Two Tests and Timing Are Important in Q Fever Diagnosis

The diagnosis of Q fever requires both an immunoassay and a molecular test to establish a definitive diagnosis and is temporally dependent.

Q fever is a zoonotic disease caused by Coxiella burnetii, a species of bacteria that is distributed globally. A diagnosis of Q fever requires serologic testing to detect the presence of antibodies to C. burnetii antigens. In most laboratories, the indirect immunofluorescence assay (IFA) is the most dependable and widely used method.

In a recent study carried out at the University Hospital (Jena, Germany), the serum of 22 patients with acute Q fever, was tested by three different methods fever in reference to the time of serum collection. The serum were tested with a commercially available enzyme-linked immunosorbent assay (ELISA) called BEP III, (Virion-Serion, Wuerzburg, Germany); an indirect fluorescent antibody test (IFAT) (Focus Diagnostics, Cypress, CA, USA). An in-house nested polymerase chain reaction (PCR) was used to amplify the DNA of the organism.

A sensitivity of 30% by ELISA and 80% by IFAT) was found for the first five days of illness and 92% by ELISA and 83% by IFAT during the sixth and eleventh day. PCR revealed a positive result in eight cases (36%) with six cases deriving from the first five days of illness. The authors concluded that ELISA aids especially in the diagnosis of Q fever after five days of illness. The benefit of PCR as an additional tool to ELISA was especially evident in the early days of serum sampling. The detection rate with IFAT within the first five days was higher than the data previously reported, where 50% of the serum samples had Immunoglobulin M (IgM)-positive IFAT titers on day six. A diagnosis with IgM-IFAT could be made in 53% (17/32) of patients during the first week after onset, and in 89% (33/37) during the second week. The results of the study were published in the October 2010, issue of Diagnostic Microbiology and Infectious Disease.

Outbreaks of Q fever are often associated with sheep and goat farms and a large outbreak has been ongoing in the Netherlands since 2007. There have also been recent outbreaks in the UK and Germany, as well as amongst US marines stationed in Iraq.

Related Links:
University Hospital
Virion-Serion
Focus Diagnostics