Serologic testing for human granulocytic ehrlichiosis at a national referral center

An indirect immunofluorescence assay (IFA) was used to identify patients wi th antibodies reactive to the human granulocytic ehrlichiosis (HGE) agent, Serum samples collected from clinically ill individuals Here submitted to t he Centers for Disease Control and Prevention bg physicians via state healt h departments from throughout the United States and tested against a panel of ehrlichial and rickettsial pathogens. Antibodies reactive to the HGE age nt were detected in 142 (8.9%) of 1,602 individuals tested. There Here 19 c onfirmed and 59 probable (n = 78) cases of HGE as defined by seroconversion or a fourfold or higher titer to the HGE agent than to the Ehrlichia chaff eensis antigens, The average age of patients with HGE Has 57 years, and mal es accounted for 53 (68%) of the patients. Cases of HGE occurred in 21 stat es; 47 (60%) of the cases occurred in Connecticut (n = 14), New York (n = 1 8), and Wisconsin (n = 15), Onset of HGE Has identified from,April through December, with cases peaking in June and July, The earliest confirmed cases of HGE occurred in 1987 in Wisconsin and 1988 in Florida. No fatalities He re reported among the 78 patients with confirmed or probable HGE. Reactivit y to the HGE agent and to either Coxiella burnetii, Rickettsia rickettsii, or Rickettsia typhi was infrequent; however, 74 (52%) of the 142 individual s who were positive for HGE had at least one serum sample that also reacted to the E. chaffeensis antigen. Thirty-four persons with confirmed or proba ble human monocytic ehrlichiosis due to E. chaffeensis also had antibodies to the HGE agent in at least one serum sample, The specific etiologic agent for 30 patients was not ascribed because of similarity of titers to both e hrlichial antigens, The use of both antigens may be required to correctly d iagnose most cases of human ehrlichiosis, especially in geographic regions where both the HGE agent and E, chaffeensis occur.