title: Evaluation of a new serological test for the detection of anti-Coxiella and anti-Rickettsia antibodies.
abstract: Coxiella burnetii and members of the genus Rickettsia are obligate intracellular bacteria. Since cultivation of these organisms requires dedicated techniques, their diagnosis usually relies on serological or molecular biology methods. Immunofluorescence is considered the gold standard to detect antibody-reactivity towards these organisms. Here, we assessed the performance of a new automated epifluorescence immunoassay (InoDiag) to detect IgM and IgG against C. burnetii, Rickettsia typhi and Rickettsia conorii. Samples were tested with the InoDiag assay. A total of 213 sera were tested, of which 63 samples from Q fever, 20 from spotted fever rickettsiosis, 6 from murine typhus and 124 controls. InoDiag results were compared to micro-immunofluorescence. For acute Q fever, the sensitivity of phase 2 IgG was only of 30% with a cutoff of 1 arbitrary unit (AU). In patients with acute Q fever with positive IF IgM, sensitivity reached 83% with the same cutoff. Sensitivity for chronic Q fever was 100% whereas sensitivity for past Q fever was 65%. Sensitivity for spotted Mediterranean fever and murine typhus were 91% and 100%, respectively. Both assays exhibited a good specificity in control groups, ranging from 79% in sera from patients with unrelated diseases or EBV positivity to 100% in sera from healthy patients. In conclusion, the InoDiag assay exhibits an excellent performance for the diagnosis of chronic Q fever but a very low IgG sensitivity for acute Q fever likely due to low reactivity of phase 2 antigens present on the glass slide. This defect is partially compensated by the detection of IgM. Because it exhibits a good negative predictive value, the InoDiag assay is valuable to rule out a chronic Q fever. For the diagnosis of rickettsial diseases, the sensitivity of the InoDiag method is similar to conventional immunofluorescence.
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital Center, Lausanne, Switzerland.
authors.forename: Alain
authors.initials: A
authors.lastname: Bizzini
authors.affiliation: Department of Infectious Diseases, Central Institute of Valais, Sion, Switzerland.
authors.forename: Olivier
authors.initials: O
authors.lastname: Péter
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital Center, Lausanne, Switzerland; Department of Obstetrics and Gynaecology, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Baud
authors.affiliation: URMITE UMR 6236, Faculté de Médecine et de Pharmacie, Marseille, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Edouard
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital Center, Lausanne, Switzerland.
authors.forename: Pascal
authors.initials: P
authors.lastname: Meylan
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital Center, Lausanne, Switzerland. Electronic address: gilbert.greub@chuv.ch.
authors.forename: Gilbert
authors.initials: G
authors.lastname: Greub
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood* / Q000276:immunology; D001907:Boutonneuse Fever / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology; D016997:Coxiella burnetii / Q000276:immunology; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007074:Immunoglobulin G / Q000097:blood* / Q000276:immunology; D007075:Immunoglobulin M / Q000097:blood* / Q000276:immunology; D051379:Mice; D011778:Q Fever / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology; D020114:Rickettsia conorii / Q000276:immunology; D012286:Rickettsia typhi / Q000276:immunology; D012698:Serologic Tests / Q000379:methods; D014437:Typhus, Endemic Flea-Borne / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology
chemical_list: D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D007075:Immunoglobulin M
keywords: Coxiella burnetii; Immunofluorescence; Multiplexed serology; Rickettsia conorii; Rickettsia typhi