Objective: To estimate the incidence of HIV-1 infection among pregnant women from central-western Brazil.
Design: Observational cross-sectional study.
Methods: A total of 54,139 pregnant women received antenatal HIV screening from a network of public healthcare centers in 2011. The incidence of confirmed HIV-1 infection was estimated using the Serological Testing Algorithms for Recent HIV Seroconversion (STARHS) methodology and BED-capture enzyme immunoassay (BED-CEIA). The yearly incidence was calculated, and adjusted incidence rates were estimated. For a subgroup of patients, protease and partial reverse transcriptase regions were retrotranscribed from plasma HIV-1 RNA and sequenced after performing a nested polymerase chain reaction.
Results: Of the participants, 20% had a pregnancy before the age of 18 and approximately 40% were experiencing their first pregnancy. Of the 54,139 pregnant women screened, 86 had a confirmed HIV-1 diagnosis, yielding an overall prevalence of 1.59 cases per 1000 women (95% CI 1.27-1.96). A higher prevalence was detected in the older age groups, reflecting cumulative exposure to the virus over time. Among the infected pregnant women, 20% were considered recently infected according to the BED-CEIA. The estimated incidence of HIV infection was 0.61 per 1000 person-years (95% CI 0.33-0.89); the corrected incidence was 0.47 per 1000 person-years (95% CI 0.26-0.68). In a subgroup of patients, HIV-1 subtype C (16.7%) was the second most prevalent form after subtype B (66.7%); BF1 recombinants (11.1%) and one case of subtype F1 (5.5%) were also detected.
Conclusion: This study highlights the potential for deriving incidence estimates from a large antenatal screening program for HIV. The rate of recent HIV-1 infection among women in their early reproductive years is a public health warning to implement preventive measures.