Development of a method for detecting Coxiella burnetii in cheese samples.

Coxiella burnetii is the causative agent of Q fever, and the main route of infection in humans is inhalation of contaminated aerosols. Although oral transmission by contaminated raw milk or dairy products is also a possible route of human infection, there have been few studies investigating the presence of C. burnetii in dairy products. We developed a new method of extracting DNA from cheese and detecting C. burnetii DNA in cheese samples with a nested PCR assay. The limit of detection was 6.0 × 102 C. burnetii particles per gram. We subsequently used this method to examine the presence of C. burnetii in cheese at commercial markets in Tokyo from June 2005 to December 2008. Twenty-eight of 147 cheese samples were found to be positive for C. burnetii DNA. However, when we assessed the viability of C. burnetii by inoculating mice with DNA-positive samples, all of the samples were found to be negative. Thus, the viability of C. burnetii appears to have been lost in these cheese samples.