The relationship between maternal-infant antibody levels and vertical transmission of HIV-1 infection

It is important for many reasons to diagnose or predict the subsequent development of HIV-1 infection in infants soon after their birth. Although least sensitive in the newborn viral culture polymerase chain reaction (PCR) and tests to detect antigen are the main methods used to determine whether babies born to HIV-1 seropositive mothers are also infected with HIV. This paper describes a useful relationship between the ratio of HIV-1 antibody levels in the baby to that in the mother (sequestration index SI) and vertically transmitted infection. Data were available for 114 infants in a cohort of 137. The ratio was related to the HIV infection status of the children by age 18 months HIV DNA PCR and HIV-specific IgA antibody detection at birth between ages 3 and 6 months and morbidity and mortality. 35 of the 137 children were diagnosed as infected by age 18 months. The mean HIV SI was 1.57 in 29 infected and 0.83 in 85 uninfected infants. The sensitivity and specificity of a threshold of SI of 1.27 for the prediction of perinatal HIV-1 infection were 41% and 98% respectively. SI was higher in the infected babies due to the combination of lower antibody titres in the transmitting mothers with raised levels in infected babies. No statistical difference was found for measles between HIV infected and uninfected groups and there was a tendency to increased morbidity and more severe disease among those with higher HIV-1 SI. While only three of 17 peripheral blood samples from infected children at birth were PCR positive all had SIs above the threshold. The overall sensitivity and specificity of PCR were 85% each. 11 of the 29 infected children were HIV-1 specific IgA positive at birth; six had a SI greater than 1.27.