Q Fever

Q fever is a worldwide zoonosis caused by the obligate intracellular gram-negative bacterium Coxiella burnetii, transmitted primarily via inhalation of contaminated aerosols from infected livestock (cattle, sheep, goats). It is a CDC Category B bioterrorism agent and a nationally notifiable disease in the United States. [1-2] Approximately 60% of infections are asymptomatic; the remaining 40% develop acute illness ranging from self-limited febrile syndrome to pneumonia or hepatitis, with <5% progressing to chronic (persistent focalized) infection. [1][3]

1. History

• Key HPI: Onset and duration of fever (median 10 days untreated), headache (often severe, retroorbital, radiating to jaw — can mimic migraine or dental pain), myalgia, fatigue, chills [1]
• Symptom characterization: Onset may be abrupt or gradual; nonproductive cough in ~50% of pneumonia cases; upper respiratory symptoms less common than in other CAP etiologies [1]
• Timing/triggers: Incubation period 14–39 days (average ~20 days); seasonal peak February–May; ask about exposure to livestock birthing products, farms, or rural environments within the prior month [4-5]
• Associated symptoms: Arthralgia, anorexia, night sweats, nausea, abdominal pain; in children — GI symptoms (diarrhea, vomiting, abdominal pain) in 50–80% and rash up to 50% [1]
• Important negatives: Absence of diarrhea (in adults), absence of upper respiratory symptoms, absence of rash (rash uncommon in adults, 5–21%) [1][4]

2. Alarm Features

• Severe headache with meningismus → rule out meningitis/encephalitis [1]
• Dyspnea, hypoxia, ARDS — rare but reported [1]
• Signs of endocarditis: new murmur, embolic phenomena (stroke, splinter hemorrhages), heart failure — especially in patients with pre-existing valvular disease or prosthetic valves [1]
• Myocarditis/pericarditis: chest pain, tachycardia out of proportion to fever, hemodynamic instability (~1% of acute cases each) [1][6]
• Pregnancy: risk of miscarriage (especially first trimester), stillbirth, premature delivery, intrauterine growth restriction [1]
• Chronic Q fever red flags: persistent fatigue, unexplained fever, weight loss, night sweats, hepatosplenomegaly, arterial/venous thromboembolism — may present months to years after acute infection [1]

3. Medications

• First-line treatment (acute): Doxycycline 100 mg PO BID × 14 days — most effective when started within the first 3 days of symptoms [1][7]
• Alternatives (if doxycycline contraindicated): moxifloxacin, clarithromycin, trimethoprim/sulfamethoxazole (TMP-SMX), rifampin [1]
• Children <8 years (mild illness): consider short course (5 days) doxycycline or TMP-SMX for 14 days; severe illness in any age → full 14-day doxycycline [1]
• Pregnancy: TMP-SMX throughout pregnancy (doxycycline contraindicated); long-term follow-up for chronic Q fever postpartum [1][8]
• Chronic Q fever: Doxycycline 100 mg BID + hydroxychloroquine 200 mg TID for ≥18 months (endocarditis) or longer depending on site of infection [1][9]
• Contraindicated: Beta-lactams and cephalosporins are ineffective against C. burnetii [5]
• Caution: Hydroxychloroquine requires baseline and periodic ophthalmologic exams and ECG monitoring for QTc prolongation [10]

4. Diet

• No specific dietary triggers or restrictions
• Avoid consumption of unpasteurized milk or dairy products — rare transmission route [1]
• Maintain adequate hydration during febrile illness
• Take doxycycline with food/water to reduce GI side effects; avoid dairy products within 2 hours of dosing

5. Review of Systems

• Constitutional: Fever, chills, fatigue, night sweats, weight loss
• HEENT: Severe headache (retroorbital), photophobia, jaw pain [1]
• Respiratory: Cough (dry), dyspnea, pleuritic chest pain
• GI: Nausea, vomiting, abdominal pain, anorexia (especially in children); hepatitis symptoms (RUQ pain, jaundice)
• Cardiovascular: Chest pain, palpitations, exertional dyspnea (myocarditis/pericarditis/endocarditis)
• Neurologic: Headache, confusion, neck stiffness (meningitis/encephalitis — rare)
• Dermatologic: Maculopapular or purpuric rash (5–21% adults, up to 50% children) [1]
• MSK: Myalgia, arthralgia
• OB/GYN: Pregnancy status, history of miscarriage

6. Collateral History and Family History

• Occupational exposure: Farming, veterinary work, slaughterhouse work, livestock processing, wool/hide handling [4]
• Animal contact: Recent contact with cattle, sheep, goats — especially parturient animals or birth products [1][11]
• Geographic/environmental: Residence within 5 km of livestock farms; rural vs. urban; recent travel to endemic areas [12]
• Household contacts: Other symptomatic individuals with similar exposure
• Family history: Pre-existing valvular heart disease (congenital or acquired) — critical for chronic Q fever risk stratification [1]
• Social context: Military deployment (historically significant exposure risk) [1]

7. Risk Factors

• Occupational: Livestock farmers, veterinarians, slaughterhouse workers, laboratory workers handling C. burnetii [1][4]
• Environmental: Proximity to infected farms, windborne aerosol exposure; organism persists in environment for years [12]
• Host factors for chronic Q fever progression: [1]
  • Pre-existing valvular heart disease (~40% develop endocarditis if acutely infected)
  • Prosthetic heart valves (highest risk)
  • Vascular grafts or aneurysms
  • Immunosuppression (transplant, HIV, cancer)
  • Pregnancy
• Demographics: Males > females; endocarditis predominantly in men >40 years [1]
• Seasonal: Peak transmission in spring (lambing/calving season) [5]

8. Differential Diagnosis

• Community-acquired pneumonia (Mycoplasma, Legionella, Chlamydophila) — clinically and radiographically indistinguishable from Q fever pneumonia [1][13]
• Influenza / viral URI — similar flu-like presentation
• Brucellosis — similar zoonotic exposure, undulant fever, hepatitis
• Leptospirosis — animal exposure, fever, hepatitis, renal involvement
• Typhoid fever — prolonged fever, headache, GI symptoms
• Rickettsial diseases (RMSF, typhus) — fever, headache, rash; tick exposure
• Infectious mononucleosis — fever, fatigue, hepatitis, lymphadenopathy
• Viral hepatitis — if hepatitis is the predominant presentation
• Culture-negative endocarditis (Bartonella, Brucella, HACEK, Whipple disease) — for chronic Q fever presenting as endocarditis [14]
• Tuberculosis — chronic fever, weight loss, night sweats

Distinguishing feature: Q fever cannot be reliably differentiated from other febrile illnesses without serologic testing or PCR. [13][15]

9. Past Medical History

• Valvular heart disease (bicuspid aortic valve, mitral valve prolapse, mitral insufficiency) — highest risk for chronic Q fever endocarditis [1]
• Prosthetic valves or vascular grafts
• Immunosuppressive conditions: organ transplant, HIV/AIDS, malignancy, immunosuppressive medications [16]
• Previous Q fever infection — lifelong risk of recrudescence if valvular disease develops later [1]
• Pregnancy history: prior adverse pregnancy outcomes, prior Q fever during pregnancy (risk of recrudescence in subsequent pregnancies) [1]

10. Physical Exam

• Vital signs: Fever (often high, >40°C in ~58% of pneumonia cases), tachycardia; hypotension if myocarditis/sepsis [5]
• General: Ill-appearing, diaphoretic
• HEENT: No specific findings; photophobia may be present
• Cardiac: New murmur (endocarditis), friction rub (pericarditis), S3 gallop (heart failure)
• Pulmonary: Crackles/rales if pneumonia; often exam is relatively benign compared to radiographic findings
• Abdomen: Hepatomegaly, splenomegaly, RUQ tenderness (hepatitis) [1]
• Skin: Maculopapular or purpuric rash (uncommon in adults); erythema nodosum (rare) [17]
• Neurologic: Meningismus (rare); altered mental status (encephalitis — rare)
• Extremities: Embolic phenomena (splinter hemorrhages, Janeway lesions, Osler nodes) in chronic endocarditis

11. Lab Studies

• CBC: WBC typically normal (leukocytosis uncommon); relative lymphopenia in ~50% [5][13]
• CRP/ESR: Elevated (CRP often markedly elevated; ESR elevated) [13][18]
• LFTs: Elevated transaminases and alkaline phosphatase (ALP elevated in ~70% of hepatitis cases); hepatitis pattern varies geographically [5][17]
• Electrolytes: Hyponatremia reported in ~28% [5]
• Troponin: If myocarditis/pericarditis suspected
• Blood cultures: Typically negative (C. burnetii does not grow on standard media) — important clue in culture-negative endocarditis [14][19]
• Serology (gold standard): [1]
  • IFA (indirect immunofluorescence assay) — most commonly used
  • Acute Q fever: Fourfold rise in phase II IgG between acute and convalescent sera (3–6 weeks apart); single phase II IgG ≥1:128 with compatible illness = probable
  • Chronic Q fever: Phase I IgG ≥1:1024 with identifiable nidus of infection [1]
  • Seroconversion typically occurs 7–15 days after symptom onset; 90% seroconvert by week 3 [1]
• PCR (C. burnetii DNA): Useful for early diagnosis before seroconversion; sensitivity ~81%, specificity ~90% on serum; sensitivity lower in some settings [20-21]

12. Imaging

• Chest X-ray (first-line for pneumonia): [1][18][22]
  • Abnormal in >96% of Q fever pneumonia cases
  • Most common: segmental or lobar consolidation (unilateral, single opacity); upper lobe predilection reported
  • Patchy infiltrates less common
  • Normal CXR possible early in disease (~10% of cases)
  • Cannot differentiate from other CAP etiologies radiographically
• CT chest (if CXR inconclusive or severe disease): [23-24]
  • Multilobar airspace consolidation
  • Nodules with halo sign (ground-glass opacity surrounding consolidation)
  • Pleural effusions (uncommon), mild lymphadenopathy
• Echocardiography: [1][25]
  • TTE recommended for all acute Q fever patients to assess for valvular lesions and risk-stratify for chronic disease
  • TEE if TTE negative/inconclusive in suspected endocarditis — vegetations detected in only ~12% of chronic Q fever endocarditis; most common finding is new/worsening valvular insufficiency
  • A negative echocardiogram does not rule out Q fever endocarditis [1]
• Imaging is unnecessary in mild, self-limited febrile illness without respiratory symptoms or cardiac concerns

13. Special Tests

• Serologic phase differentiation: [1]
  • Phase II antibody predominance → acute infection
  • Phase I IgG ≥1:1024 → chronic/persistent focalized infection
• PCR targeting IS1111 insertion element — most sensitive molecular target [20][26]
• Anticardiolipin antibodies: Positive anticardiolipin antibodies (>22 GPLU) independently associated with acute Q fever endocarditis; >60 GPLU warrants TEE [25]
• Immunohistochemistry/culture: Available at reference laboratories; culture requires BSL-3 facility [15]
• FDG-PET/CT: May be useful in chronic Q fever to identify vascular infection foci (not routinely used in acute disease)

14. ECG

• Indications: Obtain ECG if chest pain, dyspnea, tachycardia, or suspicion of cardiac involvement
• Myocarditis (~1% of acute cases): Sinus tachycardia, nonspecific ST/T-wave changes, ST elevation, low voltage, AV block, ventricular arrhythmias [6][27-28]
• Pericarditis (~1% of acute cases): Diffuse concave ST elevation, PR depression [29-30]
• Endocarditis (chronic): Conduction abnormalities if perivalvular abscess
• Dangerous patterns: High-grade AV block, wide QRS, ventricular tachycardia → consider myocarditis with hemodynamic compromise; 2 of 3 myocarditis cases in one Q fever cohort progressed to dilated cardiomyopathy [6]
• Hydroxychloroquine monitoring: Baseline and periodic ECG for QTc prolongation during chronic Q fever treatment

15. Assessment

• Acute Q fever is typically a self-limited febrile illness resolving in 2–3 weeks even without treatment; mortality <2% [1]
• Three main clinical presentations: (1) nonspecific febrile illness, (2) atypical pneumonia, (3) granulomatous hepatitis — geographic variation in predominant presentation [17][31]
• Atypical presentations: Severe headache mimicking meningitis, rash mimicking viral exanthem, culture-negative endocarditis, fever of unknown origin [1][14]
• Chronic Q fever develops in <5% of acute cases but carries up to 60% mortality if untreated (reduced to <5% with treatment); endocarditis is the most common chronic manifestation (60–78% of chronic cases) [1][3]
• Complications: Endocarditis, vascular infection, osteomyelitis, chronic hepatitis, ARDS, Q fever fatigue syndrome (months to years), adverse pregnancy outcomes [3-4]

16. Treatment Plan

Acute Q Fever

• Doxycycline 100 mg PO BID × 14 days — start empirically if clinical suspicion is high; do not delay for serologic confirmation [1]
• Symptomatic patients and those at high risk for chronic disease should be treated even if symptoms are mild [1]
• Antipyretics and supportive care as needed
• Most patients defervesce within 72 hours of starting doxycycline [1]

High-Risk Patients (Prophylaxis Against Chronic Q Fever)

• Patients with valvular disease, vascular grafts, immunosuppression, or pregnancy require close monitoring and may benefit from extended prophylactic treatment [1][13]
• In one study, 50% of high-risk patients who did not receive prophylaxis developed chronic Q fever vs. 0% who received prophylaxis [13]

Chronic Q Fever

• Doxycycline 100 mg BID + hydroxychloroquine 200 mg TID [1][9]
• Duration: ≥18–24 months for endocarditis; may vary by site of infection
• Surgical valve replacement may be required in endocarditis cases (~58% in one review) [19]
• Requires regular monitoring: serology (phase I IgG titers), ophthalmologic exams, ECG, LFTs, CBC

Pregnancy

• TMP-SMX throughout pregnancy [1][8]
• Postpartum: transition to doxycycline + hydroxychloroquine if chronic infection develops
• Avoid pregnancy for ≥1 month after acute Q fever diagnosis and treatment [1]

17. Disposition

• Discharge criteria: Mild febrile illness, hemodynamically stable, tolerating PO, no high-risk features, reliable follow-up
• Admission criteria: [1]
  • Severe pneumonia or respiratory distress
  • Hemodynamic instability
  • Suspected myocarditis, pericarditis, or endocarditis
  • Meningitis/encephalitis
  • Pregnancy with acute Q fever
  • Inability to tolerate oral medications
• Observation: Consider for patients with significant comorbidities or high-risk features for chronic disease
• Specialist consultation triggers:
  • Infectious disease: All confirmed/suspected cases; mandatory for chronic Q fever
  • Cardiology: Suspected endocarditis, myocarditis, pericarditis; echocardiographic evaluation
  • Cardiothoracic surgery: Endocarditis with valve dysfunction
  • OB/GYN: Pregnant patients with Q fever
  • Public health notification: Q fever is a nationally notifiable disease — report to local/state health department [1]

18. Follow Up / Return Precautions

• Serologic monitoring: Paired sera at 3–6 weeks post-acute illness to confirm diagnosis; then monitor phase I IgG titers at 3, 6, 12, 18, and 24 months post-diagnosis to detect progression to chronic disease [1]
• High-risk patients (valvular disease, vascular grafts, immunosuppression): Lifelong vigilance — chronic Q fever can develop months to decades after initial infection [1]
• Return precautions — seek immediate care for:
  • Recurrent or persistent fever
  • New or worsening dyspnea, chest pain, or edema
  • Embolic symptoms (sudden neurologic deficit, limb ischemia)
  • Unexplained weight loss, night sweats, fatigue
• Expected recovery: Most acute cases resolve within 2–3 weeks with treatment; fever typically resolves within 72 hours of doxycycline initiation [1]
• Q fever fatigue syndrome: Prolonged fatigue lasting months to years may occur even after successful treatment of acute infection [3]
• Women of childbearing age: Counsel regarding pregnancy risks; avoid conception for ≥1 month post-treatment; serologic monitoring in subsequent pregnancies if prior Q fever [1]

References

1. Diagnosis and Management of Q Fever--United States, 2013: Recommendations From CDC and the Q Fever Working Group. — Anderson A, Bijlmer H, Fournier PE, et al. MMWR. Recommendations and Reports : Morbidity and Mortality Weekly Report. Recommendations and Reports. 2013.

2. Research Trends and Hotspots of Q Fever Research: A Bibliometric Analysis 1990‐2019. — Farooq M, Khan AU, El-Adawy H, et al. BioMed Research International. 2021.

3. Cell death induction facilitates egress of Coxiella burnetii from infected host cells at late stages of infection. — Schulze-Luehrmann J, Liebler-Tenorio E, Felipe-López A, Lührmann A. Molecular Microbiology. 2024.

4. Current perspectives on the occurrence of Q fever: highlighting the need for systematic surveillance for a neglected zoonotic disease in Indian subcontinent. — Sahu R, Rawool DB, Dhaka P, et al. Environmental Microbiology Reports. 2021.

5. Acute Q Fever Pneumonia: A Review of 80 Hospitalized Patients. — Caron F, Meurice JC, Ingrand P, et al. Chest. 1998.

6. Clinical Implications of Cardiac Involvement in Q Fever: Findings From a Spanish Cohort. — de la Guía EM, Vázquez ML, Sancho JJB, et al. Medicina Clinica. 2026.

7. Q Fever. — Parker NR, Barralet JH, Bell AM. Lancet. 2006.

8. Q Fever During Pregnancy: A Cause of Poor Fetal and Maternal Outcome. — Carcopino X, Raoult D, Bretelle F, Boubli L, Stein A. Annals of the New York Academy of Sciences. 2009.

9. Antimicrobial Therapies for Q Fever. — Kersh GJ. Expert Review of Anti-Infective Therapy. 2013.

10. Treatment of Persistent Focalized Q Fever: Time Has Come for an International Randomized Controlled Trial. — Delahaye A, Eldin C, Bleibtreu A, et al. The Journal of Antimicrobial Chemotherapy. 2024.

11. Q Fever. — Maurin M, Raoult D. Clinical Microbiology Reviews. 1999.

12. Blood Culture-Negative Endocarditis: A Scientific Statement From the American Heart Association: Endorsed by the International Society for Cardiovascular Infectious Diseases. — DeSimone DC, Garrigos ZE, Marx GE, et al. Journal of the American Heart Association. 2025.

13. Differentiation of Acute Q Fever From Other Infections in Patients Presenting to Hospitals, the Netherlands. — Keijmel SP, Krijger E, Delsing CE, et al. Emerging Infectious Diseases. 2015.

14. Challenges in Infective Endocarditis. — Cahill TJ, Baddour LM, Habib G, et al. Journal of the American College of Cardiology. 2017.

15. Rapid and Visual Detection of Coxiella burnetii Using Recombinase Polymerase Amplification Combined with Lateral Flow Strips. — Qi Y, Yin Q, Shao Y, et al. BioMed Research International. 2017.

16. Prevention and management of infectious and tropical diseases in kidney transplant recipients residing in European outermost and overseas territories. — Cachera L, Oehler E, Abdelmoumen K, et al. Transplant Infectious Disease : An Official Journal of the Transplantation Society. 2024.

17. Natural History and Pathophysiology of Q Fever. — Raoult D, Marrie T, Mege J. The Lancet. Infectious Diseases. 2005.

18. Q Fever Pneumonia in Southwest Germany: Radiographic and Clinical Findings. — Biecker A, Bitzer M, Biecker E. RoFo : Fortschritte Auf Dem Gebiete Der Rontgenstrahlen Und Der Nuklearmedizin. 2017.

19. Q Fever Endocarditis Complicating Biventricular Failure: Diagnostic and Therapeutic Insights From a Case Report and Literature Review. — Alfehaid L, Alrubayan K, Aleanzi A, et al. Frontiers in Medicine. 2025.

20. Diagnostic Usefulness of Molecular Detection of Coxiella Burnetii From Blood of Patients With Suspected Acute Q Fever. — Bae M, Jin CE, Park JH, et al. Medicine. 2019.

21. Comparison of Paired Immunofluorescent Antibody Serology and Real-Time Polymerase Chain Reaction Testing for the Detection of Acute Q Fever Among Febrile Patients in Kilimanjaro, Tanzania, 2012-2014. — Rolfe RJ, Crump JA, Maro VP, et al. The American Journal of Tropical Medicine and Hygiene. 2025.

22. Q Fever Pneumonia: Appearance on Chest Radiographs. — Gikas A, Kofteridis D, Bouros D, et al. Radiology. 1999.

23. Q Fever Pneumonia: CT Findings. — Voloudaki AE, Kofteridis DP, Tritou IN, et al. Radiology. 2000.

24. Acute Q Fever Pneumonia: High-Resolution Computed Tomographic Findings in Six Patients. — von Ranke FM, Clemente Pessoa FM, Afonso FB, et al. The British Journal of Radiology. 2019.

25. Acute Q Fever Endocarditis: A Paradigm Shift Following the Systematic Use of Transthoracic Echocardiography During Acute Q Fever. — Melenotte C, Epelboin L, Million M, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2019.

26. Acute Q Fever in Individuals With Acute Febrile Illness & Exposure to Farm Animals: Clinical Manifestations & Diagnostic Approaches. — Sundar B, Shinde SV, Dongre SA, et al. The Indian Journal of Medical Research. 2024.

27. 2024 ACC Expert Consensus Decision Pathway on Strategies and Criteria for the Diagnosis and Management Of Myocarditis: A Report of the American College of Cardiology Solution Set Oversight Committee. — Drazner MH, Bozkurt B, Cooper LT, et al. Journal of the American College of Cardiology. 2025.

28. Diagnosis and Treatment of Acute Myocarditis: A Review. — Ammirati E, Moslehi JJ. The Journal of the American Medical Association. 2023.

29. Acute Pericarditis: Rapid Evidence Review. — Peterson TA, Turner SP, Dolezal KA. American Family Physician. 2024.

30. Natural Course of Electrocardiogram Changes and the Value of Multimodality Imaging in Acute Pericarditis. — Saeed S, Mohamed Ali A, Wasim D, et al. Cardiology. 2023.

31. Clinical Features and Complications of Coxiella burnetii Infections From the French National Reference Center for Q Fever. — Melenotte C, Protopopescu C, Million M, et al. JAMA Network Open. 2018.