National surveillance for Rocky Mountain spotted fever, 1981-1992: epidemiologic summary and evaluation of risk factors for fatal outcome.

Between 1981 and 1992, the Centers for Disease Control collected and summarized 9,223 cases of Rocky Mountain spotted fever (RMSF) reported from 46 states. Four states (North Carolina, Oklahoma, Tennessee, and South Carolina) accounted for 48% of the reports. The annual incidence per million U.S. population decreased from a high in 1981 of 5.2 to a low in 1992 of 2.0, primarily due to decreased incidence in the southeast. Case report forms were filed on 7,650 patients, of whom 4,217 had laboratory-confirmed RMSF. The age group with the highest incidence was those 5-9 years of age. Most cases (90.0%) occurred between April 1 and September 30 and included a history of tick attachment (59.6%). Reported symptoms included fever (94.0%), headache (86.2%), myalgia (82.5%), and rash (80.2%). The case-fatality ratio was 4.0%. Risk factors associated with death included older age, delay in treatment or no treatment, and treatment with chloramphenicol (compared with tetracycline); however, insufficient data existed to fully assess the confounding effect of severity of illness on antibiotic choice.