Maternal plasma viral RNA levels determine marked differences in mother-to-child transmission rates of HIV-1 and HIV-2 in The Gambia

Objectives: To determine the rates of, and risk factors for,mother-to-child transmission (MCT) of HIV-1 and HIV-2 infection in The Gambia. Design: A blinded, prospective, community-based cohort study of 29 549 preg nant women attending the eight largest antenatal clinics in The Gambia. Methods: Women were tested for HIV-1 and HIV-2 infection. infected subjects and a group of HIV-seronegative women were followed with their babies unti l 18 months after delivery. Maternal CD4 cell count percentages were measur ed before and 18 months after delivery, and the antenatal plasma viral load was determined. Babies were tested for HIV by the polymerase chain reactio n and/or serology at 2, 9 and 18 months of age. Results: The study enrolled 144 women positive for HIV-1 and 294 for HIV-2 plus 565 seronegative pregnant women: the mean antenatal percentage CD4 cel l counts of 96 HIV-1-positive, 223 HIV-2-positive and 125 HIV-seronegative mothers were 31% [95% confidence interval (Cl) 28-33], 41% (95% CI 39-42) a nd 47% (95% CI 45-49), respectively. The geometric mean antenatal plasma vi ral load of 94 HIV-1-infected women was 15 100 copies x 10(3)ml (95% Cl 10 400-19 000) which was much higher than that of 60 randomly selected HIV-2-i nfected women, which was 410 copies x 10(3)ml (95% CI 150-910) (P<0.001). T he estimated transmission rate of HIV-1 was 24.4% (95% Cl 14.6-33.9) and th at of HIV-2 was 4.0% (95% CI 1.9-7.4). Five of 17 HIV-1-positive and three of eight HIV-2-positive babies were infected after 2 months of age. Birth i n the rainy season [odds ratio (OR) 2.9; 95% CI 1.2-7.2], a low postnatal C D4 cell percentage (OR for a 10% fail 2.4; 95% Cl 1.1-5.1) and a high mater nal plasma viral load (OR for a 10-fold increase 2.9; 95% Cl 1.1-7.8) were risk factors for transmission that applied equally to both viruses. Conclusion: Low maternal HIV-2 RNA levels, which on average are 37-fold les s than in HIV-1 infection, relate to the low MCT rate of HIV-2. (C) 2000 Li ppincott Williams & Wilkins.