Use of household pesticides and the risk of aplastic anaemia in Thailand

Background. Aplastic anaemia is a severe blood dyscrasia that is more common in Thailand than in Western countries. Its aetiology remains poorly understood. Methods. A case-control study was conducted in Bangkok and two rural regions of Thailand. The effect of household pesticides was evaluated among 253 incident cases of aplastic anaemia and 1174 hospital controls. Results. A total of 54% of the cases and 61% of the controls were exposed 1-6 months previously. For most individual household pesticides and for groups classified according to chemical type (organophosphates, pyrethrins, and organochlorines), the relative risk (RR) estimates approximated 1.0; upper 95% confidence limits were below 2.0 for many comparisons. A significant association was observed for exposure to combination products containing dichlorvos and propoxur, with an overall RR estimate of 1.7 (95% confidence interval [CI] : 1.1-2.6); the estimate for regular use was 1.6 (95% CI : 0.9-2.9). Conclusions. The absence of a higher risk for the regular use of dichlorvos/propoxur reduces the credibility of the apparent association, which could well have been an artefact of multiple comparisons. We conclude that most household pesticides used in Thailand do not appear to increase the risk of aplastic anaemia.