The gram-negative intracellular bacterium Coxiella burnetii .
Most commonly through inhalation of aerosols or dust contaminated with dried birth fluids or excreta from infected animals (usually cattle, sheep, or goats). C. burnetii is highly infectious and persists in the environment. Infections via ingestion of contaminated, unpasteurized dairy products and human-to-human transmission via sexual contact have been rarely reported.
Distributed worldwide; the prevalence is highest in African and Middle Eastern countries. Reported rates of human infection are higher in France and Australia than in the United States. The largest known Q fever outbreak reported to date involved approximately 4,000 human cases and occurred during 2007–2010 in the Netherlands. Travelers who visit rural areas or farms with cattle, sheep, goats, or other livestock may be exposed to Q fever. Occupational exposure to infected animals (such as in farmers, veterinarians, butchers, meat packers, and seasonal or migrant farm workers), particularly during parturition, poses a high risk for disease transmission.
It is estimated that more than half of acute infections are mild or asymptomatic. Incubation period is typically 2–3 weeks but may be shorter after exposure to large numbers of organisms. The most common presentation of acute infection is a self-limiting influenzalike illness, with pneumonia or hepatitis in more severe acute infections. Chronic infections occur primarily in patients with preexisting cardiac valvulopathies, vascular abnormalities, or immunosuppression. Women infected during pregnancy are at risk for adverse pregnancy outcomes unless treated. The most common manifestations of chronic disease are endocarditis and endovascular infections.
Serologic evidence of a 4-fold rise in phase II IgG by indirect fluorescent antibody test between paired sera taken 3–4 weeks apart is the gold standard for diagnosis of acute infection. A single high serum phase II IgG titer (>1:128) in conjunction with clinical evidence of infection may be considered evidence of probable Q fever. PCR assays may be used on whole blood or serum samples in the early stages of illness and before initiation of antibiotic therapy. C. burnetii may be detected in infected tissues by using immunohistochemical staining or DNA detection methods or by direct isolation of the agent via culture. Q fever is a nationally notifiable disease.
Doxycycline is the treatment of choice for acute Q fever. Pregnant women, children aged <8 years with mild illness, and patients allergic to doxycycline may be treated with alternative antibiotics such as trimethoprim-sulfamethoxazole. Treatment for acute Q fever is not recommended for asymptomatic people or for those whose symptoms have resolved. Chronic C. burnetii infections require long-term combination therapy with agents such as doxycycline, hydroxychloroquine, trimethoprim-sulfamethoxazole, fluoroquinolones, and rifampin.
Avoid areas where potentially infected animals are kept, and avoid consumption of unpasteurized dairy products. A human vaccine for Q fever has been developed and used in Australia, but it is not available in the United States.
CDC website: www.cdc.gov/qfever
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Gilbert J. Kersh