Ehrlichia chaffeensis seroprevalence among children in the southeast and south-central regions of the United States.

BACKGROUND: The reported annual incidence of human monocytic ehrlichiosis, which is due to infection with Ehrlichia chaffeensis, is as high as 5.5 per million in some states, but serosurveys suggest much higher infection rates in some populations. OBJECTIVE: To estimate the prevalence of E chaffeensis infection among children aged 1 to 17 years living in the southeast and south-central United States. DESIGN: Cross-sectional serosurvey. SETTING: Seven academic pediatric medical centers in the southeastern and south-central United States. PATIENTS: Nineteen hundred ninety-nine children (approximately 300 at each center) having their blood drawn for any reason. MAIN OUTCOME MEASURE: The presence of antibody at 2 different cutoff titers to E chaffeensis, as detected by indirect immunofluorescence assay. RESULTS: Overall, 250 children (13%) had E chaffeensis antibody titers of 1:80 or higher and 61 (3%) had titers of 1:160 or higher. Age-adjusted seroprevalence rates varied widely between sites. At 1:80 or higher, the highest rate was in Winston-Salem, NC (22%), and the lowest was in Louisville, Ky (2%). At 1:160 or higher, the highest rate was in Kansas City, Mo (9%), and the lowest was in Oklahoma City, Okla (<1%). In univariate analyses, no associations were found between seroprevalence at either cutoff value and sex, race, source of specimen, or residence demographics. However, age was a significant predictor of seroprevalence at both cutoff values. In multiple logistic regression analysis, study site and age remained strong predictors of seroprevalence, but living in a nonurban ZIP code was not significantly related. CONCLUSION: Infection with E chaffeensis, or related ehrlichiae, may be more common in children than previously recognized.

Antibodies reactive to Rickettsia rickettsii among children living in the southeast and south central regions of the United States.

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 (>or=64, >or=128, and >or=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.