Presence and persistence of Coxiella burnetii in the environments of goat farms associated with a Q fever outbreak

Abstract

Q fever is a zoonotic disease caused by inhalation of the bacterium Coxiella burnetii. Ruminant livestock are common reservoirs for C. burnetii, and bacteria present in aerosols derived from the waste of infected animals can infect humans. The significance of infection from material deposited in the environment versus transmission directly from infected animals is not known. In 2011, an outbreak of Q fever cases on farms in Washington and Montana was associated with infected goats. A study was undertaken to investigate the quantity and spatial distribution of C. burnetii in the environment of these goat farms. Soil, vacuum, and sponge samples collected on seven farms epidemiologically linked to the outbreak were tested for the presence of C. burnetii DNA by quantitative PCR. Overall, 70.1% of the samples were positive for C. burnetii. All farms had positive samples, but the quantity of C. burnetii varied widely between samples and between farms. High quantities of C. burnetii DNA were in goat housing/birthing areas, and only small quantities were found in samples collected more than 50 m from these areas. Follow-up sampling at one of the farms 1 year after the outbreak found small quantities of C. burnetii DNA in air samples and large quantities of C. burnetii persisting in soil and vacuum samples. The results suggest that the highest concentrations of environmental C. burnetii are found in goat birthing areas and that contamination of other areas is mostly associated with human movement.

Fig 1

Environmental bulk and vacuum samples were collected on 7 farms in Washington and Montana. Genomic DNA was extracted from the samples and tested for the presence of C. burnetii DNA by quantitative PCR. The graph shows the number of genome equivalents per gram for each positive sample collected at each farm.

Fig 2

GPS coordinates were recorded for environmental samples collected on farm 7. The positions of the samples were mapped onto a diagram of the farm and color coded to indicate the number of genome equivalents of C. burnetii detected in the samples by quantitative PCR. Samples from the house and the truck were vacuum samples, and all others were bulk samples.

Fig 3

Environmental bulk, sponge, and vacuum samples were collected on farm 5 in June 2011 and May 2012. Air samples were collected in May 2012. Genomic DNA was extracted from the samples and tested for the presence of C. burnetii DNA by quantitative PCR. The graph shows the number of genome equivalents per gram for each positive bulk and vacuum sample, the number of genome equivalents per sponge for each sponge sample, and the number of genome equivalents per 500 liters for the air samples.

Fig 4

GPS coordinates were recorded for the bulk, sponge, and vacuum samples collected on farm 5 in June 2011 and the bulk, vacuum, and air samples collected in May 2012. The positions of the samples were mapped onto diagrams of the farm and color coded to indicate the number of genome equivalents of C. burnetii detected in the samples by quantitative PCR. For the bulk and vacuum samples, the numbers of GE/gram are reported, for the sponge samples, the numbers of GE/sponge are reported, and for air samples, the numbers of GE/500 liters are reported. Three vacuum samples were taken from the house, four sponge samples were taken from goat pens, and all other samples were bulk.