et al. 2004) or through fomites, such as contaminated straw used in industrial packaging (van Woerden et al. 2004). For example, the largest outbreak of Q fever ever reported in the UK occurred in 1989 in large, metropolitan Birmingham (West Midlands) probably as a consequence of the windborne spread of C. burnetii spores from farms outside the city (Hawker et al. 1998; Smith et al. 1993).
Less common routes of C. burnetii transmission include the ingestion of infectious raw milk, direct inoculation with contaminated material, and tick bites. Even rarer are reports of transmission within households, through sexual contact, and through blood transfusion (Milazzo et al. 2001).
Most countries have reported C. burnetii infections (Wilson 1991). Q fever is widespread in Iran, Afghanistan, and Pakistan and is common in the Arabian Peninsula and Syria (Wilson 1991). Studies conducted in Turkey and Oman have demonstrated that 8-12% of the adult populations of those countries have been exposed to the organism, and rates are higher among those who work with animals (Cetinkaya et al. 2000; Scrimgeour et al. 2003). Several clinical reports document the frequency of Q fever among Israelis; one study found that almost 6% of 346 patients who has a diagnosis of community-acquired pneumonia had laboratory evidence consistent with C. burnetii infection (Oren et al. 2005; Siegman-Igra et al. 1997).
Acute Q fever occurs within 10-17 days after exposure to contaminated aerosols. Patients most frequently present with pneumonia, hepatitis, or a self-limited, influenza-like febrile illness. The clinical presentation of Q fever appears to vary geographically; for instance, C. burnetii-induced pneumonia is more common in eastern Canada, and C. burnetii-induced hepatitis predominates in Spain. The acute phase usually lasts 1-3 weeks and resolves without specific therapy or adverse health outcomes.
The symptoms of Q fever pneumonia include prominent headache, cough, pleuritic chest pain, and fever (Tissot-Dupont et al. 1992). Radiographic findings can vary widely, although nonsegmental and segmental pleural-based opacities are a common feature. Chest films of patients who have been exposed to parturient cats often show multiple rounded opacities (Gordon et al. 1984). Although some patients with Q fever pneumonia develop acute respiratory distress syndrome, the vast majority of patients’ symptoms resolve without adverse health outcomes.
Q fever hepatitis is characterized by mildly increased transaminases, thrombocytopenia, and frequent autoantibodies. Liver biopsy often reveals a highly specific histology known as a doughnut granuloma (Travis et al. 1986).