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To study the epidemiology of human T-cell lymphotropic virus type I(HTLV- I)-associated myelopathy/tropical spastic paraparesis(HAM/TSP)in Japan,we conducted two nationwide surveys between October 1986 and March 1989.A total of 710 patients with HAM(definite HAM,589;probable HAM,121)were reported.Of the 589 patients with definite HAM,69%were residents of the areas with the highest prevalence HTLV-I in Japan.To determine the importance of blood transfusion in the pathogenesis of HAM/TSP,we performed a case-control study in the Kagoshima district in southern Japan.Significantly more patients with HAM reported a history of blood transfusion(26/129,or 20%)than did subjects in a health survey of the general population(41/1,290,or 3%;odds ratio=7.7,p<0.001)or than did hospitalized neurological patients(6/119,or 5%;odds ratio=4.8,p<0.001). Furthermore,the cumulative percentages of the intervals between blood transfusion and the onset of the symptoms of HAM fit a lognormal curve, suggesting that transfusion was an important common exposure.Blood transfusion probably transmitted HTLV-I to the patients with transfusion- associated HAM because there was a significant decrease in the number of patients with the transfusion-associated HAM who received blood after implementation of nationwide screening of blood donors in 1986(p=0.004).In the first 2 years,screening the blood supply in Japan appears to have decreased the number of reported patients with HAM by 16%. |
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