Background: Large simple trials which aim to study therapeutic interventions and epidemiological associations of human immunodeficiency virus (HIV) infection, including perinatal transmission, in Africa may have substantial rates of loss to follow-up. A better understanding of the characteristics and the impact of women and children lost to follow-up is needed.
Methods: We studied predictors and the impact of losses to follow-up of infants born in a large cohort of delivering women in urban Malawi. The cohort was established as part of a trial of vaginal cleansing with chlorhexidine during delivery to prevent mother-to-infant transmission of HIV.
Results: The HIV infection status could not be determined for 797 (36.9%) of 2156 infants born to HIV-infected mothers; 144 (6.7%) with missing status because of various sample problems and 653 (30.3%) because they never returned to the clinic. Notably, the observed rates of perinatal transmission were significantly lower in infants who returned later for determination of their infection status (odds ratio = 0.94 per month, P = 0.03), even though these infants must have had an additional risk of infection from breastfeeding. In multivariate models, infants of lower birthweight (P = 0.003) and, marginally, singletons (P = 0.09) were less likely to return for follow-up. The parents of infants lost to follow-up tended to be less educated (P < 0.001) and more likely to be in farming occupations, although one educated group, teachers and students, were also significantly less likely to return. Of these variables, infant birthweight, twins versus singletons, and maternal education were also associated with significant variation in the observed risk of perinatal transmission among infants of known HIV status.
Conclusions: Several predictors of loss to follow-up were identified in this large HIV perinatal cohort. Losses to follow-up can impact the observed transmission rate and the risk associations in different studies.
PIP: Predictors and the impact of losses to follow-up of infants born to a large HIV- infected cohort of delivering women in urban Malawi were studied. The women enrolled in an intervention trial including vaginal cleansing with chlorhexidine at the time of delivery. Findings showed that of the 2156 infants born to HIV- infected mothers, about 1359 (63.1%) had been diagnosed with HIV infection, 797 (36.9%) with undetermined status, 144 (6.7%) with missing status, and about 653 (30.3%) were never brought back for follow-up. The odds of HIV positivity decreased in the determination of infectious status (P = 0.03) despite the probability of additional transmission from breast-feeding. Late-coming and lost children of less educated parents had similar birth weight (P = 0.50) and were likely less to return. This was probably due to the fact that the fathers of the lost children were farmers. Besides, infant birth weight, twins vs. singletons, and maternal education were affiliated with significant variation in the observed risk of perinatal transmission among HIV-positive infants. Thus, with regard to the intervention trial, the LFU were approximately equal in both groups. There was no evidence that the losses were unbalanced between arms in relation to the predictors of transmission.