Q fever is caused by Coxiella burnetii, which is excreted in the urine, milk, feces, and amniotic fluid and placenta of infected animals. Excreted fluid or waste contaminates barnyard dust, which may then be inhaled by humans. Once ingested, the microorganism proliferates in macrophages (in the acidic phagolysosome vacuole) and then gains access to the blood, producing a transient bacteremia. It may invade many organs, most commonly the lungs and liver. Inflammation occurs, manifested by granulomas in the liver, spleen, and bone marrow. These classic doughnut-shaped granulomas disappear with convalescence. Risk factors include prolonged or frequent exposure to animals, immune-compromised conditions, or a history of heart valve abnormality.

Complications of Q fever include heart failure, endocarditis, pneumonia, and hepatitis. Chronic fatigue syndrome may occur 6 months after acquiring the infection.

The patient with Q fever will have a history of exposure to cattle, sheep, or goats; exposure may be indirect via barnyard dust. The incubation period is 2 to 6 weeks after exposure.

For acute Q fever, complaints include headache, myalgia, chills, and fever. Lung auscultation may reveal crackles, which may indicate pneumonia. The patient may have a dry cough. Hepatomegaly and jaundice may be present if the liver is affected. Erythema nodosum may also occur.