Introduction:
The human immunodeficiency virus (HIV) epidemic in Pakistan has transitioned from low to concentrated levels among people who inject drugs (PWIDs). Although HIV prevalence in the general population is still low (< 0.1%), the prevalence in some high-risk groups is > 5%. Although second-generation surveillance has tracked HIV-prevalence since 2004, to the best of the authors’ knowledge, no study evaluating risk factors associated with HIV seroconversion among homeless PWIDs has been conducted in the country. Therefore, we assessed the risk factors associated with HIV seroconversion among homeless PWIDs.

Material and methods:
A nested case-control study in a cohort was conducted to estimate the incidence rate of HIV among individuals receiving harm reduction services in the megacity of Karachi. Only homeless PWIDs were selected for analysis. HIV-seroconverted homeless PWIDs (n = 82) were considered cases, while homeless HIV-negative PWIDs (n = 189) were enrolled as controls.

Results:
In multivariable regression analysis, five factors, including being non-Muslim (AOR = 2.5; 95% CI: 1.1-5.6; p = 0.02), sharing of syringes (AOR = 3.9; 95% CI: 2.0-7.6; p < 0.000), source of syringes other than DIC and MSU (AOR = 2.0; 95% CI: 1.1-3.9; p = 0.03), lack of knowledge that HIV spreads through sex (AOR = 2.5; 95% CI: 1.0-6.1; p = 0.04), and frequency of daily injecting drugs (AOR = 1.3; 95% CI: 1.2-1.7; p = 0.002) were significantly associated with HIV seroconversion.

Conclusions:
Programmatic improvements in homeless injecting drug users, focused on risk reduction and public health outreach, are needed to control the HIV epidemic among PWIDs in Pakistan.