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Background: The relationship between mastitis and antiretroviral therapy among HIV-positive, breast-feeding women is unclear.Methods: In the Breastfeeding, Antiretrovirals, and Nutrition (BAN) study, conducted in Lilongwe, Malawi, 2369 mother-infant pairs were randomized to a nutritional supplement group and to one of three treatment groups: maternal antiretroviral therapy (ART), infant nevirapine (NVP) or standard of care for 24 weeks of exclusive breast-feeding and 4 weeks of weaning. Among 1472 HIV-infected women who delivered live infants between 2004 and 2007, we estimated cumulative incidence functions and sub-distribution hazard ratios (HR) of mastitis or breast inflammation comparing women in maternal ART (n = 487) or infant nevirapine (n = 492) groups to the standard of care (n = 493). Nutritional supplement groups (743 took, 729 did not) were also compared.Results: Through 28-weeks post-partum, 102 of 1472 women experienced at least one occurrence of mastitis or breast inflammation. The 28-week risk was higher for maternal ART (risk difference (RD) 4.5, 95% confidence interval (CI) 0.9, 8.1) and infant NVP (RD 3.6, 95% CI 0.3, 6.9) compared to standard of care. The hazard of late-appearing mastitis or breast inflammation (from week 5-28) was also higher for maternal ART (HR 6.7, 95% CI 2.0, 22.6) and infant NVP (HR 5.1, 95% CI 1.5, 17. 5) compared to the standard of care.Conclusions: Mastitis or breast inflammation while breast-feeding is a possible side effect for women taking prophylactic ART and women whose infants take NVP, warranting additional research in the context of postnatal HIV transmission. [ABSTRACT FROM AUTHOR]

In randomized trials to prevent breast milk transmission of human immunodeficiency virus (HIV) from mother to infant, investigators are often interested in assessing the effect of a treatment or intervention on the cumulative risk of HIV infection by time (age) t in infants who are alive and uninfected at a certain time point τ(0)  < t. Such comparisons are challenging for two reasons. First, infants are typically randomized at birth (time 0 < τ(0) ) such that comparisons between trial arms among the subset of infants alive and uninfected at τ(0) are subject to selection bias. Second, in most mother-to-child transmission (MTCT) trials competing risks are often present, such as death or cessation of breastfeeding prior to HIV infection. In this paper, we present methods for assessing the causal effect of a treatment on competing risk outcomes within principal strata. In MTCT trials, the causal effect of interest is that of treatment on the risk of HIV infection by time t > τ(0) within the principal stratum of infants who would be alive and uninfected by τ(0) regardless of randomization assignment. We develop large sample nonparametric bounds and a semiparametric sensitivity analysis model for drawing inference about this causal effect. We present a simulation study demonstrating that the proposed methods perform well in finite samples. We apply the proposed methods to a large, recent MTCT trial. [ABSTRACT FROM AUTHOR]