Infectious Diseases & Internal Medicine & Family Medicine
Q fever
Q fever is a ubiquitous zoonotic disease caused by Coxiella burnetii, an obligate intracellular bacterium of the family Coxiellaceae (formerly classified among the Rickettsiaceae). The letter «Q» comes from the English term Query («unknown»), used during the first description of the disease in Australia in 1937 by Edward Holbrook Derrick, at a time when the etiology remained mysterious. Coxiella burnetii is a gram-negative bacterium that is extremely resistant in the environment - it forms a spore-like particle (small cell variant) capable of surviving for months to years in dust, soil or dried animal products, and is resistant to heat, common disinfectants and extreme pH conditions. Its infectious dose is very low (a single bacterium can be enough to infect an immunocompetent person), making it one of the most contagious bacteria known - classified as a Category B bioterrorism agent by the US CDC. The main reservoir is domestic livestock: cattle, sheep and goats (asymptomatic carriage + massive excretion of the bacterium in placenta, amniotic fluids, milk, faeces and urine during parturition). Transmission to humans is almost exclusively by inhalation of contaminated aerosols - during animal birth, contact with abortion products, or processing of wool, hides or manure. In Quebec, Q fever is a notifiable disease (MDO) - it is endemic in breeding areas (Montérégie, Estrie, Centre-du-Québec, Chaudière-Appalaches) and is the subject of active epidemiological surveillance by the INSPQ. Clinically, Q fever takes two forms: an acute form (most often atypical pneumonia or granulomatous hepatitis, generally benign and self-limiting) and a chronic form (mainly endocarditis, dreaded and requiring prolonged treatment of 18 months to 3 years).
Epidemiology, transmission, and pathophysiology
- Animal reservoirs, transmission, and risk groups: main reservoirs: cattle + sheep + goats (ubiquitous carriage in herds - animal seroprevalence often >50 % on farms) - other secondary reservoirs: cats + dogs + rabbits + rodents + birds + ticks (possible vector but minor epidemiological role in human transmission); transmission routes: inhalation of aerosols (main route - >90 % of cases) : dust particles contaminated with abortion products + placenta + amniotic fluids + milk + faeces + urine - transmission can occur several kilometers from the exposure site in windy conditions (epidemics described 5-10 km from farms) - ingestion : rare but possible (unpasteurized raw milk + raw milk cheeses) - human-to-human transmission: exceptional (a few published cases during care of acute patients + anecdotal sexual transmission) - transfusion transmission: documented - blood donor screening in France since 2017; occupational and environmental risk groups: cattle + sheep + goat breeders + veterinarians + animal health technicians + butchers + slaughterhouse workers + farmers + microbiology laboratories (major occupational risk - strict PPE required) + residents near livestock farms + participants in agricultural fairs or markets; Quebec epidemiological context: reported cases in Quebec: 10-50 cases/year depending on the year (probably under-diagnosed - many asymptomatic cases undetected) - Q fever epidemic in the Netherlands (2007-2010 - over 4,000 reported cases - the world's largest documented epidemic) : linked to intensive goat farms + strengthened international surveillance measures; pathophysiology: inhalation of particles → ingestion by alveolar macrophages → survival and intracellular replication in phagolysosomes (the bacterium acidifies the phagolysosome to its advantage, unlike other bacteria) → hematogenous dissemination → two antigenic phases: phase I (virulent - complete lipopolysaccharide - chronic form - anti-phase I antibodies dominate) vs phase II (non-virulent - truncated LPS - acute form - anti-phase II antibodies dominate) - anti-phase I IgG / anti-phase II IgG ratio: diagnostic key to acute/chronic distinction
- Clinical presentations of acute Q fever: asymptomatic infection: 50-60 % of primary infections - seroconversion without symptoms - chance discovery during epidemiological surveys or blood donation; acute symptomatic Q fever - main presentation: severe flu-like syndrome (30-40 % of symptomatic forms): high fever (39-40°C) + intense frontal headache (highly suggestive symptom + often described as one of the most intense headaches of life) + myalgias + arthralgias + profound asthenia + chills + sweats + anorexia - abrupt onset - duration 1-3 weeks without treatment; atypical pneumonia (30-50 % of symptomatic forms): dry non-productive cough + moderate dyspnea + pleural pain - radiography: alveolar opacity (often right lower lobar) + multiple bilateral round opacities («balloon release» appearance - suggestive but not pathognomonic) + pleural effusion possible + chest CT: ground-glass opacities + condensations - differential diagnosis: legionellosis + mycoplasma + chlamydia + pneumococcus; granulomatous hepatitis (10-40 % depending on series): elevated transaminases (× 3-10 N) + alkaline phosphatases + GGT + rare jaundice - liver biopsy (if performed): fibrinous ring granulomas («ring granuloma» or «doughnut granuloma») = almost pathognomonic histological appearance of Q fever - often discovered during a routine laboratory work-up in a febrile patient; rarer forms : pericarditis + myocarditis (ECG monitoring) + meningoencephalitis + optic neuritis + erythema nodosum + orchitis; Q fever and pregnancy : major specific risk - pregnancy favors Coxiella reactivation or primary infection → miscarriage + fetal death in utero + prematurity + IUGR + risk of transition to post-partum chronic form - serological screening recommended in exposed pregnant women + cotrimoxazole (TMP-SMX) treatment throughout pregnancy if infection confirmed
- Biological diagnosis of Q fever: serology by indirect immunofluorescence (IFI) - diagnostic gold standard: acute Q fever: anti-phase II IgM ≥ 1:50 + anti-phase II IgG ≥ 1:200 (CDC criteria) - anti-phase II IgM appears at D5-J7 of infection + anti-phase II IgG at D14-J21 - seroconversion documented on 2 samples taken 3-4 weeks apart (multiplication × 4 of IgG titre) - serology is often negative in the first 7-10 days (early diagnostic blind zone); chronic Q fever (endocarditis) : IgG anti-phase I ≥ 1:800 (highly specific criterion) + IgG anti-phase II ≥ 1:200 - IgG phase I / phase II ratio >1 points to chronicity; real-time PCR on EDTA blood or tissue: high sensitivity in early acute phase (before appearance of antibodies) + decreased sensitivity after initiation of treatment + available at the National Microbiology Laboratory (NML) in Winnipeg + some university laboratories in Quebec (UHC NMLs) - Coxiella culture: reserved for biosafety level 3 (BSL-3) laboratories - never in clinical routine; other biological tests: CBC (normal or slightly elevated leukocytes + frequent thrombocytopenia - 25-50 % of cases) + transaminases + alkaline phosphatases + LDH + CRP + ESR + negative blood cultures (intracellular bacteria not cultivable on standard media); markers of chronic Q fever - monitoring under treatment: IgG anti-phase I quarterly → slow decrease under treatment (objective: IgG phase I <1:200 at end of treatment) - no decrease = therapeutic failure or relapse - duration of serological monitoring after end of treatment: 5 years minimum
Treatment and care
| Clinical form | Treatment, dosage, and duration | Tracking, resistances, and special situations |
|---|---|---|
| Acute uncomplicated Q fever Doxycycline 100 mg twice a day for 14 days |
Acute, uncomplicated Q fever responds very well to a short course of antibiotics - treatment reduces the duration of symptoms and prevents progression to chronicity in at-risk patients; doxycycline (reference treatment - absolute 1st line): 100 mg × 2/d PO (or IV if vomiting) - duration: 14 days - take with a full glass of water + in a sitting or standing position (prevention of contact esophagitis) + avoid intense sun exposure (photosensitization) - do not take with dairy products + antacids + calcium + magnesium + iron (chelation reduces absorption) - efficacy on fever : apyrexia within 72h in most cases (persistence of fever beyond D5 on doxycycline should raise suspicion of an alternative diagnosis or complication); fluoroquinolones (alternatives if contraindicated to doxycycline): levofloxacin 500 mg/d PO × 14 days + moxifloxacin 400 mg/d × 14 days + ciprofloxacin 500 mg × 2/d × 14 days - comparable efficacy in vitro + less robust clinical data than doxycycline - reserved for formal ICs to doxycycline (pregnancy + child <8 years - see below); rifampicin 600-900 mg/d : sometimes used in combination with doxycycline in severe forms or those at risk of chronicity - not as monotherapy (risk of rapid resistance); treatment of acute Q fever in children <8 years: doxycycline despite the theoretical contraindication of tooth discoloration at short therapeutic doses (14 days) - the 2006 AAP (American Academy of Pediatrics) and CDC recommend doxycycline as the reference treatment for Q fever in children of all ages (the risk of tooth discoloration is minimal at short therapeutic doses - the risk of untreated infection far outweighs it) - pediatric dosage: 2.2 mg/kg × 2/d (maximum 100 mg/dose) × 14 days | Decision to treat vs. monitoring: acute Q fever is often self-limiting in the immunocompetent - treatment is recommended if: moderate to severe symptoms (high fever + pneumonia + hepatitis) + any patient at risk of chronic form (valvulopathy + immunosuppression + pregnancy + previous cardiovascular surgery - see chronicity section) - preventive treatment questionable in mild paucisymptomatic forms in patients with no risk factors; antibiotic resistance: no documented acquired resistance to doxycycline or fluoroquinolones in the field to date - natural β-lactam resistance (intracellular beta-lactamases) + ineffective aminoglycosides + macrolides: variable efficacy in vitro + insufficient clinical data - azithromycin: modest emerging data in mild acute forms + not routinely recommended; post-treatment follow-up of acute Q fever: IFI serology at M3 + M6 after treatment to detect possible progression to chronicity - particularly in at-risk patients (valvulopathy + immunosuppression) → if IgG phase I up or ≥1:800 at M3 or M6 → echocardiography + infectiological advice + chronic Q fever treatment; compulsory declaration: any confirmed case of Q fever (positive serology according to criteria + compatible clinic) → MDO → declaration to the regional public health directorate (DSPu) + epidemiological investigation + investigation of the animal source + control measures on farms if outbreak identified |
| Chronic Q fever — endocarditis Doxycycline + hydroxychloroquine for 18–36 months |
Coxiella burnetii endocarditis is the most serious and frequent manifestation of chronic Q fever - it accounts for 60-70 % of chronic forms and is life-threatening in the absence of treatment; epidemiology of chronic Q fever: occurs in 1-5 % of patients who have had an acute Q fever - onset delay: 1-20 years after the acute episode - major risk factors for chronicization: pre-existing valvulopathy (damaged native valve or valve prosthesis - relative risk × 30 to × 100) + immunosuppression (HIV + lymphoma + prolonged corticosteroid therapy + transplantation + dialysis) + pregnancy (risk of chronic reactivation post-partum) + arterial aneurysm + vascular endoprosthesis (aortic ++); clinical presentation of Coxiella endocarditis: prolonged or recurrent fever (sometimes absent) + altered general condition + weight loss + hepatosplenomegaly + digital hippocracticism (watch-glass nails) + vascular purpura + Raynaud's phenomenon + thromboembolic manifestations + progressive heart failure + heart murmurs (often pre-existing on damaged valve) - endocarditis picture with negative blood cultures (Coxiella does not grow on the usual culture media) ; diagnostic criteria for Coxiella burnetii endocarditis (modified Duke criteria): major criterion: anti-phase I IgG ≥ 1:800 (Raoult et al.) + vegetation on echocardiography (ETT or ETO) - minor criteria: fever + predisposing factor (valvulopathy) + vascular phenomenon + positive PCR on operated valve or serum - definite endocarditis according to modified Duke: 2 major criteria OR 1 major criterion + 3 minor criteria OR 5 minor criteria; treatment of Coxiella endocarditis - combination of doxycycline + hydroxychloroquine : mechanism of synergy: doxycycline is bacteriostatic in the acidic Coxiella phagolysosome - hydroxychloroquine alkalinizes the phagolysosome (increases pH) → potentiates the bactericidal activity of doxycycline in the intracellular environment - this combination is superior to doxycycline alone (cure rate 76 % vs. 43 % - study by Raoult et al. Lancet 1999); dosage: doxycycline 100 mg × 2/d PO + hydroxychloroquine 200 mg × 3/d PO (plasma target: 0.8-1.2 µg/mL); duration: native valve: 18 months minimum - valve prosthesis or immunodepression: 36 months or for life, depending on serological response | Follow-up and monitoring under Coxiella endocarditis treatment: IFI serology every 3 months during treatment + every 6 months for 5 years after discontinuation - cure objective: anti-phase I IgG 1,000 g or treatment >5 years) + ECG (risk of QTc prolongation - particularly in association with doxycycline - monthly ECG for the first 3 months) + CBC (rare cytopenias) + blood glucose (potential hypoglycemia) + plasma hydroxychloroquine assay recommended to adapt dosage and check compliance (target value 0,8-1.2 µg/mL); valve surgery for Coxiella endocarditis : similar indications to other endocarditis (refractory heart failure + mobile vegetation + repeated embolic events + abscesses) - surgery does not replace antibiotic treatment (it accompanies it) - explanted material → Coxiella PCR + BSL-3 culture + histology (granulomas); other forms of chronic Q fever: vascular infections (infected aneurysm + aortic stent): prolonged treatment 18-24 months + surgery if complications + annual serological follow-up for life; Coxiella chronic osteomyelitis: rare + treatment 18-24 months + MRI follow-up; post-Q fever fatigue syndrome (Q fever fatigue syndrome): 10-20 % of patients after acute Q fever → persistent fatigue >6 months + pain + cognitive impairment (picture similar to chronic fatigue syndrome) → mechanism: persistence of antigen + chronic low-grade inflammation → no true infectious relapse → prolongation of antibiotics is not effective → symptomatic management (progressive exercise + CBT) + NIAID study underway on predictive biomarkers |
| Q fever and pregnancy Fetal risk — co-trimoxazole until delivery |
Pregnancy is a major risk factor for severe Q fever and chronicity. Coxiella burnetii has a particular tropism for the human placenta (intraplacental replication) and can cause serious obstetrical complications; specific risks of Q fever during pregnancy: spontaneous miscarriage (first trimester) + fetal death in utero + prematurity + intrauterine growth retardation (IUGR) + placentitis + premature delivery - risk for the mother: progression to chronic postpartum Q fever (the immunotolerant context of pregnancy favors Coxiella persistence and chronicization); screening recommendations: all pregnant women with occupational or environmental exposure to ruminants should undergo serological screening (IFI IgG and IgM phase I and II) as soon as pregnancy is diagnosed + every trimester if continuous exposure - in the event of exposure to a documented epidemic focus → extended screening recommended by public health authorities (INSPQ in Quebec); treatment of Q fever during pregnancy: cotrimoxazole (TMP-SMX - Septra): 160/800 mg × 2/d PO - reference treatment throughout pregnancy (until delivery) - mechanism: sulfonamide inhibits Coxiella dihydropteroate synthase + TMP inhibits dihydrofolate reductase → double blockade of bacterial folate synthesis - proven efficacy in reducing obstetrical complications (meta-analysis Carcopino et al.) - contraindications: allergy to sulfonamides + G6PD deficiency + severe hepatic insufficiency - precautions at the end of pregnancy (3rd trimester): risk of neonatal jaundice (competition of sulfonamide with bilirubin for albumin) → some experts recommend switching to doxycycline or stopping TMP-SMX from 36 SA (individualized decision with the obstetrical team); after delivery: serological monitoring IFI phase I at 3 months + 6 months post-partum → if IgG phase I rising or ≥1:800 → echocardiography + infectiology advice → doxycycline + hydroxychloroquine treatment 18 months if endocarditis confirmed; breastfeeding and cotrimoxazole: passage into breast milk - contraindicated in premature newborns + at risk of kernicterus + G6PD deficiency → discuss discontinuation of breastfeeding or switch to another antibiotic compatible with breastfeeding | Obstetrical and infectiological follow-up of pregnant women with Q fever: mandatory collaboration between obstetrician + infectiologist (or specialist internist) + neonatology team if prematurity foreseeable; frequent obstetrical ultrasound scans (every 28 days) to monitor fetal biometry (IUGR) + vitality + amniotic fluid - cardiotocographic recording (CTG) from 26-28 SA if high-risk pregnancy; infectiological work-up: IFI IgG + IgM phase I + II serology every 4-6 weeks during pregnancy → if IgG phase I rises despite treatment → TEE + cardiology opinion → do not delay treatment of confirmed endocarditis even during pregnancy (doxycycline is teratogenic in the 1st and 2nd trimesters - avoid if possible before 24 SA - but can be used in the last trimester if major clinical benefit); declaration and epidemiological investigation: any case of Q fever in a pregnant woman → MDO + epidemiological investigation of source + screening of other pregnant women in the area of exposure + control measures on the farm (vaccination of herds + hygienic measures during parturition); vaccination against Q fever : Coxevac vaccine (phase I killed - inactivated) available in Australia since 1989 (Qvax) + in Europe for professionals at risk in certain countries - not available in Canada + no mass vaccination currently recommended in Quebec + compulsory pre-vaccination check-up in Australia (serology + Coxiella IDR) to exclude persons already immunized (risk of severe reaction if revaccination of an immunized subject) |
| Screening and prevention for at-risk individuals Valvulopathy — immunosuppression — agricultural professionals |
The prevention of chronic Q fever relies on the early identification of individuals at risk of chronicity among those exposed to Coxiella burnetii and their systematic serological screening; people at high risk of chronicity after acute Q fever - systematic serological testing recommended in : any patient with confirmed acute Q fever + valvulopathy (native or prosthesis - risk × 30-100 of chronicization) + immunosuppression (HIV + lymphoma + transplantation + prolonged corticosteroid therapy ≥20 mg/d prednisone) + aortic aneurysm + stent + chronic dialysis + history of cardiac surgery + pregnant woman; course of action for at-risk individuals exposed to a Q fever outbreak: immediate serology + repeated at 3 and 6 weeks post-exposure - if seroconversion detected: pre-emptive treatment with doxycycline 200 mg/d × 14 days in people at risk of chronicization (valvulopathy ++) + baseline echocardiography + quarterly serological monitoring; individual and collective preventive measures: individual respiratory protection (FFP2 or FFP3 mask) when in contact with parturient animals or contaminated animal products - gloves + impermeable apron during parturition - washing hands and arms with soapy water + disinfectant after animal contact - prohibit access by pregnant women to contaminated animals and animal products. prohibit access by pregnant women + immunocompromised people + valvulopaths to lambing + calving + kidding areas for goats during the lambing season - avoid consumption of raw milk + unripened raw milk cheeses in endemic areas ; on-farm measures : mandatory reporting to the Canadian Food Inspection Agency (CFIA) of all documented animal outbreaks + restrictions on animal movements + hygienic burial of placentas and abortion products + disinfection of bedding + vaccination of herds (inactivated phase II available for animals in some countries - phase I for humans only in Australia) + reduction of airborne manure near dwellings | Pre-emptive serological screening and education of agricultural professionals: Quebec screening program (INSPQ): in the absence of a documented epidemic outbreak - no mass screening recommended in the general population - targeted screening: agricultural professionals + veterinarians + laboratory workers handling ruminant samples → annual IFI serology in endemic areas (Montérégie + Estrie + Centre-du-Québec) - information and training for farmers: increased risk during spring births + recognize symptoms of acute Q fever (fever + intense headache + pneumonia) + consult rapidly if febrile syndrome after animal contact + report repeated abortions in the herd to CFIA; occupational medicine and Q fever: agricultural workers + veterinarians + laboratory technicians exposed to Coxiella → annual occupational medical follow-up + basic IFI serology on hiring → documentation of immune status → IFI serology if suggestive symptoms post-exposure + CNESST file if occupational disease (occupational Q fever recognized as an occupational disease in Quebec); Quebec resources: INSPQ (inspq.qc.ca - fièvre Q surveillance) + Direction de santé publique régionale + Réseau de santé publique vétérinaire du Québec (RSPVQ) + Centre de référence pour agents biologiques classés - LNM Winnipeg (PCR + reference serology) + Urgences-santé and medical officers of health in the event of an outbreak. |
| Q Fever - Notifiable Disease and Bioterrorism MDO — Category B agent — INSPQ oversight |
Coxiella burnetii is classified as a Category B bioterrorism agent by the US CDC and WHO due to its extremely low infectious dose (1 bacterium is enough) + its exceptional environmental resistance + its airborne transmissibility + the possibility of aerosol production and dissemination; biohazard characteristics: heat resistance: survival at 63°C for 30 min (HTST pasteurization insufficient - requires UHT or 72°C × 15 s) + resistance to desiccation : survival >40 months in dry wool + survival in soil for several weeks - resistance to usual disinfectants (chlorine at standard concentrations) - but sensitive to ethanol 70 % + hypochlorite 0.5 % + formaldehyde 5 %; Q fever as a notifiable disease (MDO) in Canada and Quebec: any confirmed or probable case of Q fever → compulsory declaration to the medical officer of the regional public health department within 24 hours - probable case: compatible clinical syndrome + epidemiological exposure + positive serology (anti-phase II IgG ≥ 1:128 or IgM ≥ 1:32) - confirmed case: strict biological criteria (anti-phase II IgG ≥ 1:512 in acute phase or seroconversion × 4) + positive PCR; national epidemiological surveillance: Public Health Agency of Canada (PHAC) + INSPQ in Quebec + CDC Fluwatch for the international component - reporting to the national notifiable disease surveillance system (SNDMO); laboratory protective measures: handling of biological samples from patients suspected of having Q fever → BSL-2 minimum + BSL-3 recommendations for cultivation or propagation of the bacteria + wearing of N95 masks + gloves + protective goggles + working in a laminar flow hood - mandatory alert to laboratory personnel if analysis is requested on a patient suspected of having Q fever. | Management of a Q fever outbreak - Quebec public health protocol: detection of a cluster: ≥2 epidemiologically linked cases in a geographical area or workplace → activation of the regional intervention plan → epidemiological field investigation (patient interviews + exposure mapping + investigation of suspect farms) + environmental sampling (air + soil + manure); control measures in epidemic phase: temporary closure of suspect farms to outside visitors + serological screening of residents + exposed workers + information for healthcare professionals in the region (rapid alert via public health teams) + reinforcement of individual protection measures + emergency vaccination of infected herds (phase II - under veterinary supervision) + appropriate public communication (avoiding panic while ensuring clear information on risks and protective behaviors); international reference : Center national de référence - CNR Coxiella burnetii (Institut de recherche biomédicale des armées - IRBA + Institut Pasteur) in France - collaboration with LNM Winnipeg for Canada - follow-up of complex chronic cases (endocarditis) in multidisciplinary consultation (infectiology + cardiology + internal medicine) in Quebec university hospitals (CHUM + CHU Sainte-Justine + CHU de Québec + CHUS Sherbrooke). |
ℹ️
Q Fever and Negative Blood Cultures — a Classic Diagnostic Trap: Q fever is one of the most common causes of blood culture-negative endocarditis worldwide. Coxiella burnetii It does not grow on the usual culture media for bacteremia (aerobic/anaerobic blood culture bottles). In any patient with culture-negative endocarditis—particularly with an agricultural or veterinary history, pre-existing valvulopathy, or a concomitant granulomatous hepatitis picture—Q fever serology (IgG and IgM phase I and II by IFA) should be systematically requested, as well as serology for brucellosis and bartonellosis.
Situations requiring urgent medical assessment
Acute febrile illness + severe headache + recent agricultural or veterinary context → Probable acute Q fever → urgent IFA serology + empirical doxycycline without waiting for serological confirmation.
Prolonged fever + progressive heart failure + negative blood cultures + known valvulopathy → Coxiella endocarditis → urgent anti-phase I IgG + TTE + infectious disease consultation + cardiology consultation.
Pregnant woman with agricultural contact (lambing/calving) + fever or signs of threatened preterm labor → Gestational Q fever → Urgent serology + Obstetrician + Infectious disease specialist + TMP-SMX if confirmed.
Consult at Clinique Omicron
Clinique Omicron physicians evaluate patients with febrile syndrome after agricultural or veterinary exposure, prescribe initial serological testing (IFI *Coxiella burnetii* phase I and II), and provide post-treatment follow-up for acute forms. Chronic forms (endocarditis, gestational Q fever) are referred to specialized teams at university hospitals with which Clinique Omicron collaborates. Reporting to public health authorities is carried out in accordance with Quebec legal obligations. Consultations are available at several service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for medical advice from a doctor or infectious disease specialist. Chronic Q fever is a serious illness requiring specialized care.
Omicron Clinic
Need to consult a doctor?
Treatment within 24-48 hours. In-clinic or telemedicine, anywhere in Quebec.
Insurance receipts. 7j/7. No family doctor required.