HIV incidence and associated risk factors among young injection drug users

Youth are important with respect to HIV/AIDS, not only because they are at risk of infection, but it is during this period that many behaviour patterns are established that will affect their risk of infection in later life. We undertook this study to determine the rates of HIV incidence and associated risk factors among young injection drug users. Youth are of particular importance with regard to the HIV epidemic because of the window of opportunity available to prevent disease transmission. Researchers have noted that HIV infection among injection drug users (IDU) is associated with younger age and a fewer number of years injecting [1,2]. Studies have found that young female IDU are at higher risk of HIV than young male IDU [3,4]. Other studies have noted that important predictors of HIV positivity among young injectors include: cocaine and speedball injection and smoking crack cocaine [5,6]. In a recent study of young injectors, Doherty et al. [6] found that HIV incidence was associated with injecting cocaine and smoking crack cocaine daily, although there were very few cases of incident HIV during their study period. We undertook this study to determine the rates and risk factors for incident HIV infection among young injectors in a city where an explosive and ongoing HIV epidemic has occurred among IDU. Data were collected through an open cohort study, the Vancouver Injection Drug Users Study from May 1996. Participants were eligible to enrol if they had injected in the previous month and were residents of the lower mainland of Vancouver. At baseline and every 6 months, participants were eligible to complete an interviewer-administered questionnaire eliciting questions concerning sociodemographic, drug use and sexual patterns as well as testing through venous blood sample for HIV and hepatitis C. For the current analysis, youth were defined as those participants in the cohort who were 24 years of age or younger at enrolment. A nested case–control study using prospective data was undertaken to compare sociodemographic and risk factors for HIV incident youth cases versus HIV-negative youth controls (see Table 1). Risk factors for the cases were measured using behaviour data from the questionnaire administered in the 6 months before seroconversion occurred. Controls were matched with cases on the basis of age and questionnaire time period. The data were compared using contingency table analysis. All reported P values were two sided.Table 1: Comparison of sociodemographic characteristics, drug and sexual risk variables between seroinoincident youth cases (N = 16) and HIV-negative youth controls (N = 32). Among the 232 participants aged 24 years and less, the HIV incidence rate was 4.37 per 100 person-years. In total there were 16 incident cases over a 5 year study period. Despite limited statistical power, a number of strong associations were detected. Cases were more likely to be Aboriginal (56 versus 16%;P = 0.004), to have had more than 20 lifetime sexual partners (81 versus 47%;P = 0.00x), to inject cocaine daily (63 versus 19%;P = 0.002), and to use crack cocaine daily (63 versus 19%;P = 0.002). There was a marginal difference between cases and controls with respect to daily speedball injection (31 versus 9%;P = 0.055). Differences between the two groups with respect to engaging in sex trade work (50 versus 28%;P = 0.134), residing in unstable housing (69 versus 47%;P = 0.152), female sex (63 versus 41%;P = 0.153), and any condom use with casual sexual partners (31 versus 25%;P = 0.653) did not reach statistical significance. In a logistic regression analysis, we found that being Aboriginal (adjusted odds ratio 6.9, 95% confidence interval 1.8, 27.4;P = 0.05) remained significantly associated with HIV infection (data not shown). However, we feel that although this variable is highly important, other variables may not have reached statistical significance in multivariate models as a result of low statistical power, and we should not discount the importance of the variables detected in the case–control analysis. To our knowledge this is one of the few studies to examine time-relevant risk factors associated with HIV infection in a young and vulnerable population in a longitudinal fashion. The incidence rate of 4.37 per 100 person-years in a young population with short injection careers is alarming. Furthermore, the numerous drug and sexual vulnerabilities identified bodes poorly for the future of the epidemic unless immediate preventative action is taken. Our work raises a number of important issues. First, young Aboriginal individuals were at markedly elevated risk. Second, similar to other studies of young IDU, we found that smoking crack daily increased the risk of HIV infection [7–10]. Third, we also confirmed that the daily use of injection cocaine and speedballs were associated with HIV infection, as was a great number of lifetime sexual partners [5,6,9,11,12]. Of the HIV seroconverters, 63% occurred in female participants and 50% were among those engaging in sex trade work. The use of condoms with casual sexual partners was very low for both positive and negative youth, and over 50% reported living in unstable housing. The lack of statistical association should not negate the risks. Sex trade work has previously been shown to increase HIV vulnerability among young IDU [7,13,14]. Furthermore, a great number of sexual partners combined with low rates of condom use is a cause for concern. Other research efforts have shown that women, particularly young women, are at increased risk through sexual contact because of the increased efficacy of viral transmission from male to female sex partners [12,15]. The frequency and type of drug use engaged in by this group of young IDU demands a response from policy makers and community workers. In summary, our study found a high rate of new infections among young IDU engaged in dual drug and sexual risks. The very high proportion of young Aboriginals seroconverting is a cause for alarm. Canadian and increasingly American First Nations individuals are witnessing the rapid spread of the virus; urgent action is required to stem the tide of new infections [16,17]. In conclusion, targeted interventions are required among young IDU, which focus on young Aboriginal and female populations and take dual drug and sexual vulnerability into account. Cari L. Millera Mark Tyndalla,b Patricia Spittala,b Kathy Lia Nancy LaLibertea Martin T. Schechtera,b Acknowledgements We would like to thank the participants of the VIDUS project for taking the time to share their stories as well as the staff for all their hard work.

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