Q fever, also called query fever, is a bacterial infection caused by the bacteria Coxiella burnetii. The bacteria are most commonly found in cattle, sheep, and goats around the world. Humans typically get Q fever when they breathe in dust that was contaminated by infected animals. Farmers, veterinarians, and people who work with these animals in labs are at the highest risk of being infected. The highest amounts of bacteria are found in the "birth products" (placenta, amniotic fluid) of infected animals.
The disease may cause mild symptoms similar to the flu. However, many people have no symptoms at all. Mild forms of the disease may clear up in a few weeks without any treatment.
In rare cases, a more serious form of disease develops if the infection is chronic, which means it persists for six months (and there are some case reports indicating that it may persist for more than six months). A more serious form also can develop if the infection is recurrent, which means it comes back. People with heart valve problems or weak immune systems are at the highest risk of developing these types of Q fever. Chronic Q fever is very serious because it can damage a person’s vital organs, including the:
More severe or chronic forms of Q fever can be treated with antibiotics. Those at risk for Q fever can prevent the disease by disinfecting contaminated areas and washing their hands thoroughly.
Symptoms of Q fever don’t typically appear until about two to three weeks after exposure to the bacteria. However, it’s possible that you will have the infection and not show any symptoms. If symptoms do appear, they’re generally mild.
Symptoms can vary significantly from one person to another. Common symptoms of mild Q fever may include:
- a high fever
- chills or sweats
- a cough
- chest pain while breathing
- a headache
- clay-colored stools
- abdominal pain
- muscle pain
- shortness of breath
A rash is also a symptom, but it’s not common.
Q fever is caused by a bacterial infection with a bacterium called Coxiella burnetii. The bacteria are typically found in cattle, sheep, and goats. The animals transmit the bacteria in:
- fluids from giving birth
These substances can dry inside a barnyard where contaminated dust can float in the air. Humans get Q fever when they breathe in the contaminated air.
In rare cases, drinking unpasteurized milk can cause infection. The bacteria cannot be spread directly from one human to another. The exact frequency of Q fever isn’t known because most cases aren’t reported.
Since the bacteria usually infect cattle, sheep, and goats, people who are at highest risk for infection include:
- people who work around sheep
- people who work in the dairy industry
- people who work in a meat processing facilities
- people who work in research laboratories with livestock
- people who work in research laboratories with C. burnetii
- people who live close to a farm
It’s difficult for a doctor to diagnose Q fever based on symptoms alone.
Your doctor may suspect you have Q fever if you work or live in an environment that puts you at high risk for exposure and you have any of the flu-like symptoms or serious complications of Q fever. Your doctor might ask you questions about your job or if you’ve recently been exposed to barnyard or farm animals.
Q fever is diagnosed with a blood antibody test. According to the Centers for Disease Control (CDC), an antibody test frequently appears negative in the first seven to 10 days of sickness. Your doctor should use their best judgment to decide whether or not to begin treatment based on suspicion alone.
If your doctor suspects you have a chronic infection, they may order a chest X-ray and other tests to look at your lungs and a test called an echocardiogram to look at your heart valves.
Sometimes Q fever can persist or come back. This can lead to more serious complications if the infection affects your:
You’re at high risk of developing chronic Q fever if you:
- have an existing heart valve disease
- have blood vessel abnormalities
- have a weakened immune system
- are pregnant
According to the CDC, chronic Q fever occurs in less than 5 percent of infected patients. The most common and serious complication of Q fever is a heart condition called bacterial endocarditis. Endocarditis is the inflammation of the inside lining of the heart chambers and heart valves, which is called the endocardium. This can cause damage to your heart valves and may be fatal if it isn’t treated.
Other serious complications are less common. They include:
- pneumonia or other lung issues
- pregnancy problems, such as miscarriage, low birth weight, premature birth, and stillbirth
- hepatitis, which is an inflammation of the liver
- meningitis, which is an inflammation of the membrane around your brain or spinal cord
Treatment depends on the severity of symptoms.
The milder forms of Q fever usually resolve within a few weeks without any treatment at all.
More Severe Infection
Your doctor will prescribe an antibiotic. Doxycycline is the antibiotic of choice for all adults and children with severe Q fever. You should begin taking it immediately if Q fever is suspected to be the cause of your illness, even before laboratory results are available.
Standard duration of treatment is two to three weeks. The symptoms, including fever, should subside within 72 hours. Failure to respond to doxycycline may suggest that the illness isn’t Q fever.
Antibiotics are typically given for 18 months if you have chronic Q fever.
Antibiotics are usually very effective, and fatality from the disease is very uncommon. People with endocarditis, however, need an early diagnosis and antibiotics for at least 18 months for a successful outcome.
A vaccine has been successful in Australia for people who work in high-risk environments, but it isn’t currently available in the United States.
If you’re at high risk for Q fever and you aren’t vaccinated, you should take the following preventive steps:
- Properly disinfect and decontaminate exposed areas.
- Properly dispose of all birth materials after a livestock animal has given birth.
- Wash your hands properly.
- Quarantine infected animals.
- Make sure the milk you drink is pasteurized.
- Test animals routinely for infection.
- Restrict the airflow from barnyards and animal holding facilities to other areas.