First reported multistate human Q fever outbreak in the United States, 2011.

In April, 2011, the Q fever bacterium Coxiella burnetii was identified at a Washington farm where an abortion storm took place among goats. Soon after, Q fever cases were reported among visitors to the farm from Washington and Montana. A cross-sectional investigation was conducted among humans and goats associated with the index farm or with 16 other farms that purchased goats from the index farm or housed goats at the index farm for breeding purposes. Questionnaire data were analyzed, along with human and goat specimens collected for evidence of C. burnetii infection. Twenty-one persons (19%) of the 109-person cohort from Washington and Montana met the outbreak case definition of an epidemiologic link to the index farm and a C. burnetii Phase II immunoglobulin G (IgG) titer >= 1:128 by immunofluorescence assay. Seventy-one percent of cases (15 of 21) were symptomatic, compared with approximately 50% during previous Q fever outbreaks. National Q fever surveillance reports increase in frequency with age, but 29% (6 of 21) of cases during this outbreak occurred in children aged <14 years. Goat-specific Q fever risk factors included direct contact with a newborn (prevalence ratio [PR] 10.7; confidence interval [CI] 1.5, 77.4), exposure to a newborn that died (PR 5.5; CI 1.7, 18.2), exposure to a weak newborn (PR 4.4; CI 1.7, 11.6), living on a property with goats (PR 4.2; CI 1.3, 13.9), and direct contact with birth/afterbirth products (PR 2.8; CI 1.1, 6.9). Evidence of C. burnetii infection was detected in all 17 goat herds sampled (13 Washington, 3 Montana, 1 Oregon) by PCR and/or enzyme-linked immunosorbent assay. Following this investigation, Washington and Montana implemented a herd management plan to encourage best-management practices among livestock owners, reduce the potential for future outbreaks, and promote continued communication between state public health and agricultural authorities.