Trends and Measurement of HIV Prevalence in Northern Malawi
October 7, 2003
Most data on HIV prevalence in Malawi come from antenatal clinic (ANC) surveillance, so they are subject to bias. Since HIV is associated both directly and indirectly with lower fertility, ANC sources tend to underestimate HIV prevalence. Pregnant women who attend an ANC, especially the larger clinics where most surveillance is conducted, may differ in factors that may affect HIV status, such as education and area of residence.Adapted from:
This study measured HIV prevalence and risk factors using population-based data from the late 1980s to 2001 to assess the accuracy of ANC surveillance and changes over time in HIV prevalence and risk factors. HIV prevalence has been measured in Karonga District, Malawi, for more than 20 years as part of large-scale epidemiological studies of mycobacterial disease.
"To estimate HIV prevalence in the whole district and allow direct comparison between the community sample and the ANC, and between different time periods, results were directly standardized by ages, sex and area," the authors explained. They found that age- and area-standardized HIV prevalence in women ages 15-49 was 3.9 percent in 1988-1990, 12.5 percent in 1991-1993 and 13.9 percent in 1998-2001. Male HIV prevalence was 3.7 percent, 9.2 percent and 11.4 percent, respectively, for the same periods.
The age- and area-adjusted HIV prevalence in the ANC in 1999-2001 was 9.2 percent. "The underestimate can be explained largely by marriage and mobility," the authors theorized. "Reduced fertility in HIV-positive individuals was demonstrated in both ANC and community populations. A previously recommended parity-based adjustment gave an estimated female HIV prevalence of 15.0 percent," they noted.
"In this community, we have had the unusual opportunity to document the first 20 years of the HIV epidemic. The recent stabilization of HIV prevalence seen elsewhere in Malawi was also seen here," the researchers wrote. "Despite the changes in prevalence, the risk factors for HIV have been similar in all periods, with HIV being associated with occupations other than farming [particularly in skilled manual workers, clerical workers and people in professional or managerial posts], with immigration and travel, and being most common in those with most schooling. The trend with increased schooling has become less strong, unfortunately because of a rise in HIV prevalence in those without schooling rather than a fall in prevalence in the more educated. As in other populations, HIV sentinel surveillance data in ANC provide only a partial picture of the epidemic," they concluded.
08.15.03; Vol. 17; No. 12: P. 1817-1825; Amelia C. Crampin; Judith R. Glynn; Bagrey M.M. Ngwira; Frank D. Mwaungulu; Jörg M. Pönninghaus; David K. Warndorff; Paul E.M. Fine
This article was provided by CDC National Prevention Information Network. It is a part of the publication CDC HIV/Hepatitis/STD/TB Prevention News Update.