Issues of infant feeding for postnatal prevention of human T-cell leukemia/lymphoma virus type-1 mother-to-child transmission

Background: Nationwide antenatal human T-cell leukemia/lymphoma virus type-1 (HTLV-1) antibody screening has been conducted in Japan. The purpose of our study was to clarify the issues related to feeding options to prevent postnatal mother-to-child transmission. Methods: Of the pregnant carriers at 92 facilities in Japan between 2012 and 2015, 735 were followed prospectively. Among the children born to them, 313 (42.6%) children were followed up to the age of 3 and tested for HTLV-1 antibodies. The mother-to-child transmission rate was calculated for each feeding option selected before birth. Results: Among the 313 pregnant carriers, 55.0, 35.1, 6.1, and 3.8% selected short-term breast-feeding (≤3 months), exclusive formula feeding, frozen-thawed breast-milk feeding, and longer-term breast-feeding, respectively. Despite short-term breast-feeding, 8–18% of the mothers continued breast-feeding for 4–6 months. The mother-to-child transmission rate with short-term breast-feeding was 2.3% (4/172), and its risk ratio compared with that of exclusive formula feeding was not significantly different (0.365; 95% CI: 0.116–1.145). Because of the small number of children who were fed by frozen-thawed breast-milk, their mother-to-child transmission rate was not statistically reliable. Conclusions: Pregnant HTLV-1 carriers tended to select short-term breast-feeding in Japan. While short-term breast-feeding was not always easy to wean within 3 months, it may be a viable option for preventing postnatal mother-to-child transmission because the vertical transmission rate with short-term breast-feeding was not significantly higher than that with exclusive formula feeding. Increasing the follow-up rates for children born to pregnant carriers may provide clearer evidence of preventative effects by short-term breast-feeding and frozen-thawed breast-milk feeding.