Introduction Among children, the main postnatal HIV category of exposure is breastfeeding. When acute maternal infection occurs during lactation, the high maternal viral rate results in a higher risk of infant infection. There are few researches showing the impact of HIV infection on children of previously seronegative mothers, who acquire the HIV virus during breastfeeding. To elucidate the importance of this category of exposure, this study aims to evaluate HIV infection in infants assisted by a Paediatric Infectology Service in Brazil, emphasising the cases where vertical transmission occurred lately through breastfeeding.

Methods Transversal, analytical and descriptive study, with quantitative and qualitative approach analysing HIV infected patients from 0 to 16 years old. Data was collected during 2016, from charts of children assisted between 2010 and 2015. After previous selection, breastfed children of mothers who had negative HIV testing during pregnancy and/or at birth, had charts analysed in detail.

Results From a total of 122 cases, 95% were mother-to-child-transmissions. Between these cases, 11 were considered possible/confirmed late postnatal transmission through breastfeeding. This group characterisation showed that at diagnosis, 72,7% presented significant and/or recurrent symptoms of HIV infection. In 45,4%, mother and children were diagnosed at the same time and 72,7% of mothers were sexually infected.

Conclusion There was a significant prevalence of late postnatal transmission through breastfeeding in our sample. Differently from resource limited settings, most countries avoid breastfeeding by HIV infected mothers. Considering cases where women were infected only during lactation, our study highlights a gap in prevention of vertical transmission of HIV. The severity of infant symptoms, the moment of diagnosis and mother’s category of exposure confirm the importance of preventive measures and scientific improvement to reduce postnatal HIV transmission.