Human T-Lymphotropic Virus Type-I Infection, Antibody Titers and Cause-specific Mortality among Atomic-bomb Survivors

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Abstract
There have been few longitudinal studies on the long‐term health effects of human T‐lymphotropic virus type‐I (HTLV‐I) infection. The authors performed a cohort study of HTLV‐I infection and cause‐specific mortality in 3,090 atomic‐bomb survivors in Nagasaki, Japan, who were followed from 1985–1987 to 1995. The prevalence of HTLV‐I seropositivity in men and women was 99/1,196 (8.3%) and 171/1,894 (9.0%), respectively. During a median follow‐up of 8.9 years, 448 deaths occurred. There was one nonfatal case of adult T‐cell leukemia/lymphoma (incidence rate=0.46 cases/1,000 person‐years; 95% confidence interval [CI] 0.01–2.6). After adjustment for sex, age and other potential confounders, significantly increased risk among HTLV‐I carriers was observed for deaths from all causes (rate ratio [RR]=1.41), all cancers (RR=1.64), liver cancer (RR=3.04), and heart diseases (RR=2.22). The association of anti‐HTLV‐I seropositivity with mortality from all non‐neoplastic diseases (RR=1.40) and chronic liver diseases (RR=5.03) was of borderline significance. Possible confounding by blood transfusions and hepatitis C/B (HCV/HBV) viral infections could not be precluded in this study. However, even after liver cancer and chronic liver diseases were excluded, mortality rate was still increased among HTLV‐I carriers (RR=1.32, 95% CI 0.99–1.78), especially among those with high antibody titers (RR=1.56, 95% CI 0.99–2.46, P for trend=0.04). These findings may support the idea that HTLV‐I infection exerts adverse effects on mortality from causes other than adult T‐cell leukemia/lymphoma. Further studies on confounding by HCV/HBV infections and the interaction between HCV/HBV and HTLV‐I may be required to analyze the increased mortality from liver cancer and chronic liver diseases.