Listeriosis Clinical Testing Information
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This page provides healthcare providers with information on where and how to access primary testing for suspect listeriosis. Clinical specimens, such as blood or cerebrospinal fluid (CSF) should be submitted to a local laboratory, either in your area hospital or a private lab, for culture (blood culture or CSF culture). PHO does not perform testing on primary clinical specimens. Positive culture isolates will be forwarded by the local laboratory to PHO for further testing.
Clinical Testing Indications
- Symptomatic individuals with risk factors for severe illness, fever, or invasive disease warrant clinical laboratory testing if exposed to a suspect contaminated or recalled food product for Listeria (see table below).
- Testing for Listeria in asymptomatic people, including those who consumed a contaminated or recalled food product, is not recommended.
Clinical Testing Methods
- Testing for listeriosis requires routine bacterial culture of sterile site specimens (e.g. blood culture, cerebrospinal fluid).
- Stool testing is NOT a recommended method for the specific diagnosis of listeriosis. However, stool testing may be performed to rule out other causes of gastrointestinal illness.
- Serology testing is not available.
Where to Submit Clinical Specimens
- Specimens for listeriosis (e.g. blood culture) should be submitted to your hospital or private laboratory along with their specific laboratory requisition (or a regular OHIP requisition). Do not use PHO’s requisition and do not submit clinical specimens to PHO.
- If a culture becomes positive for Listeria at your hospital or private laboratory, the laboratory will forward the cultured isolate to PHO’s laboratory for identification and subtyping.
Summary of Clinical Testing Recommendations for Listeria Following Consumption of Contaminated or Recalled Food Product
The following recommendations apply in clinical instances following consumption of a contaminated or recalled food product for Listeria.
| If Presenting With | Listeria Testing Recommendations |
|---|---|
|
Asymptomatic or resolved symptoms |
|
|
Acute afebrile gastroenteritis1 with no invasive manifestations2 and no risk factor for severe illness3 |
|
|
Acute afebrile gastroenteritis1 with no invasive manifestations2 but with one or more risk factors for severe illness3 |
|
|
Acute febrile (≥ 38.1°C) gastroenteritis1 with no other invasive manifestations2 |
|
|
Invasive manifestations2
|
|
1 If gastroenteritis symptoms are present and severe (or at risk of becoming severe due to the patient’s underlying risk factors), ruling out an alternative aetiology may be advised by performing routine bacterial stool testing for Salmonella, Shigella, Campylobacter, Yersinia, and Shiga toxin-producing E. coli. Note that bacterial stool testing does not include testing for Listeria. If the patient fulfills PHO’s acceptance algorithm for viral stool testing, viral stool testing may also be considered.
2 Invasive manifestations may include headache, stiff neck, confusion, loss of balance, or convulsions.
3 Individuals with risk factors for severe illness include people with impaired immune system, neonates, elderly, and pregnant women.
4 Two sets of blood cultures should be collected from different blood draw sites. A third set of blood cultures should be drawn only if endocarditis is suspected. Consider collecting another set of blood cultures after 48 hours if the initial sets are negative and there is ongoing clinical concern for invasive listeriosis.
Food Testing Considerations
Please refer to PHO’s Food Testing webpage for information on primary testing of food and environmental products submitted by local public health units to PHO. Note that food products that are already recalled are generally not tested.
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