Q fever is a zoonotic bacterial illness affecting humans and various animals across the globe. It is caused by the bacterium Coxiella burnetii, which can survive for long periods in the environment by forming a resilient, spore-like structure. Although relatively rare in humans, the bacterium is found worldwide, except in New Zealand. The disease is named “Q” for “query” because the cause was unknown when it was first discovered in 1935 among meat workers in Queensland, Australia.
How the Infection Spreads
The primary reservoirs for Coxiella burnetii are domestic livestock, predominantly sheep, goats, and cattle. These animals often carry the bacterium without showing any signs of illness, but the organism concentrates heavily in their reproductive tissues. Infected animals shed the bacteria in their feces, urine, milk, and especially in birth products like the placenta and amniotic fluid.
Human infection occurs primarily through the inhalation of aerosols contaminated by these animal products. The bacteria can become airborne when dried-out birth materials, dust, or soil contaminated by animal excretions are disturbed. The bacterium is highly infectious, meaning inhaling even a small number of organisms can cause disease.
Transmission is strongly associated with the birthing season for livestock, typically in the spring and early summer. Direct contact is not necessary, as the bacteria can travel downwind in dust from farms and pastures, infecting people living near farms, not just those working on them.
Certain occupations carry a significantly higher risk of exposure due to their close contact with livestock and animal products. High-risk groups include farmers, veterinarians, shearers, and workers in slaughterhouses or meat-packing plants. Consuming unpasteurized milk or dairy products from infected animals is a less common but possible route of infection.
Recognizing Acute and Chronic Q Fever
The clinical presentation varies widely; approximately half of infected individuals experience no symptoms. Those who develop symptoms are categorized into two forms: acute and chronic Q fever. Acute Q fever typically manifests as a sudden, flu-like illness appearing two to three weeks after exposure.
Common symptoms of the acute form include a high fever that can last for several weeks, severe headache, chills, and muscle aches. Some patients may develop more specific complications, most commonly pneumonia or hepatitis. Acute Q fever is generally self-limiting, with most individuals recovering within a few weeks without lasting complications.
A small percentage of people will develop the more serious chronic Q fever. This persistent infection can appear months or even years after the initial exposure, sometimes even when the person was asymptomatic at first. Chronic Q fever is a life-threatening condition that most frequently involves endocarditis, an infection of the inner lining or valves of the heart.
Endocarditis can lead to a range of non-specific symptoms such as night sweats, weight loss, persistent fatigue, and shortness of breath. Individuals with a pre-existing heart valve condition, a weakened immune system, or pregnant women are at an increased risk of progressing to this severe chronic form. Less common manifestations include infections of the bones (osteomyelitis) or blood vessels (vascular infection).
Diagnosis and Treatment Protocols
Diagnosis of Q fever is often challenging because the initial symptoms resemble those of many other common infections. Laboratory confirmation relies primarily on serology, a blood test that detects antibodies produced in response to the Coxiella burnetii bacterium. Culturing the bacteria directly is rarely performed because the organism is highly infectious and poses a significant hazard to laboratory personnel.
Acute Q fever is typically treated with a two-week course of the antibiotic doxycycline, which is most effective if started within the first three days of symptoms. For pregnant women, who cannot take doxycycline due to fetal risks, an alternative antibiotic regimen is recommended. Most patients with uncomplicated acute Q fever recover fully after this short course of medication.
Treatment for chronic Q fever is significantly more intensive and prolonged due to the difficulty of eradicating the persistent infection. The standard regimen involves a combination of antibiotics, most commonly doxycycline along with hydroxychloroquine, which is taken for a minimum of 18 months. The duration of this combination therapy can extend to years, depending on the patient’s clinical response and the monitoring of their antibody levels.