Definition of Q fever:

Q fever is an infection caused by the bacteria Coxiella burnetii, which can affect the lungs, liver, heart, and other parts of the body.

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 from exposure to the 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 usually goes away on its own, lasts up to 3 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 outcome of Q fever. 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 sign is infection of the heart valves termed endocarditis.Other less common features of chronic Q fever are cirrhosis and lung scarring (interstitial pulmonary fibrosis).

Individuals at highest risk include those with underlying heart valve problems, as well as people with weakened immune systems.