title: Determination of new cutoff values for indirect immunofluorescence antibody test for Q fever diagnosis in Denmark.
abstract: Q fever is a ubiquitous zoonosis caused by Coxiella burnetii. The disease is emerging in many parts of the world, likely because of increased awareness and availability of better diagnostics. The diagnosis is primarily based on serology. Because the prevalence of the disease varies worldwide, the establishment of local cutoff values is needed. A baseline for antibodies against C. burnetii in Denmark was defined by testing sera from healthy Danish volunteers using a commercially available immunofluorescence antibody test. Cross-reactivity was studied on sera obtained from patients experiencing clinically related diseases. The cutoff titers suggested by the manufacturer were found to result in very low specificity of the test. The specificity was, however, effectively increased by using cutoff titers based on the local baseline and equal to immunoglobulin M (IgM) phase I > or =128, IgM phase II > or =256, IgG phase I > or =512, and IgG phase II > or =1024.
authors.affiliation: Statens Serum Institut, Department of Bacteriology, Mycology, and Parasitology, Copenhagen, Denmark. stv@ssi.dk
authors.forename: Steen
authors.initials: S
authors.lastname: Villumsen
authors.forename: Charlotte Svaerke
authors.initials: CS
authors.lastname: Jørgensen
authors.forename: Birgitte
authors.initials: B
authors.lastname: Smith
authors.forename: Søren
authors.initials: S
authors.lastname: Uldum
authors.forename: Peter
authors.initials: P
authors.lastname: Schiellerup
authors.forename: Karen Angeliki
authors.initials: KA
authors.lastname: Krogfelt
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood*; D016997:Coxiella burnetii / Q000276:immunology*; D003718:Denmark; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods* / Q000592:standards*; D006805:Human Experimentation; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood*; D011778:Q Fever / Q000175:diagnosis*; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity
chemical_list: D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D011933:Reagent Kits, Diagnostic