Timing of Loss of Transplacental Antibodies in Infants Born to Mothers Living With Human T-cell Lymphotropic Virus Type 1

Background: To date, evidence suggesting the optimal timing of antibody testing in human T-cell lymphotropic virus type 1 (HTLV-1)-exposed infants is lacking. Testing HTLV-1-exposed infants must balance the need for repeat testing if done too early while minimizing loss to follow-up with protracted follow-up intervals. Methods: Single-center, retrospective cohort analysis of HTLV-1 serologic testing and breastfeeding practices in infants born to HTLV-1 seropositive pregnant individuals between 01/01/2016 and 10/03/2026. Results: Nineteen children were identified, of whom 5 had positive serological tests for HTLV-1 when first tested, and 14 were seronegative on the first sample, with a median age at first negative test of 18.4 months (95% confidence interval: 6.9). None have been confirmed infected. Six children were known to have breast/chest-fed for an average of 4.5 months. Conclusions: Serologic testing of HTLV-1-exposed infants can be done at 18 months, minimizing persistent transplacental positives and follow-up attrition.