Epizootiological investigation of a Q fever outbreak and implications for future control strategies.

OBJECTIVE: To describe the epizootiological investigation of an outbreak of Q fever (Coxiella burnetii infection). DESIGN: Epidemiological study. ANIMALS: 17 goat herds in Washington, Montana, and Oregon. PROCEDURES: In April 2011, an abortion storm at a commercial goat farm in Washington was determined to be caused by C burnetii. A joint epidemiological investigation by public health and veterinary professionals was subsequently performed to assess the extent of the outbreak by performing a trace-forward of goats sold from the index farm, to determine risk factors associated with infection, and to implement control measures. A herd management plan was developed to control the outbreak and reduce risk of human exposure. Quarantine and temporary holds preventing the sale or movement of goats allowed time for trace-forward investigation, education of farmers regarding disease risk, and testing to determine the scope of the outbreak. RESULTS: 17 farms were affected; 21 human Q fever cases were identified. Bacterial shedding in feces, vaginal fluid, or milk was confirmed in 156 of 629 (25%) goats tested by PCR assay. Seroprevalence of antibodies against C burnetii in goats, determined by ELISA, was 12%. The risk for C burnetii infection in goats was highest among females, those on farms associated with human Q fever, and those on Washington farms. A protective effect was observed for goats at farms where the primary form of goat carcass disposal was burial. CONCLUSIONS AND CLINICAL RELEVANCE: This outbreak illustrated the importance of a joint investigation for zoonotic pathogens and the need to expand and strengthen relationships between medical, public health, and veterinary partners. Heightened awareness and enhanced veterinary diagnostic capabilities for C burnetii are needed to identify and control outbreaks expediently.

Coxiella burnetii serology assays in goat abortion storm.

Many commercial antibody detection enzyme-linked immunosorbent assay (ELISA) kits for Q fever utilize the Nine Mile (Montana tick) strain of Coxiella burnetii as antigen. An ELISA kit manufactured in France employs ovine placenta-sourced antigen and has been used in Europe. Sera from goats experiencing a Q fever abortion storm in the United States were used to compare the sensitivity and specificity of these 2 ELISA formats and the Q fever complement fixation test (CFT). Latent class estimates of sensitivity ranged from 97% to 100% with a specificity of 95-100% for the 2 ELISA kits. Estimates for sensitivity and specificity of the CFT were 89% and 82%, respectively. There was not a significant increase in ELISA sensitivity observed with the ovine-sourced antigen kit in this study. Real-time polymerase chain reactions performed on a portion of the sera found that 15 out of 20 sera were congruent across 4 tests for positive and negative sera.

Comparison of Q fever serology methods in cattle, goats, and sheep.

Coxiella burnetii is an obligate intracellular bacterium that is responsible for the zoonotic disease Q fever. The distribution of this agent is worldwide except for New Zealand, and infection can be asymptomatic in both human beings and animals. Chronic exposures can produce abortions, stillbirths, and infertility issues in animals and endocarditis in human beings. A commercial enzyme-linked immunosorbent assay (ELISA) kit marketed in the European Union was purchased to compare C. burnetii antibody detection methods. The current study examined the agreement of ELISA and complement fixation results in over 668 diagnostic ruminant sera submitted to the National Veterinary Services Laboratories for Q fever serologic testing. The majority of combined sera (548) were negative on both tests. Fifty-seven of the combined sera were positive on both tests. There were 45 combined sera with low complement fixation titers at 1:10 and negative ELISA results. The results were surprising given the expectations that ELISA methods, by nature, amplify detection of antibody-antigen interactions leading to higher sensitivity. Potential mechanisms for these discrepant results are discussed.