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.

Analysis of recombinant proteins for Q fever diagnostics

“…One protein found to be weakly reactive in the present study was the highly published antigen, CBU_1910 (Com1) 32 . Com1 had previously been identified as seroreactive against human and rodent sera with sensitivity and specificity ranging from 37.5% to 100% and 71% to 100%, respectively 13,33,34 . Interestingly, this antigen performed poorly in this study when tested against serum from naturally infected goats.…”

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

“…The performance of this technique was recently compared with that of a gold standard microimmunofluorescence technique. It showed heterogenous performances, with a low sensitivity for primary infection due to low reactivity of phase II antigens but an excellent performance for persistent infection, with 100% sensitivity in the detection of phase I antigens (348).…”

The Rickettsioses

“…72 Fortunately, this cross reactivity enables the serologic diagnosis of a rickettsiosis despite the numerous species and strains in nature. 73 When participating in the care of a traveler with a potential rickettsiosis, this cross reactivity is important, as some geographic areas have several endemic rickettsial species. Enzyme-linked immunosorbent assays are also commercially available for the diagnosis of SFG and typhus group rickettsioses but give more qualitative results (reactive versus non reactive) rather than the titer reported with IFA.…”