What is Q fever?

What is Q Fever

Q fever is a zoonotic disease caused by the bacterium Coxiella burnetii that can cause acute or chronic illness in humans, transmitted primarily through inhalation of contaminated aerosols from infected animals, particularly livestock. 1

The Causative Organism

• Coxiella burnetii is a unique intracellular bacterium that is extremely resistant to physical stresses including heat and desiccation, allowing it to survive in the environment for months to years. 1
• The organism is highly infectious, with as few as one organism potentially causing clinical infection. 2
• It develops spore-like forms that contribute to its environmental persistence and makes it capable of traveling on wind currents for miles. 1, 3

Animal Reservoirs and Transmission

• Cattle, sheep, and goats are the primary reservoirs, though infection has been confirmed in multiple vertebrate species including wildlife, domestic mammals, birds, and reptiles. 1
• The highest numbers of organisms are shed in birth products (placenta, amniotic fluid), although viable organisms can also be shed in urine, milk, and feces of infected animals. 1, 4
• The majority of animal infections are asymptomatic, making identification of infected animals challenging. 1

How Humans Get Infected

• The most common mode of transmission is inhalation of infectious aerosols directly from birth fluids of infected animals or via inhalation of dust contaminated with dried birth fluids or excreta. 1
• The bacteria can become airborne and travel considerable distances—in one outbreak, cases were documented in persons living 10 miles from the source farm. 1
• Less common routes include ingestion of raw milk and dairy products, or contact with contaminated clothing. 1
• Person-to-person transmission is possible but rarely reported, with rare cases documented through blood transfusion, bone marrow transplantation, and sexual transmission. 1

Clinical Manifestations

Acute Q Fever

• Approximately 40-60% of infections are asymptomatic, with only seroconversion occurring. 1, 2
• Symptomatic acute Q fever typically manifests 2-3 weeks after exposure as a nonspecific febrile illness, pneumonia, or hepatitis. 1
• The most frequently reported symptoms include fever (lasting a median of 10 days untreated), fatigue, chills, myalgia, and severe debilitating headaches. 1, 5
• Nonproductive cough occurs in approximately 50% of patients with Q fever pneumonia. 5
• Acute Q fever has a low mortality rate (<2%) and most patients defervesce within 72 hours of doxycycline treatment. 1, 5

Chronic Q Fever

• Chronic disease is rare (<5% of patients with acute infections) and typically manifests months to years after initial infection. 1
• Chronic Q fever endocarditis is the most common manifestation, occurring primarily in patients with preexisting valvular heart disease, vascular grafts, or arterial aneurysms. 1
• Unlike acute Q fever, chronic Q fever endocarditis is always fatal if untreated. 1
• Routine blood cultures are negative in patients with chronic Q fever endocarditis, making diagnosis extremely difficult. 1
• Vegetative lesions are visualized by echocardiography in only approximately 12% of patients. 1

Who is at Risk

Occupational Risk Factors

• Persons whose work involves contact with animals are at increased risk, including slaughterhouse workers, veterinarians, farmers, and laboratory workers. 1
• However, 79% of reported U.S. cases occur in patients not in previously defined high-risk occupations, and 60% occur in patients who do not report livestock contact. 1

Geographic and Demographic Factors

• Living in a rural area or within 10 miles of a farm housing livestock increases risk. 1, 5
• The reported incidence is higher among persons aged ≥40 years, with persons aged 60-64 years having the highest age-related risk in the United States. 1
• Males have a higher risk for symptomatic Q fever illness than females. 1
• Acute Q fever cases in the United States peak in the spring, correlating with livestock birthing times. 1

Diagnosis

• Paired serum samples showing fourfold change in IgG antibody titer to C. burnetii phase II antigen by immunofluorescence assay is the gold standard for diagnosis. 5, 6
• A single IgG titer ≥1:128 to phase II antigen in a patient ill >1 week indicates probable acute infection. 5, 6
• PCR testing on whole blood or serum during the first 2 weeks of symptoms can provide early diagnosis. 5, 6
• Chronic infection is distinguished by a rising phase I IgG titer. 1

Treatment

• Doxycycline is the antibiotic of choice for Q fever. 7, 2, 4
• For acute Q fever, a 14- to 21-day course of doxycycline is typically used. 2
• Early treatment within the first 3 days of symptoms is most effective, and treatment should not be delayed while awaiting laboratory confirmation if Q fever is strongly suspected. 5, 6
• For chronic infections such as endocarditis, 18 months of doxycycline supplemented with hydroxychloroquine is currently the best therapy. 2, 4

Public Health Significance

• Q fever is a nationally notifiable disease in the United States. 1
• The largest known outbreak involved approximately 4,000 human cases during 2007-2010 in the Netherlands, linked to dairy goat farms. 1
• Its highly infectious nature and aerosol route of transmission make C. burnetii a possible agent of bioterrorism. 2, 8