HIV prevalence and incidence in rural Tanzania: results from 10 years of follow-up in an open-cohort study.

BACKGROUND: Tanzanian antenatal clinic surveillance data suggest stabilizing HIV levels. Data from an open cohort in northern Tanzania provide robust estimates of prevalence and incidence. METHODS: Between 1994 and 2004, 19 rounds of household-based demographic surveillance and 4 rounds of individually linked HIV serologic surveys were conducted. Longitudinal knowledge of individuals' testing histories is used to allow for effects of selective participation on prevalence estimates; multiple imputation procedures allow for interval censoring effects on incidence. RESULTS: A total of 16,820 adults donated blood for HIV testing in at least 1 of 4 serologic surveys. HIV prevalence increased steadily from 6.0% in 1994/1995 to 8.3% in 2000/2001, leveling out thereafter. HIV incidence increased sharply from 0.8% in 1994 to 1997 to 1.2% per thousand in 1997 to 2000, remaining high (1.1%) in 2000 to 2003. In roadside areas, incidence fell in the last interval, especially among women, but in remote rural areas, incidence rose slightly. CONCLUSIONS: HIV spread is continuing in rural areas, suggesting a need for more intensive HIV prevention efforts and antiretroviral interventions. The leveling off in prevalence is attributable to a combination of high mortality among HIV-infected persons and a slight decrease in incidence in roadside villages.