Predictors of HIV seroconversion among injection drug users in Tijuana, Mexico
S.A. Strathdee1, R. Lozada2, A. Vera1, R.A. Pollini1, R. Melanie1, D. Abramovitz1, C. Magis-Rodriguez3
1Univ of California San Diego, Medicine, La Jolla, United States, 2Prevencasa A.C., Tijuana, Mexico, 3CENSIDA, Mexico City, Mexico
Objective: A growing body of literature has identified the HIV 'risk environment' as being pivotal to shaping HIV risks at the individual level, but few prospective studies have examined the influence of such factors in low and middle-income countries. We studied predictors of HIV seroconversion among IDUs in Tijuana, a Mexico-U.S. border city.
Methods: Beginning in April 2006, injection drug users (IDUs) were recruited using respondent driven sampling (RDS) and underwent semi-annual surveys and testing for HIV, TB and syphilis. Weighted Cox regression was used to identify predictors of HIV seroconversion, adjusting for correlations between recruiter and recruit and gender.
Results: Of 1056 IDUs, 893 (84.6%) were HIV-negative at baseline and attended ≥1 follow-up visit, among whom HIV incidence was 0.412 among males (95% CI: 0.082-0.741) and 2.026 among females (95% CI:0.250-3.802)]. Factors independently associated with HIV seroconversion included i) biologic factors: syphilis titers ≥1:8 (Adjusted Relative Hazards (AdjRH): 11.15, p< 0.0001), ii) individual factors: high perceived threat of acquiring HIV (adjRH: 6.57; p=0.01), iii) social environmental factors: number of family/friends who are IDUs (AdjRH:1.09 per 5 people; p< 0.0001) or HIV-positive (AdjRH:1.47 per 5 people; p< 0.0001); iv) policy environmental factors: obtaining syringes most often from pharmacies (AdjRH:0.17; p=0.02), and having previously been tested for HIV (AdjRH:0.12; p=0.004). There were no significant gender differences in multivariate analyses.
Conclusions: Factors relating to the social and policy environment were strong predictors of HIV seroconversion in Tijuana. In addition to providing sterile syringes through pharmacies and needle exchange programs, these venues should be used to improve coverage of HIV/STI testing and treatment. Behavioral and structural interventions to alter social norms and the risk environment are needed to curtail HIV transmission in Tijuana.
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