Rocky Mountain Spotted Fever -- United States, 1982

For 1982, a provisional total of 979 cases of Rocky Mountain spotted fever (RMSF) in the United States was reported to CDC. On the basis of this figure, the RMSF incidence rate was 0.42 cases/100,000 population.

The South Atlantic states accounted for 521 (53%) of the reported cases. The seven highest RMSF rates were for North Carolina (225 cases, 3.74/100,000 population), South Carolina (106 cases, 3.31/100,000), Oklahoma (76 cases, 2.39/100,000), Virginia (73 cases, 1.33/100,000), Tennessee (59 cases, 1.27/100,000), Maryland (50 cases, 1.17/100,000), and Georgia (52 cases, 0.92/100,000) (Figure 1).

States submitted case report forms for 834 (85%) of reported cases. Of these, 400 (48%) were confirmed by serologic testing (a 4-fold increase in antibody titer between acute- and convalescent-phase serum specimens by complement fixation , indirect fluorescent antibody , indirect hemagglutination , latex agglutination (LA), or microagglutination ; or a single convalescent titer 1:16 or higher or 1:64 or higher in a clinically compatible case); by isolation of spotted fever group rickettsiae; or by fluorescent antibody staining of biopsy or autopsy specimens. An additional 95 patients (11%) had "probable" cases by a 4-fold increase or a single convalescent titer 1:320 or higher in the Weil-Felix (OX-19, OX-2) agglutination tests, or by a single convalescent titer 1:128 or higher by LA or IHA. The other 339 cases (41%) were reported on the basis of clinical diagnoses alone. Fifty-three percent of the patients were under 20 years of age; 61% were male; and 89% were white.

Ninety-five percent of patients became ill between April 1 and September 30. Symptoms reported included fever (98%), headache (89%), rash on torso (88%), and rash on palms of hands or soles of feet (71%). Eighty-one percent of patients were hospitalized. Sixty-seven percent of patients for whom exposure information was available reported a tick bite or attachment within 14 days before onset of illness. The case fatality rate (4.7%) was higher for persons 30 years of age or older (10.2%) than for younger individuals (2.1%), higher for persons with unknown or no tick exposure (7.2%) than for persons reporting a tick bite or attachment (3.1%), and higher for persons not reporting treatment with tetracycline or chloramphenicol (7.8%) than for those who received such antibiotic therapy (4.3%).

Twenty-five percent of 558 patients for whom a history was available reported travel outside the county of residence within 14 days before onset of illness. Forty-five percent of these patients indicated travel to one of the seven states reporting the highest incidence of RMSF in 1982. Reported by Respective state epidemiologists; Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Following the rapid rise of RMSF in the United States during the 1970s, infection rates remained approximately the same from 1977 to 1981 and dropped slightly in 1982 (Figure 2). The predominance of RMSF in the southeastern United States, the higher incidence of the disease among younger persons, and the case fatality rate (which has fluctuated between 3% and 8% since 1970) have changed little in recent years. Consistent with previous findings (1), the 1982 data indicate that fatality continues to be associated with age 30 years or older, failure to obtain a history of exposure to ticks, and lack of appropriate antibiotic treatment. Travel history for 25% of patients for whom information was available indicates that travel to highly endemic areas may be critical in diagnosing the disease, especially in areas where RMSF does not commonly occur.

The new case report form, used since 1981, continues to provide valuable information concerning symptoms, hospitalization, treatment, tick exposure, travel, and laboratory results pertaining to cases of RMSF. The percentage of total reported cases (85%), for which these case report forms were received in 1982, was slightly lower than that in 1981 (91%). However, the higher proportion of laboratory confirmed cases (48% in 1982, 35% in 1981) suggests that the more sensitive and specific laboratory tests to confirm RMSF cases may have achieved wider use. It must be emphasized, however, that RMSF confirmation is of epidemiologic importance and cannot usually be expected to occur before 10-14 days after onset of illness. Therefore, diagnosis must rely on clinical (fever, headache, rash, myalgia) and epidemiologic (tick exposure) criteria, and treatment with tetracycline or chloramphenicol must be initiated before laboratory confirmation is available.

Prevention of RMSF entails frequent inspection of persons when tick exposure is likely. Ticks are best removed by grasping with tweezers as close as possible to the point of attachment and by pulling slowly and steadily. If tweezers are unavailable, fingers protected with facial tissue may be used. If bare hands touch the tick during removal, the hands should be washed thoroughly with soap and water, because tick secretions can be infective. Because of technical difficulties and delays in handling tick specimens, routine testing of ticks removed from patients is not recommended. Instead, when a tick bite occurs, the patient and family should be educated about the incubation period of RMSF (3-12 days) and should be instructed to seek medical attention promptly if RMSF symptoms occur. No vaccine against RMSF is currently available.

Reference

1. Hattwick MA, O'Brien RJ, Hanson BF. Rocky Mountain spotted fever: epidemiology of an increasing problem. Ann Intern Med 1976;84(6):732-9.

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