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 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 persists for six months or more (chronic) or comes back (recurrent). 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 heart, liver, brain, and lungs.
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.
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 their urine, feces, milk, and fluids from giving birth. These fluids 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 human to human. The exact frequency of Q fever is not known, since most cases are unreported.
Since the bacteria usually infect cattle, sheep, and goats, people who are at highest risk for infection include:
- sheep and dairy workers
- people who work in a meat processing facility
- people who work in research laboratories with livestock
- people who work in research laboratories with Coxiella burnetii
- people who live close to a farm
Symptoms of Q fever do not typically appear until about two to three weeks after exposure to the bacteria. However, according to the Centers for Disease Control and Prevention, up to half of humans infected with the bacteria do not show symptoms at all (CDC). If symptoms do appear, they are generally mild.
Symptoms can vary significantly from person to person. More common symptoms of mild Q fever may include:
- high fever
- chills and/or sweats
- chest pain while breathing
- clay-colored stools or diarrhea
- abdominal pain
- muscle pain
- shortness of breath
Uncommon symptoms include rash.
Sometimes Q fever can persist or come back. This can lead to more serious complications if the infection affects your heart, liver, lungs, and brain.
You are 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 five percent of infected patients. The most common and most serious complication is a heart condition called endocarditis. Endocarditis is the inflammation of the inside lining of the heart chambers and heart valves (endocardium). This can cause damage to your heart valves and may be fatal.
The CDC estimates that the proportion of untreated patients who die due to endocarditis is 25 to 60 percent. The overall proportion of people who die due to Q fever is very low. In hospitalized patients, the percentage of patients who die because of their infection is less than two percent(CDC).
Other less common, but still serious, complications include:
- pneumonia or other lung issues
- pregnancy problems (such as miscarriage, low birth weight, premature birth, and stillbirth)
- hepatitis (inflammation of the liver)
- meningitis (inflammation of the membrane around your brain or spinal cord)
It is difficult for a doctor to diagnose Q fever based on symptoms alone.
A doctor may suspect Q fever in a patient who works and/or lives in an environment that puts him or her at high risk for exposure and shows any of the flu-like symptoms or serious complications of Q fever. A doctor might ask you questions about your occupation or if you’ve recently been exposed to barnyard or farm animals.
Q fever is diagnosed with a blood antibody test. According to the CDC, an antibody test frequently appears negative in the first seven to 10 days of sickness. Your doctor should use his or her best judgment to decide whether or not to begin treatment based on suspicion alone.
If your doctor suspects chronic infection, he or she may order other tests, including a chest X-ray to look at your lungs and a test called an echocardiogram to look at your heart valves.
Treatment depends on the severity of symptoms.
The milder forms of Q fever usually resolve within a few weeks without any treatment at all (Mayo Clinic).
More Severe Infection
Your doctor will prescribe an antibiotic. Doxycycline is the antibiotic of choice for all adults and children with severe illness and should begin 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. Symptoms, including fever, should subside within 72 hours. Failure to respond to doxycycline may suggest that the illness is not Q fever.
Antibiotics are typically given for 18 months.
A vaccine has been successful in Australia for people who work in high-risk environments, but it is not yet available in the United States.
In high-risk people who are not vaccinated, the following precautions should be taken to prevent the disease:
- properly disinfecting and decontaminating exposed areas
- disposing properly of all birth materials after a livestock animal has given birth
- properly washing hands
- quarantining infected animals
- drinking only pasteurized milk
- testing animals routinely for infection
- using measures to restrict airflow from barnyards and animal holding facilities to other areas
The prognosis with antibiotics is generally very good, and fatality from the disease overall is very low. Patients with endocarditis, however, need an early diagnosis and antibiotics for at least 18 months for a successful outcome.