ABSTRACT
Ninety-five acute- and convalescent-phase serum specimens from 48 patients suspected of having rickettsial or Legionella infections were assayed for antibodies to Coxiella burnetii, the causative agent of Q fever. To evaluate the specificity of the indirect enzyme-linked immunosorbent assay (ELISA) for human Q fever, we compared the ELISA results with those of the indirect immunofluorescence antibody (IFA) test. The ELISA data were analyzed by two different criteria for a positive test. The first criterion for positive results by ELISA was based upon diagnostic titers established in a study of 150 subjects who had no demonstrable cellular or humoral immune responses to C. burnetii phase I or phase II whole cells or phase I lipopolysaccharide. The second criterion was based upon diagnostic antibody titers in a study of 51 subjects who had been diagnosed as having clinical Q fever and had fourfold or greater rises in humoral immune responses to C. burnetii phase I and phase II whole-cell antigens. A comparison of the ELISA and IFA test results of the 95 serum specimens indicated excellent agreement between the tests (Kappa = 92.9%; P < 0.05). None of the 38 patients whose etiologies were confirmed serologically as Legionnaires' disease or rickettsial diseases other than Q fever were classified as positive for C. burnetii by the ELISA. Only one patient identified by the IFA test as having Q fever was not scored positive by the ELISA. These results suggest that the ELISA is useful for epidemiologic screening and as a diagnostic test for human Q fever.
Subject(s)
Antibodies, Bacterial/blood , Coxiella burnetii/immunology , Enzyme-Linked Immunosorbent Assay , Q Fever/diagnosis , Acute Disease , Convalescence , Diagnosis, Differential , Ehrlichiosis/diagnosis , Evaluation Studies as Topic , Fluorescent Antibody Technique , Humans , Reproducibility of Results , Rocky Mountain Spotted Fever/diagnosis , Sensitivity and Specificity , Seroepidemiologic Studies , Typhus, Endemic Flea-Borne/diagnosisABSTRACT
A prospective, seroepidemiologic study of spotted fever group rickettsiae (SFGR) and Ehrlichia infections was done among 1194 US military personnel exposed in a heavily tick-infested area of Arkansas in 1990. Seroconversion (4-fold) and seroprevalence rates were determined by indirect immunofluorescent antibody assays. Seroconversions to SFGR occurred in 30 persons (2.5%), whereas seroconversion to Ehrlichia species occurred in 15 (1.3%). The majority of seroconverters did not report symptoms (22/30 [73%] of SFGR seroconverters; 10/15 [67%] of Ehrlichia species seroconverters). History of tick attachment was associated with seroconversion to SFGR (relative risk [RR] = 4.3, P < .001) and Ehrlichia species (RR = 3.6, P < .05). Use of permethrin-impregnated uniforms significantly decreased risk of infection (P < .01); use of bed nets increased risk by 4-fold. Tickborne infections represent a significant threat to military personnel training in areas in which these infections are endemic.