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

This study assesses the predictive value of the ratio of HIV-1 antibodies in the newborn at birth to that in the mother for perinatally transmitted infection confirmed subsequently by age 18 months. The ratio of HIV-1 (EIA) antibody levels in the baby at birth to that in the seropositive mother after the first trimester (sequenstration index SI) was available in 114 of a perinatal cohort of 137 infants. We related this ratio to the HIV infection status of the children by 18 months, HIV-1 DNA PCR and HIV-specific IgA antibody detection at birth, between 3 and 6 months, and morbidity and mortality. Thirty-five of the 137 (26 per cent) children were diagnosed as infected by 18 months. The mean (SD) HIV SI was 1.57 (0.88) in 29 infected and 0.83 (0.42) in 85 uninfected infants (P < 0.0001). Sensitivity and specificity of a threshold SI of 1.27 (mean +/- 2 SD of uninfected group) for the prediction of perinatal HIV-1 infection were 41 and 98 per cent, respectively. The reason for the higher SI in the infected babies is the combination of lower antibody titres in the transmitting mothers with raised levels in the infected babies. A similar analysis of antibody ratios showed no statistical differences for measles and tetanus (P > 0.1) between HIV infected and uninfected groups. There was a tendency to increased morbidity (Pearson's correlation coefficient r = 0.31) and more severe disease in those with higher HIV-1 SI. Three of 17 (18 per cent) peripheral blood samples from infected children at birth were PCR positive; all had SI's above the threshold. Overall sensitivity and specificity of PCR were 85 per cent each. Eleven of the 29 infected children were HIV-1 specific IgA positive at birth; six (64 per cent) of these had an SI > 1.27. This simple SI of HIV-1 EIA antibodies at birth is comparable to elaborate techniques in its power to predict perinatally acquired infection. It may be a cheap, reliable and rapid screening test for vertically transmitted HIV-1 infection.