Description

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.

Epidemiology

• 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 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.
• The highest concentration of C. burnetii is in products of conception (amniotic fluid and placenta) (1):
  • Also excreted in urine, feces, and milk
• Transmission
  • Typically inhalation of infected aerosol droplets: infected barnyard dust, air conditioning (1)
  • Consumption of unpasteurized dairy products
  • Percutaneous exposure
  • Human-to-human transmission via infected parturient women; transplacental transmission, sexual intercourse, fomite transmission, tick bites, blood transfusion, and bone marrow transplantation

Incidence

• United States
  • 0.3 cases per million per year (2)
  • Acute cases 75–90% of reported (2)
  • Reported cases in every state: >50% from seven states where livestock farming is common (2,3)
    • California, Colorado, Illinois, Kentucky, Missouri, Tennessee, Texas
• Worldwide
  • 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

Prevalence
Estimated seroprevalence in the United States is 3% in healthy adults and 10–20% in high-risk occupations (ranchers, livestock handlers). Q fever is underdiagnosed and underreported (2).

Etiology and Pathophysiology

• C. burnetii is an obligate intracellular bacterium with a pleomorphic membrane similar 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 can cause disease
  • Class B bioterrorism agent
  • Incubation period is 1 to 3 weeks.
• 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 (syndrome of 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. Symptoms persist for >1 year with a 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).

Genetics
Genetic factors do not influence clinical course.

Risk Factors

• Occupational: farmers, slaughterhouse workers, veterinarians, or other animal handlers; laboratory personnel; individuals 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 immunocompromised.

Pediatric Considerations
Often a self-limited, milder acute illness; chronic Q fever is rare. GI symptoms in 50–80%; skin rash in 50% (3)
Pregnancy Considerations
Q fever in the 1st trimester increases risk of chronic Q fever and obstetric complications.

General Prevention

Vaccine is not commercially available in the United States:

• Registered in Australia and given to slaughterhouse workers
• Efficacious in specific populations; duration of immunogenicity is uncertain (3,5).