Author:
Kampschreur Linda M.,Oosterheert Jan Jelrik,Koop Annemarie M. C.,Wegdam-Blans Marjolijn C. A.,Delsing Corine E.,Bleeker-Rovers Chantal P.,De Jager-Leclercq Monique G. L.,Groot Cornelis A. R.,Sprong Tom,Nabuurs-Franssen Marrigje H.,Renders Nicole H. M.,van Kasteren Marjo E.,Soethoudt Yvonne,Blank Sybrandus N.,Pronk Marjolijn J. H.,Groenwold Rolf H. H.,Hoepelman Andy I. M.,Wever Peter C.
Abstract
ABSTRACTDiagnosis of chronic Q fever is difficult. PCR and culture lack sensitivity; hence, diagnosis relies mainly on serologic tests using an immunofluorescence assay (IFA). Optimal phase I IgG cutoff titers are debated but are estimated to be between 1:800 and 1:1,600. In patients with proven, probable, or possible chronic Q fever, we studied phase I IgG antibody titers at the time of positive blood PCR, at diagnosis, and at peak levels during chronic Q fever. We evaluated 200 patients, of whom 93 (46.5%) had proven, 51 (25.5%) had probable, and 56 (28.0%) had possible chronic Q fever. Sixty-five percent of proven cases had positiveCoxiella burnetiiPCR results for blood, which was associated with high phase I IgG. Median phase I IgG titers at diagnosis and peak titers in patients with proven chronic Q fever were significantly higher than those for patients with probable and possible chronic Q fever. The positive predictive values for proven chronic Q fever, compared to possible chronic Q fever, at titers 1:1,024, 1:2,048, 1:4,096, and ≥1:8,192 were 62.2%, 66.7%, 76.5%, and ≥86.2%, respectively. However, sensitivity dropped to <60% when cutoff titers of ≥1:8,192 were used. Although our study demonstrated a strong association between high phase I IgG titers and proven chronic Q fever, increasing the current diagnostic phase I IgG cutoff to >1:1,024 is not recommended due to increased false-negative findings (sensitivity < 60%) and the high morbidity and mortality of untreated chronic Q fever. Our study emphasizes that serologic results are not diagnostic on their own but should always be interpreted in combination with clinical parameters.
Publisher
American Society for Microbiology
Subject
Microbiology (medical),Clinical Biochemistry,Immunology,Immunology and Allergy
Cited by
29 articles.
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