Coxiella burnetii DNA, but not viable bacteria, in dairy products in France

Abstract

Transmission by the oral route of Coxiella burnetii is controversial. Our objective was to evaluate dairy products in the transmission of Q fever. Pasteurized, unpasteurized, and thermized dairy products were tested for C. burnetii by using a quantitative polymerase chain reaction specific for IS1111 and IS30A spacers, culturing in human embryonic lung fibroblasts cells, and inoculation into BALB/c mice. We tested 201 products and C. burnetii was identified in 64%. Cow milk origin products were more frequently positive than goat or ewe products (P = 0.006 and P = 0.0001, respectively), and industrial food was more frequently positive than artisanal food (P < 0.0001). Food made from unpasteurized milk contained higher bacteria concentrations than food made from pasteurized milk (P = 0.02). All cultures were negative and mice did not show signs of illness. Farm animals are highly infected in France but consumption of cheese and yogurt does not seem to pose a public health risk for transmission of Q fever.

Figure 1.

Comparison between cycle threshold (Ct) values and log10 values of the number (nb) of copies/mL of the Coxiella burnetii IS1111 spacer region, France.

Figure 2.

Geometric mean and 95% confidence intervals of log10 number of Coxiella burnetii DNA copies/mL in pasteurized versus unpasteurized products and in artisanal versus industrial products, France.

Figure 3.

Geometric mean and 95% confidence intervals of log10 number of Coxiella burnetii DNA copies/mL in ewe, goat, and cow milk products from pasteurized and unpasteurized products, France.

Figure 4.

Geometric mean and 95% condidence intervals of log10 number of Coxiella burnetii DNA copies/mL in ewe, goat and cow milk products from artisanal and industrial products, France.