Q fever is a bacterial infection spread primarily from livestock to humans through contaminated air. It’s caused by a remarkably hardy organism called Coxiella burnetii, which can survive in the environment for months or even years. Most people recover fully from an initial infection, but a small percentage develop a chronic form that can cause serious heart complications. In the United States, roughly 178 acute cases and 34 chronic cases were reported in 2019, with the highest rates in western and Great Plains states where livestock ranching is common.
How the Bacteria Spreads
Sheep, goats, and cattle are the primary source of human infections. The bacteria concentrates heavily in placental tissue, amniotic fluid, and birth products, so the highest risk comes during animal births. When these materials dry out, the bacteria becomes airborne in dust particles. Breathing in even a tiny amount is enough to cause infection. You don’t need to be in direct contact with the animals. People have contracted Q fever simply by living downwind of an infected farm.
Other transmission routes include drinking unpasteurized milk, handling contaminated wool or hides, and (rarely) tick bites. The disease is especially common among farmworkers, veterinarians, and slaughterhouse employees. Person-to-person spread is extremely uncommon.
What makes C. burnetii unusual is its ability to form a spore-like particle that resists heat, drying, and many disinfectants. These particles can remain infectious on sheep wool for 7 to 10 months, on fresh meat for over a month in the refrigerator, and in dry milk powder for more than 40 months at room temperature. This environmental toughness is a major reason the bacteria spreads so effectively through dust and air.
Symptoms of Acute Q Fever
Illness typically develops two to three weeks after exposure. Many people with acute Q fever experience it as a flu-like illness: high fever, chills, sweats, severe headache, muscle aches, and fatigue. Some also develop nausea, vomiting, diarrhea, chest pain, cough, or unexplained weight loss.
In more severe cases, the infection can settle in the lungs (causing pneumonia) or the liver (causing hepatitis). About half of all people infected with C. burnetii never develop noticeable symptoms at all, which means the true number of infections is likely far higher than what gets reported. For those who do get sick, the acute illness generally resolves with treatment within a couple of weeks.
When It Becomes Chronic
Fewer than 5% of people with an acute infection go on to develop chronic Q fever, but this form of the disease is far more dangerous. The most serious complication is endocarditis, an infection of the heart valves that can develop months or even years after the initial illness. People with pre-existing heart valve problems, weakened immune systems, or who were pregnant at the time of infection face the highest risk of chronic disease.
Chronic Q fever can also affect blood vessels, causing infected aneurysms. Because the chronic form progresses slowly and symptoms can be vague (persistent low-grade fever, night sweats, weight loss), it sometimes goes undiagnosed for a long time. Left untreated, chronic Q fever endocarditis can be fatal.
Post-Q Fever Fatigue
Even after the acute infection clears, a significant number of people experience prolonged fatigue that can last years. Studies have found that up to 69% of patients still report fatigue five years after their initial Q fever episode. Ten years later, 68% reported fatigue of some duration, and about 20% met the formal criteria for chronic fatigue syndrome. Compared to people who were never infected, Q fever survivors are substantially more likely to deal with lasting tiredness, reduced social functioning, and respiratory issues. This post-Q fever fatigue syndrome tends to begin suddenly, unlike the gradual onset seen in other forms of chronic fatigue.
How Q Fever Is Diagnosed
Diagnosing Q fever relies mainly on blood tests that detect antibodies your immune system produces against C. burnetii. The bacteria has two distinct phases, and the pattern of antibodies tells doctors whether the infection is acute or chronic. In acute infection, antibodies against the “phase II” form of the bacteria dominate. In chronic infection, the pattern flips: “phase I” antibodies rise higher, with a confirmed chronic diagnosis when phase I antibody levels reach a specific threshold and there’s an identifiable site of ongoing infection, such as a damaged heart valve.
During the early days of illness, a DNA-based blood test (PCR) can detect the bacteria directly. This test works best early on. For chronic Q fever, PCR on blood alone has low sensitivity, so antibody testing remains the primary diagnostic tool. Tissue biopsies from an infected site can also be tested when needed.
Because early symptoms look like many other infections, Q fever is easy to miss. Telling your doctor about any recent contact with livestock, farm environments, or animal birth products can make the difference between a quick diagnosis and weeks of uncertainty.
Treatment for Acute and Chronic Cases
Acute Q fever is treated with a standard course of the antibiotic doxycycline, taken twice daily for 14 days. Most people respond well and recover fully. Starting antibiotics early in the illness improves outcomes.
Chronic Q fever requires a much longer and more intensive approach. Treatment combines doxycycline with hydroxychloroquine (a drug that helps the antibiotic work more effectively inside cells) for a minimum of 18 months in cases involving heart valve or blood vessel infections. Some patients need treatment for even longer, with the duration guided by how their antibody levels respond over time and whether symptoms improve. The extended treatment timeline reflects how deeply the bacteria embeds itself in tissues during chronic infection.
Where Q Fever Occurs
Q fever is found worldwide, with the notable exception of New Zealand. In the United States, more than a third of reported cases come from just three states: California, Texas, and Iowa. The geographic pattern tracks closely with livestock density. Australia has historically had high rates as well, particularly among agricultural workers.
The Netherlands experienced a massive outbreak between 2007 and 2010, with thousands of cases linked to dairy goat farms, highlighting how quickly Q fever can spread when conditions align. Outbreaks tend to peak during spring lambing and calving seasons, when large amounts of contaminated birth material enter the environment.
Prevention and Vaccination
Australia is currently the only country with a licensed human vaccine against Q fever, marketed as Q-Vax. Before receiving the vaccine, you must undergo both a blood test and a skin test. This pre-vaccination screening identifies people who have already been infected without knowing it. Vaccinating someone with prior exposure can trigger a severe hypersensitivity reaction, so the screening step is mandatory. If testing shows evidence of past infection, the vaccine is not given, because you’re already immune.
The vaccine is not funded under Australia’s national immunization program, so recipients typically pay out of pocket. No Q fever vaccine is currently approved in the United States or Europe.
Without a vaccine, prevention centers on reducing exposure. Proper disposal of animal birth products, avoiding unpasteurized dairy, wearing protective equipment when working with livestock, and keeping animal birthing areas away from public spaces all lower risk. Windborne spread means that even people who don’t work directly with animals but live near livestock operations should be aware of Q fever during birthing seasons.