Two distinct epidemics: the rise of HIV-1 and decline of HIV-2 infection between 1990 and 2007 in rural Guinea-Bissau.

Objectives: To assess changes in HIV incidence and prevalence in Caió, a rural area of Guinea-Bissau, between 1990 and 2007.

Design: Three cross-sectional community surveys.

Methods: In 1990, 1997, and 2007, surveys were conducted among adults. The prevalence of HIV-1 and of HIV-2 was estimated for each survey, and incidence rates were calculated for the first (1990-1997) and second period (1997-2007).

Results: The HIV-1 incidence was approximately 4.5/1000 person-years in the two periods, whereas the HIV-2 incidence decreased from 4.7 (95% confidence interval 3.6-6.2) in the first to 2.0 (95% confidence interval 1.4-3.0) per 1000 person-years in the second period (P < 0.001). HIV-1 prevalence rose from 0.5% in 1990 to 3.6% in 2007, and HIV-2 prevalence decreased from 8.3% in 1990 to 4.7% in 2007. HIV-1 prevalence was less than 2% in 15 to 24 year olds in all surveys and was highest (7.2%) in 2007 among 45 to 54 year olds. The HIV-2 prevalence was fivefold higher in older subjects (> or =45 yr) compared with those less than 45 years in both sexes in 2007.

Conclusions: HIV-1 incidence is stable, and its prevalence is increasing, whereas HIV-2 incidence and prevalence are both declining. In contrast with what has been observed in other sub-Saharan countries, HIV-1 prevalence is lower in younger age groups than older age groups.