Population-based prevalence and incidence studies on HIV-1 infection were started in the Kagera region of Tanzania in 1987. The prevalence and incidence of infection with Treponema pallidum was studied to enable development of better strategies for STD control. Serological diagnosis of a past or treated infection with Troponema pallidum was made by seropositivity only to TPHA testing while active syphilis was diagnosed by seropositivity to both VDRL and TPHA tests. Seroconversion was measured in 1989 by finding TPHA serologically positive individuals during the follow-up period among the initially seronegative study population of 1987. The overall prevalence of active syphilis in the total sample of adults in the region was found to be 5.9% while that of past syphilis was 13.5%. The association between the prevalence of HIV-1 infection and syphilis of both types was found to be highly significant. However, the association between one pre-existing infection and seroconversion in the other was present but not statistically significant. The overall incidence of syphilis based on seroconversion in a cohort of adults in the region was found to be 11.6 per 1000 person-years at risk. In view of these findings, syphilis is a significant health problem in the region with a high level of transmission and efforts should be made to control it. Intervention studies should use these base-line data and monitor changes in syphilis incidence which may indicate changes in sexual behaviour. Such indicators could also be useful for evaluating the impact of interventions directed at reducing the transmission of HIV, syphilis and other STDs in the region.
PIP: Population-based prevalence and incidence studies on HIV-1 infection were started in the Kagera region of Tanzania in 1987. In 1989, a follow-up population-based serosurvey was conducted in the same population with the aim of determining the incidence of HIV-1 infection in the region. In 1987 multi-stage cluster sampling technique was employed to visit all the households selected and to choose at random 1 adult between 15 and 54 years old and 1 child under 15 years old. Syphilis serological examination was done on 2307 adults; 135 had active infection (both VDRL and TPHA positive), 1837 were negative, and 24 had false positive serology (VDRL positive and TPHA negative). The overall prevalence of active syphilis in the regional study sample was 5.9%, while that of past syphilis infection was 13.5%. The prevalence of past infection with syphilis in the rural areas (12.1%) was statistically significantly different from that in the urban area (17.8%, p 0.001). The prevalence of both types of infection increased with age in both rural and urban areas (p 0.001), except for active infection in the urban area (p 0.05). Analysis determining the association between HIV-1 infection and treponemal disease of both types found that there was a highly significant association between the 2 infections after controlling for the number of sexual partners in 3 categories of 0-1, 2-4, and 5 or more sexual partners an individual had had during the 8 years before 1987 (Mantel Haenszel weighted odds ratio 2.38). Between 1987 and 1989 the mean risk period for syphilis seroconversion of the 1133 individuals tested, was 1.82 years with a range between 1.20 and 2.49 years. The overall incidence was 11.6 per 1000 person-years at risk. The highest incidence was in the urban zone (15.4 per 1000 person-years at risk) and the lowest in the Karagwe rural zone (6.5 per 1000 person-years at risk). There was but a weak association between 1 pre-existing infection and seroconversion in the other as indicated by the risk ratios, which were more than unity.