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