Provirus load in breast milk and risk of mother-to-child transmission of human T lymphotropic virus type I

In a prospective study of 101 mother-child pairs in Jamaica, we examined the association of provirus load in breast milk and the risk of mother-to-child transmission of human T lymphotropic virus type I. The provirus load in breast milk was a strong predictor of risk of transmission to children ( relative risk, 2.34/quartile), after adjustment for other known risk factors. The risk of transmission increased from 4.7/1000 person-months when the provirus load in breast milk was <0.18% to 28.7/1000 person-months when it was >1.5%. Provirus detection in maternal breast milk predicted transmission months before infection in children was detected by serologic testing.