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Zoonotic disease caused by Coxiella burnetii, a hearty organism that can survive for years in soil
- Infected animals are usually asymptomatic, although repeated pregnancy losses can occur.
- Infection in humans results in illness ranging from mild symptomatology to chronic disease.
- Endemic worldwide except in New Zealand
- Point-source outbreaks also occur.
- Primary reservoirs are farm animals (cattle, goats, sheep) and urban pets (dogs, cats, rabbits) (1).
- Environmental reservoirs are wild animals: mammals, birds, reptiles, and ticks. Ticks may act as vectors but are not a necessary link in transmission (1).
- Acanthamoeba castellanii may also be a reservoir (1).
- The highest concentration of C. burnetii is present in products of conception (amniotic fluid and placenta):
- Also excreted in urine, feces, and milk
- Typically inhalation of infected aerosol droplets: infected barnyard dust, air conditioning (1)
- Consumption of unpasteurized dairy products
- Percutaneous exposure
- Human-to-human transmission: Infected parturient women, sexual intercourse, fomite transmission, transplacental transmission, tick bites, blood transfusion, and bone marrow transplantation are other means of transmission.
- United States
- Largest reported outbreak of Q fever was in the Netherlands from 2007 to 2010.
- Incidence increases with age; 5 times more likely to occur in patients >15 years
- Male > female (2.5:1); males more often symptomatic
Estimated seroprevalence in the United States is 3% in healthy adults and 10–20% in high-risk occupations. Q fever is underdiagnosed and underreported (2).
Etiology and Pathophysiology
- C. burnetii is an obligate intracellular bacterium with a pleomorphic membrane akin to gram-negative bacteria; prefers mononuclear phagocytes but can infect other cell lines (3)
- Resistance to heat, drying, and disinfectants allows organism to survive and promotes environmental spread. This makes source identification difficult.
- Highly infectious, one organism sufficient to cause disease
- Class B bioterrorism agent
- Incubation period is 1 to 3 weeks (1).
- Clinically relevant antigenic variation
- Phase I (wild type); virulent natural phase found in infected animals and humans. In chronic Q fever infection, phase I antibodies are higher.
- Phase II is less infectious in immunocompetent mammals and is typically found after laboratory processing. Antibodies to phase II are higher in acute Q fever infection.
- C. burnetii in nonimmune persons causes:
- Asymptomatic infection (60%)
- Mild illness (36–38%)
- Severe illness and hospitalization (2–4%) (4)
- Acute Q fever with mild illness
- Self-limited flulike illness that resolves after 1 to 3 weeks and is often undiagnosed
- Acute Q fever with severe illness
- Presents as atypical pneumonia, encephalitis, aseptic meningitis, prolonged fever of unknown origin, myocarditis, pericarditis, or hepatitis
- Pneumonia is more likely in older patients, can last up to 90 days; often mistaken as viral
- Hepatitis is more common in younger patients and is a granulomatous process.
- Rare: hemolytic or hypoplastic anemia, orchitis, thyroiditis, pancreatitis (inappropriate secretion of antidiuretic hormone [SIADH]), glomerulonephritis, bone marrow necrosis, acalculous cholecystitis, panniculitis, splenic rupture, or epididymitis (4)
- Post-Q fever fatigue syndrome: occurs in 20% of patients with acute Q fever. Patients have symptoms for >1 year, elevated antibody titres, and lack of clinical and laboratory evidence for chronic Q fever (3).
- Chronic Q fever is defined as infection lasting >6 months. It may develop months or years after the initial infection in a vulnerable host:
- Affects 1–5% of persons with acute Q fever
- Most common manifestation is endocarditis (60–70%). Less common manifestations include osteomyelitis, vascular aneurysms, prosthetic infections, pulmonary interstitial fibrosis, pericardial effusion, pulmonary pseudotumor, lymphoma-like illness, amyloidosis, and mixed cryoglobulinemia (4).
Genetic factors do not influence clinical course.
- Occupational: farmers, abattoir (slaughterhouse) workers, veterinarians, or other animal handlers; laboratory personnel, and people handling unpasteurized dairy products, wool, or animal hides
- Living in a rural area within 10 miles of a farm with cattle, sheep, or goats (3)
- Recent travel/military service in areas of higher risk (agricultural communities, Netherlands, Middle East)
- Tobacco smoking (1)
- Consumption of raw milk
- Risk for progression from acute to chronic Q fever is seen with increased age, preexisting valvular heart disease, prosthetic joints, and immunocompromise.
Often a self-limited, milder acute illness; chronic Q fever is rare. GI symptoms in 50–80%; skin rash in 50% (3)
Q fever in the 1st trimester increases risk of chronic Q fever and obstetric complications.
Vaccine is not commercially available in the United States:
- Registered in Australia and given to abattoir workers
- Efficacious in specific populations; duration of immunogenicity is uncertain (5).