Objective: To assess the validity of extrapolation from sentinel data by comparing the HIV-1 prevalence of various sentinel groups with that of the general population in Mwanza Region, Tanzania.
Methods: In a population survey, 4161 individuals were selected in a stratified random cluster sample. Sentinel groups (all in the age group 15-54 years) included blood donors (n = 1090); patients examined at district hospitals for the presence of malaria parasites (n = 1488), anaemia (n = 1339), or syphilis (n = 33); and antenatal clinic attenders (n = 1193). The HIV-1 serostatus of individuals selected from the population survey was tested using enzyme-linked immunosorbent assay (ELISA) and Western blot; 51% of the blood donors were tested using HIVCHEK, and all others using ELISA. HIV-1 prevalence was standardized for age, sex, and urban/non-urban location.
Results: HIV-1 prevalence (standardized by age, sex, and residence) in Mwanza Region was 4.0% (3.0% in non-urban areas and 11.3% in town). The standardized HIV-1 prevalences in the sentinel groups were: blood donors, 4.5%; patients with fever, 11.6%; patients with anaemia, 8.9%; urban sexually transmitted disease patients, 27.1%; urban antenatal clinic attenders, 11.8%. The crude prevalence in blood donors was 6.0%.
Conclusion: Blood donors who are related to blood recipients appear to be a representative sentinel group in this region, provided that data are standardized for age, sex, and urban/non-urban location. Patients with fever and antenatal clinic attenders may reflect trends, but data from patients with fever markedly overestimate, and data from antenatal clinic attenders underestimate, population HIV-1 prevalence. Because self-selection of blood donors may become more pronounced, this comparison should be repeated later or elsewhere, should the opportunity arise.
PIP: When full-scale surveys of HIV-1 prevalence are not possible, sentinel surveillance is conducted at specific sites with specific population groups. In this study, 2 sentinel groups have been monitored since 1989 in the Mwanza region on the shores of Lake Victoria in Tanzania. The groups included blood donors in all hospitals of the region an prenatal clinic attenders in Mwanza Municipality. Also considered specifically for this study were outpatients from all 6 district hospitals (including 2 roadside hospitals) who had given blood samples. Population survey data on HIV prevalence between August 1990 and February 1991 were available for reference use. The sample included 1090 blood donors aged 15-54 years, 800 outpatients from district hospitals, and 1193 pregnant women attending a prenatal clinic. Blood donors (49%) were tested with enzyme immunosorbent assay (ELISA). Outpatients provided capillary blood samples collected on filter paper, of which 4605 samples were further tested with ELISA. 1866 were excluded because of age, inadequate samples, or missing data. The results of the comparison of HIV prevalence in the sentinel group and in the population survey showed that in both groups HIV-1 infection was more common in women, particularly those 15-34 years old, than in men, who were particularly affected in the 25-44 year old group. Blood donors, who were mostly male and related to the recipient, showed a crude HIV-1 prevalence of 6% (65 out of 1090). Rates were standardized, and standardized prevalence ratios were calculated. In the general population in both surveys, prevalence was 4.5%. Men had a higher prevalence in non-urban areas. Among outpatients with fever who gave blood for anemia, the crude prevalence was 9% (115 out of 1339). Prevalence was higher in the sentinel group. Of the 33 sexually transmitted diseases outpatients screened for syphilis, 33% (11) were seropositive. Prenatal clinic attenders had a HIV-prevalence of 12% (138 out of 1193).