The epidemiology of tropical myositis in the Mengo Districts of Uganda.

In the five-year period 1964-68 1,335 patients were admitted to Mulago Hospital, Kampala, with tropical myositis. The marked increase in the number of admissions during the study period is attributed to a change in the utilization of the hospital rather than to a true increase in the incidence of the disease. There was found to be only slight variation in incidence between different age and sex groups and there was no convincing evidence that immigrants from high altitude areas, where the disease is rare, were at different risk. There was statistically significant month-to-month variation in admission rates but there was no apparent correlation with rainfall, and no marked seasonal variation. During the quinquennium there was a changing pattern of admission rates for patients from different counties, and some evidence of 'space-time' clustering. These findings are compatible with the primary muscle damage being induced by a virus or the presence of aberrant hookworm larvae, but an ingested toxin cannot be excluded. Trauma may also play a role in determining localization of the disease in some cases.