Barbra A. Richardson, Grace John-Stewart, Claire Atkinson, Ruth Nduati, Kristjana Ásbjörnsdóttir, Michael Boeckh, Julie Overbaugh, Vincent Emery, Jennifer A. Slyker

 Cytomegalovirus (CMV) is associated with morbidity and mortality in HIV-exposed infants. We assessed the effect and relative contribution of breastfeeding on infant CMV acquisition in the setting of maternal HIV infection.  Between 1993-1998 pregnant, HIV-infected women in Nairobi, Kenya were randomized to breastfeeding or formula feeding in an HIV transmission study. Women were allocated equally between treatment arms, and the study was not blinded. The primary endpoint of this nested study was time to infant CMV infection.  CMV infection was assessed in 138 breastfed and 134 formula-fed infants. Baseline characteristics were similar between arms. Breastfed infants acquired CMV earlier than formula-fed infants (median 4.26 vs. 9.87 months, p<0.001), and had a higher 1-year probability of CMV infection (0.89 vs. 0.69, p<0.001). Breastfeeding was associated with a 1.6-fold increased risk of infant CMV independent of infant HIV status (multivariable HR=1.61, 95%CI=1.20-2.16, p=0.002). Approximately one third of CMV infections occurred peripartum, 40% through breastfeeding, and the remainder through non-breast milk modes.  Preventing CMV acquisition may be a priority for HIV-exposed infants, but there is a narrow window of opportunity for intervention. Approaches that reduce maternal cervical and breast milk CMV reactivation may help delay infant infection.