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Epidemiologic Notes and Reports Rocky Mountain Spotted Fever -- United States, 1987

In 1987, 592 cases of Rocky Mountain spotted fever (RMSF) were reported to CDC, a 22% decrease from the 755 cases reported in 1986; the incidence of RMSF decreased to 0.24/100,000 in 1987, from 0.32/100,000 in 1986. The state with the highest rate was Oklahoma (2.7/100,000); other states with high rates were North Carolina (1.3/100,000), Kansas (1.2/100,000), Tennessee (1.2/100,000), South Carolina (1.1/100,000), and Maryland (1.0/100,000) (Figure 1). Thirty-nine percent of the cases were reported from the South Atlantic region and 20% from the West South Central region.

Case report forms were submitted on 446 (75.3%) of the total cases. Information from these forms showed that 57.8% of the cases were laboratory-confirmed, 9.2% were classified as probable RMSF, and the remainder were not confirmed (frequently because specific serologic testing was not performed) (1). Of the 446 patients, 64.8% were male, 82.6% had an onset of symptoms between April and July, and 62.6% had a history of tick bite within 14 days before the onset of symptoms. Symptoms included fever (91.5%), headache (75.6%), rash (78.7%), and rash on palms or soles (49.1%). The triad of fever, headache, and rash was present in 58.7% of the cases. The overall case-fatality rate was 3.1%. The case-fatality rate was 1.3% among patients under 30, 5.6% among those 30 years of age and older, and 11.5% among those 70 years of age and older. Among patients with a history of recent tick bite, the case-fatality rate was 2.7%; patients with no known tick bite or attachment had a case-fatality rate of 4.7%. Reported by: Viral and Rickettsial Zoonoses Br, Div of Viral Diseases, Center for Infectious Diseases, CDC. Editorial Note: Although most states reported fewer cases of RMSF in 1987 than in 1986, the number of cases reported from Maryland increased from 29 in 1986 to 46 in 1987, and the number reported by Kansas rose from 10 to 30. This was the largest number of cases (and the highest incidence) reported from Maryland since 1981 and the largest number ever reported from Kansas. The reason for these increases is unknown; neither state reported changes in their methods of surveillance.

In 1987, four cases of RMSF were reported among residents of New York City. All four persons apparently acquired the infection in the Bronx; none had traveled outside New York City within the 3 weeks before the onset of illness (2). One patient, the only one to report a tick bite, died, possibly because diagnosis and treatment were delayed. These cases are the first laboratory-confirmed cases acquired in New York City, raising the possibility that other urban foci of RMSF may exist.

The 3.1% case-fatality rate for 1987 is the lowest rate recorded since forms for case reports were introduced in 1970 (3). Fatalities are more common among older patients and patients who do not have a history of tick bite. Persons in the latter group often do not obtain prompt treatment, thus increasing their risk of a fatal outcome.

Since no vaccine is available for RMSF, the best preventive measure is to avoid tick-infested areas. If this is not possible, persons entering such areas should wear protective clothes and use a tick repellant. Ticks attached to a person's body are best removed by grasping them with fine tweezers at the point of attachment and pulling gently (4). If fingers are used to remove ticks, they should be protected with facial tissue and washed afterwards.

A diagnosis of RMSF should be considered whenever a patient has an unexplained febrile illness, even if there is no history of tick bite or of travel to an area known to be endemic for the disease. If RMSF is suspected, persons over 8 years of age-- except pregnant women--should be treated with tetracycline. Chloramphenicol is the recommended treatment for pregnant women and for children 8 years of age and under. Treatment should be started as soon as possible after the onset of symptoms. References

  1. Fishbein DB, Kaplan JE, Bernard KW, Winkler WG. Surveillance of Rocky Mountain spotted fever in the United States, 1981-1983. J Infect Dis 1984;150:609-11.

  2. Salgo MP, Telzak EE, Currie B, et al. A focus of Rocky Mountain spotted fever within New York City. N Engl J Med 1988;318:1345-8.

  3. Centers for Disease Control. Rocky Mountain spotted fever--United States, 1980. MMWR 1981;30:318-20.

  4. Needham GR. Evaluation of five popular methods for tick removal. Pediatrics 1985;75:997-1002.

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