The aim of this study is to describe a Q fever outbreak that affected the staff of a machine-tool factory in the Basque Country between 2009/12/20 and 2010/02/23. Study subjects were interviewed using a Q fever specific questionnaire and tested for Q fever serology (immunofluorescence assay with phase II antigen) and detecting Coxiella burnetii DNA using real-time PCR. We interviewed and tested 40 employees (90% of the staff). 33 employees, all of them men, had positive serology (attack rate 82.5%, 95% CI: 70.2–94.8). Mean age was 43.7 years (95% CI: 38.7–48.7) in positive men, 33.7 years (95% CI: ？16.6–83.9) in negative men, and 36.25 (95% CI: 27.5–45.0) in women (all negatives). 15 cases (45.5%) were asymptomatic, 9 (27.3%) had flu-like symptoms, and the other 9 (27.3%) had developed radiologically confirmed pneumonia. We obtained 28 blood samples, 22 faeces samples, 11 milk samples, and one vaginal swab from 28 goats resting in a stable near the factory. Serology was positive in 18 goats (64.3%). All environmental samples were negative. 1. Introduction and Background Q fever is a ubiquitous zoonosis caused by Coxiella burnetii, an obligate intracellular coccobacillus, whose incubation period varies from two to six weeks, depending on the infective dose and host. Most cases are asymptomatic (60%) or have mild flu-like symptoms. Only 20% of infected patients seek medical attention, 2 to 3% are admitted to a hospital and the case fatality ratio is 1 to 2% [1, 2]. Symptomatic patients present with a sudden onset of high fever, chills, severe headache, and dyspnoea. In some patients, the clinical course is complicated by pericarditis, myocarditis, pancreatitis, or haemolytic anaemia. A small proportion of infected patients develop chronic Q fever. Endocarditis is the most frequent complication, about 1% of patients, following Q fever. The most important reservoir are sheep, goats, and cattle. Domestic animals such as dogs, cats, rabbits, and birds can also carry the disease. Ticks are thought to spread the disease among animals. Infected animals excrete the bacteria in milk, faeces, urine, and in high concentrations in amniotic fluid and the placenta. The animals are often asymptomatic except for increased incidence of spontaneous abortion. Infection in humans occurs through inhalation of contaminated aerosols or ingestion of unpasteurised milk. C. burnetii is resistant to chemical and physical disinfectants. A small inoculums is sufficient to cause clinical illness. Human-to-human transmission does not usually occur, although it has been described
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