Seroprevalence of Coxiella burnetii in Washington State domestic goat herds.

A caprine herd seroprevalence of Coxiella burnetii infection was determined by passive surveillance of domestic goat herds in Washington State. Serum samples (n=1794) from 105 herds in 31 counties were analyzed for C. burnetii antibodies using a commercially available Q fever antibody enzyme-linked immunosorbent assay (ELISA) test kit. The sera were submitted to the Washington Animal Disease Diagnostic Laboratory for routine serologic screening over an approximate 1-year period from November, 2010, through November, 2011. To avoid bias introduced by testing samples from ill animals, only accessions for routine screening of nonclinical animals were included in the study. A standard cluster sampling approach to investigate seroprevalence at the herd level was used to determine optimal study sample size. The results identified C. burnetii antibodies in 8.0% of samples tested (144/1794), 8.6% of goat herds tested (9/105), and 25.8% of counties tested (8/31). Within-herd seroprevalence in positive counties ranged from 2.9% to 75.8%. Counties with seropositive goats were represented in the western, eastern, southeastern, and Columbia basin agricultural districts of the state. To our knowledge this is the first county-specific, statewide study of C. burnetii seroprevalence in Washington State goat herds. The findings provide baseline information for future epidemiologic, herd management and public health investigations of Q fever.