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Clinical and Diagnostic Laboratory Immunology, 03 1994, 189-196, Vol 1, No. 2
HT Dupont, X Thirion and D Raoult
Q fever, a worldwide zoonosis caused by Coxiella burnetii, lacks clinical
specificity and may present as acute or chronic disease. Because of this
polymorphism, serological confirmation is necessary to assess the
diagnosis. Although microimmunofluorescence is our reference technique, the
cutoff titers that are currently used to make a diagnosis of active or
chronic Q fever were determined years ago with limited series of patients
and sera. We determined the titers of immunoglobulin G (IgG), IgM, and IgA
against both phases (I and II) of Coxiella burnetii. Rheumatoid factor was
removed before testing IgM and IgA. We report here the various cutoff
titers and the kinetics of antibody development from 2,218 first serum
samples of patients, among whom 208 suffered from acute Q fever and 53 had
chronic Q fever. In active Q fever, we have defined a low cutoff (phase II
IgG titer < or = 100) below which the diagnosis cannot be made and would
need further confirmation and confirmed a high cutoff (phase II IgG titer
> or = 200 and phase II IgM titer > or = 50) over which the diagnosis
can be made. For chronic Q fever diagnosis, phase I IgA titers are not
contributive despite previous works claiming their usefulness; a phase I
IgG titer of > or = 800 is highly predictive (98%) and sensitive (100%).
We have also studied the possibility of rejecting or evoking the diagnosis
of chronic Q fever by phase II IgG and IgA titers. This method is useful
when phase I testing is not available, but the sensitivity remains low
(57%).
Copyright © 1994 by the American Society for Microbiology. All rights reserved.
Q fever serology: cutoff determination for microimmunofluorescence
Unite des Rickettsies, CNRS EP J 0054, Marseille, France.
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