JMIR Publications

ABSTRACT

Background:

Direct measures of HIV incidence are needed to assess the population-level impact of prevention programs but are scarcely available in subnational epidemic hotspots of sub-Saharan Africa. We created a sentinel HIV incidence cohort within a community-based program that was providing home-based HIV testing to all residents of Namibia's Zambezi region, where approximately 24% of the adult population was estimated to be living with HIV.

Objective:

Our objectives were to estimate HIV incidence, detect correlates of HIV acquisition, and assess the feasibility of the sentinel, community-based approach to HIV incidence surveillance in a subnational epidemic hotspot.

Methods:

Following the program's initial home-based testing (Dec 2014-Jul 2015), we purposefully selected ten clusters of 60-70 households each and invited residents who were HIV negative and age >=15 years to participate in the cohort. Consenting participants completed behavioral interviews and a second HIV test approximately one year later (Mar-Sep 2016). We used Poisson models to calculate HIV incidence rates between baseline and follow-up and multivariable Cox proportional hazard models to assess correlates of seroconversion.

Results:

Among 1,742 HIV-negative participants, 1,624 (93.2%) completed follow-up. We observed 26 seroconversions in 1,954 person-years (PY) of follow-up, equating to an overall incidence rate of 1.33 per 100 PY (95% CI 0.91-1.95). Among women, incidence was 1.55 per 100 PY (95% CI 1.12-2.17) and significantly higher among those who were age 15-24 years and residing in rural areas (adjusted hazard ratio [aHR] 4.26, 95% CI 1.39-13.13, P =0.01), residing in the Ngweze suburb of Katima Mulilo city (aHR 2.34, 95% CI 1.25-4.40, P =0.01), had no prior HIV testing in the year before cohort enrolment (aHR 3.38, 95% CI 1.04-10.95, P =0.05), and had engaged in transactional sex (aHR 17.64, 95% CI 2.88-108.14, P =0.02). Among men, HIV incidence was 1.05 per 100 PY (95% CI 0.54-2.31) and significantly higher among those who were age 40-44 years (aHR 13.04, 95% CI 5.98-28.41, P <0.001) and had sought HIV testing outside the study between baseline and follow-up (aHR 8.28, 95% CI 1.39-49.38, P =0.02). No seroconversions occurred among circumcised men and persons with partners on antiretroviral treatment.

Conclusions:

Nearly three decades into Namibia’s generalized HIV epidemic, these are the first estimates of HIV incidence for its highest prevalence region. By creating a sentinel incidence cohort from the infrastructure of an existing community-based testing program, we were able to characterize current transmission patterns, identify risk factors for HIV acquisition, and provide insight into the efficacy of prevention interventions in a subnational epidemic hotspot. This study demonstrates an efficient, scalable framework for longitudinal HIV incidence surveillance that can be implemented in diverse sentinel sites and populations.