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A new interesting article has been published in J Clin Microbiol. 2019 Jul 31. pii: JCM.00539-19. doi: 10.1128/JCM.00539-19. and titled:

Introduction to the measurement of the avidity of anti-Coxiella burnetii IgG in the diagnosis of Q fever.

Authors of this article are:

Luciani L, L’ollivier C, Million M, Amphoux B, Edouard S, Raoult D.

A summary of the article is shown below:

Due to the atypical serological profile of some patients with primary Q fever infection who do not develop IgM against Coxiella burnetii, we developed an avidity test to distinguish recent or past infections. We tested 39 sera from 26 patients sampled at different stages of the disease by immunofluorescence with conventional assay and after urea treatment. We observed a strong avidity in the 15 sera with infection > 6 months and a low avidity for sera from patients with recent infection. A complete denaturation of the antibody-antigen complex was observed for patients with a time since the beginning of infection < 1 month and a mean of 2.06 ± 0.54 lowered titers when the infection was less than 3 months old. That is statistically significant compared to sera of infection greater than 6 months (mean 0.20±0.41) and sera with infection between 3 to 6 months (mean 1.17±0.41), p=0.0022 and p<0.0001. These results were visualized by Western blot. We concluded that high avidity (≤ 1 lowered titer) ruled out infection during the last 6 months and that complete denaturation was related to an infection which had occurred within the previous 3 months. Between these two situations, the avidity test is non-conclusive. We suggest using an avidity test for atypical Q fever serology that could be misclassified as residual antibodies (IgG against C. burnetii detected without active or recent infection) and for pregnant women risking obstetrical complications. This new test will dramatically improve the diagnosis and management of patients with Q fever.Copyright © 2019 American Society for Microbiology.
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