Background:

Antenatal Clinic-based surveillance data suggests stabilizing HIV levels in Tanzania. Data from an open demographic surveillance cohort in Northern Tanzania provide robust estimates of prevalence and incidence trends. These can help us to interpret results from national HIV surveillance.
Methods:

The Kisesa open cohort study conducted 19 rounds of household based demographic surveillance and 4 rounds of individually linked HIV serological surveys between 1994 and 2004. HIV testing was anonymous, based on informed consent without result disclosure. The effect of selective participation in sero-surveys on prevalence and incidence estimates is investigated, using longitudinal knowledge of individuals' testing histories. In addition, incidence estimates make allowance for interval censoring using a multiple imputation procedure for sero-conversion dates.
Results:

16,820 adults were interviewed and donated blood specimens for HIV testing in at least one of the four serological surveys. HIV prevalence increased steadily from 6.0% in 1994/95 to 8.3% in 2000/01, levelling out thereafter. HIV incidence increased sharply between the first and second intervals, (from 0.8% in 1994-97 to 1.2% per thousand in 1997-2000) remaining at a high level (1.1%) in 2000-03. In roadside areas incidence fell in the last inter-survey interval, especially among women, contributing to a decline in roadside prevalence, but in remote rural areas incidence (and thus prevalence) rose slightly.
Conclusion:

HIV spread is continuing in the rural part of the population suggesting a need for more intensive HIV prevention efforts and ART interventions. The levelling off in prevalence is due to a combination of high mortality among HIV infected, and a slight decrease in incidence in roadside villages.