Sera from 487 women attending antenatal clinics in two areas of Manicaland were tested for the presence of HIV-1 infection. In the Honde Valley and Rusitu Valley areas, 24,3 pc and 14 pc respectively, were found to be infected. HIV-1 infection was found to be associated with age, marital status and location. Younger women, non-married women and women living in the Honde Valley were all more likely to be infected. There was also a weak association with level of education, with women with secondary education being at greater risk of being infected. The unadjusted overall figures for HIV-1 prevalence from the antenatal clinics were shown to provide a poor indication of the relative levels of prevalence of infection in the two study areas because of differences in the age structure and religious affiliations of the antenatal clinic and study populations. Similar problems may exist in sentinel surveillance data and would distort comparisons between locations and over time, especially during periods of rapid fertility change. In particular, the age bias is liable to exaggerate differences between urban and rural populations in developing societies. Where comparable information is available for the general population and sample sizes permit, this problem may be overcome by collecting basic socio-demographic data on the individuals tested and then applying standardization techniques. In the Honde Valley and Rusitu Valley example, the levels of HIV-1 prevalence after adjusting for age differences are 18,4 pc and 13,2 pc respectively.
PIP: The results of two human immunodeficiency virus (HIV) seroprevalence surveys conducted among pregnant women in rural Zimbabwe during 1993-94 suggest that selection biases can limit the general relevance such surveys. Screening of sera from 487 women attending antenatal clinics in Honde Valley and Rusitu Valley, Manicaland, Zimbabwe, revealed HIV prevalence rates of 24.3% and 14.0%, respectively. Infection rates were highest among unmarried women in their 20s living in the Honde Valley; also observed were weak associations with a secondary school education and low parity. When logistic regression was used, only marital status and age retained statistical significance. Women 25-30 years old were 50% more likely to be HIV-positive than those in the broader 15-30 year age group. However, a comparison of this data set with data from parallel, unlinked sociodemographic surveys (4961 respondents) conducted in the study areas in 1994 indicates that women in their 20s were over-represented in the antenatal clinic group. After the HIV rates in Honde Valley and Rusitu Valley were adjusted for age differences, they fell to 18.4% and 13.2%, respectively. Religion comprised a second potential source of bias. 28% of women in the Honde Valley were Marange Apostolic; they were less likely than women from other religions to visit a health clinic and thus be covered in antenatal clinic surveys.