Estimating HIV prevalence on the border in San Diego

Background: HIV/AIDS surveillance systems do not include individuals who are HIV-infected and unaware of their status. Various methods exist to estimate all individuals who are HIV-infected (prevalence). As part of the development of a multi-state, bi-national HIV/AIDS epidemiologic profile, HIV prevalence was estimated for San Diego County.

Methods: HIV prevalence for San Diego County was estimated with the UNAIDS/WHO Workbook method for concentrated epidemics. The Workbook combines estimates for populations at lower risk with those at higher risk to produce an overall estimate of adult prevalence. Population size estimates and prevalence estimates for risk groups were identified from a statewide meeting of HIV/AIDS researchers, published papers and local data.

Results: The mean HIV prevalence among adults (ages 15-49) using the Workbook method for San Diego County was 0.78%, using a 2007 population estimate. This results in an estimated 12,556 adults living with HIV/AIDS (LWHA). Of these, 4.5% are female, 2.8% injection drug users, and 92.6% men who have sex with men. The Workbook method estimate count (12,556) is 11.5% lower than other local estimates that indicate approximately 14,000 LWHA.

Conclusions: Strengths of the Workbook method include speed and ease of use, availability free online, ability to add user-defined groups and providing a standardized framework. The primary limitation is finding reliable population and prevalence estimates for risk groups. Improved data inputs would likely lead to more precise and accurate estimates of prevalence. Rapid estimates of HIV/AIDS prevalence can assist health departments in better assessing and responding to local epidemics.