THE EPIDEMIOLOGY OF MELIOIDOSIS IN UBON-RATCHATANI, NORTHEAST THAILAND

Background. Melioidosis, or infection with Pseudomonas pseudomallei is an important cause of morbidity and mortality in South East Asia and Northern Australia, The epidemiology of melioidosis in Ubon Ratchatani , Northeast Thailand was studied over a 5-year period from 1987 to 199 1. Methods. Rates and, when possible, the risks of developing melioido sis were calculated. The numerator was the number of culture-proven ca ses of melioidosis seen in the 1000-bed referral hospital of the provi nce. The denominators were obtained from the population census, a surv ey of Health, Welfare and Use of Traditional Medicine, and the North E astern Meteorological Centre, Thailand. Results. The average incidence of human melioidosis was 4.4 (95% confidence interval [CI] : 3.8-5.0) per 100 000. The disease affected all ages with the highest incidence in 40-60 years olds. Melioidosis was 1.4 (95% CI: 0.4-5.3) times more common in males than females. The disease showed a significant season al variation in incidence, and a strong linear correlation with rainfa ll (r = 0.7, 95% CI : 0.5-0.9) Adults exposed to soil and water in the ir work (most were rice farmers) had an increased risk of melioidosis (in the 40-59 year age group, relative risk = 4.1, 95% CI : 2.4-6.9). Most adult patients had an underlying disease (mainly diabetes mellitu s) predisposing them to this infection. Conclusion. Melioidosis may re sult from either acute exposure to the organism in the soil and water, or 're-activation' of an asymptomatic childhood infection (by an unid entified possibly infective seasonal cofactor). The results from this analysis are consistent with both hypotheses. Further epidemiological studies a re needed to identify risk factors so that optimal strategie s for control of melioidosis may be developed.