A sero-epidemiological study on mother-to-child transmission of HTLV-I in southern Kyushu, Japan.

In vertical transmission of HTLV-I the duration of breast-feeding seems to be an important risk factor. In this study, we made prospective and retrospective surveys on the rate of vertical transmission of HTLV-I in infants and their siblings born to HTLV-I seropositive mothers. The results obtained were as follows. (1) In the prospective study, 885 of the 16,283 pregnant women examined were HTLV-I seropositive, and the seropositive rate was 5.4%. The seroconversion rates of short-term (< 7 months) and long-term (> or = 7 months) breast-feeders were 3.8% (1/26 cases) and 25.0% (1/4 cases) respectively, and the rate of bottle-feeders was 5.6% (10/177 cases). Short-term breast-feeding tended to yield a lower seroconversion rate of infants. In addition, the seroconversion rate of short-term breast-feeders was nearly equal to that of bottle-feeders: 3.8% vs. 5.6%. (2) In the retrospective study, the seroconversion rates of short-term and long-term breast-feeders in their siblings were 4.5% (3/67 cases) and 14.0% (19/136 cases) respectively. There was a significant difference between the 2 groups (p < 0.01). Thus, the results of our retrospective and prospective studies suggest that short-term breast-feeding might lessen the risk of breast-milk-borne transmission of HTLV-I from carrier mothers to their children.