Rocky Mountain Spotted Fever -- United States, 1984
For 1984, a provisional total of 847 cases of Rocky Mountain
spotted fever (RMSF) in the United States was reported to the MMWR,
for an incidence rate of 0.36 cases per 100,000 population.
Oklahoma
had the highest incidence rate (119 cases; 3.6/100,000). Other
states
with high RMSF rates were North Carolina (178 cases; 2.9/100,000),
South Carolina (80 cases; 2.4/100,000), Arkansas (28 cases;
1.2/100,000), Tennessee (49 cases; 1.0/100,000), Montana (8 cases;
1.0/100,000), Virginia (48 cases; 0.9/100,000), and Georgia (48
cases;
0.8/100,000) (Figure 1).
States submitted case report forms for 717 (85%) of the cases
reported to the MMWR. Of the 717 cases, 399 (56%) were confirmed
either by serologic testing, isolation of spotted fever group
rickettsia, or fluorescent antibody staining of biopsy or autopsy
specimens. Serologic confirmation requires a single complement
fixation (CF) titer 1:16 or higher or single indirect fluorescent
antibody (IFA) titer 1:64 or higher or fourfold rise in the CF,
IFA,
microagglutination (MA), latex agglutination (LA), or indirect
hemagglutination (IHA) assays. An additional 66 patients (9%) were
classified as "probable" cases as indicated by a fourfold rise in
titer or single titer 1:320 or higher in the Weil-Felix assay
(Proteus
0X-19 or 0X-2) or a LA, MA, or IHA titer 1:128 or higher. The
other
252 diagnoses (35%) were supported by clinical findings alone.
Ninety-six percent of the patients became ill between April 1 and
September 30.
Like that of previous years (1,2), 1984 surveillance revealed
that
51% of the patients were under 20 years of age; 61% were male; and
91%
were white. Symptoms reported included fever (96%), headache
(90%),
myalgias (86%), rash (84%), and rash on the palms of the hands or
on
the soles of the feet (61%). Seventy-five percent of the patients
were hospitalized. Sixty-six percent of patients for whom exposure
information was available reported a tick bite within 14 days of
onset
of illness. The case-fatality rate (3.6%) was higher for older
individuals and for persons not receiving treatment with either
tetracycline or chloramphenicol. Of the 613 patients from whom
information about treatment and clinical outcome was available,
only
13 (2%) received neither chloramphenicol nor tetracycline. Of
these
13 patients, three (23%) died, compared with 16 deaths (3%) among
the
600 patients who received treatment with chloramphenicol or
tetracycline. For persons 30 years of age or older, the
case-fatality
rate was 6.5%, compared with 2.0% for individuals under 30.
Reported by Div of Viral Diseases, Center for Infectious Diseases,
CDC.
Editorial Note
Editorial note: RMSF, the most commonly reported rickettsial
infection in the United States, is transmitted to humans by ticks.
The incidence of infection begins to increase in April and is
highest
in May and June.
After the rapid increase in RMSF noted in the United States
during
the 1970s, infection rates remained approximately the same from
1977
through 1981, when a decrease in the number of cases began. In
1984,
25% fewer cases were reported than in 1983, and all states
reporting
over 10 cases in 1984 reported either a decrease or no change in
number of cases from 1983. This decrease occurred in both of the
major foci of RMSF in the United States, the West South Central and
South Atlantic states. The West South Central states reported 45%
fewer cases, and the South Atlantic states, 18% fewer cases. The
reason for the decrease in RMSF is not known but does not seem
attributable to reporting artifact. The decrease was widespread
geographically, occurred in both the cases reported to the MMWR and
in
cases reported by case report forms, was distributed uniformly over
the April 1-September 30 period, and occurred in the absence of any
changes in the reporting system. The decrease may be part of a
cyclic
pattern of RMSF incidence that appears to be occurring for the
second
time since reporting began in 1920 (3) (Figure 2).
Laboratory confirmation of a clinical diagnosis of RMSF by
serologic or other methods remains important in distinguishing RMSF
from other diseases with similar clinical presentations, even
though
treatment frequently precedes confirmation. Laboratory
confirmation
is also important for improving the specificity of national RMSF
surveillance. The importance of obtaining serologic confirmation
of
clinically diagnosed cases has been reinforced by a recent study
that
showed at least 36% of clinically diagnosed cases in an endemic
area
were found not to be RMSF when serologic testing was performed (4).
No vaccine against RMSF is currently available; RMSF is best
prevented by inspecting persons who may have been exposed to ticks.
If discovered, ticks should be removed by grasping them with
tweezers
as close as possible to the point of attachment and pulling slowly
and
steadily. Fingers, protected with facial tissue, may be used when
tweezers are not available. Because ticks' secretions can be
infective, hands should always be washed after removal of ticks.
Particularly during the spring and summer months in RMSF-endemic
areas
and during the 3-12 day period after bites or exposures to ticks,
RMSF
should be considered and medical treatment sought by any individual
who develops fever, myalgia, or headache, even in the absence of
rash
(5). Failure to treat cases with tetracycline or chloramphenicol,
particularly early in disease, remains a risk factor for deaths
from
RMSF (5,6).
References
Bernard KW, Helmick CG, Kaplan JE, Winkler WG. Surveillance of
Rocky Mountain spotted fever in the United States, 1978-1980.
J
Infect Dis 1982;146:297-9.
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.
Hattwick MA, O'Brien RJ, Hanson BF. Rocky Mountain spotted
fever:
epidemiology of an increasing problem. Ann Intern Med
1976;84:732-9.
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.
Helmick CG, Bernard KW, D'Angelo LJ. Rocky Mountain spotted
fever: clinical, laboratory, and epidemiological features of
262
cases. J Infect Dis 1984;150:480-8.
Hattwick MA, Retailliau H, O'Brien RJ, Slutzker M, Fontaine RE,
Hanson B. Fatal Rocky Mountain spotted fever. JAMA
1978;240:1499-503.
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