Impact of statistical adjustment for frequency of venue attendance in a venue-based survey of men who have sex with men

Sensitivity analysis of selection bias: a graphical display by bias-correction index

Background

In observational studies, how the magnitude of potential selection bias in a sensitivity analysis can be quantified is rarely discussed. The purpose of this study was to develop a sensitivity analysis strategy by using the bias-correction index (BCI) approach for quantifying the influence and direction of selection bias.

Methods

We used a BCI, a function of selection probabilities conditional on outcome and covariates, with different selection bias scenarios in a logistic regression setting. A bias-correction sensitivity plot was illustrated to analyze the associations between proctoscopy examination and sociodemographic variables obtained using the data from the Taiwan National Health Interview Survey (NHIS) and of a subset of individuals who consented to having their health insurance data further linked.

Results

We included 15,247 people aged ≥20 years, and 87.74% of whom signed the informed consent. When the entire sample was considered, smokers were less likely to undergo proctoscopic examination (odds ratio (OR): 0.69, 95% CI [0.57-0.84]), than nonsmokers were. When the data of only the people who provided consent were considered, the OR was 0.76 (95% CI [0.62-0.94]). The bias-correction sensitivity plot indicated varying ORs under different degrees of selection bias.

Conclusions

When data are only available in a subsample of a population, a bias-correction sensitivity plot can be used to easily visualize varying ORs under different selection bias scenarios. The similar strategy can be applied to models other than logistic regression if an appropriate BCI is derived.

Uptake of Mpox vaccination among transgender people and gay, bisexual and other men who have sex with men among sexually-transmitted infection clinic clients in Vancouver, British Columbia

OBJECTIVES

As the primary public health strategy for controlling the 2022 Mpox outbreak, it is critical to evaluate the impact of Mpox vaccination campaigns for transgender people and gay, bisexual and other men who have sex with men (T/GBM). We measured vaccine uptake and associated factors among T/GBM clients of an urban STI clinic in British Columbia (BC).

METHODS

We conducted a cross-sectional online survey between August 8-22, 2022 of clients who had attended the STI clinic, 5-7 weeks following the first-dose Mpox vaccination campaign in BC. We drew on a systematic review of factors associated with vaccine uptake to develop survey questions, and measured vaccine uptake among vaccine-eligible T/GBM.

RESULTS

Overall, 51% of T/GBM had received the first dose of the vaccine. The sample (331 participants) was majority White and university educated, identified as a man and gay, 10% had trans experience, and 68% met eligibility criteria for vaccination. Among vaccine-eligible participants identifying as T/GBM, 66% had been vaccinated; being unvaccinated was more common among participants identifying as bisexual or heteroflexible/mostly straight, and who spent less time with other T/GBM. Eligible yet unvaccinated participants had lower perceived susceptibility, and reported fewer cues to action (e.g., fewer saw information promoting the vaccine), and increased constraints to vaccine access; vaccine barriers related to accessing clinics and privacy were common. The majority (85%) of those eligible and unvaccinated at time of survey were willing to receive the vaccine.

CONCLUSION

In this sample of STI clinic clients, vaccine uptake among eligible T/GBM was high in the initial weeks following a Mpox vaccination campaign. However, uptake was patterned on social gradients with lower uptake among T/GBM who may be less effectively engaged by available promotion channels. We recommend early, intentional and diverse engagement of T/GBM populations in Mpox and other targeted vaccination programs.

"No Place for Old Men": Immigrant Duration, Wage Theft, and Economic Mobility among Day Laborers in Denver, Colorado

Day laborers are a highly vulnerable population, due to their contingent work arrangements, low socioeconomic position, and precarious immigration status. Earlier studies posited day labor as a temporary bridge for recent immigrants to achieve more stable employment, but recent studies have observed increasing duration of residence in the United States among foreign-born day laborers. This article draws on 170 qualitative interviews and a multi-venue, year-long street corner survey of 411 day laborers in the Denver metropolitan area to analyze how duration in the United States affects day laborers' wages, work, and wage theft experiences. Compared to recent immigrants, foreign-born day laborers with longer duration in the United States, we found, worked fewer hours and had lower total earnings but also had higher hourly wages and lower exposure to wage theft. We draw on qualitative interviews to address whether this pattern represented weathering, negative selection, or greater discernment. Rather than upward or downward mobility, long duration immigrant day labors had more jagged incorporations experiences. Interviews suggest that day laborers draw on experience to mitigate the risk of wage theft but that the value of experience is undercut by the fierce competition of daily recruitment, ultimately highlighting the compounding vulnerabilities facing longer duration and older immigrant day laborers. The article highlights duration as an understudied precarity factor which can adversely impact the economic assimilation of long duration immigrants who persist in contingent markets like day labor.

Improving Underestimation of HIV Prevalence in Surveys Using Time-Location Sampling

We sought to find a method that improves HIV estimates obtained through time-location sampling (TLS) used to recruit most-at-risk populations (MARPs). The calibration on residuals (CARES) method attributes weights to TLS sampled individuals depending on the percentile to which their logistic regression residues belong. Using a real country database, provided by EMIS-2010, with 9591 men who have sex with men (MSM) and an HIV prevalence of 12.1%, we simulated three populations (termed "pseudo-populations") with different levels of HIV. From each pseudo-population, 1000 TLS samples were drawn, and the HIV prevalence estimated by the TLS method and by the CARES method were recorded and compared with the HIV prevalence of the 9591 men. Results showed that the CARES method improves estimates given by the TLS method by getting closer to the real HIV prevalence.

Estimating Hidden Population Sizes with Venue-based Sampling: Extensions of the Generalized Network Scale-up Estimator

BACKGROUND

Researchers use a variety of population size estimation methods to determine the sizes of key populations at elevated risk of human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS), an important step in quantifying epidemic impact, advocating for high-risk groups, and planning, implementing, and monitoring prevention, care, and treatment programs. Conventional procedures often use information about sample respondents' social network contacts to estimate the sizes of key populations of interest. A recent study proposes a generalized network scale-up method that combines two samples-a traditional sample of the general population and a link-tracing sample of the hidden population-and produces more accurate results with fewer assumptions than conventional approaches.

METHODS

We extended the generalized network scale-up method from link-tracing samples to samples collected with venue-based sampling designs popular in sampling key populations at risk of HIV. Our method obviates the need for a traditional sample of the general population, as long as the size of the venue-attending population is approximately known. We tested the venue-based generalized network scale-up method in a comprehensive simulation evaluation framework.

RESULTS

The venue-based generalized network scale-up method provided accurate and efficient estimates of key population sizes, even when few members of the key population were sampled, yielding average biases below ±6% except when false-positive reporting error is high. It relies on limited assumptions and, in our tests, was robust to numerous threats to inference.

CONCLUSIONS

Key population size estimation is vital to the successful implementation of efforts to combat HIV/AIDS. Venue-based network scale-up approaches offer another tool that researchers and policymakers can apply to these problems.

Prevalence of hepatitis C infection, screening and associated factors among men who have sex with men attending gay venues: a cross-sectional survey (PREVAGAY), France, 2015

Background

Over the last 20 years, Hepatitis C virus (HCV) infection prevalence has dramatically increased among HIV-infected men who have sex with men (MSM) in many countries worldwide. It is suspected that this increase is primarily driven by sexual behaviours linked to blood exposure. Monitoring these behaviours is crucial to understand the drivers of the epidemic. This study assessed the prevalence of chronic HCV infection among MSM attending gay venues and associated chronic HCV risk factors. HCV screening and associated factors were described.

Methods

The cross-sectional survey PREVAGAY, based on time-location sampling, was conducted in 2015 among MSM attending gay venues in 5 French metropolitan cities. A self-administered questionnaire was completed and capillary whole blood on dried blood spots (DBS) collected. Possible factors associated with chronic HCV prevalence and with HCV screening in the previous year were investigated using Poisson regression.

Results

Chronic HCV infection prevalence from DBS analysis was 0.7% [IC95%: 0.3–1.5] in the study’s 2645 participants and was 3.0% [1.5–5.8] in HIV-positive MSM. It was significantly higher in those who reported the following: (lifetime) slamming (with or without the sharing of injection equipment); (during the previous year) fisting and chemsex, unprotected anal intercourse with casual partners, using gay websites and/or of mobile-based GPS applications, and having more than 10 sexual partners.

Only 41.3% [38.2–44.5] of the participants reported HCV screening during the previous year. Screening was significantly more frequent in MSM under 30 years of age, those who were HIV-positive, those vaccinated against hepatitis B and meningococcus C, and those who reported the following (during the previous year): more than 10 sexual partners, at least one sexually transmitted infection and fisting.

Conclusion

Chronic HCV infection prevalence in MSM attending gay venues was significantly higher in HIV-positive MSM and in those with risky sexual behaviours. Reflecting current screening recommendations for specific populations, previous HCV screening was more frequent in HIV-positive individuals and those with risky sexual behaviours. Nevertheless, HCV screening coverage needs to be improved in these populations. Comprehensive medical management, which combines screening and linkage to care with prevention strategies, is essential to control HCV among MSM.

"Starfish Sampling": a Novel, Hybrid Approach to Recruiting Hidden Populations

We sought to leverage the strengths of time location sampling (TLS) and respondent-driven sampling (RDS) for surveys of hidden populations by combing elements of both methods in a new approach we call "starfish sampling." Starfish sampling entails random selection of venue-day-time units from a mapping of the locations where the population can be found, combined with short chains of peer referrals from their social networks at the venue or presenting to the study site later. Using the population of transmen in San Francisco as a case example, we recruited 122 eligible participants using starfish sampling: 79 at randomly selected venues, 11 on dating applications, and 32 by referral. Starfish sampling produced one of the largest community-recruited samples specifically for transmen to date. Starfish sampling is a flexibility method to recruit and sample hidden populations for whom conventional TLS and RDS may not work in theory or practice.

Effects of Multiple Forms of Information Bias on Estimated Prevalence of Suicide Attempts According to Sexual Orientation: An Application of a Bayesian Misclassification Correction Method to Data From a Systematic Review

Multiple epidemiologic studies demonstrate a disparity in suicide risk between sexual minority (lesbian, gay, bisexual) and heterosexual populations; however, both "exposure" (sexual minority status) and outcome (suicide attempts) may be affected by information bias related to errors in self-reporting. We therefore applied a Bayesian misclassification correction method to account for possible information biases. A systematic literature search identified studies of lifetime suicide attempts in sexual minority and heterosexual adults, and frequentist meta-analysis was used to generate unadjusted estimates of relative risk. A Bayesian model accounting for prior information about sensitivity and specificity of exposure and outcome measures was used to adjust for misclassification biases. In unadjusted frequentist analysis, the relative risk of lifetime suicide attempt comparing sexual minority with heterosexual groups was 3.38 (95% confidence interval: 2.65, 4.32). In Bayesian reanalysis, the estimated prevalence was slightly reduced in heterosexual adults and increased in sexual minority adults, yielding a relative risk of 4.67 (95% credible interval: 3.94, 5.73). The disparity in lifetime suicide attempts between sexual minority and heterosexual adults is greater than previously estimated, when accounting for multiple forms of information bias. Additional research on the impact of information bias in studies of sexual minority health should be pursued.

Planned and Unplanned Drug Use during a Night out at an Electronic Dance Music Party

BACKGROUND

Electronic dance music (EDM) parties at nightclubs and festivals are high-risk scenes for drug use. Although intention to use drugs (such as ecstasy) has been shown to be the most proximal determinant of use, little is known regarding the extent to which drug use is unplanned in this high-risk scene.

METHODS

We surveyed 954 adults entering EDM parties in New York City in 2017 and asked about planned drug use that night. A quarter (n = 236) completed the optional online follow-up survey which asked about drug use during their outing. We examined prevalence and correlates of planned and unplanned use.

RESULTS

A fifth (21.0%) of attendees reported planning to use a specific drug the night of the party and over a third (35.4%) reported using a drug later that night. A quarter (26.6%) used in an unplanned manner. Unplanned marijuana use was most common (10.7%), followed by unplanned use of ecstasy (7.3%), cocaine (4.7%), amphetamine (1.4%), LSD (1.3%), and MDA (1.1%). Unplanned initiation of ecstasy and PMA also occurred. Unplanned drug use was more likely to occur among those recruited outside of nightclubs compared to festivals. Non-heterosexual participants and those with a college degree or higher were also more likely to engage in unplanned marijuana use compared to heterosexual and less educated participants, respectively.

CONCLUSIONS

Unplanned drug use is common at EDM parties. Results can inform prevention and harm reduction in these scenes as unplanned use may exacerbate potential adverse outcomes related to drug use and often extreme party environments.

New Challenges in HIV Research: Combining Phylogenetic Cluster Size and Epidemiological Data

An exciting new direction in HIV research is centered on using molecular phylogenetics to understand the social and behavioral drivers of HIV transmission. SPOT was an intervention designed to offer HIV point of care testing to men who have sex with men at a community-based site in Montreal, Canada; at the time of testing, a research questionnaire was also deployed to collect data on socio-demographic and behavioral characteristics of participating men. The men taking part in SPOT could be viewed, from the research perspective, as having been recruited via a convenience sample. Among men who were found to be HIV positive, phylogenetic cluster size was measured using a large cohort of HIV-positive individuals in the province of Quebec. The cluster size is likely subject to under-estimation. In this paper, we use SPOT data to evaluate the association between HIV transmission cluster size and the number of sex partners for MSM, after adjusting for the SPOT sampling scheme and correcting for measurement error in cluster size by leveraging external data sources. The sampling weights for SPOT participants were calculated from another study of men who have sex with men in Montreal by fitting a weight-adjusted model, whereas measurement error was corrected using the simulation-extrapolation conditional on covariates approach.

Time location sampling in men who have sex with men in the HIV context: the importance of taking into account sampling weights and frequency of venue attendance

Sex between men is the most frequent mode of HIV transmission in industrialised countries. Monitoring risk behaviours among men who have sex with men (MSM) is crucial, especially to understand the drivers of the epidemic. A cross-sectional survey (PREVAGAY), based on time-location sampling, was conducted in 2015 among MSM attending gay venues in 5 metropolitan cities in France. We applied the generalised weight share method (GWSM) to estimate HIV seroprevalence for the first time in this population, taking into account the frequency of venue attendance (FVA). Our objectives were to describe the implementation of the sampling design and to demonstrate the importance of taking into account sampling weights, including FVA by comparing results obtained by GWSM and by other methods which use sample weights not including FVA or no weight. We found a global prevalence of 14.3% (95% CI (12.0-16.9)) using GWSM and an unweighted prevalence of 16.4% (95% CI (14.9-17.8)). Variance in HIV prevalence estimates in each city was lower when we did not take into account either the sampling weights or the FVA. We also highlighted an association of FVA and serological status in the most of investigated cities.

Lifetime prevalence of suicidal ideation among men who have sex with men: a meta-analysis

BACKGROUND

Suicide is a leading cause of death among men who have sex with men (MSM) and suicidal ideation may put individuals at higher risk of suicide. A great disparity of lifetime prevalence of suicidal ideation among MSM was observed across studies, indicating the importance of a reliable estimation of the pooled lifetime prevalence. However, the only one published meta-analysis estimating the pooled lifetime prevalence of suicidal ideation among MSM was conducted in 2008 with only 2 eligible studies. Subsequently, there was a rapid increase of publications about lifetime suicidal ideation among MSM, suggesting that an update on the pooled lifetime prevalence of suicidal ideation among MSM was necessary. Therefore, this study aimed to update the estimation of the pooled lifetime prevalence of suicidal ideation among MSM.

METHODS

Electronic databases of PubMed, CINAHL, Scopus (social science), Embase and PsycInfo were searched until September 2017 to identify relevant studies. Cross-sectional studies exploring the lifetime prevalence of suicidal ideation among MSM were enrolled. Heterogeneity was evaluated using the Cochran Q test and quantified using the I ² statistic. The possibility of publication bias was assessed using both Begg's rank test and Egger's linear test, and an Egger's funnel plot for asymmetry was presented. Subgroup analyses were performed according to the geographic area, sample source and HIV status.

RESULTS

Nineteen studies with a total of 26,667 MSM were included, of which 9374 were identified with suicidal ideation. A high degree of heterogeneity (P ≤ 0.001, I ² =99.2%) was observed among the eligible studies, with the reported prevalence ranging from 13.18 to 55.80%. The pooled lifetime prevalence of suicidal ideation among MSM by a random effects model was 34.97% (95% confidence interval: 28.35%-41.90%). Both the Begg's rank test and Egger's linear test indicated low possibility of publication bias. Subgroup analyses showed that the lifetime prevalence of suicidal ideation among MSM differed significantly by geographic area, sample source and HIV status (P < 0.05).

CONCLUSIONS

The high pooled lifetime prevalence of suicidal ideation among MSM found in this meta-analysis significantly underscores the importance of early assessment of suicidal ideation among MSM, as well as the need for strengthening the psychological interventions.

Development of an HIV Testing Dashboard to Complement the HIV Care Continuum Among MSM, PWID, and Heterosexuals in Washington, DC, 2007-2015

BACKGROUND

We developed an HIV testing dashboard to complement the HIV care continuum in selected high-risk populations. Using National HIV Behavioral Surveillance (NHBS) data, we examined trends in HIV testing and care for men who have sex with men (MSM), persons who inject drugs (PWID), and heterosexuals at elevated risk (HET).

METHODS

Between 2007 and 2015, 4792 participants ≥18 years old completed a behavioral survey and were offered HIV testing. For the testing dashboard, proportions ever tested, tested in the past year, testing HIV-positive, and newly testing positive were calculated. An abbreviated care continuum for self-reported positive (SRP) persons included ever engagement in care, past year care, and current antiretroviral (ARV) use. The testing dashboard and care continuum were calculated separately for each population. Chi-square test for trend was used to assess significant trends over time.

RESULTS

Among MSM, lifetime HIV testing and prevalence significantly increased from 96% to 98% (P = 0.01) and 14%-20% (P = 0.02) over time; prevalence was highest among black MSM at all time points. HIV prevalence among female persons who inject drugs was significantly higher in 2015 vs. 2009 (27% and 13%; P < 0.01). Among heterosexuals at elevated risk from 2010 to 2013, annual testing increased significantly (45%-73%; P < 0.001) and the proportion newly diagnosed decreased significantly (P < 0.01). Self-reported positive MSM had high levels of care engagement and antiretroviral use; among self-reported positive persons who inject drugs and heterosexuals at elevated risk, past year care engagement and antiretroviral use increased over time.

CONCLUSIONS

The HIV testing dashboard can be used to complement the HIV care continuum to display improvements and disparities in HIV testing and care over time.

Disclosure of Sexual Orientation by Gay and Bisexual Men in Government-Administered Probability Surveys

PURPOSE

Researchers are increasingly using national population surveys (NPS) to understand the health of gay and bisexual men (GBM). However, valid inference from these surveys depends on accurate identification of GBM.

METHODS

We asked 8126 GBM in an anonymous, online, community-recruited survey about their willingness to reveal their sexual orientation in NPS.

RESULTS

Overall, 30% indicated that they would not reveal their sexual orientation; however, there were differences in frequencies according to sexual orientation, relationship status, age, HIV status, living environment, education, income, and ethnicity.

CONCLUSION

NPS might not be fully representative of GBM due to misclassification errors stemming from unwillingness to disclose.

Lifetime Prevalence of Suicide Attempts Among Sexual Minority Adults by Study Sampling Strategies: A Systematic Review and Meta-Analysis

BACKGROUND

Previous reviews have demonstrated a higher risk of suicide attempts for lesbian, gay, and bisexual (LGB) persons (sexual minorities), compared with heterosexual groups, but these were restricted to general population studies, thereby excluding individuals sampled through LGB community venues. Each sampling strategy, however, has particular methodological strengths and limitations. For instance, general population probability studies have defined sampling frames but are prone to information bias associated with underreporting of LGB identities. By contrast, LGB community surveys may support disclosure of sexuality but overrepresent individuals with strong LGB community attachment.

OBJECTIVES

To reassess the burden of suicide-related behavior among LGB adults, directly comparing estimates derived from population- versus LGB community-based samples.

SEARCH METHODS

In 2014, we searched MEDLINE, EMBASE, PsycInfo, CINAHL, and Scopus databases for articles addressing suicide-related behavior (ideation, attempts) among sexual minorities.

SELECTION CRITERIA

We selected quantitative studies of sexual minority adults conducted in nonclinical settings in the United States, Canada, Europe, Australia, and New Zealand.

DATA COLLECTION AND ANALYSIS

Random effects meta-analysis and meta-regression assessed for a difference in prevalence of suicide-related behavior by sample type, adjusted for study or sample-level variables, including context (year, country), methods (medium, response rate), and subgroup characteristics (age, gender, sexual minority construct). We examined residual heterogeneity by using τ(2).

MAIN RESULTS

We pooled 30 cross-sectional studies, including 21,201 sexual minority adults, generating the following lifetime prevalence estimates of suicide attempts: 4% (95% confidence interval [CI] = 3%, 5%) for heterosexual respondents to population surveys, 11% (95% CI = 8%, 15%) for LGB respondents to population surveys, and 20% (95% CI = 18%, 22%) for LGB respondents to community surveys (Figure 1). The difference in LGB estimates by sample type persisted after we accounted for covariates with meta-regression. Sample type explained 33% of the between-study variability.

AUTHOR'S CONCLUSIONS

Regardless of sample type examined, sexual minorities had a higher lifetime prevalence of suicide attempts than heterosexual persons; however, the magnitude of this disparity was contingent upon sample type. Community-based surveys of LGB people suggest that 20% of sexual minority adults have attempted suicide.

PUBLIC HEALTH IMPLICATIONS

Accurate estimates of sexual minority health disparities are necessary for public health monitoring and research. Most data describing these disparities are derived from 2 sample types, which yield different estimates of the lifetime prevalence of suicide attempts. Additional studies should explore the differential effects of selection and information biases on the 2 predominant sampling approaches used to understand sexual minority health.

Assessing Sample Bias among Venue-Based Respondents at Medical Marijuana Dispensaries

Venue-based sampling is the identification of, and outreach to, locations visited by the population of interest for the purpose of collecting data. The method is frequently used to reach specific populations, commonly referred to as "hidden populations." Medical marijuana users represent a hidden population of persons who use marijuana for medicinal purposes. We examine whether venue-based procedures introduce selection or non-respondent bias into the study. The venue based sampling procedures employed for the UCLA Medical Marijuana Study used a two-stage, venue-based sampling approach. First, analyses were conducted to assess potential bias within dispensaries that agreed to participate in the surveys. Secondly, analyses were conducted to examine differences among patrons who responded to surveys. Overall, selection bias was generally absent among study results. Results also illuminated the minimal respondent bias observed among the survey respondents. Results suggest that the use of dispensaries to access and survey medical marijuana users is a viable option to gather patient information that adequately represents the greater population of medical marijuana users in Los Angeles. Thus, recommendations and conclusions based on findings from venue-based studies of medical marijuana users at dispensary sites serve to impartially inform meaningful research.

A Venue-Based Survey of Malaria, Anemia and Mobility Patterns among Migrant Farm Workers in Amhara Region, Ethiopia

BACKGROUND

Mobile populations present unique challenges to malaria control and elimination efforts. Each year, a large number of individuals travel to northwest Amhara Region, Ethiopia to seek seasonal employment on large-scale farms. Agricultural areas typically report the heaviest malaria burden within Amhara thereby placing migrants at high risk of infection. Yet little is known about these seasonal migrants and their malaria-related risk factors.

METHODS AND FINDINGS

In July 2013, a venue-based survey of 605 migrant laborers 18 years or older was conducted in two districts of North Gondar zone, Amhara. The study population was predominantly male (97.7%) and young (mean age 22.8 years). Plasmodium prevalence by rapid diagnostic test (RDT) was 12.0%; One quarter (28.3%) of individuals were anemic (hemoglobin <13 g/dl). Nearly all participants (95.6%) originated from within Amhara Region, with half (51.6%) coming from within North Gondar zone. Around half (51.2%) slept in temporary shelters, while 20.5% regularly slept outside. Only 11.9% of participants had access to a long lasting insecticidal net (LLIN). Reported net use the previous night was 8.8% overall but 74.6% among those with LLIN access. Nearly one-third (30.1%) reported having fever within the past two weeks, of whom 31.3% sought care. Cost and distance were the main reported barriers to seeking care. LLIN access (odds ratio [OR] = 0.30, P = 0.04) and malaria knowledge (OR = 0.50, P = 0.02) were significantly associated with reduced Plasmodium infection among migrants, with a similar but non-significant trend observed for reported net use the previous night (OR = 0.16, P = 0.14).

CONCLUSIONS

High prevalence of malaria and anemia were observed among a young population that originated from relatively proximate areas. Low access to care and low IRS and LLIN coverage likely place migrant workers at significant risk of malaria in this area and their return home may facilitate parasite transport to other areas. Strategies specifically tailored to migrant farm workers are needed to support malaria control and elimination activities in Ethiopia.

A comparative analysis of behaviors and sexual affiliation networks among men who have sex with men in Hong Kong

In Hong Kong, men who have sex with men (MSM) account for a significant proportion of HIV infections. While perceived as a hidden population, they constitute a distinct social network shaped by their differential use of unique channels for sex partnership. To characterize their pattern of connectivity and association with high-risk sexual behaviors, 311 MSM were recruited via saunas and the internet to participate in a questionnaire survey. Internet recruits were younger, and many (31/43) were solely reliant on the internet to seek sex partners, while visiting a similar number of venues as the sauna recruits (p = 0.98). Internet users generally had a high frequency of unprotected anal intercourse (UAI). MSM who had visited only a single venue reported more UAI with their regular partners (adjusted OR 6.86, 1.88-24.96) and sought fewer casual partners than those frequenting multiple venues (adjusted OR 0.33, 0.19-0.60). This study provides evidence for the heterogeneity of the sexual affiliation networks of MSM in Hong Kong. High HIV risk of UAI could be offset by fewer casual partners in certain venues, the implications of which would need to be explored in longitudinal studies. Methodologically, internet sampling was very efficient in identifying sex networking venues, while internet recruits gave a high retention rate for updating profiles. However, sampling at high centrality saunas did not necessarily identify the MSM-affiliating venues in the networks efficiently. The sampling strategy of MSM survey should therefore be objective-driven, which may differ for health message dissemination and social marketing, versus HIV surveillance or risk assessment.

Seroprevalence of hepatitis C and correlates of seropositivity among men who have sex with men in Vancouver, Canada: a cross-sectional survey

OBJECTIVES

We sought to determine the prevalence of hepatitis C virus (HCV) infection among men who have sex with men (MSM) in Vancouver, Canada, and associations of risk behaviours with HCV serostatus.

METHODS

We used data from the ManCount Study, a cross-sectional survey of MSM selected through a venue-based, time-location sampling method. Bivariate analyses and multivariate logistic regression modelling were used to determine correlates of HCV seropositivity. Bivariate analyses of participants who reported no history of injection drug use (IDU) were used to explore sexual behaviours associated with HCV seropositivity.

RESULTS

HCV seroprevalence was 4.9% (56/1132). Among HCV-seropositive participants who responded to the question, 22.4% (11/49) were unaware of their HCV-seropositive status, 84.9% (45/53) reported a history of IDU and 60.7% (34/56) were HIV positive by dried blood spot. Multivariate modelling found previous IDU (adjusted OR (AOR): 26.30, 95% CI 11.15 to 62.03), receiving goods, drugs or money for sex (AOR 4.98, 95% CI 2.43 to 10.20) and current smoking (AOR 3.46, 95% CI 1.47 to 8.16) were associated with HCV seropositivity. Among MSM who reported no history of IDU, HCV seropositivity was associated with bleeding after receptive anal sex (p=0.001) and a previous diagnosis of gonorrhoea (p=0.007).

CONCLUSIONS

HCV seroprevalence among a sample of MSM is higher than the general population and associated with a history of IDU. Among those who did not report IDU, we found evidence that suggests sexual exposure could be the route of transmission.

Design-based inference in time-location sampling

Time-location sampling (TLS), also called time-space sampling or venue-based sampling is a sampling technique widely used in populations at high risk of infectious diseases. The principle is to reach individuals in places and at times where they gather. For example, men who have sex with men meet in gay venues at certain times of the day, and homeless people or drug users come together to take advantage of services provided to them (accommodation, care, meals). The statistical analysis of data coming from TLS surveys has been comprehensively discussed in the literature. Two issues of particular importance are the inclusion or not of sampling weights and how to deal with the frequency of venue attendance (FVA) of individuals during the course of the survey. The objective of this article is to present TLS in the context of sampling theory, to calculate sampling weights and to propose design-based inference taking into account the FVA. The properties of an estimator ignoring the FVA and of the design-based estimator are assessed and contrasted both through a simulation study and using real data from a recent cross-sectional survey conducted in France among drug users. We show that the estimators of prevalence or a total can be strongly biased if the FVA is ignored, while the design-based estimator taking FVA into account is unbiased even when declarative errors occur in the FVA.

Nonprobability and probability-based sampling strategies in sexual science

With few exceptions, much of sexual science builds upon data from opportunistic nonprobability samples of limited generalizability. Although probability-based studies are considered the gold standard in terms of generalizability, they are costly to apply to many of the hard-to-reach populations of interest to sexologists. The present article discusses recent conclusions by sampling experts that have relevance to sexual science that advocates for nonprobability methods. In this regard, we provide an overview of Internet sampling as a useful, cost-efficient, nonprobability sampling method of value to sex researchers conducting modeling work or clinical trials. We also argue that probability-based sampling methods may be more readily applied in sex research with hard-to-reach populations than is typically thought. In this context, we provide three case studies that utilize qualitative and quantitative techniques directed at reducing limitations in applying probability-based sampling to hard-to-reach populations: indigenous Peruvians, African American youth, and urban men who have sex with men (MSM). Recommendations are made with regard to presampling studies, adaptive and disproportionate sampling methods, and strategies that may be utilized in evaluating nonprobability and probability-based sampling methods.

The comparability of men who have sex with men recruited from venue-time-space sampling and facebook: a cohort study

Background

Recruiting valid samples of men who have sex with men (MSM) is a key component of the US human immunodeficiency virus (HIV) surveillance and of research studies seeking to improve HIV prevention for MSM. Social media, such as Facebook, may present an opportunity to reach broad samples of MSM, but the extent to which those samples are comparable with men recruited from venue-based, time-space sampling (VBTS) is unknown.

Objective

The objective of this study was to assess the comparability of MSM recruited via VBTS and Facebook.

Methods

HIV-negative and HIV-positive black and white MSM were recruited from June 2010 to December 2012 using VBTS and Facebook in Atlanta, GA. We compared the self-reported venue attendance, demographic characteristics, sexual and risk behaviors, history of HIV-testing, and HIV and sexually transmitted infection (STI) prevalence between Facebook- and VTBS-recruited MSM overall and by race. Multivariate logistic and negative binomial models estimated age/race adjusted ratios. The Kaplan-Meier method was used to assess 24-month retention.

Results

We recruited 803 MSM, of whom 110 (34/110, 30.9% black MSM, 76/110, 69.1% white MSM) were recruited via Facebook and 693 (420/693, 60.6% black MSM, 273/693, 39.4% white MSM) were recruited through VTBS. Facebook recruits had high rates of venue attendance in the previous month (26/34, 77% among black and 71/76, 93% among white MSM; between-race P=.01). MSM recruited on Facebook were generally older, with significant age differences among black MSM (P=.02), but not white MSM (P=.14). In adjusted multivariate models, VBTS-recruited MSM had fewer total partners (risk ratio [RR]=0.78, 95% CI 0.64-0.95; P=.01) and unprotected anal intercourse (UAI) partners (RR=0.54, 95% CI 0.40-0.72; P<.001) in the previous 12 months. No significant differences were observed in HIV testing or HIV/STI prevalence. Retention to the 24-month visit varied from 81% for black and 70% for white MSM recruited via Facebook, to 77% for black and 78% for white MSM recruited at venues. There was no statistically significant differences in retention between the four groups (log-rank P=.64).

Conclusions

VBTS and Facebook recruitment methods yielded similar samples of MSM in terms of HIV-testing patterns, and prevalence of HIV/STI, with no differences in study retention. Most Facebook-recruited men also attended venues where VTBS recruitment was conducted. Surveillance and research studies may recruit via Facebook with little evidence of bias, relative to VBTS.

Relationship between disclosure of same-sex sexual activity to providers, HIV diagnosis and sexual health services for men who have sex with men in Vancouver, Canada

OBJECTIVES

Men who have sex with men (MSM) report challenges to accessing appropriate health care. We sought to understand the relationship between disclosure of same-sex sexual activity to a health care practitioner (HCP), sexual behaviour and measures of sexual health care.

METHODS

Participants recruited through community venues and events completed a questionnaire and provided a blood sample. This analysis includes only individuals with self-reported HIV negative or unknown serostatus. We compared participants who had disclosed having same-sex partners with those who had not using chi-square, Wilcoxon Rank Sum and Fisher's exact tests and used logistic regression to examine those variables associated with receiving an HIV test.

RESULTS

Participants who had disclosed were more likely to have a higher level of education (p&lt;0.001) and higher income (p&lt;0.001), and to define themselves as "gay" or "queer" (p&lt;0.001). Those who had not disclosed were less likely to report having risky sex (p=0.023) and to have been tested for HIV in the previous two years (adjusted odds ratio 0.23, 95% confidence interval: 0.16-0.34). There was no difference in undiagnosed HIV infection (3.9% versus 2.6%, p=0.34). Individuals who had disclosed were also more likely to have been tested for gonorrhea and syphilis, and more likely to have ever been vaccinated against hepatitis A and hepatitis B (p&lt;0.001 for all).

CONCLUSIONS

While generally reporting lower risk behaviour, MSM who did not disclose same-sex sexual activity to their HCP did have undiagnosed HIV infections and were less likely to have been tested or vaccinated. Strategies to improve access to appropriate sexual health care for MSM are needed.

Community mapping and respondent-driven sampling of gay and bisexual men's communities in Vancouver, Canada

Literature suggests formative research is vital for those using respondent-driven sampling (RDS) to study hidden populations of interest. However, few authors have described in detail how different qualitative methodologies can address the objectives of formative research for understanding the social network properties of the study population, selecting seeds and adapting survey logistics to best fit the population. In this paper we describe the use of community mapping exercises as a tool within focus groups to collect data on social and sexual network characteristics of gay and bisexual men in the metropolitan area of Vancouver, Canada. Three key themes emerged from analysing community maps along with other formative research data: (1) connections between physical spaces and social networks of gay and bisexual men, (2) diversity in communities and (3) substance use linked to formation of sub-communities. We discuss how these themes informed the planning and operations of a longitudinal epidemiological cohort study recruited by RDS. We argue that using community mapping within formative research is a valuable qualitative tool for characterising network structures of a diverse and differentiated population of gay and bisexual men in a highly developed urban setting.