Definition
An infection caused by the bacteria Coxiella burnetii , which can cause pneumonia and hepatitis (liver inflammation) in its early stages, and infection of the heart valves (endocarditis) if the condition becomes chronic (persisting over time).

Alternative Names
Query fever

Causes, incidence, and risk factors

Q fever is found around the world and is caused by the bacteria Coxiella burnetii. The bacteria affects sheep, goats, cattle, dogs, cats, birds, rodents and ticks, as well as some other animals. Infected animals shed this bacteria in urine, feces, birth products and milk.

Humans usually acquire Q fever by inhaling contaminated droplets excreted by infected animals. Consumption of raw milk has also been associated with infection in rare cases. People at highest risk for this infection are veterinarians, farmers, sheep and dairy workers, as well as laboratory workers who work with this organism.

The incubation period (time to development of symptoms) for early (acute) Q fever is approximately 20 days. In acute Q fever, the three main sets of symptoms include flu-like syndrome, pneumonia and hepatitis. Flu-like syndrome is usually self- limited; lasts up to three weeks; and may involve high fevers, headaches and muscle aches.

Pneumonia can occur in up to a third of individuals. Most cases are relatively mild and include fever and cough, yet some severe cases have been reported. Hepatitis is another common consequence of Q Fever, and it can occur alone or with concurrent pneumonia. Other less common features of acute Q fever include rashes, meningitis, myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of heart lining).

Chronic Q fever develops in individuals who have been infected for over 6 months without effective treatment. Its main feature is infection of the heart valves termed endocarditis. Individuals at highest risk include those with underlying heart valve abnormalities, as well as people with weakened immune systems. Other less common features of chronic Q fever are infection of aneurysms, liver dysfunction (cirrhosis) and lung scarring (interstitial pulmonary fibrosis).

Prevention
People at risk (e.g., farmers, veterinarians) should adhere to adequate disinfection and disposal of potentially infectious animal products. Pasteurization of milk can also help prevent Q fever. Prompt treatment can prevent early Q fever from becoming chronic.

Symptoms

Acute Q fever:

flu-like: fever, headache, muscle pains
pneumonia: fever, cough, chest pain upon breathing, shortness of breath
hepatitis: jaundice, clay colored stools, fever
Chronic Q fever: prolonged fever, night sweats, chills, fatigue, shortness of breath.

Signs and tests
The diagnosis of Q fever should be suspected in individuals with appropriate exposure histories who develop flu-like symptoms, pneumonia, hepatitis, or endocarditis. The mainstay for diagnosis of Q fever is a blood antibody test (serology) -- as it is very difficult to grow the causative bacteria in culture.