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Antibodies Reactive to
Rickettsia rickettsii Among Children Living in
the Southeast and South Central Regions of the United
States
Gary S. Marshall, MD; Gordon
G. Stout, BS; Richard F. Jacobs, MD;
Gordon E. Schutze, MD; Helene Paxton,
MS; Steven C. Buckingham, MD;
John P. DeVincenzo, MD; Mary Anne Jackson,
MD; Venusto H. San Joaquin, MD;
Steven M. Standaert, MD; Charles R.
Woods, MD; and the Tick-Borne Infections in
Children Study (TICS) Group
Arch Pediatr Adolesc Med. 2003;157:443-448.
Background The reported annual
incidence of Rocky Mountain spotted fever in
the United States is 2.2 per million, but studies
have suggested that human infection with
Rickettsia rickettsii may be more common.
This study estimated the prevalence of antibodies
reactive to R rickettsii among children
living in the southeastern and south central
United States.
Study Design Approximately 300 specimens were
obtained from children at each of 7 pediatric
referral centers (N = 1999). Serum was tested
for R rickettsii antibodies by means of indirect
immunofluorescence antibody assay. Three different
cutoff titers ( 64, 128, and
256) represented increasing levels of
stringency to define positive specimens.
Results Overall, 12.0% of children had R
rickettsii antibody titers of at least
64; 7.3%, at least 128; and 4.3%, at least
256. Strong relationships were seen between increasing
age and seroprevalence at each cutoff titer.
Remarkably, 6.4% of children aged 13 to 17
years had titers of at least 256. Age-adjusted
seroprevalence rates at titers of at least 64
varied from 21.9% in Little Rock, Ark, to
3.5% in Louisville, Ky. At titers of at least
256, seroprevalence ranged from 7.7% in Nashville,
Tenn, to 1.8% in Winston-Salem, NC. Only site and
age group were strong predictors of
seropositivity; a weak association was seen
with nonurban residence.
Conclusions To our knowledge, this is the
largest serosurvey of rickettsial infection
in children in the United States. Within the
limitations of the immunofluorescence antibody assay,
these data suggest that infections with R
rickettsii or antigenically related
spotted-fever group rickettsiae may be common and
subclinical. The results also have
implications for the interpretation of single
immunofluorescence antibody assay titers in children
with suspected Rocky Mountain spotted fever.
From the Departments of Pediatrics, University
of Louisville School of Medicine, Louisville, Ky (Dr
Marshall and Mr Stout), University of Arkansas for
Medical Sciences, Little Rock (Drs Jacobs and Schutze),
University of Tennessee Health Sciences Center, Memphis
(Drs Buckingham and DeVincenzo), University of Missouri,
Kansas City (Dr Jackson), University of Oklahoma Health
Sciences Center, Oklahoma City (Dr San Joaquin), and
Wake Forest University School of Medicine,
Winston-Salem, NC (Dr Woods); PanBio InDx, Inc,
Baltimore, Md (Ms Paxton); and Department of Medicine,
Vanderbilt University School of Medicine, Nashville,
Tenn (Dr Standaert).
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This Month in Archives of Pediatrics &
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Arch Pediatr Adolesc Med. 2003;157:413.
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