Analysis of risk factors for fatal rocky mountain spotted fever: Evidence for superiority of tetracyclines for therapy

Epidemiologic and clinical characteristics of fatal and nonfatal cases of R ocky Mountain spotted fever (RMSF) were compared to identify risk factors f or death caused by this disease. Confirmed and probable RMSF cases reported through US national surveillance for 1981-1998 were analyzed. Among 6388 R MSF patients, 213 died (annual case-fatality rate, 3.3%; range, 4.9% in 198 2 to 1.1% in 1996). Use of tetracycline-class antibiotics for treatment of RMSF increased significantly in the 1990s, compared with use in the 1980s. Older patients, patients treated with chloramphenicol only, patients for wh om tetracycline antibiotics were not the primary therapy, and patients for whom treatment was delayed greater than or equal to5 days after the onset o f symptoms were at higher risk for death. Although the case-fatality rate w as lower in the 1990s than in the 1980s, risk factors for fatal RMSF were s imilar. Despite the availability of effective antibiotics, RMSF-related dea ths continue to occur because of delayed diagnosis and failure to use appro priate therapy.