Abstract 979 Poster Session IV, Tuesday, 5/4 (poster 138)

The yearly incidence rate of RMSF in endemic areas is as high as 3 per 100,000 persons. However, the occurrence of unrecognized, mild illness has been suggested. In order to estimate the prevalence of prior infection with R. rickettsii, the causative agent of RMSF, serum or plasma specimens from approximately 300 children having blood drawn for any reason at each of 5 southeastern U.S. centers were collected. Specimens and controls were blindly tested by IFA for IgG antibodies to R. rickettsii. Centers differed significantly in racial distribution and origin of specimens (hospital admission vs out-patient visit). Overall, 31 (2.1%) of 1468 children were positive at the screening dilution of 1:32, and 23 of these had titers ≥ 1:64. The seropositive rate was highest in Little Rock, AR (11/296 [3.7%]) and lowest in Winston-Salem, NC (1/311 [0.3%]). Univariate analyses showed no associations between specimen origin, gender or race and seropositivity. However, seroprevalence rates increased with age group as follows: 1 to 6 yrs old- 3/362 (0.8%); 7 to 12 yrs old- 10/520 (1.9%); 13 to 18 yrs old- 18/586 (3.1%) (P < .02. Chi-square for trend). Multivariate analyses that include residence setting are being conducted. Within the limitations of convenience sampling, these data suggest that R. rickettsii infection may be more common than previously thought, warranting population-based studies.

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