As an ‘evergreen’ document the PHI Guide is revised and updated to reflect current changes in field of microbiology laboratory testing and regulations. Printed versions of this document should be checked against the Public Health Ontario website to ensure the most recent version is being referenced.
Environmental swab testing supports foodborne illness outbreaks and investigations. Public Health Inspectors can review requirements and guidelines before submitting environmental swabs to PHO for testing.
PHO Laboratory performs microbiological pathogen specific testing of environmental swabs to support foodborne outbreak investigations. Environmental swabs processed during foodborne outbreak investigations will be tested for the presence or absence of a specified clinically confirmed bacterial pathogen from a physical environment (e.g., cutting board, meat slicer, etc.).
Instruction for sample selection of swabs for an outbreak investigation:
To identify the source of the pathogen, selection of sampling sites for the investigation should be informed by environmental and epidemiological factors. Random sampling may delay the identification of the source of the outbreak. Samples deemed as most likely to be positive should be sampled and submitted first.
PHO Laboratory should be notified prior to sample submission to allow for preparation of materials required for testing. Please contact the laboratory by calling PHO Laboratory Customer Service Centre at 416-235-6556 or toll free 1-877-604-4567.
Containers for Sampling
Environmental swabs are available from the PHO Laboratory warehouse and can be ordered by calling the PHO Laboratory Customer Service Centre at 416-235-6556 or toll free 1-877-604-4567. The swab vial contains neutralizing solution as transport medium. This medium is able to neutralize quaternary ammonium compounds and phenolic disinfectants.
Each sample and its accompanying requisition must be labeled with a unique identifier.
The following steps are recommended to organize and minimize sample collection time:
Investigate before sampling to determine a sampling plan.
Ensure all materials required are available prior to collection.
Label sample container using a permanent marker.
Complete requisition(s) before or after, never during, sample collection.
After collection, double check to ensure the sample unique identifier on the sample container and requisition are legible and match.
Using aseptic technique, open the sterile swab container; grasp the handle end of the swab.
Remove the swab aseptically being careful not to touch any portion that might be inserted into the vial.
Moisten the swab head and press out the excess solution against the interior wall of the vial with a rotating motion.
Hold the swab handle to make a 30 ° angle contact with the surface. Rub the surface slowly and thoroughly over approximately 50 cm2 of the surface three times, reversing direction between strokes.
After the area has been swabbed, using aseptic technique, return the swab to the vial.
Complete all sections of the Environmental Microbiology Investigation Requisition with appropriate information to ensure accurate tracking of sampling. Check “Other analysis” and record the specific pathogen of interest name, e.g., Listeria monocytogenes, in the same area.
Ensure samples are submitted to the laboratory under refrigeration conditions (2 – 8 °C) in a manner that will not leak during transport.
Leaking swab vials will be rejected by the laboratory. Ensure the vial is closed tightly to prevent leakage resulting in sample rejection.
Absence of a unique identifier linking sample(s) to a sampling location on a requisition will result in rejection of sample(s) by the laboratory.
For an investigation where sampling areas are smaller and physically different, a new swab should be used for each different area.
For an investigation where the sample area is large, multiple sections may be swabbed with one swab. Sampling details should be accurately recorded to ensure traceability when laboratory results are received to ensure appropriate interpretation of results.
Laboratory Acceptance Criteria
The accuracy of the test results may be affected by improper collection, handling and/or shipping. Swab samples that do not meet the acceptance criteria may be rejected by the laboratory and a new sample may be re-submitted with a newly completed requisition. The acceptance criteria are outlined below.
Swab samples must be received from an authorized board of health submitter.
Swabs will only be accepted for testing to support a foodborne outbreak investigation.
The requisition must be completed upon receipt at the laboratory, including date and location of collection. If a sample is received without a requisition it will not be processed; however, the sample will be held for 24 hours.
The requisition must have a unique identifier that matches the unique identifier on the swab collection vial.
Environmental swabs are available from the PHO Laboratory warehouse and can be ordered by calling PHO Laboratory Customer Service Centre at 416-235- 6556 or toll free 1-877-604-4567. Unapproved swabs will not be accepted.
The sample container must be secure to avoid leaks during transport.
The sample temperature must meet the requirements listed below upon receipt at the laboratory:
Swabs should be shipped with cold packs to maintain a temperature between 2.0 to 8.0 °C during transport to the laboratory.
Swabs received frozen or greater than room temperature may be rejected and not processed.
Reporting and Interpretation of Test Results
The following tables outline the reporting limits and interpretation of the environmental swab analyses. Information such as collection conditions, time and date, and sanitation details should be considered when interpreting swab results.
Foodborne pathogens should not be detected from a ready-to-eat food preparation surface swab and would indicate poor food handling, inadequate work surface sanitation practices or possible contamination from an ill food handler. Appendix C: Major Foodborne Diseases: General Features provide additional information regarding the organisms incubation period, clinical symptoms, mode of transmission and associated foods.