A decrease in mother-to-child transmission of human T lymphotropic virus type I (HTLV-I) in Okinawa, Japan

To investigate the chronologic change of mother-to-child transmission of human T lymphotropic virus type I (HTLV-I) in Okinawa, Japan, the presence of antibody to HTLV-I was tested in 4,187 healthy residents between, 4,528 nursery school children, and 3,837 pregnant women between 1968 and 2000. The chronologic change of the feeding method and the length of the breast-feeding period among 1,117 healthy mothers from 1937 to 1995 were also obtained by interview. Age-adjusted prevalence of HTLV-I among healthy residents decreased from 9.1% in 1968-1970 to 7.8% in 1981-1984 and to 6.3% in 1996-1998. The crude prevalence of antibody to HTLV-I among healthy residents less than 20 years old decreased significantly from 4.6% in 1968-1970 to 0.1% in 1996-1998 (P < 0.0001). The prevalence of antibody to HTLV-I among nursery school children decreased significantly over the study period, from a high of 1.8% in 1984 to a low of 0.2% in 1998 (P = 0.03). The prevalence among pregnant women decreased significantly from 5.6% in 1989-1992 to 3.7% in 1997-2000 (P = 0.0275). Prior to 1967, all healthy mothers breast-fed their children. After 1968, the use of bottled and mixed milk (breast milk and bottled milk) increased, with bottled milk becoming predominant after 1990 (89%). The percentage of healthy mothers breast-feeding for more than one year significantly decreased from 68.3% in 1937-1947 to 0.4% in 1990-1995 (P < 0.0001). Infection with HTLV-I in Okinawa has decreased mainly due to a reduction in the number of mothers breast-feeding and a shortening of the breast-feeding period. However, because the mother-to-child transmission rate among non-breast-feeders decreased from 12.8% in 1986-1991 to 3.2% in 1995-1999, there may be other factors involved in the decrease in mother-to-child transmission.