reference list of identified articles. Results Network correlates of drug equipment sharing are multi-factorial and include structural factors (network size, density, position, turnover), compositional factors (network member characteristics, role and quality of relationships with members) and behavioural factors (injecting norms, patterns of drug use, severity of drug addiction). Factors appear to be related differentially to equipment sharing. Conclusions Social network characteristics are associated with drug injection risk behaviours and should be considered alongside personal risk behaviours in prevention programmes. Recommendations for future research into the social networks of IDUs are proposed.

Objective: To identify and compare the drug-injecting network characteristics of cocaine and heroin injectors associated with a risk of HIV and hepatitis C virus (HCV). Methods: Active injectors were recruited from syringe exchange and methadone programs. Characteristics of all participants and their social networks were elicited. Regression analysis using generalized estimating equations examined the network characteristics of injection drug users (IDUs) relative to cocaine or heroin use in the past 6 months. Results: Of 282 IDUs, 228 (81%) used cocaine and 54 (19%) used heroin as their primary injected drug. In analyses adjusted for age and gender, cocaine injectors compared with heroin injectors were more likely to live in unstable housing (odds ratio [OR] = 3.55, 95% confidence interval [CI]: 1.49 to 8.40), self-report HCV infection (OR = 4.69, 95% CI: 2.14 to 10.31), and have a greater number of IDUs in their social network (OR = 1.61, 95% CI: 1.14 to 2.28) and were less likely to be polydrug users (OR = 0.06, 95% CI: 0.02 to 0.16) and to have social support (OR = 0.97, 95% CI: 0.95 to 0.99). The injecting networks of cocaine users were more likely to have members who were older (OR = 1.08, 95% CI: 1.04 to 1.12), had a history of shooting gallery use (OR = 2.27, 95% CI: 1.08 to 4.76), and had shorter relationships with the subject (OR = 0.91, 95% CI: 0.85 to 0.97). Conclusions: Beyond personal behaviors, HIV and HCV infection risk seems to be linked to social network traits that are determined by drug type. Prevention efforts to control the spread of bloodborne viruses among IDUs could benefit from tailoring interventions according to the type of drug used.

Purpose Persistence of sexually transmitted infections (STI) in a population is due to the activities of a small proportion of the population with STI, who transmit infection on average to one or more susceptible sex partners during an infectious period. Within these groups, the average number of transmissions by infectious people to susceptible people in a closed group is measured by the reproductive number; a threshold, above which endemic infection is likely occur and below which, in the rest of the population, it is unlikely to occur. We hypothesized that people with repeated bacterial STI's and their sex partners include the theoretical core group and that they differ from singly infected noncore individuals. Methods Data on infected individuals and nominated sex partners for the years 1990–1992 were extracted from the notifiable disease and health insurance registries in Manitoba, Canada. Individuals with repeated gonorrhea, chlamydia and coinfected infections were compared using logistic regression, and reproductive numbers were calculated using sex partner data. Results Of the three groups, the coinfected were youngest, and they were largely of aboriginal descent and had the lowest incomes. Repeaters were older; they had higher incomes, and there were fewer aboriginal people in this group. Chlamydia repeaters had even higher incomes, and this group comprised the least number of aboriginal people. The reproductive numbers showed the same gradient; (1.09, 1.01, and 2.41, respectively.) Conclusions These data show that these groups do not contribute equally to STI endemicity and indicate that sexual network structure affects epidemic thresholds.

This study describes the epidemiology and ethnography of an outbreak of infectious syphilis in Vancouver, British Columbia. Between 1996 and 1999, British Columbias's rate of infectious syphilis rose from 0.5 to 3.4 per 100 000, with a dense concentration of cases among sex trade workers, their clients, and street-involved people in the downtown eastside area of Vancouver. Sexual networks were imported cases with secondary spread (dyads and triads), large densely connected dendritic networks of sex trade workers and clients, or occasional starburst networks among gay men. Only 232 of 429 partners were documented as having been treated (54% of those named, or 0.9 per case). The geographical and demographic concentration of this outbreak led to consideration of a programme of focused mass treatment with single dose azithromycin.

Objective We previously identified a high prevalence of Hepatitis C (HCV) amongst solvent-using injection drug users (S-IDU) relative to other injection drug users within the same locality. Here we incorporated social network variables to better characterize some of the behavioural characteristics that may be putting this specific subgroup of IDU at elevated disease risk. Methods A cross-sectional survey of at-risk populations was carried out in Winnipeg, Canada in 2009. Individuals reporting any history of injection drug and/or solvent use were included in the study. Associations between subgroup membership, infection with HCV and HIV and individual and social network variables were examined. Results In relation to other IDU, S-IDU were more likely to be infected with HCV, to report ever having shared a syringe, and to associate with other IDU. They were further differentiated in terms of their self-reported sexual orientation, ethnicity and in the injection drugs typically used. Conclusion Solvent use stands as a proxy measure of numerous other characteristics that put this group of IDU at higher risk of infection. Provision of adequate services to ostracized subpopulations may result in wider population-level benefits.

Background Methods for accessing large sexual networks are essential for investigating the mechanisms for the spread of sexually transmitted infections. Goal Four samples of cases were compared with the total population to determine which identified the largest networks. Study Design Individuals with positive test results for chlamydia during a 6-month period were selected from a laboratory database and linked with sex partner information from a notifiable disease registry. Sexual networks were constructed for a random sample, people with positive results from two or more tests for chlamydia, people with positive tests results for both gonorrhea and chlamydia, and the preceding two groups combined. Results The coinfected people combined with the repeaters yielded the highest proportion (47.8%) of large networks (>10 people), followed by the coinfected people, the repeaters, and finally the random sample. Conclusions People coinfected with chlamydia and gonorrhea and those with repeated chlamydial infection present ideal opportunities for both research and prevention.

Background: There is little understanding about how the social networks of cocaine injectors are different from those of heroin users and about how such differences are associated with injection risk behaviours. Therefore, the objective of this study was to compare drug-injecting network characteristics of cocaine and heroin injectors believed to be associated with a risk of bloodborne infections. Methods: Active injection drug users (IDUs) were recruited between April 2004 and January 2005 from three syringe exchange and two methadone treatment programs in Montreal, Canada. Characteristics of each participant and of up to 10 social network members (IDU and non-IDU) with whom frequent contact had occurred in the past month were elicited using a structured, interviewer-administered questionnaire. The current analysis focussed on the drug-injecting network members. Logistic regression was used to examine network characteristics in relation to cocaine and heroin injection. Results: Of 282 study subjects, 81% used cocaine and 19% used heroin as their primary injected drug in the past 6 months. Compared to heroin injectors, participants who injected cocaine had lower odds of knowing their network members for a longer time (OR=0.92, 0.85–0.99), were more likely to report a larger IDU network (OR=1.64, 1.18–2.29) and have IDU partners who had a history of attending shooting galleries (OR=2.42, 1.05–5.56). Interpretation: This study identified high-risk network-related factors associated with bloodborne infections in cocaine injectors. Prevention efforts may benefit from tailoring interventions according to type of drug used, with particular attention to the drug injecting-network of IDUs.

Globally, incidence of Neisseria gonorrhoeae infection is once again the highest of the bacterial sexually transmitted infections. The bacterium can produce serious complications in those infected, and emerging resistance to third generation cephalosporins could usher in an era of potentially untreatable gonorrhea. This research aimed to identify risk factors for antibiotic resistant gonorrhea infection among clients at a Shanghai sexually transmitted infection clinic over two time periods, 2004–2005 and 2008–2011. Demographic and risk factor behavior data, and biological samples for antimicrobial resistance analysis, were collected. Statistical models were built to identify risk factors associated with probable resistance to ceftriaxone and resistance to penicillin and tetracycline. High levels of ciprofloxacin resistance (98%) in our sample precluded examining its risk factors; all isolates were susceptible to spectinomycin. Overall (P

Background and Objectives: Despite sharing common modes of transmission, characteristics of individuals infected with Chlamydia trachomatis differ in several respects from those with Neisseria gonorrhoeae infection. Further characterization of women at high risk for chlamydial infection is needed to deliver appropriate and effective preventive, diagnostic, and therapeutic care to this population. Goal of this Study: The demographic and socioeconomic characteristics of women with laboratory confirmed chlamydia, gonorrhea, or coinfection were compared with those of control women who tested negative for both pathogens. Study Design: A random sample of 400 women in Manitoba, Canada, who had undergone testing for sexually transmitted diseases at a public health laboratory in 1988 were studied. After linkage with medical insurance and census databases, logistic regression analysis was used to compare age, ethnicity, urban status, and mean income (using postal codes) of women with gonorrhea alone, chlamydia alone, and coinfection, with the same data for women who tested negative for both organisms. Results: Young age, North American Indian status, urban residence, and low mean income according to postal code were significantly associated with gonococcal and chlamydial infection in the study population, compared with women who tested negative for both infections. Young age, Indian status, and urban residence also were associated with gonorrhea infection alone. Only young age and Indian status were associated with chlamydial infection. Mean incomes of women with chlamydial infection alone and control subjects were higher than those of women with gonorrhea and gonorrhea and chlamydia coinfection. Conclusions: Differences in the demographic and socioeconomic characteristics of women with gonorrhea, chlamydia, and coinfection suggest the existence of multiple reservoirs of infection due to these agents in the study population. The preventive, diagnostic, and therapeutic strategies of sexually transmitted disease control programs must be adapted to the individual needs of identified high-risk groups.

Our objective was to examine the association between HIV and HCV discordant infection status and the sharing of drug equipment by injection drug users (IDUs). IDUs were recruited from syringe exchange and methadone treatment programmes in Montreal, Canada. Characteristics of participants and their injecting partners were elicited using a structured questionnaire. Among 159 participants and 245 injecting partners, sharing of syringes and drug preparation equipment did not differ between concordant or discordant partners, although HIV-positive subjects did not share with HIV-negative injectors. Sharing of syringes was positively associated with discordant HIV status (OR = 1.85) and negatively with discordant HCV status (OR = 0.65), but both results were not statistically significant. Sharing of drug preparation equipment was positively associated with both discordant HIV (OR = 1.61) and HCV (OR = 1.18) status, but both results were non-significant. Factors such as large injecting networks, frequent mutual injections, younger age, and male gender were stronger predictors of equipment sharing. In conclusion, IDUs do not appear to discriminate drug equipment sharing partners based at least on their HCV infection status. The results warrant greater screening to raise awareness of infection status, post-test counselling to promote status disclosure among partners, and skill-building to avoid equipment sharing between discordant partners.

Objectives. We used cluster analysis to subdivide a population of injection drug users and identify previously unknown behavioral heterogeneity within that population. Methods. We applied cluster analysis techniques to data collected in a cross-sectional survey of injection drug users in Winnipeg, Manitoba. The clustering variables we used were based on receptive syringe sharing, ethnicity, and types of drugs injected. Results. Seven clusters were identified for both male and female injection drug users. Some relationships previously revealed in our study setting, such as the known relationship between Talwin (pentazocine) and Ritalin (methylphenidate) use, injection in hotels, and hepatitis C virus prevalence, were confirmed through our cluster analysis approach. Also, relationships between drug use and infection risk not previously observed in our study setting were identified, an example being a cluster of female crystal methamphetamine users who exhibited high-risk behaviors but an absence or low prevalence of blood-borne pathogens. Conclusions. Cluster analysis was useful in both confirming relationships previously identified and identifying new ones relevant to public health research and interventions.

Increases in the rates of sexually transmitted infections (STIs) suggest that control programmes may not be effectively targeting diverse subpopulations. The objective of this investigation was to examine STI transmission within different groups, using both social network analysis and cluster analysis. Routine partner notification data were analysed from individuals diagnosed with, or exposed to an STI in Manitoba. Groups were identified and characterized. Three different clusters of groups were identified, comprised of demographically and clinically distinct individuals. A greater understanding of disease transmission patterns within these groups will aid in the development of targeted education and prevention programmes for all STIs.

Using social network analysis, we investigated how communal meeting places can link injection drug user (IDU) populations and create opportunities for the transmission of bloodborne pathogens. In our locale, specific hotels played a key role in the injection drug scene. Within this hotel network some IDU injected at only one hotel while others injected at multiple hotels; this latter group potentially acted as spatial bridges linking relatively distinct hotel networks. Pathogen prevalence showed a gradation with the highest prevalence occurring at the centre of the network. Consistent with pathogen prevalence, people most central to the network were more likely to engage in risky injection practices. Incorporating geographic place into analyses involving IDU can contribute to an understanding of pathogen transmission patterns in an area and assist public health efforts to develop targeted intervention programs.

Background The use of sexual network analysis has the potential to further our understanding of sexually tranmitted disease (STD) epidemics and contribute to the development of more effective targeted control strategies. Goal To use sexual network analysis to study transmission patterns of chlamydia and gonorrhea in Manitoba, Canada. Study Design Routinely collected case/contact information gathered by public health nurses was used to construct the sexual network. Results Components within the sexual network ranged in size from 2 to 82 people. Two types of components, designated radial and linear, were described. Large linear components resembled the theoretical structure of STD core groups. Geographic analysis of the largest components demonstrated the potential for STD transmission between isolated rural communities and within different areas of an urban center. Conclusions The application of sexual network analysis on a provincial basis demonstrated the importance of a centralized, coordinated approach to STD control. The analysis highlights the need for a greater understanding of the causative factors promoting the formation of different component types, the homogeneity and heterogeneity of behaviors within and between components, and the temporal stability of these patterns.

We conducted a comparative evaluation of the Chlamydiazyme (Abbott Laboratories), PACE 2 (Gen-Probe), and AMP-CT (Gen-Probe) assays for the detection of Chlamydia trachomatis in endocervical samples. Specimens from 787 females were included in the study. The sensitivities of the PACE 2 and Chlamydiazyme assays in comparison to the results of the AMP-CT assay were 79.3 and 63.4%, respectively. The specificities of the Chlamydiazyme and PACE 2 assays were 100%. All of the positive specimens detected in this study were positive by the AMP-CT assay. On the basis of the final results of the comparison, the prevalence of C. trachomatis in the population was 10.4%. Retesting of specimens whose results were in the intermediate zone by the PACE 2 assay by a probe competition assay identified some additional true-positive specimens. Amplification assay testing of such specimens did not significantly increase the yield. The majority of specimens which tested positive by the AMP-CT assay only were not in the intermediate zone by the PACE 2 assay. We were unable to identify demographic or clinical factors which could predict those individuals who tested positive by amplified tests but not by nonamplified tests. The Gen-Probe PACE 2 assay proved to be superior to the Chlamydiazyme assay for the screening and diagnosis of C. trachomatis infections in female endocervical specimens.

Background An outbreak of infectious syphilis among men who have sex with men (MSM) in Toronto began in 2002 and peaked in 2009 when 579 cases were reported. We developed an internet-based enhanced surveillance tool to investigate HIV coinfection, sexual risk behaviours, and social networks among a sample of cases in 2010. Methods Males with infectious syphilis in Toronto from 15 April 2010 to 30 June 2010 were invited to complete a self-administered online survey. Data were collected on sexual partners, risk behaviours, condom use, and venues where respondents looked for sex partners in the 6 months before syphilis infection. We assessed key survey variables by HIV status, and carried out social network analyses to examine links between cases, sexual contacts and venues. Results Of 84 eligible cases, 46 were successfully contacted and 27 completed the survey. Three of 27 respondents (11%) identified sexual contacts and 16 (59%) reported having multiple sex partners during routine case follow-up. In the online survey, almost all men (n=26) reported at least one male sex partner in the six months before syphilis infection (median 5 partners; IQR 2–12). HIV prevalence among respondents was 70% (vs 35% among non-respondents, p Conclusions A substantial proportion of men in our sample reported multiple sex partners and low condom use. As respondents were predominantly HIV-positive MSM with seroconcordant sex partners, risk behaviours, venue attendance and patterns of condom use may not be representative of all MSM with syphilis in Toronto. Nevertheless, collection of behavioural data using an online survey allowed for enhanced descriptive analyses beyond the scope of routine surveillance. In addition to social network analyses, these data are useful to inform targeted prevention and control efforts.

Introduction Globally, substantial heterogeneity in the prevalence of HIV and other sexually transmitted infections (STIs) among most at-risk populations (MARPs) has been demonstrated. Examining factors related to heterogeneity can inform targeted programming. In Winnipeg, Canada, particularly high risk for HIV and hepatitis C (HCV) has been observed in injection drug users (IDUs) with a history of solvent use (S-IDUs). However, comparisons to other MARPs have been limited. Thus this study examined the association between HIV/STIs and S-IDUs in comparison to IDUs and other MARPs. Methods Data were from a 2008 to 2009 cross-sectional study of Winnipeg MARPs (IDUs, sex work- and street-involved individuals); subjects were recruited through respondent-driven sampling (RDS) methods. Adjusted ORs (AORs) from multivariable logistic regression models were estimated, examining the risk of HIV, HCV and HIV/HCV co-infection, and corrected for RDS-chain clustering using generalised estimating equations. Results Total sample was 499, of which 13% recently injected drugs (ie, last 6 months), 5% recently inhaled solvents, 6% were recent S-IDUs, and 76% did not inject drugs or inhale solvents. HIV and HCV prevalence among recent S-IDU was 21% and 79%, respectively; HIV/HCV co-infection was 18%. In multivariable models, S-IDUs were at highest risk of HIV (AOR: 3.6, 95% CI: 1.6% to 7.9%; p Conclusions Solvent use occurs among the most marginalised of MARPs, representing unique and complicated drug use trajectories. As the HIV epidemic in Canada becomes increasingly complex, examination of outlier populations such as S-IDU can inform public health by elucidating important pathways by which structural, environmental and individual factors interact to create the highest risk for HIV/STIs and other bloodborne pathogens.