Interventions to prevent vertical transmission of HIV-1: effect on viral detection rate in early infant samples

Objective: To determine whether mode of delivery or the use of maternal or neonatal antiretroviral prophylaxis influence the age when HIV-1 can first be detected in infected infants, particularly the probability of detection at birth. Methods: In a collaboration between four multicentre studies, data on 422 H IV-1 infected infants who were assessed by HIV-1 DNA PCR or cell culture be fore 14 days of age were analysed. Weibull mixture models were used to esti mate the cumulative proportion of infants with detectable levels of HIV-1 a ccording to use of maternal/neonatal antiretroviral therapy (mainly zidovud ine monotherapy) and mode of delivery. Results: HIV-1 was detected in 162 infants (38%) when they were first teste d, at a median age of 2 days. At birth, it was estimated that 36% [95% conf idence interval (CI), 31-41%] of infants have levels of virus that can be d etected by DNA PCR or cell culture. This percentage was not associated with either mode of delivery (35% for vaginal delivery versus 40% for cesarean section delivery; P = 0.4) or the use of maternal or neonatal antiretrovira l prophylaxis. Among infants with undetectable levels of HIV-1 at birth, th e median time to viral detectability was estimated to be 14.8 days (95% CI, 12.9-16.8 days). This time was increased by 15% (95% CI, -11 to 48%; P = 0 .3) among infants who were exposed to antiretroviral therapy postnatally co mpared with infants who were not exposed. No effect was observed for mode o f delivery. Conclusions: The outcome of an early virological test for HIV-1 is thought to be related directly to the timing of transmission and cesarean section d elivery primarily reduces the risk of intrapartum transmission. The absence of an association between mode of delivery and viral detectability at birt h was therefore unexpected. There was no evidence that foetal or neonatal e xposure to prophylactic zidovudine delays substantially the diagnosis of in fection, although this cannot be inferred for combination antiretroviral th erapy. (C) 2000 Lippincott Williams & Wilkins.