Trends in the seroprevalence of HTLV-1 in Japanese blood donors in Nagasaki Prefecture, 2000–2006

Abstract

Human T-cell leukemia virus type-1 (HTLV-1) is the established cause of adult T-cell leukemia/lymphoma. Monitoring time trends in HTLV-1 seroprevalence in blood donors is important to assess the safety of the blood supply in the viral endemic area. We analyzed changes in HTLV-1 seroprevalence in 48,415 first-time blood donors who donated blood from 2000 to 2006 in Nagasaki prefecture, an endemic area in Japan. The donors were divided into 10-year birth cohorts: before 1950, 1951-1960, 1961-1970, 1971-1980, and 1981-1990. Among the first-time blood donors, 622 were tested positive for HTLV-1 (overall seroprevalence: 1.28%, [95%CI: 1.19-1.39]). Seroprevalence was significantly high in the birth cohort of before 1950 (6.22%) and declined with birth-year. The time trend of the birth-cohort specific seroprevalence showed almost no change within each birth cohort, except for the birth cohort of 1981-1990 that showed a significantly declining trend (P for trend = 0.006). Among the birth cohort of 1981-1990, the seroprevalence was stable among those born during 1981 to 1986 (0.66-0.83%), but was lower among those born during 1987 to 1990 (0-0.38%). Detail analyses showed that HTLV-1 seroprevalence among blood donors clearly declined in those born after 1987.Keywords: HTLV-1, blood donors, seroprevalence, birth cohort analysis 3 IntroductionHuman T-cell leukemia virus type-1 (HTLV-1) is the etiological agent for adult T-cell leukemia/lymphoma (ATLL) and other HTLV-1-associated diseases [1][2][3]. The virus is transmitted through three routes: mother-to-infant, sexual contact, and blood transfusion [4][5][6][7]. In mother-to-infant transmission, breast-feeding has been reported to be the dominant route [8]. To prevent milk-borne transmission, a prefecture-wide intervention program named the ATLL Prevention Program (APP) started in August 1987 in Nagasaki prefecture, an HTLV-1 endemic area in Japan [9][10][11]. The APP involved the screening of pregnant women for HTLV-1 and the intervention to instruct the virus carrying mothers to refrain from breast-feeding. To prevent blood-borne transmission, a nationwide routine serological screening for HTLV-1 of donated blood was launched in 1986 all over Japan [4].Monitoring time trends in HTLV-1 infection rates in blood donors is important to assess the safety of the blood supply and to estimate population risks in the viral endemic area. Previous studies of Japanese blood donors reported that the age-specific HTLV-1 seroprevalence steadily declined over the decades [12][13][14][15]. Birth-cohort effects, changing the length of breast-feeding, sanitary improvement, and the dilution effect caused by HTLV-1-negative immigrants have been discussed as reasons for the declining trend [15][16][17]. Although such an age-specific analysis is commonly used for epidemiological studies, it sometimes obscures important trends that can occur within people born at different times. An alternative method of analyzing trends in viral seroprevalence is to examine birth-cohort specific tre...

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