An Overview of Q Fever

An Uncommon Bacterial Infection

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Q fever is an uncommon bacterial infection which may be acute or chronic. It was first identified in Australia in 1937. The "Q" in Q Fever stands for "query," as it was not initially known what caused the fever. The infection is typically spread to humans from animals, most often livestock. People who work closely with animals, such as farmers and veterinarians, may be more at risk of acquiring it.

Acute Q fever symptoms
Illustration by Emily Roberts, Verywell

Symptoms

Almost half of the people who acquire Q fever won't show symptoms (this is called asymptomatic). When a person does feel sick, they usually experience mild, flu-like symptoms. Most people who develop acute Q fever will get better even if they don't go to the doctor. However, in rare cases, people develop chronic Q fever. This is a more serious form of the infection.

The symptoms of Q fever will vary in severity depending on whether the infection is acute or chronic. How the disease presents is also different depending on where a person lives. For example, in the United States, a person with Q fever typically presents with pneumonia. In Europe, Q fever tends to manifest in the liver, often presenting as hepatitis.

If a person with Q fever develops pneumonia it is usually mild. However, some people may develop a more serious condition called acute respiratory distress syndrome (ARDS). Rarely, a person who has contracted Q fever may have neurological symptoms such as inflammation of the membrane covering the brain and spinal cord (meningoencephalitis). In some cases, Q fever causes inflammation in the sac around the heart (pericarditis) or the heart muscle itself (myocarditis).

People with Q fever typically develop respiratory symptoms within the first five days, including:

  • a dry (nonproductive) cough.
  • chest pain.
  • sore throat.
  • trouble breathing.

Acute Q Fever

Symptoms of acute Q fever usually develop within two to three weeks after a person is exposed, but it may take as long as six weeks. The onset of symptoms can be quite abrupt and a person may think they are coming down with the flu (influenza) or a bad cold.

Symptoms of Acute Q Fever

  • Headache
  • Fatigue, malaise, and muscle aches
  • High fever (may be over 105 degrees Fahrenheit)
  • Chills and/or sweating
  • Loss of appetite
  • Abdominal pain, nausea, vomiting
  • Diarrhea

After a person has acute Q fever, they may also develop a set of symptoms called post Q fever fatigue syndrome. While it's not known how many people develop the syndrome after getting sick with Q fever, approximately 20 percent of patients report having recurring fatigue, fevers, muscle and joint pain, as well as other symptoms.

People who have preexisting or underlying heart problems or disease may be at higher risk. They are also more at risk for developing chronic Q fever.

Estimates made by the Centers for Disease Control and Prevention (CDC) indicate fewer than 5 percent of patients with acute Q fever go on to develop chronic Q fever.

Chronic Q Fever

The symptoms of chronic Q fever may develop months or years after an acute infection. A person may not remember being exposed or even feeling sick around the time the infection was in the acute phase. However, if it progresses to the chronic stage, Q fever can cause serious illness and complications.

Chronic Q fever almost always presents with inflammation inside the heart or in the valves (infective endocarditis). Some research suggests that chronic Q fever may also contribute to a person's lifetime risk of developing cardiovascular disease. If it goes untreated, endocarditis can be fatal. People with chronic Q fever may also have a host of other symptoms.

Symptoms of Chronic Q Fever

  • Heart failure
  • Fever
  • Fatigue
  • Joint pain
  • Unintended weight loss
  • Shortness of breath and/or trouble breathing
  • Light sweats

In some cases, people with chronic Q fever can develop bone infections (osteomyelitis) or infections in other organ systems, such as the liver and blood vessels.

Causes

Q fever is caused by Coxiella burnetii (C. burnetii) bacterium. C. burnetii is a type of zoonotic bacteria, meaning it is found in animals but can be spread to humans when they come into contact with them. Livestock, such as cattle and sheep, are the most common source (also called a reservoir) for the bacteria, though it has also been found in domestic animals, including dogs and cats.

People who work closely with animals, such as farmers and veterinarians, are more likely to be exposed to Q fever.

Animals can carry the bacteria without getting sick, but they can spread it to humans who are vulnerable to the illness it causes. The bacterium is found in the milk, feces, and urine produced by an animal. If a person is near these fluids and secretions, they may breath in particles containing the bacteria after they are released into the air. In particular, when a pregnant animal gives birth, the bacteria are abundant in placenta and amniotic fluid, both of which are commonly encountered by humans who may be assisting with labor and delivery.

In rare cases, people have contracted Q fever from drinking raw milk or being bitten by a tick found on an animal carrying C. burnetii. 

The bacteria that causes Q fever is extremely hardy. It can survive extreme temperatures, powerful disinfectants, and other environments or measures that would easily kill other types of bacteria. It's also a virulent bacterium, which means that while other pathogens might require a high number of particles to infect humans, it only takes a few C. burnetii bacteria to make humans sick. 

Due to these attributes, the United States had tested C. burnetii as a potential biological warfare agent. The pathogen is still considered a category B bioterrorism agent by the CDC.

Diagnosis

Q fever has been diagnosed in men, women, and children of all racial backgrounds. The C. burnetii organism has been found everywhere in the world except for New Zealand. While it can spread any time of year, it seems to be more common in the spring and early summer. Q fever has primarily been diagnosed in adults; children diagnosed with the infection usually do not have symptoms and are less likely than adults to have severe illness or complications as a result.

Researchers aren't sure exactly how many people in the world have Q fever; it's likely that many people are never diagnosed because they don't have any symptoms. Others have such mild symptoms that they don't seek medical attention, and they get better without treatment.

In 1999, Q fever became a reportable disease in the United States. This means that medical professionals who diagnose a case of the illness are required to report it to the state health department and the CDC. In the first few years after the agency started tracking them, only 50 cases were reported in the United States.

Like many infectious illnesses, a person is more likely to be exposed and become infected if they travel to a part of the world where it is common (endemic). Reported cases of Q fever often occur in people who live, work, or travel in groups, especially members of the military.

The illness seems to be diagnosed more often in men than women, but it's believed that this could be because men may be more likely to be employed in professions that are at risk for exposure (such as working on farms or in slaughterhouses).

Q fever is not very common and many doctors may never see a case throughout their careers. Due to its rarity, even if a patient has symptoms of Q fever, the diagnosis may not be easy to make. After doing a thorough physical exam and talking to a person about their symptoms, a doctor will also take a person's travel and employment history into consideration if they are considering a diagnosis of Q fever.

The tests used to diagnose Q fever don't look for the bacterium, but rather, the presence of antibodies released in response. However, these tests will not be able to detect antibodies until a week or two after a person becomes infected.

If a doctor thinks Q fever is likely based on the patient's symptoms and risk factors, they will usually start treatment before a blood test confirms the diagnosis. Because the pathogen is very infectious, specimens are usually sent to biosafety level 3 safety lab for culture.

Tests a doctor may order to diagnose Q fever include:

  • tests to rule out other causes for a person's symptoms such as tick-borne disease or more common viral or bacterial infections.
  • routine blood tests like a complete blood count (CBC) to check for low red blood cells (anemia) and see if white blood cell levels are abnormally low or high.
  • liver function or kidney function tests.
  • a test called indirect immunofluorescence antibody (IFA) to look for antibodies in tissue.
  • other serologic techniques to confirm the presence of antibodies.
  • a blood sample given when the infection is acute may be tested using a polymerase chain reaction (PCR) assay.
  • other FDA-approved tests may be available at certain hospitals or through the CDC.

If a doctor suspects a person may be at risk for developing complications of Q fever, such as severe pneumonia or endocarditis, they may order other tests or procedures to monitor for them. These tests may also be used months or years later if chronic Q fever is suspected.

Additional tests that may be needed include:

  • transoesophageal echocardiography to diagnose endocarditis.
  • electrocardiography (ECG).
  • chest x-ray.
  • liver function tests or biopsy to diagnose hepatitis.

Medical professionals and laboratories may also send samples to the CDC for testing.

Treatment

If a person has symptoms and a doctor has high clinical suspicion of Q fever, antibiotics will be prescribed even before testing confirms the diagnosis. This is due to the fact that the resulting complications of Q fever can be very serious. People who don't have any symptoms or who are found to have Q fever after they start feeling symptoms usually don't need treatment. However, their doctor may decide to prescribe antibiotics if they believe the person is at risk for developing chronic Q fever or other complications.

The first antibiotic a doctor will prescribe to treat Q fever is doxycycline. The best outcomes occur when patients begin taking antibiotics within the first three days of illness. Patients who are pregnant and cannot take doxycycline may be given another antibiotic commonly known as Bactrim (trimethoprim/sulfamethoxazole), which can be taken up to 32 weeks into pregnancy.

Others who are unable to take doxycycline due to an allergy or other health condition may be prescribed other antibiotics such as Bactrim, moxifloxacin, clarithromycin, rifampin, tetracycline, chloramphenicol, ciprofloxacin, ofloxacin, or hydroxychloroquine. However, doxycycline is considered the first-line treatment for Q fever for both children and adults.

People with acute Q fever who are prescribed antibiotics need to be sure to take the full prescribed course—typically 14 days. People with chronic Q fever often need to take antibiotics for a longer period—a year to 18 months in typical cases. In some cases, years of treatment and monitoring may be necessary.

If a person develops chronic Q fever and has complications such as damage or disease in their heart, they may require additional treatment. In some cases, the heart valves may need to be surgically repaired. People who develop hepatitis may need to take other medications in addition to antibiotics.

If a person has developed chronic Q fever and its associated health problems, they will usually need to see several different doctors to manage the infection and prevent further complications. Consults with cardiologists, hepatologists, cardiothoracic surgeons, and infectious disease specialists may be helpful. They will usually need to have tests to look for antibodies for at least two years after contracting Q fever.

People who work in professions that are at high risk or who travel to areas where Q fever is more common can take several steps to help prevent contracting the infection, including:

  • avoid drinking raw milk or consuming other unpasteurized dairy products.
  • isolate potentially infected animals and avoid exposure.
  • use appropriate infection prevention and waste disposal procedures when working in close quarters with animals, particularly when delivering offspring or handling excretions.
  • for people who have heart disease or other risk factors, education and counseling about the risk of Q fever is useful when working, living, or traveling in places where exposure may occur.
  • appropriate isolation and decontamination procedures if exposure has occurred.

While a vaccine for Q fever is available in Australia, no vaccine has been approved in the United States.

A Word From Verywell

Q fever is a bacterial infection typically spread to humans through contact with animals, particularly livestock. The infection is usually acute but may become chronic. As many as half of those who get acute Q fever will not show symptoms. In both children and adults, the first-line treatment is the antibiotic doxycycline. If a person develops chronic Q fever, they may need medical monitoring and treatment for up to four years. Preventing Q fever relies on reducing exposure and practicing proper hygiene when working, living, or traveling in places that put a person at risk for exposure.

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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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