Current Trends
Rocky Mountain Spotted Fever -- United States, 1988
In 1988, state health departments reported 615 cases of Rocky
Mountain
spotted fever (RMSF) to CDC, an increase of 3.9% from the 592 cases
reported in 1987. The incidence was 0.3 per 100,000. Of the 615
cases,
200 (32.5%) were reported from the South Atlantic region and 149
(24.2%) from the West South Central region. Oklahoma had the
highest
rate (97 cases, 3.0 per 100,000); other states with high rates were
North Carolina (108 cases, 1.7 per 100,000), Arkansas (32 cases,
1.3
per 100,000), Missouri (57 cases, 1.1 per 100,000), and Kansas (26
cases, 1.0 per 100,000) (Figure 1).
Detailed case report forms were submitted on 555 (90.2%) of the
615
cases. Of these, 362 (65.2%) were laboratory-confirmed*, 31 (5.6%)
were
classified as prob able**, and 162 (29.2%) were not confirmed.
Males
accounted for 63.8% of cases; onset of symptoms occurred between
April
1 and July 31 in 81.2%, and a tick bite was reported in 62.8%.
Fever
was reported in 92.8% of cases, headache in 84.7%, rash in 76.5%,
and
rash on palms in 50.6%. The overall case-fatality rate for 1988 was
3.9%: 8.2% for persons greater than 30 years of age and 1.3% for
persons less than or equal to 30.
Reported by: State health departments. Viral and Rickettsial
Zoonoses
Br, Div of Viral and Rickettsial Diseases, Center for Infectious
Diseases, CDC.
Editorial Note
Editorial Note: Although the total number of RMSF cases reported in
1988 increased minimally from 1987, large increases occurred in
several
states: Missouri (from 19 cases in 1987 to 57 in 1988), Arkansas
(from
12 to 32 cases), South Dakota (from one to seven cases), and
Kentucky
(from 13 to 30 cases). The increase in Missouri may reflect an
extension of the area in which RMSF is endemic in the West South
Central states (1). Reported cases in Maryland and Tennessee
decreased
52.2% and 32.0%, respectively, in 1988.
The case-fatality rate for 1988 increased to 3.9% from 3.1% in
1987,
reflecting an increase in fatal cases and/or better surveillance.
As in
previous years, the case-fatality rate was higher in older patients
and
in those without a history of tick bites. Because diagnosis may be
delayed in persons without a history of a tick bite, the likelihood
of
serious or fatal complications increases for this group.
Because no vaccine exists for RMSF, the best preventive measure is
avoidance of tick-infested areas. Persons who must enter these
areas
should wear protective clothes and use tick repellant. The most
widely
used tick repellant is N,N-diethyl-m-toluamide (DEET), the active
ingredient in most popular brands of insect repellant. Although
DEET is
effective in repelling ticks (as well as chiggers, flies,
mosquitos,
and biting flies), toxic and allergic side effects have been
reported
(2,3). Ticks attached to a person's body should be removed by
grasping
them with fine tweezers at the point of attachment and pulling
gently
(4). When fingers are used instead of tweezers, they should be
protected using facial tissue and washed afterwards.
RMSF should be considered in all patients with an unexplained
febrile
illness, especially those with a history of tick bite or travel to
areas with endemic RMSF. If RMSF is suspected, treatment with
tetracycline or chloramphenicol should be promptly instituted. For
children less than or equal to 8 years of age and pregnant women,
chloramphenicol is the preferred treatment (5). Cases of RMSF
should be
reported to CDC through state health departments.
References
Taylor JP, Istre GR, McChesney TC. The epidemiology of Rocky
Mountain spotted fever in Arkansas, Oklahoma, and Texas, 1981
through
1985. Am J Epidemiol 1988;127:1295-301.
Abramowicz M, ed. Insect repellents. Med Lett Drugs Ther
1989;31:45-7.
Miller JD. Anaphylaxis associated with insect repellant
(Letter). N
Engl J Med 1982;307: 1341-2.
Needham GR. Evaluation of five popular methods for tick removal.
Pediatrics 1985;75: 997-1002.
Fishbein DB. Treatment of Rocky Mountain spotted fever. JAMA
1988;260:3192.
*A case is considered serologically confirmed if testing reveals an
indirect fluorescent antibody (IFA) titer of greater than or equal
to
1:64, a complement-fixation (CF) titer of greater than or equal to
1:16, or a fourfold rise in titer by the CF, IFA,
microagglutination
(MA), latex agglutination (LA), or indirect hemagglutination (IHA)
assays.
**A case is considered probable if testing reveals a fourfold rise
in
titer or a single titer greater than or equal to 1:320 in the
Weil-Felix assay or an LA, MA, or IFA single titer of greater than
or
equal to 1:128.
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