Prevalence and spatial distribution of Coxiella burnetii seropositivity in northern Australian beef cattle adjusted for diagnostic test uncertainty.

Q fever is a zoonotic disease caused by infection with Coxiella burnetii transmitted from animals including, but not limited to, cattle, sheep and goats. The infection in cattle is typically sub-clinical with some evidence suggesting associated reproductive loss. There is currently limited data on the true prevalence and distribution of coxiellosis in beef cattle across northern Australia. During this study, 2,012 sera samples from beef cattle managed on commercial farms located in Queensland and the Northern Territory were tested using an indirect immunofluorescent assay (IFA) for serological evidence of IgG antibodies against C. burnetii. Bayesian latent class models were used to estimate the true prevalence, adjusted for diagnostic test sensitivity and specificity and incorporating the hierarchical structure of the cattle within farms and regions. In this study, cattle in the Northern Territory had lower estimated true prevalence than cattle within most regions of Queensland with the exception of south-east Queensland. Results from this study have described the geographic distribution and estimated the true prevalence of antibodies to C. burnetii in a sample of extensively managed beef cattle located across the tropical grazing regions of northern Australia.

Potential animal and environmental sources of Q fever infection for humans in Queensland.

Q fever is a vaccine-preventable disease; despite this, high annual notification numbers are still recorded in Australia. We have previously shown seroprevalence in Queensland metropolitan regions is approaching that of rural areas. This study investigated the presence of nucleic acid from Coxiella burnetii, the agent responsible for Q fever, in a number of animal and environmental samples collected throughout Queensland, to identify potential sources of human infection. Samples were collected from 129 geographical locations and included urine, faeces and whole blood from 22 different animal species; 45 ticks were removed from two species, canines and possums; 151 soil samples; 72 atmospheric dust samples collected from two locations and 50 dust swabs collected from domestic vacuum cleaners. PCR testing was performed targeting the IS1111 and COM1 genes for the specific detection of C. burnetii DNA. There were 85 detections from 1318 animal samples, giving a detection rate for each sample type ranging from 2.1 to 6.8%. Equine samples produced a detection rate of 11.9%, whilst feline and canine samples showed detection rates of 7.8% and 5.2%, respectively. Native animals had varying detection rates: pooled urines from flying foxes had 7.8%, whilst koalas had 5.1%, and 6.7% of ticks screened were positive. The soil and dust samples showed the presence of C. burnetii DNA ranging from 2.0 to 6.9%, respectively. These data show that specimens from a variety of animal species and the general environment provide a number of potential sources for C. burnetii infections of humans living in Queensland. These previously unrecognized sources may account for the high seroprevalence rates seen in putative low-risk communities, including Q fever patients with no direct animal contact and those subjects living in a low-risk urban environment.

Q fever seroprevalence in metropolitan samples is similar to rural/remote samples in Queensland, Australia.

Q fever is a vaccine preventable disease; however, despite this, high notification numbers are still recorded annually in Australia. We investigated the seroprevalence of Coxiella burnetii, the Q fever agent, in a Queensland sample population. Notification data (N = 6425) from 1984-2008 were collated, identifying high risk areas of Q fever exposure. Of these 177 were recorded in children. Serum samples were collected from Queensland and screened using both an immunoflourescence assay at 1:10 dilution and a commercially available ELISA kit. Results were collated based on age, geographical location and sex. From 1988 Queensland samples screened, 103 were identified as Q fever IgG-positive, giving a seroprevalence of 5.2% (95% CI 4.3-6.2%). Seroprevalence in the rural/remote population was 5.3% (95% CI 4.6-6.6%), and the metropolitan Brisbane population, which is considered not at risk, was 5.0% (95% CI 3.7-6.7%). Sixty-three seropositive males and 40 females were identified, along with an increase in seropositivity with increasing age. The seropositivity of children was 1.3% (95% CI 0.7-2.3%) from 844 samples. We have shown that both metropolitan and paediatric populations which are considered low risk of Coxiella exposure have surprisingly high seropositivity. These emerging groups require further investigation and consideration for the introduction of preventive measures.