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Current Trends Rocky Mountain Spotted Fever - United States, 1986

For 1986, a provisional total of 755 cases of Rocky Mountain spotted fever (RMSF) was reported to the MMWR for an incidence rate of 0.32 cases per 100,000 population. Oklahoma had the highest rate (104 cases, 3.2/100,000), and North Carolina reported the most cases (129 cases, 2.1/100,000). South Carolina was the only other state with a rate > 1.0/100,000 (71 cases, 2.1/100,000) (Figure 1). The South Atlantic region, with a rate of 0.83/100,000, accounted for 333 (44%) of the total number of cases.

Report forms were submitted on 654 cases (87%). Three hundred and fifty of these (54%) were laboratory confirmed, and 304 (46%) were probable or not confirmed *. Characteristics of these cases were similar to those observed in other recent years. In 1986, the median age of patients was 24 years. Forty-five percent of patients were <= 20 years of age, 62% were male, and 92% were white. Ninety-five percent of patients experienced onsets of illness during the period April 1-September 30; 47% experienced onsets in May and June. Sixty-two percent reported tick bites. Symptoms included fever (94%), headache (89%), and myalgia (87%). Eighty-seven percent of patients had rash, which, for 53% percent, was located on the palms and/or soles.

The overall fatality rate was 3.0%. The rate was higher for individuals >= 40 years of age (5.8%) than for those <40 years of age (1.9%). The fatality rate was lower for persons who had been bitten by ticks (1.5%) than for those with no known exposure to ticks (6.6%).

  • Confirmation criteria have been published previously (1).

Reported by: R Tanala, College of Veterinary Medicine, Univ of Minnesota, St Paul, Minnesota. Viral and Rickettsial Zoonoses Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The number of reported cases and the national incidence rate of RMSF increased slightly in 1986. However, incidence in the two major RMSF endemic regions (the South Atlantic and the West South Central regions *) and most of the rest of the country has fallen considerably since the early 1980s. In the South Atlantic states, the rate rose from 0.76/100,000 population in 1970 to a peak of 1.91/100,000 in 1981 and has now fallen to 0.83/100,000. In the West South Central region, the rate rose from 0.20/100,000 in 1970 to 1.44/100,000 in 1983 and is now 0.53/100,000. The reason for the recent decrease is unknown. It should also be noted that the proportion of actual cases represented by the provisional total of reported cases is unknown.

The best method of preventing RMSF is to avoid tick-infested areas. Persons who cannot should wear protective clothing and use tick repellent while in tick-infested areas. In addition, exposed areas of the body should be checked every few hours for tick attachment. Ticks should be removed by grasping them gently with tweezers as close as possible to the point of attachment and pulling slowly and steadily (2). The bite should be cleansed like any skin wound, especially if tick mouth parts remain. Ticks can be removed by hand, but fingers should be protected with tissue paper and washed afterward. Persons living or working in tick- infested areas should be made aware of tick-borne diseases and their prevention. No vaccine is available for RMSF, although research continues in this area (3).

Patients with symptoms of RMSF should usually be treated with tetracycline or chloramphenicol before the results of serologic testing are available because diagnostic titers are not present in the majority of patients before the second week of illness (4). Treatment should be considered for symptomatic patients who have been in an RMSF endemic area even if they do not have a rash and were not exposed to ticks. The absence of both rash and a history of tick exposure has been shown to delay presumptive diagnosis and, therefore, to increase the fatality rate among this group (5). Physicians are encouraged to report suspected cases of RMSF to state and local health departments. Most state health departments can perform serologic testing for RMSF.

References

  1. CDC. Rocky Mountain spotted fever-United States, 1985. MMWR 1986;35:247-9.

  2. Needham GR. Evaluation of five popular methods for tick removal. Pediatrics 1985;75:697-1002.

  3. McDonald GA, Anacker RL, Garjian K. Cloned gene of Rickettsia rickettsii surface antigen: candidate vaccine for Rocky Mountain spotted fever. Science 1987;235:83-5.

  4. Kaplan JE, Schonberger LB. The sensitivity of various serologic tests in the diagnosis of Rocky Mountain spotted fever. Am J Trop Med Hyg 1986;35:840-4.

  5. Hattwick MAW, Retailliau H, O'Brien RJ, Slutzker M, Fontana RE, Hanson B. Fatal Rocky Mountain spotted fever. JAMA 1978;240:1499-1503.



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