Q Fever (Coxiella burnetii) – Serology and PCR

Conformément au Règlement de l’Ontario 671/92 de la Loi sur les services en français, les renseignements d’analyses de laboratoire liés à la présente page ne sont offerts qu’en anglais parce qu’ils sont de nature scientifique ou technique et destinés uniquement à l’usage des fournisseurs de soins de santé qualifiés et non aux membres du public.

Background
This page provides testing information for Q fever at Public Health Ontario (PHO). The causative agent of Q fever is the intracellular bacterium Coxiella burnetii.

Updates as of November 24, 2025:

Effective November 29, 2025, PHO will discontinue Q fever (Coxiella burnetii) IgM serology testing. IgM testing is associated with low clinical specificity and can persist for more than a year in some patients, limiting its diagnostic value. As a result, IgM results are not recommended for clinical diagnosis or public health management of suspected Q fever cases.
IgG testing for Q fever will remain routinely available at PHO and is the recommended method for individuals with compatible exposure history and clinical presentation. The following sections were added: testing indications, methods, performance, limitations, and result interpretation.
PCR testing information was added.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 22 nov. 2025.

Testing Indications

Testing is indicated for individuals with relevant exposure history and clinical presentation compatible with suspected acute (also known as primary) or chronic (also known as persistent focalized) Q fever.

If acute infection is suspected, blood PCR and serology may be considered within the first 2 weeks of illness with follow-up convalescent serology collected 3-6 weeks later. If chronic infection is suspected, serology with or without PCR of biopsied tissues may be considered.^1,2

As a disease of public health significance (DoPHS) in Ontario, additional disease-specific information is available in the Ontario Health Public Health Standards Appendix 1 for Disease: Q Fever.

Acceptance/Rejection Criteria

Requests will only be accepted if the following information is provided:

clinical history
symptom onset date
relevant exposure history (e.g., contact with infected animals, residence near a farm or livestock operation, consumption of unpasteurized dairy products)

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Q fever or Coxiella burnetii PCR or molecular	General Test Requisition	Whole Blood	1.0 ml whole blood	EDTA tube
Q fever or Coxiella burnetii serology or antibody	General Test Requisition	Serum	5.0 ml whole blood or 1.0 ml serum	Serum Separator Tubes (SST)
Q fever or Coxiella burnetii PCR or molecular	General Test Requisition	Tissue biopsy (e.g. heart valve, graft)	N/A	Empty sterile container

Submission and Collection Notes

Complete all fields of the test requisition including:

clinical history (including antibiotics if administered)
symptom onset date
relevant exposure history

Note: Specimens may be delayed or rejected if they are not the appropriate specimen type, have insufficient volume, or are not accompanied by relevant patient information.

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or delay in testing.

Timing of Specimen Collection

For acute/primary infection, an acute serum (collected early after the onset of symptoms) and a convalescent serum (collected 3-6 weeks later) is required for serological confirmation.

For PCR in acute/primary infection, whole blood samples should ideally be collected within the first two weeks of symptom onset and prior to the initiation of antibiotic therapy, but treatment should never be withheld if required based on the patient’s clinical status. PCR in chronic infection can be considered at any time on biopsy tissues.

Limitations

Grossly haemolysed, icteric, lipemic or microbial contaminated sera or plasma are unsuitable for serological testing.

Storage and Transport

Centrifuge serum if using SST. To prevent erroneous results due to the presence of fibrin, ensure that complete clot formation has taken place prior to centrifugation of samples.
Blood samples should be stored at 2-8°C following collection and shipped on ice packs to PHO’s laboratory as soon as possible.
Tissue samples should be stored frozen following collection and shipped on dry ice to PHO’s laboratory as soon as possible.
All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Coxiella burnetii serology is performed once per week at PHO’s laboratory Toronto site. Turnaround time is up to 14 calendar days from receipt at PHO.

Coxiella burnetii PCR is forwarded to the National Microbiology Laboratory (NML) in Winnipeg. Turnaround time for PCR is up to 21 calendar days from receipt at PHO.

Test Methods

Method: Coxiella burnetii serology is performed using a commercial Focus Diagnostics indirect immunofluorescence antibody (IFA) IgG assay. This assay provides semi-quantitative detection of IgG antibodies to phase II (early) and phase II (late) C. burnetii antigens.

Coxiella burnetii PCR is performed at NML using a laboratory-developed real-time PCR specific for the IS111 and IS30 insertion sequence elements of C. burnetii.

Performance and Limitations: IFA serology sensitivity and specificity vary by time from symptom onset. Results may be negative in the first weeks of illness. Phase II IgG titres may take 2-4 weeks to become detectable, while phase I IgG titres may take 4-6 weeks to become detectable. Phase II IgG titres peak and decline within months of primary infection but usually persist at low levels for years. Residual background seropositivity in healthy populations may be detectable from past infection in the absence of disease. Phase I IgG titres peak and decline within months of primary infection and become undetectable within years, except in cases of chronic/persistent infection. However, serology results alone are usually insufficient for the clinical diagnosis of chronic Q fever and should be combined with clinical data.^3,4

Blood PCR sensitivity during acute infection is estimated between 26% to 98%, with highest sensitivity seen within the first week of symptom onset and lowered thereafter to below 50%. Blood PCR should not be used to rule out infection due to its limited sensitivity. Biopsy tissue PCR sensitivity is not well established. Overall specificity is estimated from 90% to 100%^3,5,6,7

Algorithm

If serology is positive, reactive titres are reported between 1:16 and 1:8,192. If titre measurements greater than 1:8,192 are needed following a positive result for patient management, contact PHO’s Customer Service Centre.

Interpretation

In acute/primary infection, phase II IgG titres appear first and are higher than phase I IgG titres. Two serum samples showing a fourfold or higher increase in phase II IgG titres over 3-6 weeks are needed for serological diagnosis.

In chronic/persistent focalized infection, phase I IgG titres rise significantly over months and often exceed phase II IgG titres. However, it is not uncommon for patients with acute/primary infection to develop similar high phase I IgG titres in the first few months that eventually regress. Serology is not sufficient for diagnosis and clinical correlation is always required.

Coxiella burnetii IFA serology interpretations:

Phase II IgG Titre Result	Phase I IgG Titre Result	Interpretation
≤ 1:128	< 1:16	No specific serologic evidence of infection. A negative test during the first two weeks of illness does not rule out infection. If acute/primary infection is suspected, repeat collection in 3-6 weeks to assess for seroconversion.
≥ 1:256	< 1:16	Serological evidence of possible recent infection. If acute/primary infection is suspected, repeat collection in 3-6 weeks to assess for fourfold increase in phase II titres.
≥ Phase I titre	≥ 1:16	Serological evidence of possible recent or remote infection. If acute/primary infection is suspected, repeat collection in 3-6 weeks to assess for fourfold increase in phase II titres.
< Phase I titre	≥ 1:16 and ≤ 1:512	Serological evidence of possible remote infection. If chronic/persistent focalized infection is suspected, repeat collection in 3-6 weeks to assess for increase in phase I titres.
< Phase I titre	≥ 1:1,024	Serological evidence of possible chronic/persistent focalized infection. Clinical correlation required.

Coxiella burnetii PCR interpretations:

Coxiella burnetii PCR Result	Interpretation
Negative	No evidence of C. burnetii DNA. A negative result does not exclude the diagnosis of Q fever.
Positive	C. burnetii DNA detected

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Positive specimens are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

References

Centers for Disease Control and Prevention. Q Fever [Internet]. Atlanta: Centers for Disease Control and Prevention; [cited 2024 Sept. 11]. Available from: https://www.cdc.gov/q-fever/about/index.html
Anderson A, Bijlmer H, Fournier PE, Graves S, Hartzell J, Kersh GJ, Limonard G, Marrie TJ, Massung RF, McQuiston JH, Nicholson WL, Paddock CD, Sexton DJ. Diagnosis and management of Q fever--United States, 2013: recommendations from CDC and the Q Fever Working Group. MMWR Recomm Rep. 2013 Mar 29;62(RR-03):1-30. Erratum in: MMWR Recomm Rep. 2013 Sep 6;62(35):730. PMID: 23535757.
van der Hoek W, Versteeg B, Meekelenkamp JC, Renders NH, Leenders AC, Weers-Pothoff I, Hermans MH, Zaaijer HL, Wever PC, Schneeberger PM. Follow-up of 686 patients with acute Q fever and detection of chronic infection. Clin Infect Dis. 2011 Jun 15;52(12):1431-6. doi: 10.1093/cid/cir234. PMID: 21628483.
Herremans T, Hogema BM, Nabuurs M, Peeters M, Wegdam-Blans M, Schneeberger P, Nijhuis C, Notermans DW, Galama J, Horrevorts A, van Loo IH, Vlaminckx B, Zaaijer HL, Koopmans MP, Berkhout H, Socolovschi C, Raoult D, Stenos J, Nicholson W, Bijlmer H. Comparison of the performance of IFA, CFA, and ELISA assays for the serodiagnosis of acute Q fever by quality assessment. Diagn Microbiol Infect Dis. 2013 Jan;75(1):16-21. doi: 10.1016/j.diagmicrobio.2012.09.001. Epub 2012 Oct 5. PMID: 23041450.
Wielders CC, Wijnbergen PC, Renders NH, Schellekens JJ, Schneeberger PM, Wever PC, Hermans MH. High Coxiella burnetii DNA load in serum during acute Q fever is associated with progression to a serologic profile indicative of chronic Q fever. J Clin Microbiol. 2013 Oct;51(10):3192-8. doi: 10.1128/JCM.00993-13. Epub 2013 Jul 17. PMID: 23863573; PMCID: PMC3811622.
Jaton K, Peter O, Raoult D, Tissot JD, Greub G. Development of a high throughput PCR to detect Coxiella burnetii and its application in a diagnostic laboratory over a 7-year period. New Microbes New Infect. 2013 Oct;1(1):6-12. doi: 10.1002/2052-2975.8. Epub 2013 Sep 18. PMID: 25356317; PMCID: PMC4184484.
Ghanem-Zoubi N, Mustafa-Hellou M, Zahran M, Gazit L, Shalaginov R, Dabaja-Younis H, Szwarcwort M. The integration of Coxiella burnetii PCR testing in serum into the diagnostic algorithm of suspected acute Q fever in an endemic setting. J Clin Microbiol. 2024 Apr 10;62(4): e0170323. doi: 10.1128/jcm.01703-23. Epub 2024 Mar 12. PMID: 38470022; PMCID: PMC11005359.