The epidemiology of Rocky Mountain spotted fever in Arkansas, Oklahoma, and Texas, 1981 through 1985.

From 1981 through 1985, a total of 851 laboratory-confirmed cases of Rocky Mountain spotted fever were reported in Arkansas, Oklahoma, and Texas. Annual incidence rates in each state increased from 1981 through 1983, ranging from a 17% increase in Arkansas to a 137% increase in Texas. In the period 1984 through 1985, the annual incidence rates in each state decreased over 50%. A total of 519 cases were males. A majority of cases (51%) were 19 years of age or younger. April through August were the months of onset of symptoms for 83% of the cases. Differences in distribution of month of onset of symptoms were noted when comparing age groups and state of residence of the cases. The case-fatality ratio was 4.7%. Case-fatality ratios were higher in blacks and in older age groups. An endemic focus of Rocky Mountain spotted fever exists in Arkansas, Oklahoma, and Texas. The annual incidence trend for spotted fever in these three states is dissimilar to the trends in other states.