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Current Trends Rocky Mountain Spotted Fever -- United
States, 1985
For 1985, a provisional total of 700 cases of Rocky Mountain
spotted fever (RMSF) was reported to MMWR, an incidence rate of
0.29
cases per 100,000 population. Oklahoma had the highest incidence
rate
(94 cases, 2.8/100,000). North Carolina reported the largest
number
of cases (143 cases, 2.3/100,000). Two other states had incidence
rates of 1/100,000 or higher--South Carolina (73 cases,
2.2/100,000)
and Kansas (27 cases, 1.1/100,000) (Figure 1).
States submitted case report forms for 587 (84%) of the 700
reported cases. Of these 587 cases, 335 (57%) were
laboratory-confirmed by either serologic testing, isolation of
spotted
fever group rickettsia, or fluorescent antibody staining of biopsy
or
autopsy material. A case is considered serologically confirmed if
testing reveals an indirect fluorescent antibody titer (IFA) of
1:64
or greater, a complement fixation (CF) titer of 1:16 or greater, or
a
fourfold rise in titer by the CF, IFA, microagglutination (MA),
latex
agglutination (LA), or indirect hemagglutination (IHA) assay. An
additional 34 (6%) cases were classified as probable cases, as
indicated by a fourfold rise in titer or a single titer 1:320 or
higher in the Weil-Felix assay or an LA, MA, or IHA single titer of
1:128 or higher. The other 218 (37%) cases were supported by
clinical
diagnoses alone.
The 1985 surveillance revealed case characteristics similar to
those previously reported. Ninety-five percent of patients
reported
onset of illness between April 1 and September 30, with 66%
becoming
ill in May, June, or July. Sixty percent of patients were male;
41%
were under 20 years of age; and 90% were white. Symptoms reported
included fever (94%), headache (88%), and myalgia (85%). A rash
was
reported by 83% and, of these, 73% reported that the rash was noted
on
the palms or soles. Seventy-three percent of the patients were
hospitalized. The overall case-fatality rate was 4%. The
case-fatality rate was higher for blacks (16%) than whites (3%) and
was higher for individuals 40 years of age or older (9%) than for
individuals under age 40 years (2%). Of the patients for whom
exposure histories were available, 68% reported a tick bite or
attachment, and an additional 24% reported being in a tick-infested
area within 14 days (but no tick bite or attachment). Eight
percent
did not have a known exposure of either type.
Reported by Viral and Rickettsial Zoonoses Br, Div of Viral
Diseases,
Center for Infectious Diseases, CDC. Editorial Note
Editorial Note: The number of reported RMSF cases has waned
considerably from the peak of 1,192 cases (0.51/100,000) reported
in
1981 (1). The increase in the early 1970s appeared simultaneously
in
many regions of the United States and was stimulated by the 1970
initiation of a CDC surveillance program (2). The rate of RMSF
reported in the South Atlantic states, which increased steadily
from
0.76/100,000 in 1970 to a peak of 1.91/100,000 in 1980, has now
fallen
to 0.82/100,000 (Figure 2). Excluding the South Atlantic states,
the
rate of RMSF in the other states rose through 1977 and remained
fairly
constant between 1978 and 1985 (Figure 2). For the third
consecutive
year, Oklahoma reported the highest incidence of any state.
Although the number of reported deaths has decreased with the
decrease in the number of reported cases, the case-fatality rate
has
changed little over the last 5 years. Morbidity and mortality may
be
decreased by knowledge of the epidemiology and early clinical signs
of
RMSF (3). RMSF should be suspected, and treatment with
chloramphenicol or tetracycline strongly considered, among
residents
of, or visitors to, RMSF-endemic areas who report fever, headache,
and
myalgias, even without a rash, particularly during April through
October. Symptoms and signs referable to the pulmonary system
(such
as cough or rales), the gastrointestinal system (such as nausea,
vomiting, or abdominal pain), or the central nervous system (such
as
stupor, meningismus, or ataxia), are seen with RMSF and should not
delay diagnosis or treatment (3). Special attention is warranted
for
individuals 40 years of age and older, who have a greater
likelihood
of a fatal outcome, and dark-skinned individuals, in whom a rash
may
be more difficult to diagnose.
In a recent study of RMSF in a hyperendemic area, a tick bite
or
exposure was reported for 85% of serologically confirmed cases,
compared with 54% of matched controls (4). Rash was reported in
84%
of the serologically confirmed cases. However, in 16% of patients,
a
rash was never noted, and in an additional 10%, a rash did not
develop
until later than the fifth day after onset of the illness.
Prevention of RMSF is best accomplished by careful inspection
of
persons who may have been exposed to ticks. Ticks should be
removed
by grasping them with tweezers as closely as possible to the point
of
attachment and pulling slowly and steadily (5). If a portion of
the
mouth part remains, it should be treated like any other small
foreign
body; it may cause irritation, but it will not increase the risk of
contracting RMSF. The fingers, protected with tissue paper, may be
used to remove a tick from a person if tweezers are not available,
but
should always be washed after the removal of a tick. The fingers
should not be used to detick dogs. Persons living and working in
tick-infested areas should be educated about the prevention,
symptoms,
and signs of the disease. No vaccine against RMSF is currently
available. RMSF cases should be reported to appropriate local and
state health departments.
References
CDC. Rocky Mountain spotted fever--United States, 1981. MMWR
1982;31:261-3.
Hattwick MAW, Peters AH, Gregg MB, et al. Surveillance of
Rocky
Mountain spotted fever. JAMA 1973; 225:1338-43.
Woodward TE. Rocky Mountain spotted fever: epidemiological and
early clinical signs are keys to treatment and reduced
mortality.
J Infect Dis 1984;150:465-8.
Wilfert CM, MacCormack JN, Kleeman K, et al. Epidemiology of
Rocky Mountain spotted fever as determined by active
surveillance. J Infect Dis 1984;150:469-79.
Needham GR. Evaluation of five popular methods for tick
removal.
Pediatrics 1985;75:997-1002.
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