Sentinel surveillance for HIV-1 among pregnant women in a developing country: 3 years' experience and comparison with a population serosurvey

Abstract

Objectives: To establish unlinked, anonymous sentinel surveillance for HIV-1 among pregnant women attending an antenatal clinic, to determine age-specific seroprevalences, to monitor trends and to compare seroprevalence with that detected by a population serosurvey. To establish the sustainability and costs of surveillance.

Design: Sentinel surveillance for HIV through serial collection of unlinked, anonymous seroprevalence data from antenatal care; comparison of sentinel data with those from a population serosurvey; financial and general audit of the sentinel surveillance.

Setting: A community antenatal clinic in a large urban centre, Mwanza Municipality, Tanzania, eastern Africa, between October 1988 and September 1991.

Patients: Pregnant women attending for antenatal care.

Main outcome measure: Age-specific HIV-1 seroprevalences, trends over time, difference from age-specific population seroprevalences, sustainability and costs.

Results: Overall HIV-1 seroprevalence was 11.5% (95% confidence interval, 10.5-12.4); differences in age-specific prevalences were not significant. There was no clear evidence of change in seroprevalence over the study period in any age group, although there was some indication of a rise in some age groups in 1988-1989. Sentinel surveillance among pregnant women may have significantly underestimated population HIV-1 seroprevalence for women under the age of 35 years. HIV-1 surveillance proved feasible and sustainable. Additional recurrent costs were US$1.7 per specimen for unlinked anonymous testing and US$0.57 per woman for syphilis screening.

Conclusions: HIV-1 seroprevalence did not change significantly over 3 years, probably implying a substantial incidence of HIV-1 infection. In this setting seroprevalence in pregnant women may have underestimated population seroprevalence in women aged under 35 years. With modest inputs and good organization unlinked anonymous HIV-1 sentinel surveillance of pregnant women can be introduced and sustained in an African setting. This may usefully be carried out in conjunction with syphilis screening.

PIP: Between October 1989 and September 1991, health workers took blood samples from pregnant women attending Makongoro Clinic in Mwanza, Tanzania, to determine age-specific HIV-1 seroprevalence in pregnant women, trends over 3 years, and the feasibility, sustainability, and costs of HIV monitoring and to compare age-specific seroprevalences in pregnant women with those of all women. Overall, HIV prevalence among pregnant women stood at 11.5%. Even though the younger and older age groups had lower seroprevalence than the other age groups (10% for those under 20 years old, 11% for 30-34 year olds, and 8.3% for = or 35 year olds vs. 12.8% for 25-29 year olds and 12.3% for 20-24 year olds), the differences were not significant. HIV seroprevalence appeared to increase in 1988-89 in most age groups, but no significant evidence of a linear trend occurred during the study period for any age group. This absence of significant change in HIV seroprevalence over 3 years likely indicated a considerable HIV incidence. The population serosurvey revealed an HIV seroprevalence of 15.1% among the general adult female population, suggesting that the sentinel surveillance among pregnant women could have greatly underestimated population HIV seroprevalence for women under 35 years old (p = .02). Sentinel surveillance improved the clinic's ability to detect anemia and reintroduced syphilis screening. Unlinked anonymous testing resulted in additional recurrent costs of S$1.7/specimen. Syphilis screening added recurrent costs of US$0.57/woman. These findings indicated that health workers in Africa can successfully introduce and maintain anonymous HIV-1 sentinel surveillance of pregnant women and this can be accomplished with concurrent syphilis screening.