Effectiveness of a city-wide program to prevent mother-to-child HIV transmission in Lusaka, Zambia

Abstract

Objective: To determine the population effectiveness of a city-wide perinatal HIV prevention program.

Design: An anonymous surveillance of newborn cord blood for HIV serology and nevirapine (NVP).

Methods: All 10 public-sector delivery centers in Lusaka, Zambia participated. All mother-infant pairs delivering during the 12-week surveillance period at the participating centers and who received antenatal care at a public-sector facility in Lusaka were included in the study. The main outcome measure was population NVP coverage, defined as the proportion of HIV-infected women and HIV-exposed infants in the population that ingested NVP.

Results: Of 8787 women in the surveillance population, 7204 (82%) had been offered antenatal HIV testing, of which 5149 (71%) had accepted, and of which 5129 (99%) had received a result. Overall, 2257 of 8787 (26%) were cord seropositive. Of the 1246 (55%) cord blood seropositive women who received an antenatal HIV test result, 1112 (89%) received a positive result; the other 134 comprise seroconverters and clerical errors. Only 751 of 1112 (68%) women who received a positive antenatal test result and a NVP tablet for ingestion at labor onset had NVP detected in the cord blood (i.e., maternal non-adherence rate was 32%). A total of 675 infants born to 751 adherent mothers (90%) received NVP before discharge. Thus, only 675 of 2257 (30%) seropositive mother-infant pairs in the surveillance population received both a maternal and infant dose of NVP.

Conclusions: Successful perinatal HIV prevention requires each mother-infant pair to negotiate a cascade of events that begins with offering HIV testing and continues through adherence to the prescribed regimen. This novel surveillance demonstrates that failures occur at each step, resulting in reduced coverage and diminished program effectiveness.

Figures

Fig. 1. Surveillance study profile

We obtained cord blood specimens from 98% of public sector deliveries in Lusaka during the 3-month surveillance period. Of these, 86% attended antenatal care within Lusaka and at a public-sector facility (and thus where prevention of mother-to-child HIV transmission services were being offered.) These 8787 women and their infants represent the ‘surveillance population’ to which we refer in the text. 26% of mothers in the surveillance population were HIV-infected as determined by cord blood serologic testing.

Fig. 2. Attrition cascade among women in the surveillance population

This Figure demonstrates the sequence of events that members of the surveillance population negotiated in order to achieve prevention of mother-to-child HIV transmission service coverage. Step A (leftmost bars) represents all the women in the surveillance population, stratified by HIV serostatus. Coverage, defined as the proportion of infected-exposed mother–infant pairs that received both the maternal and infant nevirapine (NVP) doses was 675/2257, or 30%. *Of 1246 cord blood seropositive women who received an HIV test result in antenatal care, 1112 received a positive test result. The remaining 134 comprise false-negative antenatal tests, false-positive cord blood tests, clerical errors, and seroconversions between the first test and delivery. †Twenty-eight women who were HIV seronegative on cord blood testing were given an HIV-positive test result and NVP tablet in antenatal care; five of these adhered to the maternal and infant dose. ANC, antenatal clinic.

Fig. 3. Population nevirapine (NVP) coverage and reasons for failed coverage among 2257 cord blood seropositive mothers and infant in the surveillance population

ANC, antenatal clinic.