Epidemiology of aplastic anemia in Thailand. Thai Aplastic Anemia Study Group

A population-based case-control study of aplastic anemia has been conducted in Thailand since 1989. This is the largest single epidemiologic study of aplastic anemia ever performed. The objectives have been to document the incidence of the disease and to study the etiologic factors in a case-control analysis. The overall incidence of aplastic anemia was 3.9 per million per year in Bangkok, two times higher than in the West; 3.0 per million in Songkla; and 5.0 per million in Khonkaen. A difference appears in the age incidence pattern between Bangkok and the two rural areas, with double incidence peaks at ages 15 to 24 and over 60 in Bangkok, yet a more steady increase in incidence with increasing age in the rural areas. With regard to possible etiologic factors, there is a strong inverse association between incidence of the disease and socioeconomic status as determined by total household income and years of education. There are also significant positive associations with occupational exposure to solvents and agricultural pesticides. Only a few drugs, including thiazide diuretics, sulfonamide, and mebendazole are associated with the disease. There continues to be no evidence of association with chloramphenicol. The etiologic fraction for all associated drugs is lower than 5%. Household pesticide use is not associated with the disease. Exposure to hepatitis A virus is a risk indicator for aplastic anemia and may be a surrogate marker for another enteric infectious agent.