Behavioural surveillance: the value of national coordination

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.

Epidemiological HIV infection surveillance among subjects with risk behaviours in the city of Messina (Sicily) from 1992 to 2015

INTRODUCTION

Epidemiological studies are a key element in determining the evolution and spread of HIV infection among the world population. Knowledge of the epidemiological dynamics improves strategies for prevention and monitoring.

METHODS

We examined 2,272 subjects who voluntarily underwent HIV testing from January 1992 to December 2015. For each subject, an anonymous form was completed to obtain information on personal data, sexual habits and exposure to risk factors.

RESULTS

The number of subjects undergoing the screening test has increased over the years and the average age of the tested subjects has decreased over time. The main motivation for undergoing HIV testing is unprotected sex. Although heterosexual subjects taking the test were more numerous than homosexuals in this study, an increase in the latter over time should be highlighted.

CONCLUSIONS

Although the number of tests performed has increased over the years, the persistence of unprotected sex shows an inadequate perception of risk. Therefore, it is necessary to implement programmes to increase the general awareness of HIV infection. It is also essential to undertake constant monitoring of behaviour, risk perception and the application of the screening test via surveillance systems in order to implement effective and efficient prevention.

Asking about Sex in General Health Surveys: Comparing the Methods and Findings of the 2010 Health Survey for England with Those of the Third National Survey of Sexual Attitudes and Lifestyles

Objectives

Including questions about sexual health in the annual Health Survey for England (HSE) provides opportunities for regular measurement of key public health indicators, augmenting Britain's decennial National Survey of Sexual Attitudes and Lifestyles (Natsal). However, contextual and methodological differences may limit comparability of the findings. We examine the extent of these differences between HSE 2010 and Natsal-3 and investigate their impact on parameter estimates.

Methods

Complex survey analyses of data from men and women in the 2010 HSE (n = 2,782 men and 3,588 women) and Natsal-3 undertaken 2010–2012 (n = 4,882 men and 6,869 women) aged 16-69y and resident in England, both using probability sampling, compared their characteristics, the amount of non-response to, and estimates from, sexual health questions. Both surveys used self-completion for the sexual behaviour questions but this was via computer-assisted self-interview (CASI) in Natsal-3 and a pen-and-paper questionnaire in HSE 2010.

Results

The surveys achieved similar response rates, both around 60%, and demographic profiles largely consistent with the census, although HSE participants tended to be less educated, and reported worse general health, than Natsal-3 participants. Item non-response to the sexual health questions was typically higher in HSE 2010 (range: 9–18%) relative to Natsal-3 (all <5%). Prevalence estimates for sexual risk behaviours and STI-related indicators were generally slightly lower in HSE 2010 than Natsal-3.

Conclusions

While a relatively high response to sexual health questions in HSE 2010 demonstrates the feasibility of asking such questions in a general health survey, differences with Natsal-3 do exist. These are likely due to the HSE’s context as a general health survey and methodological limitations such as its current use of pen-and-paper questionnaires. Methodological developments to the HSE should be considered so that its data can be interpreted in combination with those from dedicated sexual health surveys, thus improving our ability to monitor trends in sexual health.

Who is omitted from repeated offline HIV behavioural surveillance among MSM? Implications for interpreting trends

Repeated behavioural surveillance should sample all epidemiologically relevant subgroups to provide a complete picture of trends in HIV risk behaviours. Web-based recruitment has been mooted but little empirical data exist on country experiences. We describe who is omitted from three rounds of a conventional offline-only surveillance programme among men who have sex with men (MSM) 2006-2011, but recruited subsequently on Internet dating sites, and the implications of this for understanding trends. The latter were younger, less gay identified and less gay community attached. Importantly, they reported different partnering patterns, lower condom use with casual and fuckbuddy-type male partners, and lower rates of HIV testing, compared to MSM routinely captured in offline surveillance. The replacement of offline socio-sexual activity by the Internet among many MSM means that current venue-based surveillance systems may underestimate risk behaviours, overlook trends among unsampled online MSM, and misinterpret trends observed in sampled MSM due to "sample drift" of most-at-risk MSM.

HIV infection among ethnic minority and migrant men who have sex with men in Britain

OBJECTIVE

To examine human immunodeficiency virus (HIV) infection among men who have sex with men (MSM) from different ethnic and migrant groups living in Britain.

METHODS

In 2007-2008, a diverse national sample of MSM living in Britain was recruited through Web sites, in sexual health clinics, bars, clubs, and other venues. Men completed an online survey that included questions on HIV testing, HIV status, and sexual behavior.

RESULTS

Nine hundred and ninety-one ethnic minority MSM, 207 men born in Central or Eastern Europe (CEE), 136 men born in South or Central America, and 11,944 white British men were included in the analysis. Self-reported HIV seropositivity was low for men of South Asian, Chinese, and "other Asian" ethnicity (range, 0.0%-5.8%) and for men born in CEE (4.5%) but elevated for men born in South or Central America (18.7%), compared with white British men (13.1%) (P < 0.001). There were no significant differences between these groups in high-risk sexual behavior (P = 0.8). After adjusting for confounding factors in a multivariable model, substantial differences in the odds of HIV infection remained for South Asian and Chinese MSM as well as for migrants from CEE, but not for other groups, compared with white British men; for example, South Asian men, adjusted odds ratio 0.43, 95% confidence interval 0.23, 0.79, P = 0.007.

CONCLUSION

There were marked differences in self-reported HIV seropositivity between ethnic minority, key migrant, and white British MSM in this study but not in high-risk sexual behavior. This highlights the importance of health promotion targeting MSM from all ethnic and migrant groups in Britain.

Respondent-driven sampling and the recruitment of people with small injecting networks

Respondent-driven sampling (RDS) is a form of chain-referral sampling, similar to snowball sampling, which was developed to reach hidden populations such as people who inject drugs (PWID). RDS is said to reach members of a hidden population that may not be accessible through other sampling methods. However, less attention has been paid as to whether there are segments of the population that are more likely to be missed by RDS. This study examined the ability of RDS to capture people with small injecting networks. A study of PWID, using RDS, was conducted in 2009 in Sydney, Australia. The size of participants' injecting networks was examined by recruitment chain and wave. Participants' injecting network characteristics were compared to those of participants from a separate pharmacy-based study. A logistic regression analysis was conducted to examine the characteristics independently associated with having small injecting networks, using the combined RDS and pharmacy-based samples. In comparison with the pharmacy-recruited participants, RDS participants were almost 80% less likely to have small injecting networks, after adjusting for other variables. RDS participants were also more likely to have their injecting networks form a larger proportion of those in their social networks, and to have acquaintances as part of their injecting networks. Compared to those with larger injecting networks, individuals with small injecting networks were equally likely to engage in receptive sharing of injecting equipment, but less likely to have had contact with prevention services. These findings suggest that those with small injecting networks are an important group to recruit, and that RDS is less likely to capture these individuals.

Central and East European migrant men who have sex with men in London: a comparison of recruitment methods

Background

Following the expansion of the European Union, there has been a large influx of Central and East European (CEE) migrants to the UK. CEE men who have sex with men (MSM) represent a small minority within this population that are none-the-less important to capture in sexual health research among the CEE migrant community. This paper examines the feasibility of recruiting CEE MSM for a survey of sexual behaviour in London using respondent driven sampling (RDS), via gay websites and in GUM clinics.

Methods

We sought CEE MSM to start RDS chain referral among GUM clinic attendees, our personal contacts and at gay events and venues in central London. We recruited CEE MSM (n = 485) via two popular websites for gay men in Britain (March-May 2009) and at two central London GUM clinics (n = 51) (July 2008-March 2009).

Results

We found seventeen men who knew other CEE MSM in London and agreed to recruit contacts into the study. These men recruited only three men into the study, none of whom recruited any further respondents, and RDS was abandoned after 7 months (July 2008-January 2009). Half of the men that we approached to participate in RDS did not know any other CEE MSM in London. Men who agreed to recruit contacts for RDS were rather more likely to have been in the UK for more than one year (94.1% vs 70.0%, p = 0.052). Men recruited through gay websites and from GUM clinics were similar.

Conclusions

The Internet was the most successful method for collecting data on sexual risk behaviour among CEE MSM in London. CEE MSM in London were not well networked. RDS may also have failed because they did not fully understand the procedure and/or the financial incentive was not sufficient motivation to take part.

Mapping HIV/STI behavioural surveillance in Europe

BACKGROUND

Used in conjunction with biological surveillance, behavioural surveillance provides data allowing for a more precise definition of HIV/STI prevention strategies. In 2008, mapping of behavioural surveillance in EU/EFTA countries was performed on behalf of the European Centre for Disease prevention and Control.

METHOD

Nine questionnaires were sent to all 31 member States and EEE/EFTA countries requesting data on the overall behavioural and second generation surveillance system and on surveillance in the general population, youth, men having sex with men (MSM), injecting drug users (IDU), sex workers (SW), migrants, people living with HIV/AIDS (PLWHA), and sexually transmitted infection (STI) clinics patients. Requested data included information on system organisation (e.g. sustainability, funding, institutionalisation), topics covered in surveys and main indicators.

RESULTS

Twenty-eight of the 31 countries contacted supplied data. Sixteen countries reported an established behavioural surveillance system, and 13 a second generation surveillance system (combination of biological surveillance of HIV/AIDS and STI with behavioural surveillance). There were wide differences as regards the year of survey initiation, number of populations surveyed, data collection methods used, organisation of surveillance and coordination with biological surveillance. The populations most regularly surveyed are the general population, youth, MSM and IDU. SW, patients of STI clinics and PLWHA are surveyed less regularly and in only a small number of countries, and few countries have undertaken behavioural surveys among migrant or ethnic minorities populations. In many cases, the identification of populations with risk behaviour and the selection of populations to be included in a BS system have not been formally conducted, or are incomplete. Topics most frequently covered are similar across countries, although many different indicators are used. In most countries, sustainability of surveillance systems is not assured.

CONCLUSION

Although many European countries have established behavioural surveillance systems, there is little harmonisation as regards the methods and indicators adopted. The main challenge now faced is to build and maintain organised and functional behavioural and second generation surveillance systems across Europe, to increase collaboration, to promote robust, sustainable and cost-effective data collection methods, and to harmonise indicators.

Sexual health of ethnic minority MSM in Britain (MESH project): design and methods

Background

Men who have sex with men (MSM) remain the group most at risk of acquiring HIV infection in Britain. HIV prevalence appears to vary widely between MSM from different ethnic minority groups in this country for reasons that are not fully understood. The aim of the MESH project was to examine in detail the sexual health of ethnic minority MSM living in Britain.

Methods/Design

The main objectives of the MESH project were to explore among ethnic minority MSM living in Britain: (i) sexual risk behaviour and HIV prevalence; (ii) their experience of stigma and discrimination; (iii) disclosure of sexuality; (iv) use of, and satisfaction with sexual health services; (v) the extent to which sexual health services (for treatment and prevention) are aware of the needs of ethnic minority MSM.

The research was conducted between 2006 and 2008 in four national samples: (i) ethnic minority MSM living in Britain; (ii) a comparison group of white British MSM living in Britain; (iii) NHS sexual health clinic staff in 15 British towns and cities with significant ethnic minority communities and; (iv) sexual health promotion/HIV prevention service providers. We also recruited men from two "key migrant" groups living in Britain: MSM born in Central or Eastern Europe and MSM born in Central or South America.

Internet-based quantitative and qualitative research methods were used. Ethnic minority MSM were recruited through advertisements on websites, in community venues, via informal networks and in sexual health clinics. White and "key migrant" MSM were recruited mostly through Gaydar, one of the most popular dating sites used by gay men in Britain. MSM who agreed to take part completed a questionnaire online. Ethnic minority MSM who completed the online questionnaire were asked if they would be willing to take part in an online qualitative interview using email.

Service providers were identified through the British Association of Sexual Health and HIV (BASHH) and the Terrence Higgins Trust (THT) CHAPS partnerships. Staff who agreed to take part were asked to complete a questionnaire online.

The online survey was completed by 1241 ethnic minority MSM, 416 men born in South and Central America or Central and Eastern Europe, and 13,717 white British MSM; 67 ethnic minority MSM took part in the online qualitative interview. In addition 364 people working in sexual health clinics and 124 health promotion workers from around Britain completed an online questionnaire.

Discussion

The findings from this study will improve our understanding of the sexual health and needs of ethnic minority MSM in Britain.

Men who have sex with men in Great Britain: comparison of a self-selected internet sample with a national probability sample

OBJECTIVES

To compare the characteristics of a self-selected, convenience sample of men who have sex with men (MSM) recruited through the internet with MSM drawn from a national probability survey in Great Britain.

METHODS

The internet sample (n = 2065) was recruited through two popular websites for homosexual men in Great Britain in May and June 2003. This sample was compared with MSM (n = 117) from the National Survey of Sexual Attitudes and Lifestyles (Natsal), a probability sample survey of adults resident in Great Britain conducted between May 1999 and February 2001.

RESULTS

No significant differences were observed between the samples on a range of sociodemographic and behavioural variables (p>0.05). However, men from the internet sample were younger (p<0.001) and more likely to be students (p = 0.001), but less likely to live in London (p = 0.001) or report good health (p = 0.014). Although both samples were equally likely to report testing for HIV, men from the internet sample were more likely to report a sexually transmitted infection in the past year (16.9% v 4.8%, adjusted odds ratio 4.14, 95% CI 1.76 to 9.74; p = 0.001), anal intercourse (76.9% v 63.3%; p = 0.001) and unprotected anal intercourse in the past 3 months (45% v 36.6%; p = 0.064).

CONCLUSIONS

The internet provides a means of recruiting a self-selected, convenience sample of MSM whose social and demographic characteristics are broadly similar to those of MSM drawn from a national probability survey. However, estimates of high-risk sexual behaviour based on internet convenience samples are likely to overestimate levels of sexual risk behaviour in the wider MSM population.

Use of crystal methamphetamine among gay men in London

AIM

To examine the use of crystal methamphetamine (crystal meth) and its association with high-risk sexual behaviour among gay men in London.

DESIGN

Cross-sectional surveys using self-administered questionnaires.

SETTINGS

National Health Service (NHS) out-patient human immunodeficiency virus (HIV) treatment clinic in London; NHS HIV testing/sexual health clinics in London; central London gyms.

PARTICIPANTS

HIV-positive gay men attending the HIV treatment clinic in 2002-03 (n = 388); HIV-negative gay men attending the HIV testing/sexual health clinics in 2002-03 (n = 266); gay men using the gyms between January and March 2003 (n = 445), 2004 (n = 653) and 2005 (n = 494).

MEASUREMENTS

Percentage of gay men who reported: (i) using crystal meth in the previous 12 months; (ii) using other recreational drugs (e.g. cocaine, ecstasy, ketamine); (iii) high-risk sexual behaviour in the previous 3 months.

FINDINGS

The percentage of gay men who had used crystal meth in the previous year varied by sample (HIV treatment clinic, 12.6%; HIV testing/sexual health clinics, 8.3%; gyms, 19.5%; P < 0.001) but did not change over time in the gyms (19.8%, 20.7%, 17.8%; P = 0.5). In all samples, the majority of men used crystal meth only once or twice a year. Most crystal meth users (> 80%) had taken other recreational drugs. Crystal meth and other drug users were more likely to report high-risk sexual behaviour than other men, e.g. HIV treatment clinic sample: crystal meth users, 34.7%; other drug users, 18.9%, non-users, 10.6%, P < 0.001. Cause and effect could not be established.

CONCLUSION

Among gay men in London surveyed in clinics, approximately one in 10 reported using crystal meth in the previous 12 months (HIV-positive men 12.6%; HIV-negative men 8.3%). Most men used it infrequently--only once or twice a year. There was no evidence of increasing use of crystal meth between 2003 and 2005.

Changing patterns of sexual behaviour in the era of highly active antiretroviral therapy

PURPOSE OF REVIEW

To describe changing patterns of sexual behaviour in the era of highly active antiretroviral therapy among gay/bisexual men in Europe, Canada, USA and Australia.

RECENT FINDINGS

While there has been a substantial increase in high-risk sexual behaviour among gay men since 1996, this now appears to be levelling off in some cities. Overall the empirical evidence does not support the suggestion that taking highly active antiretroviral therapy or having an undetectable viral load leads to risky sexual behaviour among people with HIV. Nor can HIV treatment optimism alone explain the recent increase in high-risk sexual behaviour. Since 1996, an increasing number of gay men have begun to use the Internet to look for sexual partners. By serosorting on the Internet, HIV-positive men are more likely to meet online, rather than off-line, other HIV-positive men for unprotected sex. While serosorting does not present a risk of HIV transmission to an uninfected person, it does present a risk of other sexually transmitted infections and co-infection with resistant virus for HIV-positive men themselves. This review also explores emerging behaviours such as barebacking and strategic positioning as well as the role of crystal meth and Viagra.

SUMMARY

The review reminds us of the complexity of human and sexual behaviour. Among gay men, sexual behaviour in the era of highly active antiretroviral therapy has been characterized by risk reduction and stabilization as well as increasing risk. These changing patterns provide a new challenge as well as new opportunities for HIV prevention.

Web-based behavioral surveillance among men who have sex with men: a comparison of online and offline samples in London, UK

OBJECTIVE

To compare the characteristics of men who have sex with men (MSM) surveyed online (through gay Internet chat rooms and profiles) and offline (in community venues) in London, UK.

METHODS

In February and March 2002, 879 MSM completed a self-administered pen-and-paper questionnaire distributed in central London gyms (offline sample). In May and June 2002, 1218 London MSM completed a self-administered questionnaire online, accessed through Internet chat rooms and profiles on gaydar and gay.com.

RESULTS

Compared with men surveyed offline, those surveyed online were significantly less likely to only have sex with men (89 vs. 94%), to be in a relationship with a man (44 vs. 52%), or to have been tested for HIV (68 vs. 80%) (P < 0.001). Men recruited online were also younger (mean age, 34 vs. 36 years) and less likely to have had a higher education (67 vs. 79%) (P < 0.001). However, differences between online and offline samples were less pronounced for HIV-positive men and more pronounced for HIV-negative men and those who had never been tested for HIV. Regardless of HIV status, men recruited online were more likely to report high-risk sexual behavior (i.e., unprotected anal intercourse with a partner of unknown or discordant HIV status) than men surveyed offline (32 vs. 22%, P < 0.001). Men recruited online were also significantly more likely to have used the Internet to look for sex (85 vs. 45%, P < 0.001); for HIV-positive and negative men, seeking sex on the Internet was associated with high-risk sexual behavior (P < 0.01). In multivariate analysis, after controlling for confounding factors, being surveyed online was independently associated with high-risk sexual behavior for HIV-negative and never-tested men (HIV-negative men, adjusted odds ratio for online vs. offline samples, 1.73; 95% CI, 1.23, 2.42; P < 0.01; never-tested men adjusted odds ratio 2.45; 95% CI, 1.40, 4.29; P < 0.01). This was not the case for HIV-positive men (adjusted odds ratio for online vs. offline samples, 1.32; 95% CI, 0.69, 2.50; P = 0.4).

CONCLUSION

The Internet offers valuable opportunities for conducting behavioral surveillance among MSM because it reaches some men who may not be easily accessed in the community yet who are at high risk for HIV and sexually transmitted diseases. Comparisons of the social, demographic, and behavioral characteristics of online and offline samples must, however, take into account the confounding effects of HIV status and seeking sex on the Internet.

Gay men who look for sex on the Internet: is there more HIV/STI risk with online partners?

OBJECTIVE

To examine whether the excess risk for HIV and sexually transmitted infection (STI) seen among gay men who look for sex through the Internet occurs with men they meet online (through the Internet) rather than offline (in bars, clubs, etc).

METHODS

In 2002-2003, 4225 London gay men were surveyed in an HIV treatment clinic, HIV testing clinic, gyms and on UK Internet sites (gaydar and gay.com). All men completed a self-administered questionnaire concerning Internet use and sexual risk behaviour. Unprotected anal intercourse (UAI) with a partner of unknown or discordant HIV status was classified as non-concordant.

RESULTS

Between 40 and 50% of men surveyed in the clinics and gyms used the Internet to look for sex. HIV-positive men who looked for sex through the Internet were more likely to report UAI with HIV-positive casual partners they met online rather than offline (clinic sample: met online only 9.9%, met offline only 3.8%, McNemar P < 0.05). Regardless of HIV status, however, men who looked for sex through the Internet were no more likely to report UAI with non-concordant casual partners they met online than offline (eg, HIV-negative men, Internet sample: met online only 9.7%, offline only 11.1%, McNemar P = 0.6).

CONCLUSIONS

In London, HIV-positive gay men appear to meet casual UAI partners of the same status through the Internet. This presents a risk for STI transmission. However, gay men were no more likely to meet casual UAI partners of unknown or discordant HIV status--which presents a risk for HIV transmission--online rather than offline.

Monitoring trends in sexual behaviour and HIV/STIs in Peru: are available data sufficient?

OBJECTIVES

To review and summarise various types of Peruvian evidence on sexual behaviour, HIV/STI exposure and risk, and discuss how to increase its usefulness for HIV/STI risk trend monitoring in Peru.

METHODS

Review HIV sentinel surveillance conducted by the Ministry of Health; data from the Demographic and Health Surveys (DHS); and academic publications on sexual behaviour in combination with biological markers. Changes over time, quality of data, size of studies, and intended audience are discussed.

RESULTS

Data from HIV sentinel surveillance showed very high (8-23%) HIV seroprevalence among men having sex with men, but stable, relatively low figures among female sex workers (1%) and antenatal clinic patients (under 0.5%). DHS data suggest that single women increased their sexual activity throughout the 1990s but did not raise their contraceptive use accordingly, resulting in increased early conceptions. The contribution of condoms to overall contraceptive protection increased threefold in 1992-2000. According to the 1996 survey, men become sexually active 2.5 years earlier than women, but marry or cohabit four years later than women; women marry or cohabit 1.5-2.5 years after first sex, whereas men take eight years to do so. Finally, published studies confirmed dramatic differences in HIV prevalence between men who have sex with men and other populations, and also suggested patterns of bridging from men to women.

CONCLUSIONS

Data available from the three sources are numerous, although limitations of each approach reduce their monitoring utility: Ministry of Health studies should select better sentinel populations and timely process behavioural data. Future demographic surveys should incorporate an AIDS risk perspective and include men.

The Internet and HIV study: design and methods

BACKGROUND

The Internet provides a new meeting ground, especially for gay men, that did not exist in the early 1990s. Several studies have found increased levels of high risk sexual behaviour and sexually transmissible infections (STI) among gay men who seek sex on the Internet, although the underlying processes are not fully understood. Research funded by the UK Medical Research Council (2002-2004) provided the opportunity to consider whether the Internet represents a new sexual risk environment for gay and bisexual men living in London.

METHODS

The objectives of the Internet and HIV study are to: (i) measure the extent to which gay men living in London seek sexual partners on the Internet; (ii) compare the characteristics of London gay men who do and do not seek sex on the Internet; (iii) examine whether sex with Internet-partners is less safe than with other sexual partners; (iv) compare use of the Internet with other venues where men meet sexual partners; (v) establish whether gay men use the Internet to actively seek partners for unprotected anal intercourse; (vi) determine the potential for using the Internet for HIV prevention. These objectives have been explored using quantitative and qualitative research methods in four samples of London gay men recruited and interviewed both online and offline. The four samples were: (i) gay men recruited through Internet chat rooms and profiles; (ii) HIV positive gay men attending an NHS hospital outpatients clinic; (iii) gay men seeking an HIV test in an NHS HIV testing or sexual health clinic; (iv) gay men recruited in the community.

RESULTS

Quantitative data were collected by means of confidential, anonymous self-administered questionnaires (n>4000) completed on-line by the Internet sample. Qualitative data were collected by means of one-to-one interviews (n = 128) conducted either face-to-face or on-line.

CONCLUSION

The strength of the Internet and HIV study is its methodological plurality, drawing on both qualitative and quantitative research among online and offline samples, as well as taking advantage of recent advances in web survey design. The study's findings will help us better understand the role of the Internet in relation to gay men's sexual practice.

LCR testing for gonorrhoea and chlamydia in population surveys and other screenings of low prevalence populations: coping with decreased positive predictive value

OBJECTIVE

Nucleic acid amplification tests have facilitated field based STD studies and increased screening activities. However, even with highly specific tests, the positive predictive value (PPV) of such tests may be lower than desirable in low prevalence populations. We estimated PPVs for a single LCR test in a population survey in which positive specimens were retested.

METHODS

The Baltimore STD and Behavior Survey (BSBS) was a population based behavioural survey of adults which included collecting urine specimens to assess the prevalence of gonorrhoea and chlamydial infection. Gonorrhoea and chlamydial infection were diagnosed by ligase chain reaction (LCR). Nearly all positive results were retested by LCR. Because of cost considerations, negative results were not confirmed. Predicted curves for the PPV were calculated for a single testing assuming an LCR test sensitivity of 95%, and test specificities in the range 95.0%-99.9%, for disease prevalences between 1% and 10%. Positive specimens were retested to derive empirical estimates of the PPV of a positive result on a single LCR test.

RESULTS

579 participants age 18-35 provided urine specimens. 20 (3.5%) subjects initially tested positive for chlamydial infection, and 39 (6.7%) tested positive for gonococcal infection. If positive results on the repeat LCR are taken as confirmation of a "true" infection, the observed PPV for the first LCR testing was 89.5% for chlamydial infection and 83.3% for gonorrhoea. This is within the range of theoretical PPVs calculated from the assumed sensitivities and specificities of the LCR assays.

CONCLUSIONS

Empirical performance of a single LCR testing approximated the theoretically predicted PPV in this field study. This result demonstrates the need to take account of the lower PPVs obtained when such tests are used in field studies or clinical screening of low prevalence populations. Repeat testing of specimens, preferably with a different assay (for example, polymerase chain reaction), and disclosure of the non-trivial potential for false positive test results would seem appropriate in all such studies.