Detection and risk factors of Coxiella burnetii infection in dairy cattle based on bulk tank milk samples in center of Iran.

Infection with Coxiella burnetii has a worldwide distribution in ruminants and is associated with abortions and reproductive problems in this group of animals. This study aimed to determine the prevalence of C. burnetii DNA in bulk tank milk (BTM) of dairy cattle herds and to identify the risk factors of infection. This cross-sectional study was conducted in spring 2015. A total of 163 BTM samples from 74 commercial and 89 traditional dairy cattle herds in Isfahan, Iran was tested for the IS1111 transposon of C. burnetii by real-time polymerase chain reaction (PCR). A checklist containing general information of the herds was filled for each farm. Data were analyzed using univariate tests (chi square and t-tests) and multivariable binary logistic regression analysis. Bacterial DNA was detected in 8.6% of the samples (95% CI: 4.2- 12.9). In univariate analysis, the prevalence rate was higher in traditional herds than in commercial herds (n=12; 13.5% vs. n=2; 2.7%; P=0.01). The prevalence rate was inversely associated with the size and infection control score of the herd. In multivariable binary logistic regression, however, only herd size was found to be related with the infection rate, i.e. herds with ≥80 cattle were less likely to be infected (OR: 0.07; 95% CI: 0.01- 0.77; P=0.03). The only identified risk factor for this infection was the herd size. In fact, smaller herds (size <80) were more likely to be infected.