Coccidioides — Serology

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Background
Serologic testing (antibody) for Coccidioides and other fungi is available at Public Health Ontario. Please note, the specific serologic test request must be clearly indicated on the requisition form.

Fungal infections can be challenging to diagnose as symptoms are often non-specific and can mimic bacterial, viral, other fungal infections or malignancy. Culture remains the gold standard for the diagnosis of most invasive fungal infections; however, results of fungal serological tests can often be used to aid in the diagnosis and/or management of specific fungal infections and fungal allergies.

Coccidioides immitis/posadasii is endemic to the southwestern USA, or northern Mexico and causes coccidioidomycosis (Valley Fever). It is not endemic to Canada but can be seen in people that have returned from travel to endemic areas.

For information on fungal culture please refer to:

For other fungal serology testing refer to:

Updates as of September 14, 2026

This page contains test information specific to Coccidioides Serology and replaces the information previously published under Fungal Serology.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 14 sept. 2026.

Testing Indications

Serologic testing for Coccidioides species is indicated in patients with suspected pulmonary or disseminated coccidioidomycosis with a travel history to endemic regions (e.g. Southwestern U.S.)¹

Acceptance/Rejection Criteria

Test request is rejected if:

inappropriate specimen type is submitted
specimen volume is insufficient for testing
required patient information and relevant clinical history are not provided on the requisition
specific fungal agent’s name (i.e. Coccidioides) is not specified on the requisition. “Fungal serology” is not an acceptable request.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Coccidioides Serology	General Test Requisition	Serum	1.0 ml serum	Collect blood in serum separator tubes (SST)

Submission and Collection Notes

Complete all fields of the requisition form, including:

Test(s) requests (indicate the specific fungus/fungi being requested) and indication(s) for testing.
Patient setting/population/source
Travel history (location and dates) to endemic area (if requesting Coccidioides serology)
Symptoms
Onset date

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. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay. .

Timing of Specimen Collection

An acute serum sample (collected early after the symptom onset) and a convalescent (collected 2–3 weeks later) may be required for laboratory diagnosis.

Limitations

Haemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing.

Storage and Transport

Centrifuge serum if using SST.

Samples should be stored at 2–8°C following collection and shipped on ice packs to PHO as soon as possible. For transportation, place specimen in biohazard bag and seal.
All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Coccidioides testing is performed once per week at Public Health Ontario’s Toronto location.

TAT for Coccidioides serology is up to 10 business days after receipt.

Test Methods

Coccidioides serology is screened by EIA which detects IgM (against TP antigens) and IgG (against CF antigens). Results will be reported as “Non-Reactive”, “Indeterminate” or “Reactive”. Samples which are reactive for IgG or IgM will be further tested by Immunodiffusion.

Coccidioides is confirmed by Immunodiffusion and detects ID-TP and ID-CF band precipitins.

Limitations:
A negative result does not rule out the possibility of current infection or previous exposure.

Interpretation

The following table provides possible test results with associated interpretations:

Coccidioides immitis EIA and Immunodiffusion
	EIA Result		Immunodiffusion Result		Interpretation
Scenario	IgM	IgG	TP Band	CF Band	Interpretation
1.	Non-Reactive	Non-Reactive	Not done	Not done	No detectable level of antibody against Coccidioides immitis¹
2.	Indeterminate	Indeterminate	Not done	Not done	Coccidioides immitis antibody status inconclusive.²
3.	Indeterminate	Non-Reactive	Not done	Not done	Coccidioides immitis antibody status inconclusive.²
4.	Non-Reactive	Indeterminate	Not done	Not done	Coccidioides immitis antibody status inconclusive.²
5.	Reactive	Reactive	Reactive	Reactive	Serologic evidence of acute or recent infection.
6.	Reactive	Reactive	Reactive	Non-Reactive	Serologic evidence of acute or recent infection.
7.	Reactive	Reactive	Partial	Reactive	Serologic evidence of infection.³
8.	Reactive	Reactive	Non-Reactive	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
9.	Reactive	Reactive	Reactive	Partial	Serologic evidence of acute or recent infection.
10.	Reactive	Reactive	Partial	Partial	Coccidioides immitis antibody status inconclusive.²
11.	Reactive	Reactive	Non-Reactive	Partial	Coccidioides immitis antibody status inconclusive.²
12.	Reactive	Reactive	Partial	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
13.	Reactive	Indeterminate	Reactive	Reactive	Serologic evidence of acute or recent infection.
14.	Reactive	Indeterminate	Reactive	Non-Reactive	Serologic evidence of acute or recent infection.
15.	Reactive	Indeterminate	Non-Reactive	Reactive	Serologic evidence of infection.³
16.	Reactive	Indeterminate	Non-Reactive	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
17.	Reactive	Indeterminate	Reactive	Partial	Serologic evidence of acute or recent infection.
18.	Reactive	Indeterminate	Partial	Reactive	Serologic evidence of infection.³
19.	Reactive	Indeterminate	Partial	Partial	Coccidioides immitis antibody status inconclusive.²
20.	Reactive	Indeterminate	Non-Reactive	Partial	Coccidioides immitis antibody status inconclusive.²
21.	Reactive	Indeterminate	Partial	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
22.	Reactive	Non-Reactive	Reactive	Reactive	Serologic evidence of acute or recent infection.
23.	Reactive	Non-Reactive	Reactive	Non-Reactive	Serologic evidence of acute or recent infection.
24.	Reactive	Non-Reactive	Non-Reactive	Reactive	Serologic evidence of infection.
25.	Reactive	Non-Reactive	Non-Reactive	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
26.	Reactive	Non-Reactive	Reactive	Partial	Serologic evidence of acute or recent infection.
27.	Reactive	Non-Reactive	Partial	Reactive	Serologic evidence of infection.
28.	Reactive	Non-Reactive	Partial	Partial	Coccidioides immitis antibody status inconclusive.²
29.	Reactive	Non-Reactive	Non-Reactive	Partial	Coccidioides immitis antibody status inconclusive.²
30.	Reactive	Non-Reactive	Partial	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
31.	Indeterminate	Reactive	Reactive	Reactive	Serologic evidence of acute or recent infection.
32.	Indeterminate	Reactive	Reactive	Non-Reactive	Serologic evidence of acute or recent infection.
33.	Indeterminate	Reactive	Non-Reactive	Reactive	Serologic evidence of recent, past or chronic infection.
34.	Indeterminate	Reactive	Non-Reactive	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
35.	Indeterminate	Reactive	Reactive	Partial	Serologic evidence of infection.
36.	Indeterminate	Reactive	Partial	Reactive	Serologic evidence of recent, past or chronic infection.
37.	Indeterminate	Reactive	Partial	Partial	Coccidioides immitis antibody status inconclusive.²
38.	Indeterminate	Reactive	Non-Reactive	Partial	Coccidioides immitis antibody status inconclusive.²
39.	Indeterminate	Reactive	Partial	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
40.	Non-Reactive	Reactive	Reactive	Reactive	Serologic evidence of acute or recent infection.
41.	Non-Reactive	Reactive	Reactive	Non-Reactive	Serologic evidence of infection.
42.	Non-Reactive	Reactive	Non-Reactive	Reactive	Serologic evidence of recent, past or chronic infection.
43.	Non-Reactive	Reactive	Non-Reactive	Non-Reactive	Coccidioides immitis antibody status inconclusive.²
44.	Non-Reactive	Reactive	Reactive	Partial	Serologic evidence of infection.
45.	Non-Reactive	Reactive	Partial	Reactive	Serologic evidence of recent, past or chronic infection.
46.	Non-Reactive	Reactive	Partial	Partial	Coccidioides immitis antibody status inconclusive.²
47.	Non-Reactive	Reactive	Non-Reactive	Partial	Coccidioides immitis antibody status inconclusive.²
48.	Non-Reactive	Reactive	Partial	Non-Reactive	Coccidioides immitis antibody status inconclusive.²

Coccidioides Interpretation Comments:

A non-reactive serologic test result does not rule out the possibility of current infection. If coccidiomycosis is suspected, resubmit a new specimen for repeat serology or submit appropriate specimens for culture.
An inconclusive serologic test result does not rule out the possibility of infection. If coccidiomycosis is suspected, resubmit a new specimen for repeat serology or submit appropriate specimens for culture.
Advise follow-up specimen for repeat serology if clinically indicated.

Coccidioides immitis immunodiffusion results are reported for both ID-TP and ID-CF bands (precipitins) as “Non-Reactive”, “Partial” or “Reactive”. Formation of ID-TP bands is evidence of acute or recent infection. Formation of ID-CF bands is evidence of recent past or chronic Coccidioides infection. ID-TP and ID-CF bands may be reported as partial bands; this should be interpreted as an inconclusive result.

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.

References

Theel ES, Kus JV, Grys TE, Ampel NM, Schwartz IS, Zhang SX. Practical guidance for clinical microbiology laboratories: antibody and antigen detection methods for dimorphic fungal infections. Clin Microbiol Rev. 2025;38(2): e00005-20. Available from: https://journals.asm.org/doi/10.1128/cmr.00005-20#