Q fever, also known as Balkan grippe and nine mile fever, is a zoonotic disease caused by the rickettsia-like organism Coxiella burnetii. The distribution is worldwide, but Q fever is more prevalent in Africa, Australia, the Middle East, and Central America.

Cattle, sheep, and goats are the main reservoirs, and transmission to humans typically occurs by direct contact with the body fluids of infected animals and with inhalation of C burnetii in aerosolized body fluids and contaminated dust. Ingestion of contaminated milk or meat is a less common mode of transmission, as are tick bites.

Coxiella burnetii is resistant to heat, drying, and common disinfectants. In a bioterrorism attack, the most likely method of dispersal would be an aerosolized release. Q fever has been designated by the CDC as a Category B bioterrorism agent.

Very few organisms are required to cause illness. The incubation period of Q fever depends on the number of organisms in the exposure, although 2-3 weeks is typical. It may be as short as 5 days following a massive exposure, as might be the case in a bioterrorism attack.

Initial symptoms of Q fever include high fever, chills, headache, malaise, myalgia, confusion, sore throat, sweats, nausea, vomiting, diarrhea, and abdominal pain. Pneumonia with nonproductive cough, chest pain, and rales may occur in 30%-50% of cases after 4-5 days. Fever can persist for up to 2 weeks. Hepatitis may occur in some cases. The overall mortality rate is 1%-2%.

Chronic disease may develop and persist for more than 6 months. The chronic form can occur up to 20 years after initial infection. The disease may progress to endocarditis or aseptic meningitis. In some individuals, Q fever can affect the kidneys, thyroid, or genitals.

The prevalence of Q fever is unclear; half of those infected remain asymptomatic. Person-to-person transmission is not known to occur. Infection results in lifelong immunity.