Estimating population attributable risk for hepatitis C seroconversion in injecting drug users in Australia: implications for prevention policy and planning

Objective   To determine risk factors and estimate their population-level contribution to hepatitis C virus (HCV) burden.
Methods   Established and potentially modifiable risk factors were estimated using partial population attributable risk ( PAR_p ) in a cohort of new injecting drug users (IDUs) in Sydney, Australia.
Results   A total of 204 hepatitis C seronegative IDUs were recruited through street-based outreach, methadone clinics and needle and syringe programmes (NSPs) and followed-up at 3–6-monthly intervals. A total of 61 HCV seroconversions were observed during the follow-up [overall incidence rate of 45.8 per 100 person-years (95% confidence interval: 35.6–58.8)]. Overall, five potentially modifiable risk factors (sharing needles/syringes, sharing other injecting equipment, assisted injecting, frequency of injection and not being in drug treatment) accounted for approximately 50% of HCV cases observed.
Conclusion   While sharing needles/syringes or other injecting equipment were associated most strongly with increased risk of HCV infection, the PAR_p associated with these behaviours was relatively modest (12%) because they are relatively low-prevalence behaviours. Our analyses suggest that more HCV infection could be avoided by changing more common, but less strongly associated behaviours such as assisted injecting or daily injecting. Results suggest that to have a very substantial effect on HCV, a range of risk factors need modifying. The most efficient use of scarce resources in reducing HCV infections will require complex balancing between the PAR for a given risk factor(s), the efficacy of interventions to actually modify the risk factor, and the cost of these interventions.     

Determinants of HIV infection and recent risk behaviour among injecting drug users in Berlin by site of recruitment

This study investigated differences in prevalence and determinants of HIV infection, and in recent risk behaviour (previous 6 months) among injecting drug users (IDUs) who are in contact with different types of services for IDUs in Berlin. Participants (n = 557) were recruited from drug-free long-term treatment centres, a storefront agency and a syringe exchange bus. HIV seroprevalence was lowest (3.9%) at the treatment centres, and highest among IDUs at the storefront agency (20.7%). In logistic regression, independent risk factors for HIV infection were duration of injecting drug use, borrowing syringes in prison, sex with HIV-positive partners, and prostitution. Syringe sharing in prison was the most important independent determinant of HIV infection among all three subpopulations of IDUs. Participants entering long-term treatment were most likely, and IDUs at the syringe exchange bus were least likely to have borrowed and passed on syringes in the previous 6 months. In logistic regression, site of recruitment was independently associated with recent borrowing of syringes, but not with condom use. Injection of drugs other than heroin only, and injecting in prisons, were also independent predictors of recent borrowing. The results indicate that IDUs entering treatment form an important target group for health education. There is a need for AIDS prevention measures in prisons. The comparatively low levels of recent injection risk behaviour among IDUs at the syringe exchange bus suggest that this type of intervention may be effective in harm reduction.     

广东省静脉吸毒人员共用针具影响因素的Logistic回归分析

目的探讨广东省静脉吸毒人员共用针具的影响因素,以及针具交换项目对预防吸毒人员共用针具的效果。方法采用社区干预研究的方法,选择各方面因素比较类似的两个镇,一个作为干预社区,一个为对照社区。干预区采用针具交换干预措施,对照区不采取任何干预措施,为期10个月。于干预前后分别采用滚雪球的方式抽取注射吸毒者进行断面调查,以评估共用针具的影响因素。影响因素的确定采用Logistic单因素分析,对有显著意义的变量进行多因素Logistic逐步回归分析。结果干预前后分别调查了428和429名静脉吸毒者。干预后干预组和对照组最近30天内共用针具率分别为20.4%和35.3%,差异有显著性（χ^2=11.83,P=0.001）。多因素Logistic逐步回归分析结果显示：知晓艾滋病知识（OR=0.62,95%CI：0.45～0.85）、20～30岁年龄组（OR=1.41,95%CI：1.04～1.91）、使用多种毒品（OR=2.21,95%CI：1.53～3.19）、注射吸毒的年限（OR=2.38,95%CI：1.43～3.99）、重复使用注射器（OR=2.94,95%CI：2.06～4.19）、一次买4支针以上（OR=0.53,95%CI：0.33～0.86）、买针不方便（OR=2.08,95%CI：1.38～3.12）及是否看过艾滋病宣传折页或宣传画（OR=0.59,95%CI：0.42～0.83）,是影响吸毒者共用针具的主要原因。结论针具交换项目有效地降低了静脉吸毒人员共用针具率,知晓艾滋病知识、针具交换项目的宣传及针具的可及性,是针具共用的预防因素;而青年人群、使用多种毒品及注射吸毒时间较长等,是共用针具的危险因素。因此今后的针具交换项目应该针对这些危险因素才能达到控制艾滋病在静脉吸毒人群中的传播。     

Correlates of Receptive and Distributive Needle Sharing Among Injection Drug Users in Kabul,Afghanistan

We describe receptive and distributive needle/syringe sharing among injection drug users (IDUs) in Kabul, Afghanistan. In this cross-sectional study, IDUs completed an interviewer-administered questionnaire. Logistic regression identified correlates of needle sharing in the last six months. Receptive and distributive sharing in the last six months were reported by 28.2% and 28.7% of participants, respectively, and were both independently associated with reported difficulty obtaining new syringes (Receptive sharing: AOR = 2.60, 95% CI: 1.66–4.06; Distributive: AOR = 1.56, 95% CI: 1.02–2.39). Receptive and distributive sharing are common among IDU in Kabul; scaling up availability of sterile, no-cost injecting equipment is urgently needed.     

Correlates of receptive and distributive needle sharing among injection drug users in Kabul, Afghanistan

We describe receptive and distributive needle/syringe sharing among injection drug users (IDUs) in Kabul, Afghanistan. In this cross-sectional study, IDUs completed an interviewer-administered questionnaire. Logistic regression identified correlates of needle sharing in the last six months. Receptive and distributive sharing in the last six months were reported by 28.2% and 28.7% of participants, respectively, and were both independently associated with reported difficulty obtaining new syringes (Receptive sharing: AOR = 2.60, 95% CI: 1.66-4.06; Distributive: AOR = 1.56, 95% CI: 1.02-2.39). Receptive and distributive sharing are common among IDU in Kabul; scaling up availability of sterile, no-cost injecting equipment is urgently needed.     

Gender differences in sharing injecting equipment by drug users in England

The study investigates whether the higher rates of sharing needles and syringes reported by female injecting drug users (IDUs) also occur in sharing other types of injecting equipment. Structured interviews were carried out with 181 IDUs in two cities (100 in Bournemouth, 81 in Bath), with almost equal numbers of males and females in each sample, recruited through needle exchanges and 'snowballing'. Almost all (92%) had shared some equipment in the previous six months: 40% had shared syringes in the month before interview. Several methods of assessing sharing found that women received previously used injecting equipment significantly more often than men. Significantly more males had passed on equipment other than syringes in the previous six months. Fine-grained analyses of 547 injecting episodes found that women received needles and syringes, and syringes significantly more often than did men. The pattern of gender differences reported suggests that women are at higher risk of blood borne viral infections because they receive more types of used equipment and do so more frequently. These results have implications for practice and research.     

Background demographics and risk behaviors of injecting drug users in Karachi, Pakistan.

OBJECTIVE: To find the prevalence of HIV infection and risk behaviors among injecting drug users (IDUs) in Karachi, Pakistan. DESIGN: A cross-sectional study of IDUs conducted in Karachi, Pakistan from February through June 1996. RESULTS: Of the 242 IDUs, 11 (4%) refused HIV testing. One (0.4%; 95% confidence interval (CI) = 0.37-0.48%) was HIV positive. All subjects were male. Over the past 6 months 47% had engaged in receptive needle sharing, 38% had perceived a change in their social network, 22% had had sexual intercourse, of whom only 7% always used condoms, and none had washed their needles with bleach. Younger age (28 vs. 31 years; p = 0.01), younger age at first injection (25 vs. 28 years; p = 0.001), fewer years of schooling (3 vs. 5 years; p = 0.001), lower monthly income (70 dollars vs. 80 dollars; p = 0.03), inhaling fumes of heroin from a foil in the year before injecting (OR = 4.8; CI = 2.2-10.3), injecting first time with heroin (OR = 3.6; CI = 1.2-12.6), having a temporary job (OR = 2.5; CI = 1.2-5.2), and a perceived change in one's social network (OR = 4.4; CI = 2.4-7.9) were all associated with receptive needle sharing. IDUs who knew about HIV spread through contaminated needles were less likely to share (OR = 0.4; CI 0.2-0.8). In the final logistic regression model receptive needle sharing was associated with inhaling of fumes of heroin on a foil in the year prior to injecting (adjusted OR = 5.6; CI = 2.6-12.0), a perceived change in one's social network (adjusted OR = 4.0; CI = 2.2-7.4), and inversely associated with age at first time of injection (beta = -0.07; p = 0.002). CONCLUSION: Background HIV prevalence was low among IDUs in Karachi despite high-risk behavior in 1996. In order to control HIV transmission among IDUs in Pakistan, continual HIV surveillance with well-coordinated and effective HIV risk reduction, and drug demand reduction programs need to be implemented among drug users.     

Hepatitis C virus infection, HIV co-infection, and associated risk among injecting drug users in Togliatti, Russia

The objective of this study was to estimate the prevalence of hepatitis C virus (HCV) infection and co-infection with HIV among injecting drug users (IDUs) in Togliatti City, Russia. Unlinked anonymous cross-sectional survey of IDUs recruited from community settings, with oral fluid sample collection for HCV and HIV antibody (anti-HCV, anti-HIV) testing, was carried out. The anti-HCV prevalence was 87% (357/411), anti-HIV prevalence 56% (234/418), and 93% (214/230) of HIV-positive IDUs were co-infected with HCV. Only 23% (94/411) of those HCV positive self-reported as such. In an adjusted model, increased odds of HCV positivity were associated with needle and syringe, as well as injecting paraphernalia sharing in the last four weeks. IDUs injecting more than once with the same needle also had raised odds. There were no marked associations between HCV positivity and the duration of injecting or age group. Almost all IDUs were HCV positive, and almost all HIV-positive IDUs were HCV co-infected. There is an urgent need to maximize syringe distribution coverage, develop health promotion targeting HCV prevention for IDUs, and improve access among IDUs to treatments for HIV and HCV infection.     

The effect of a needle and syringe exchange on a methadone maintenance unit

In November 1986, a pilot needle and syringe exchange was established in Sydney adjacent to a methadone maintenance unit. A retrospective study was carried out to determine the effect of increasing the availability of sterile needles and syringes on the treatment outcome of the methadone maintenance unit. In this study, an increase in availability of sterile needles and syringes was not found to be associated with an increase in the presence of illicit injectable drugs in the urine specimens of clients of the methadone programme compared to a control methadone unit where there was no known change in needle and syringe availability. This study suggests that an increase in the availability of sterile needles and syringes does not appear to lead to an increase in the frequency of intravenous drug use. The possibility of drug and alcohol treatment centres acting as needle and syringe exchange or distribution outlets therefore requires consideration.     

Unsafe injecting practices among attendees of syringe exchange programmes in France

Aims. To describe syringe exchange programme attendees and their injection practices. Design. Crosssectional study (one week in 1998). Data were collected through a standardized questionnaire. Setting. 60/74 syringe exchange programmes (SEPs) in France. Participants. Clients requesting syringes in 60 SEPs. Measurements. Self-reports of drug use, injecting behaviour, sexual behaviour, serological status (HIV, HBV, HCV). Prevalence of unsafe injecting practices in the previous month such as: syringe sharing; and sharing other injection paraphernalia. Findings. 1004 questionnaires were collected (response rate: 50%). The mean age of respondents was 30 years, and 70% were males. Among individuals tested, HIV reported prevalence was 19.2%, HCV 58.4% and HBV 20.8%. The mean duration of drug use was 11 years. Eighty-five percent were polydrug users and buprenorphine high-dosage was the substance most used (73%). In the previous month, 45% of the participants had re-used a syringe, 93% injected at least daily (mean 3.6 injections per day), 18% shared a syringe and 71% shared injection paraphernalia. In multivariate analyses, unsafe injecting practices were associated with heroin and cocaine use and with living in a couple. The cluster analysis identified five categories of IDUs: users of buprenorphine-HD (45% of the responders), morphine-sulphate (17%), benzodiazepines and other legal drugs (13%), methadone associated with other legal drugs (13%) and crack-cocaine (13%). The buprenorphine–HD group had better social status and safer injection practices. Conclusions. In France, despite an increase in the accessibility to syringes and substitution treatments, unsafe injecting practices persist among SEP attenders. Interventions should stress the importance of using sterile material for each injection, even with a steady sex partner.     

The impact of the needle and syringe-exchange programme in Amsterdam on injecting risk behaviour

We interviewed a group of 145 injecting drug users (IDUs) in Amsterdam about their drug use, participation in a needle-exchange programme and needle sharing. Approximately 1 year later 60 IDUs were followed up. IDUs who exchange regularly ('exchangers') are older, inject longer and are more often in contact with methadone programmes. Exchanging is associated neither with an increase in injecting nor with lending needles to other IDUs. The risk level of injecting of the exchangers is much lower than that of the non-exchangers. From this it can be concluded that a needle exchange is an effective prevention programme against the spread of HIV infection. However, efforts have to be made to reach the group of younger short-term injectors and those IDUs who are not in contact with methadone-maintenance programmes. Since there are indications that regular injectors in particular exchange, and since young male injectors are more at risk of borrowing independent of exchanging, it is argued that an exchange programme should be complemented with other prevention approaches, i.e. intensive counselling and the spread of leaflets with information on cleaning used needles with bleach.     

针具交换结合同伴宣传对注射吸毒人群吸毒行为的影响

目的通过同伴宣传和针具交换项目减少吸毒者的共用注射器行为，降低吸毒人群中艾滋病病毒的传播流行。方法通过卫生工作人员和同伴宣传员向吸毒者提供清洁针具并回收污染针具，发放宣传折页，张贴宣传画以及对吸毒者进行面对面的宣传等措施，在广西壮族自治区某县注射吸毒者中开展了为期一年的针具交换和同伴宣传项目。在干预前后分别进行基线和终期横断面调查，通过对比两次调查中吸毒者自我报告的高危注射行为等变化情况对于预效果进行评估。结果基线调查205人，终期调查234人。终期调查时吸毒者的针具共用率、水和容器的共用率分别为30．34％、33．33％和11．54％，均显著地低于基线调查(分别为60．59％、62．69％和61．00％)；同基线调查相比，终期调查中吸毒者的每日注射毒品次数也显著减少。结论针具交换结合同伴宣传干预措施不仅能显著减少吸毒者对针具、清洗水和容器等的共用行为，还能有效降低吸毒者的针具共用频率，同时并不会增加吸毒者的毒品注射次数。     

Syringe possession arrests are associated with receptive syringe sharing in two Mexico-US border cities.

AIMS: To identify factors associated with receptive syringe sharing among injection drug users (IDUs) and elucidate the association between syringe possession arrests and syringe sharing. DESIGN: Cross-sectional study. SETTING: Mexican border cities of Tijuana, Baja California and Ciudad Juarez, Chihuahua. PARTICIPANTS: IDUs in Tijuana (n = 222) and Ciudad Juarez (n = 206) were recruited using respondent-driven sampling (RDS). IDUs were > or = 18 years and had injected illicit drugs in the past month. MEASUREMENTS: An interviewer-administered survey was used to collect quantitative data on socio-demographic, behavioral and contextual characteristics, including self-reported syringe sharing and arrests for syringe possession. Associations with receptive syringe sharing were investigated using logistic regression with RDS adjustment. FINDINGS: Overall, 48% of participants reported ever being arrested for carrying an unused/sterile syringe, even though syringe purchase and possession is legal in Mexico. Arrest for possessing unused/sterile syringes was associated independently with receptive syringe sharing [adjusted odds ratio (AOR) = 2.05; 95% confidence interval (CI): 1.26, 3.35], as was injecting in a shooting gallery (AOR = 3.60; 95% CI: 2.21, 5.87), injecting in the street (AOR = 2.05; 95% CI: 1.18, 3.54) and injecting methamphetamine (AOR = 2.77; 95% CI: 1.41, 5.47) or cocaine (AOR = 1.96; 95% CI: 1.15, 3.36). More than half of participants (57%) had been arrested for possessing a used syringe; in a second model, arrest for used syringe possession was also associated independently with receptive sharing (AOR = 2.87; 95% CI: 1.76, 4.69). CONCLUSIONS: We documented high levels of syringe-related arrests in two Mexican-US border cities and an independent association between these arrests and risky injection practices. Public health collaborations with law enforcement to modify the risk environment in which drug use occurs are essential to facilitate safer injection practices.     

Needle and Syringe Sharing Practices Among Injecting Drug Users in Tehran: A Comparison of Two Neighborhoods,One with and One Without a Needle and Syringe Program

This study was conducted to compare needle and syringe sharing practices among injecting drug users (IDUs) in two neighborhoods, one with and one without a needle and syringe program (NSP). In 2005, 419 street-based IDUs were interviewed at specific locations in two neighborhoods where IDUs are known to congregate. We compared self-reported needle and syringe access and use between IDUs from a neighborhood with an active NSP to IDUs from a neighborhood without such an intervention. A significantly smaller proportion of IDUs from the former neighborhood reported having used a shared needle/syringe over a 1-month period (21.0%) compared to IDUs from the latter neighborhood (39.9%; adjusted odds ratio, 0.24; 95% confidence interval, 0.13–0.45). These findings indicate that access to an NSP may reduce needle and syringe sharing practices. Therefore, these programs should be intensified in settings with concentrated HIV epidemics among IDUs in Iran.     

Risk behaviors and antibody hepatitis B and C prevalence among injecting drug users in south-western Sydney, Australia

BACKGROUND AND AIM: Hepatitis C virus (HCV) infection is now the leading notifiable disease in Australia. The current study aimed to determine the prevalence of HCV and hepatitis B virus (HBV) infection and associated risk behaviors among injecting drug users (IDUs) screened in south-western Sydney as part of a multisite prospective cohort study. METHODS: Using a combination of snowball sampling and word-of-mouth recruitment strategies, 377 IDUs were interviewed using a structured questionnaire and tested for exposure to HCV and HBV. Entry criteria were injecting drug use in the previous 6 months and antibody HCV serostatus not known to be positive. RESULTS: More than one-third (36.6%) tested HCV antibody positive and one-quarter (28%) had been exposed to HBV. Independent predictors of HCV seropositivity were HBV core antibody positive serostatus, incarceration in the past year, injecting in public, Asian ethnicity and duration of injecting. Individual risk behaviors, including sharing needles and syringes, sharing other injecting equipment and being injected by others, were not significant in either bivariate or multivariate models. CONCLUSIONS: Results indicate an urgent need for structural interventions designed to reduce the exposure of IDUs, particularly indigenous Australian and Asian injectors, to risk environments. Structural interventions, including population-based hepatitis B immunization, expanded access to needle and syringe programs and drug treatment, prison diversion programs and medically supervised injecting facilities, should be incorporated into existing blood-borne virus prevention efforts.     

Hepatitis C virus infection and needle exchange use among young injection drug users in San Francisco.

Young injection drug users (IDUs) in San Francisco may be at high risk for hepatitis C virus (HCV) infection despite access to several needle exchange venues. The authors conducted a cross-sectional study from 1997 to 1999 in San Francisco to estimate the prevalence and incidence of antibody to HCV (anti-HCV) among street-recruited IDUs under age 30, and to examine risk behaviors and sources of sterile needles. Among 308 participants, the prevalence of anti-HCV was 45%. Using statistical modeling, incidence of HCV infection was estimated to be 11 per 100 person years. Independent risk factors for anti-HCV included age (odds ratio [OR], 1.17 per year; 95% confidence interval [CI], 1.05-1.30), years injecting (OR, 1.21 per year; 95% CI, 1.10-1.34), years in San Francisco (OR, 1.06 per year; 95% CI, 1.00-1.14), first injected by a sex partner (OR, 4.06; 95% CI, 1.74-9.52), injected daily (OR, 3.85; 95% CI, 2.07-7.17), ever borrowed a needle (OR, 2.56; 95% CI, 1.18-5.53), bleached last time a needle was borrowed (OR, 0.50; 95% CI, 0.24-1.02), snorted or smoked drugs in the prior year (OR, 0.48; 95% CI, 0.26-0.89), and injected by someone else in the prior month (OR, 0.50; 95% CI, 0.25-0.99). In the prior month, 88% used at least 1 of several needle exchange venues, and 32% borrowed a needle. We conclude that anti-HCV prevalence is lower than in previous studies of older IDUs, but 11% incidence implies high risk of HCV infection in a long injecting career. Despite access to sterile needles, borrowing of needles persisted.     

The social context of HIV risk behaviour by drug injectors in Ho Chi Minh City, Vietnam

A combined research approach with both quantitative and qualitative methods was used to contextualize risk behaviour among injecting drug users (IDUs) in Ho chi Minh City (HCMC), Vietnam, in April 1997. A total of 630 IDUs (330 inside and 300 outside the rehabilitation centre) were recruited to the study. Very high-risk injecting behaviour among IDUs in the past, including sharing needles, syringes and drug solutions from the same drug pot in shooting galleries, may explain why HIV prevalence among IDUs in HCM has been growing rapidly. IDUs who had in the past injected on the street, used syringes from shooting galleries, were injected by drug dealers and/or joined in needle sharing were more likely to be sharing needles and syringes currently. Condom use was low, and was mainly with female sex workers but not with regular partners. Both IDUs who continue to use shooting galleries and shooting gallery owners should be educated on the necessity of using clean injecting equipment and on how to clean it properly. Co-ordination between ministries and agencies involved in HIV/AIDS and drugs programmes is needed to create policies for supportive environments to bring about changes in both drug use and HIV risk behaviours.     

High street prices of syringes correlate with strict syringe possession laws

The current epidemic of injection drug use in the United States and abroad has precipitated an increase in transmission of infectious diseases, including human immunodeficiency virus (HIV), hepatitis B, hepatitis C, and human T-lymphotrophic virus II (HTLV-II) in injection drug users (IDUs) who share syringes and other injection equipment. Sharing is often due to a lack of available sterile syringes, which is, in part, a result of laws and regulations controlling the purchase and possession of syringes. These laws, in turn, raise the price of questionably sterile black market syringes, inadvertently encouraging the reuse and sharing of syringes. To date, very little information has been gathered on the street price of syringes in different communities. We surveyed 42 needle exchange programs (NEPs) in the United States in July and August 1998 to determine the street prices of syringes. The relationship among local laws regulating syringe possession, the enforcement of those laws, and street syringe prices was examined. There was a strong correlation between the presence of syringe possession laws and higher street syringe price ($2.87 vs. $1.14, p< .01). In areas with syringe possession laws, cost was significantly higher when laws were perceived to be enforced strictly ($3.66 vs. $2.08, p<.01). Street prices for syringes are an easily quantifiable indirect measure of availability of sterile syringes and may reflect syringe sharing and reuse.     

Sharing spoons: a risk factor for HIV-1 infection in Vienna

Sharing of needles and syringes plays a central role in HIV-1 transmission among intravenous drug users (IVDUs). There have been several suggestions to protect the injecting population from further harm, but focused mainly on the use of sterile needles and syringes as well as information about safer sexual behavior. This study examined a total of 366 IVDUs at the drug dependence out-patient ward of the Psychiatric University Clinic of Vienna. HIV-1 antibodies were found in 29.7% (58) in 1989 and in 26.9% (42) in 1990. The results show that in 1989 14% and in 1990 5% IVDUs who never shared needles or syringes or other drug paraphernalia were found to be HIV-1 positive. In spite of the high information standard among Viennese drug addicts on risk reduction, the underestimated co-factors during drug administration might be responsible for a further HIV-1 transmission. Educational interventions on this subject should address even IVDUs who do not share needles and have adjusted to ‘safer sex’ practices.     

Syringe HIV seroprevalence and behavioural and demographic characteristics of intravenous drug users in Sydney, Australia, 1987

The contents of needles and syringes returned by intravenous drug users to two Sydney needle and syringe exchange centres were analysed for HIV antibodies by the enzyme-linked immunosorbent assay (ELISA). Reactive and borderline samples were further tested by the Western blot method. Basic demographic and needle sharing data were also collected from the clients of the exchanges. Of a sample of 1544 returned syringes, 48 (3%) were confirmed as containing HIV-infected blood. The proportion of infected syringes at exchange 2 was 6% (33 out of 545), which was significantly greater (P less than 0.05) than the proportion of exchange 1 at 1.5% (15 out of 999). The difference in seroprevalence between the two centres may be related to the behavioural characteristics of the client populations that attended each of the exchanges. The maintenance of a low syringe HIV seroprevalence (1-1.5%) over a 7-month period at one exchange may indicate that the availability of sterile needles and syringes prevented transmission of HIV among the clients of that exchange. HIV antibody testing of the contents of used syringes is a potentially valuable method of monitoring HIV infection among intravenous drug users. In this study, syringe exchange schemes have proved to be suitable venues for investigating the demographic characteristics and risk-taking behaviours of this population.