title: Incidence of human T-lymphotropic virus 1 infection in adolescent and adult blood donors in Japan: a nationwide retrospective cohort analysis.
abstract: BACKGROUND
  Human T-lymphotropic virus 1 (HTLV-1) infection has an especially high prevalence in Japan. Transmission has been confirmed in infancy through breastfeeding; however, little is known about the epidemiological aspects of new HTLV-1 infections later in life. We aimed to estimate the nationwide annual number of new HTLV-1 infections among adolescents and adults in Japan.
  
  
  METHODS
  In this retrospective cohort analysis, we assessed new HTLV-1 infections of repeat blood donors aged 16-69 years between Jan 1, 2005, and Dec 31, 2006, in the Japanese Red Cross Blood Centres database. We used results of antibody tests done in repeat blood samples collected until Dec 31, 2011, to assess the number who seroconverted to HTLV-1. We calculated the incidence density by dividing the number of seroconverters by the number of person-years of follow-up, and then extrapolated densities to regional populations to estimate the annual number of new HTLV-1 infections.
  
  
  RESULTS
  We included 3 375 821 HTLV-1-seronegative blood donors (2 100 915 men and 1 274 906 women). Within a median follow-up of 4·5 years (IQR 2·3-5·8), 532 people (204 men and 328 women) had seroconverted. The incidence density was significantly higher in women (6·88 per 100 000 person-years; 95% CI 6·17-7·66) than in men (2·29 per 100 000 person-years; 95% CI 1·99-2·62; p<0·0001). The estimated annual number of new HTLV-1 infections was 4190 (95% CI 4064-4318) with 975 (914-1038) infections in men and 3215 (3104-3328) in women.
  
  
  CONCLUSIONS
  New HTLV-1 infections in adolescents and adults are an important public health concern in Japan and preventive strategies are needed to reduce new transmission.
  
  
  BACKGROUND
  Ministry of Health, Labour, and Welfare of Japan; Japan Agency for Medical Research and Development.
authors: Central Blood Institute, Japanese Red Cross, Tokyo, Japan.
authors: Masahiro
authors: M
authors: Satake
authors: Department of Frontier Life Science, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan. Electronic address: masakoiwng@nagasaki-u.ac.jp.
authors: Masako
authors: M
authors: Iwanaga
authors: Kyushu Block Blood Center, Japanese Red Cross, Fukuoka, Japan.
authors: Yasuko
authors: Y
authors: Sagara
authors: Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan.
authors: Toshiki
authors: T
authors: Watanabe
authors: Department of Safety Research on Blood and Biological Products, National Institute of Infectious Diseases, Tokyo, Japan.
authors: Kazu
authors: K
authors: Okuma
authors: Department of Safety Research on Blood and Biological Products, National Institute of Infectious Diseases, Tokyo, Japan.
authors: Isao
authors: I
authors: Hamaguchi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001782:Blood Donors / Q000706:statistics & numerical data*; D005260:Female; D015490:HTLV-I Infections / Q000097:blood / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D015368:Human T-lymphotropic virus 1 / Q000302:isolation & purification*; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies