Modeling HIV prevalence estimates in California

Background: Health departments typically depend on HIV/AIDS Surveillance data to monitor the HIV/AIDS epidemic. New HIV estimation software permits systematic assessment of concentrated epidemics. The goal of this study was to estimate HIV prevalence among men and women aged 15-49 years in California.

Methods: The WHO/UNAIDS Workbook Method was used to estimate and project adult HIV prevalence. U.S. Census data were used to obtain age and gender-specific estimates for California populations. Population and HIV prevalence estimates for MSM, MSM-IDUs, IDUs, and low-risk heterosexuals were obtained from published articles, results of a statewide meeting of HIV/AIDS researchers, and the CDHS Office of AIDS. Numbers of HIV-positive men and women were estimated for each at-risk group and then aggregated. Low and high HIV prevalence estimates were calculated.

Results: Nearly 18 million adults aged 15-49 lived in California in 2006. The estimated number of persons living with HIV in the state was between 54,883 and 205,916 (mean=119,197). HIV prevalence was 0.67%. More than 90% of infections were among men. The largest number of persons with HIV across California were MSM (45,000 to 162,000), MSM-IDUs (5,000 to 22,500) and IDUs (1,800 to 12,500).

Conclusions: HIV prevalence estimates for California, using the WHO/UNAIDS Workbook Method, provide an enhanced understanding of the statewide HIV/AIDS epidemic. Estimation techniques may be particularly useful for public health jurisdictions and regions that do not yet have well established HIV/AIDS surveillance systems. A unique advantage of the estimation software is that it allows for systematic forecasting of future HIV/AIDS trends.