Zoonotic obligate intracellular bacterium causing acute febrile pneumonia/hepatitis and chronic culture-negative endocarditis; classic exposure is parturient livestock.
Also known as: Coxiella burnetii, query fever, Q fever endocarditis, Q fever hepatitis
Epidemiology
Worldwide zoonosis with reservoirs in cattle, sheep, goats, and ticks. The US sees a few hundred reported cases annually, often in ranchers, veterinarians, abattoir workers, and military personnel returning from the Middle East. Highly infectious by aerosol — a CDC Tier 1 select agent.
🔒 Free preview limit reached
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Q Fever (Coxiella burnetii) outline — plus all 514 diagnoses, 3,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Free to start · No credit card · Cancel anytime
Risk factors
- Exposure to parturient livestock, birth products, or contaminated dust
- Occupational: farmers, veterinarians, slaughterhouse workers, laboratory workers
- Unpasteurized dairy consumption
- Pre-existing valvular heart disease, prosthetic valves, vascular grafts (predispose to chronic endocarditis)
- Pregnancy (risk of placental infection and fetal loss)
- Immunocompromise
Pathophysiology
Inhaled organisms infect alveolar macrophages, replicate within phagolysosomes, and disseminate to liver, spleen, and bone marrow. Granulomatous inflammation produces the characteristic 'doughnut' (fibrin-ring) granulomas on liver biopsy. Phase II antigen predominates in acute disease and Phase I antigen rises in chronic infection — the basis of serologic staging.
Clinical presentation
Symptoms
- Acute: high fever, severe headache (often retro-orbital), myalgias, fatigue, dry cough
- Granulomatous hepatitis: RUQ pain, anorexia
- Atypical pneumonia: cough, dyspnea, fever
- Chronic: prolonged low-grade fevers, weight loss, fatigue, dyspnea; often a new murmur
Signs / physical exam
- Fever often very high; relative bradycardia
- Hepatomegaly or splenomegaly
- Pulmonary crackles in pneumonia presentation
- Heart murmur and embolic findings in chronic endocarditis
- Pregnant patients can be asymptomatic but with placental infection
Classic findings
Sheep farmer with fever, headache, transaminitis, and 'doughnut' granulomas on liver biopsy.
Differential diagnosis
- Atypical pneumonia (Mycoplasma, Chlamydia, Legionella) — Similar dry cough and fever; livestock exposure favors Q fever
- Viral hepatitis — Hepatocellular pattern with markedly elevated transaminases; serology distinguishes
- Brucellosis — Same occupational and dairy exposure; serology and culture differentiate
- Culture-negative endocarditis (Bartonella, HACEK) — Coxiella is one of the leading causes; pre-existing valve disease and rising Phase I IgG support
- Tuberculosis — Granulomatous hepatitis and chronic illness; AFB stains, IGRA
Diagnostic workup
Diagnostic criteria
Acute: clinical syndrome plus Phase II IgG ≥1:128 (or fourfold rise). Chronic: persistent infection (≥3 months) plus Phase I IgG ≥1:1024.
Labs
- Coxiella Phase I and Phase II IgG, IgM by IFA
- Acute disease: rise in Phase II IgG (often ≥1:128)
- Chronic disease: Phase I IgG ≥1:1024 or fourfold rise
- PCR on serum or tissue useful early before serology positive
- LFTs: transaminases 2-3x normal; alkaline phosphatase elevated
- Blood cultures negative (intracellular pathogen)
Imaging
- Chest x-ray: patchy infiltrates, often atypical
- Liver biopsy (rarely needed): fibrin-ring 'doughnut' granulomas
- Echocardiogram in chronic Q fever — vegetations or valvular damage
- PET/CT may identify vascular graft and aortic infections in chronic disease
Treatment
First-line
- Acute Q fever: doxycycline (cat scratch, Q fever, brucellosis, RMSF) 100 mg PO BID for 14 days
- Children <8 and pregnancy: TMP-SMX (long course in pregnancy through delivery to reduce fetal loss)
- Chronic Q fever / endocarditis: doxycycline 100 mg BID PLUS hydroxychloroquine 200 mg TID (alkalinizes phagolysosome) for ≥18 months for native valve, ≥24 months for prosthetic
- Monitor Phase I IgG and IgG to track therapeutic response
Acute Q fever (uncomplicated)
- Doxycycline 14 days
- Avoid corticosteroids except in severe disease
Chronic Q fever / endocarditis
- Doxycycline + hydroxychloroquine 18-24+ months
- Valve replacement frequently required
Pregnancy
- TMP-SMX through pregnancy
- Post-delivery doxycycline + hydroxychloroquine if seroconverts to chronic disease
Second-line / adjunct
- Public health reporting required
- Risk-stratify patients with pre-existing valvulopathy after acute Q fever (serial Phase I IgG)
Complications
- Chronic Q fever endocarditis and vascular infection
- Granulomatous hepatitis
- Atypical pneumonia
- Spontaneous abortion, preterm delivery, low birth weight
- Post-Q fever fatigue syndrome
- Osteomyelitis
PANCE pearls
- Phase II IgG dominates in acute disease; Phase I IgG dominates in chronic Q fever — opposite of intuition.
- Chronic Q fever endocarditis is the prototype of culture-negative endocarditis; combine doxycycline and hydroxychloroquine.
- Doxycycline is the workhorse: cat scratch, Q fever, brucellosis, RMSF, tularemia, ehrlichiosis, anaplasmosis.
- Suspect Q fever in any febrile patient with livestock exposure and unexplained transaminitis.
- Coxiella is highly stable in the environment and is a CDC Tier 1 select agent — laboratory exposures need post-exposure doxycycline.
References
- CDC 2013 — CDC Diagnosis and Management of Q Fever — United States, 2013 (Anderson et al., MMWR Recomm Rep 2013;62(RR-03))
- AHA 2015 — AHA Scientific Statement on Infective Endocarditis (Baddour et al., Circulation 2015)
Practice Infectious Disease questions on FirstPassPA
Turn this outline into retention. 3,500+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Start studying free →
Browse all 514 diagnoses