People who inject drugs (PWID) are at higher
risk of acquiring HIV due to risky injection and sexual
practices. We measured HIV prevalence and behaviors
related to acquisition and transmission risk at two time
points (2007 and 2012) in Zanzibar, Tanzania. We conducted
two rounds of behavioral and biological surveillance
among PWID using respondent-driven sampling,
recruiting 499 and 408 PWID, respectively. Through
faceto- face interviews, we collected information on
demographics as well as sexual and injection practices. We
obtained blood samples for biological testing. We analyzed
data using RDSAT and exported weights into STATA for
multivariate analysis. HIV prevalence among sampled
PWID in Zanzibar was 16.0 % in 2007 and 11.3 % in
2012; 73.2 % had injected drugs for 7 years or more in
2007, while in the 2012 sample this proportion was 36.9 %.
In 2007, 53.6 % reported having shared a needle in the past
month, while in the 2012 sample, 29.1 % reported having
done so. While 13.3 % of PWID in 2007 reported having
been tested for HIV infection and received results in the
past year, this proportion was 38.0 % in 2012. Duration of
injection drug use for 5 years or more was associated with
higher odds of HIV infection in both samples. HIV prevalence
and indicators of risk and preventive behaviors
among PWID in Zanzibar were generally more favorable in
2012 compared to 2007—a period marked by the scale-up
of prevention programs focusing on PWID. While
encouraging, causal interpretation needs to be cautious and
consider possible sample differences in these two crosssectional
surveys. HIV prevalence and related risk
behaviors persist at levels warranting sustained and
enhanced efforts of primary prevention and harm
reduction.