Estimation of annual HIV transmission rates in the United States, 1978-2000.

The HIV/AIDS epidemic in the United States generally has been characterized by AIDS case incidence and AIDS-associated death rates; in a more limited fashion, the epidemic has also been described by AIDS prevalence; population-specific HIV prevalence; and HIV incidence statistics. However, HIV transmission rate information (i.e., the rate of transmission from persons living with HIV to HIV-seronegative persons) has received relatively little attention. The purpose of the present paper is to estimate the annual HIV transmission rate (from HIV-seropositive to HIV-seronegative persons) in the United States for the time period 1978-2000 and to discuss the practical utility of the findings. Using as input annual AIDS-associated deaths and HIV incidence (both variables, especially the latter, contain some element of uncertainty), the model described here finds that HIV transmission rates have dropped dramatically in the United States since the beginning of the epidemic and stayed approximately between 4.00-4.34% during the 1990s. This implies a programmatic success in that for more than roughly 95% of persons living with HIV in any given year, no HIV transmission occurs. Research is urgently needed to fully understand the circumstances that allow the remaining instances of HIV transmission to take place; moreover, serostatus-appropriate HIV-related services are needed to disrupt these remaining instances of transmission.