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Q Fever

By William A. Petri, Jr, MD, PhD

Q fever is related to rickettsial diseases and is caused by Coxiella burnetii.

  • Some people have mild symptoms, but most have flu-like symptoms, such as a fever, a severe headache, chills, extreme weakness, and muscle aches.

  • A few people develop chronic Q fever, a severe disease that can affect the heart.

  • If people have typical symptoms and may have been exposed to sheep, cattle, or goats, doctors suspect Q fever and may do blood tests and examine a sample of infected tissue to confirm the infection.

  • People with Q fever are treated with an antibiotic, usually for a few weeks, but if chronic Q fever develops, treatment is needed for months or years.

Rickettsiae are a type of bacteria that can live only inside the cells of other organisms (see also Overview of Rickettsial Infections).

Q fever occurs worldwide. The bacteria that cause Q fever live mainly in sheep, cattle, and goats. Infected animals shed the bacteria in their milk, urine, and stool (feces). People are infected when they inhale airborne droplets containing the bacteria or consume contaminated raw milk. Very rarely, the disease is transmitted from person to person.

People at risk of developing Q fever include the following:

  • Veterinarians

  • Meat processing plant workers

  • Slaughterhouse and dairy workers

  • Livestock farmers

  • Researchers at laboratories where sheep are kept

  • People who live within several miles downwind from a farm with infected animals


About 9 to 28 days after bacteria enter the body, symptoms begin suddenly. Some people have mild symptoms, but most have flu-like symptoms. Symptoms include fever, a severe headache, chills, extreme weakness, muscle aches, loss of appetite, and sweating, but no rash. The lungs are often affected, causing an unproductive cough, chest pain, and shortness of breath (caused by pneumonia). Symptoms may be severe in older people and in people who have been weakened (debilitated) by a disorder.

Occasionally, the liver is involved. People then have pain in the upper right part of the abdomen and sometimes jaundice.

Women who are infected during pregnancy have an increased risk of a miscarriage or delivery before the baby is due.

Chronic Q fever is a severe disease that occurs in fewer than 5% of infected people. The risk is greatest for the following:

  • Pregnant women

  • People whose immune system has been weakened by a disorder or drugs

  • People who have a heart valve disorder

In about 60 to 70% of people with chronic Q fever, the lining of the heart and usually the heart valves are infected (called Q fever endocarditis).

Without treatment, only 1% of people with Q fever die, but death is more likely if the heart is affected.


  • Blood tests and biopsy of infected tissue

  • Sometimes a chest x-ray

Symptoms of Q fever resemble those of other disorders and thus do not help doctors with the diagnosis. If doctors suspect Q fever, they ask whether people were at or near a farm because the bacteria that cause Q fever live mainly in cattle, sheep, and goats.

Doctors may do blood tests that detect antibodies to the bacteria. But these test cannot detect the antibodies until at least several days after the illness begins. Thus, these tests do not help doctors diagnose the infection immediately after someone becomes ill but can help confirm the diagnosis.

To confirm the diagnosis, doctors may do an immunofluorescence assay or use the polymerase chain reaction (PCR) technique.

If people have a cough or other respiratory symptoms, doctors take a chest x-ray.


Measures to prevent Q fever involve mainly using appropriate sanitation and testing (for the bacteria) in facilities where sheep, cattle, and goats are kept. Consuming only pasteurized milk and milk products can also help.

In Australia, a vaccine is available and has been used to prevent the infection in people likely to be exposed (such as slaughterhouse and dairy workers, livestock farmers, and laboratory workers).This vaccine is not available in the United States.

Before giving people the vaccine, doctors do blood and skin tests to determine whether people already have immunity to Q fever. If people already have immunity, vaccinating them can cause severe reactions near the injection site.


  • Antibiotics

The initial infection is treated with the antibiotic doxycycline, taken by mouth. People take the antibiotic until they improve and have had no fever for about 5 days, but they must take it for at least 7 days. Typically, 2 to 3 weeks of treatment is required.

If the heart is affected, treatment is given for months to years. Typically, treatment is given for at least 18 months, but some people need to be treated their entire life. People are usually given doxycycline plus hydroxychloroquine. Both are taken by mouth. To determine when treatment can be stopped, doctors periodically examine the person and do blood tests.

For Q fever endocarditis, antibiotic treatment is often only partially effective, and surgery is needed to replace the damaged heart valves (see Figure: Replacing a Heart Valve).

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