Rocky mountain spotted fever in the United States, 1993-1996.

During 1993 through 1996, 2,313 cases of Rocky Mountain spotted fever (RMSF) were reported to the Centers for Disease Control and Prevention (CDC) by 42 states and the District of Columbia through the National Electronic Telecommunications System for Surveillance (NETSS). During this same interval, 1,752 case report forms (CRFs) were submitted to CDC and 1,253 (70%) of the cases were categorized as confirmed RMSF by laboratory testing. On the basis of analyses performed with NETSS data, the average annual RMSF incidence during 1993-1996 was 2.2 cases per million persons; the incidence rose from 1.8 in 1993 to 3.3 per million persons in 1996. Incidence for confirmed cases was highest among children 5-9 years of age (3.7 per million) and lowest among individuals older than 70 years of age (1.4 per million). The south Atlantic region accounted for the largest proportion of confirmed cases (52%). The case-fatality rate was highest among persons 70 years of age and older (9.0%) and lowest among adults 40-49 years of age (0.6%).