Study of cross-reaction between Coxiella burnetii and Legionella pneumophila using indirect immunofluorescence assay and immunoblotting.

Patients with Q fever and legionellosis may present identical clinical symptom. Differentiation of these diseases is made by serology, mainly the indirect immunofluorescence assay (IFA). Using IFA the authors tested 154 Q fever positive sera from 55 patients with acute Q fever and 28 patients with chronic Q fever for Legionella pneumophila antibodies and 57 sera from 57 patients with legionellosis for Coxiella burnetii antibodies. Of the 211 sera tested, four sera from different patients had antibodies to both C. burnetii and L. pneumophila. Using cross-adsorption studies and protein immunoblotting, no cross-reaction between C. burnetii and L. pneumophila antibodies could be identified. The moderate antibody titers against L. pneumophila in two Q fever patients and vice versa for one legionellosis patient are consistent with the incidence of seroprevalence in healthy blood donors and were not due to cross-reactivity. One patient was identified with concurrent Q fever and legionellosis.