Chronic Q fever delivered through ticks, may manifest within a few weeks to many years after the initial infection. Hepatitis may manifest as fever of unknown origin. Liver biopsy may show granulomas, which should be differentiated from other causes of liver granulomas (eg, TB, sarcoidosis, histoplasmosis, brucellosis, tularemia, syphilis).

Endocarditis resembles viridans group subacute bacterial endocarditis; the aortic valve is most commonly affected, but vegetations may occur on any valve. Marked finger clubbing, arterial emboli, hepatomegaly, splenomegaly, and a purpuric rash may occur.

The case-fatality rate is only about 1% in untreated patients but is higher in those with endocarditis. Some patients with neurologic involvement have residual impairment.

The incubation period averages 18 to 21 days (range 9 to 28 days). Acute Q fever is often asymptomatic; in other patients, it begins abruptly with influenza-like symptoms: fever, severe headache, chills, severe malaise, myalgia, anorexia, and sweats. Fever may rise to 40° C and persist 1 to > 3 weeks.

Rarely, acute Q fever manifests as encephalitis or meningoencephalitis.

Respiratory symptoms (a dry nonproductive cough, pleuritic chest pain) appear 4 to 5 days after onset of illness. These symptoms may be particularly severe in elderly or debilitated patients. During examination, lung crackles are commonly noted, and findings suggesting consolidation may be present. Unlike rickettsial diseases, acute Q fever does not cause a rash.