Passive surveillance as an instrument to identify risk factors for fatal Rocky Mountain spotted fever: is there more to learn?

National surveillance for Rocky Mountain spotted fever (RMSF) dates from 1920; however, the collection of detailed epidemiologic, clinical, and laboratory data on RMSF by using case report forms began in 1970. Despite issues with compliance and changes in case definitions, surveillance data have permitted researchers to assess risk factors for fatal RMSF quantitatively. Factors consistently associated with increased risk of death include severity of disease, older age, lack of tick bite, absence of classic symptoms, delay in diagnosis and initiation of appropriate antibiotic treatment, and treatment with chloramphenicol only. In several studies, treatment with a tetracycline has been shown to be protective. The continuation of current passive surveillance activities may allow researchers to refine their estimates of risk but is unlikely to produce novel results. Modified surveillance activities could focus on evaluating the risk for fatal RMSF among special populations, monitoring appropriate antibiotic use, and assessing new diagnostic tests.