ncubation period is usually two to three weeks.^[8] The most common manifestation is mild flu-like symptoms with abrupt onset of fever, malaise, profuse perspiration, severe headache, myalgia (muscle pain), joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion and gastrointestinal symptoms, such as nausea, vomiting and diarrhea. The fever lasts approximately seven to 14 days.^{[citation needed]}

Approximately half of infected individuals exhibit no symptoms.^[8]

During the course, the disease can progress to an atypical pneumonia, which can result in a life-threatening acute respiratory distress syndrome (ARDS), whereby such symptoms usually occur during the first four to five days of infection.^{[citation needed]}

Less often, Q fever causes (granulomatous) hepatitis, which may be asymptomatic or becomes symptomatic with malaise, fever, liver enlargement (hepatomegaly) and pain in the right upper quadrant of the abdomen. Whereas transaminase values are often elevated, jaundice is uncommon. Retinal vasculitis is a rare manifestation of Q fever.^[9]

The chronic form of Q fever is virtually identical to inflammation of the inner lining of the heart (endocarditis),^[10] which can occur months or decades following the infection. It is usually fatal if untreated. However, with appropriate treatment, the mortality falls to around 10%.