Leptospirosis: an emerging health problem in Thailand.

Leptospirosis is an emerging health problem in Thailand, with dramatic increases in reported incidence since 1996. The annual number of reported leptospirosis cases increased from 398 cases in 1996 to 14,285 cases in 2000. In 2001, 2002, and 2003, the number of reported cases decreased, but still remained high at 10,217, 6,864, and 4,958 cases, respectively. The epidemiological characteristics of leptospirosis in Thailand include a peak incidence in September and October in association with the rainy season. A vast majority of the cases (90%) were reported in the Northeast region. The case fatality rate was as high as 4.4%, having a predominant association with male farmers aged 15 to 45 years. Outpatient cases were approximately 9 times more common than admitted cases, with an apparent recent shift in the pattern of infecting serovars among reservoir animals and humans.