Decrease of human T-cell lymphotropic virus type I prevalence and low incidence among pregnant women from a high endemic ethnic group in French Guiana.

To assess the prevalence and incidence of human T-cell lymphotropic virus type I (HTLV-I), 4,234 pregnant women of different ethnic origins were tested before each delivery between 1991 and 1997 in a high HTLV-I endemic area of French Guiana. HTLV-I was significantly more prevalent among ethnic groups of African descent as the Noir-Marrons (4.8%, 95% confidence interval [CI]: 4.0-5.6) and Haitians (5%, 95% CI 1.6-8.4). An age dependence of HTLV-I seroprevalence was observed. The mean age of Noir-Marron HTLV-I seronegative women was lower than for HTLV-I seropositive women (24. 7 vs. 28.6, p < 0.001). A decline in HTLV-I seroprevalence was observed, particularly in the Noir-Marron younger than 21 years old (p = 0.04). For five HTLV-I seroconversions observed, the incidence per 100 women-years in the Noir-Marron group was 0.19 (95% CI 0.02-0. 35) for all women, 0.32 in those 25 years old or younger (95% CI 0-0. 64), and 0.07 in those older than 25 years (95% CI 0-0.2). This observation was inconsistent with HTLV-I seroprevalence observed for those 25 years old or younger (2.8%) and those older than 25 (8.3%). These data demonstrate, for the first time outside Japan, a birth cohort effect for HTLV-I in a highly endemic ethnic group. Copyright 2000 Wiley-Liss, Inc.