GAS – Group A Streptococcus – Outbreak

Testing Indications

Contact Public Health Ontario laboratories prior to collecting samples (ID Protocol Appendix A chapter GAS, invasive section 6.6)

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

GAS – Group A Streptococcus – Outbreak

Pure viable subculture of the organism on appropriate media  (eg Blood Agar) or a swab of a pure subculture in Amies transport medium2,3

Submission and Collection Notes


Complete all fields on the Reference Bacteriology Requisition, including:

  • test requested 
  • specimen source
  • culture information 
  • presumptive identification
  • clinical /epidemiology

If a swab or broth is received the TAT will be delayed by at least 24 hours.


Primary cultures are unacceptable; they should be processed in the originating lab and will be rejected.


  • Mixed or non-viable cultures will not be tested. The submitter will be contacted by telephone. A written report will be issued to indicate that the test has been rejected.
  • The submitting laboratory will be contacted regarding isolates or specimens from outbreaks that are submitted inappropriately (e.g.  mis-labelled/un-labelled).

Storage and Transport

Label the specimen with the patient’s full 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 testing delay.

Place specimen in biohazard bag and seal. Specimen should be transferred to the laboratory within 48-72 hours of collection.

Special Instructions

Specimens should be transferred within 48-72 hours of collection.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Isolates are confirmed as GAS prior to further investigation

Emm typing: up to two weeks for outbreak specimens

PFGE: up to two weeks

Test Methods

All Group A Streptococcus isolates are identified/confirmed by:

  • gram stain
  • latex agglutination


Results are reported to the ordering physician or health care provider as indicated on the requisition and to the health unit.

Additional Information

Criteria and considerations:

  • The health unit must be involved.
  • The situation must meet criteria for declaring a GAS outbreak as defined in the ID Protocol Appendix A chapter GAS, invasive section 6.5 Outbreak Case Definition. 
  • The outbreak must have been assigned an iPHIS outbreak number OR See cluster –related non- outbreak GAS (below).
  • The invasive index case isolate must be available. Other historical isolates may also be available. If these were not previously submitted to PHO laboratory then the health unit should attempt to locate them at the original testing laboratory and have purity plates sent under the outbreak number. If the index case is not available then the utility of testing must be discussed with the microbiologist.
  • he microbiologist or designate approves outbreak -level testing which includes Pulsed Field Gel Electrophoresis (PFGE) performed at PHO laboratory and emm-typing performed at the National Microbiology Laboratory (NML).

Process for approved outbreaks:

  • PHO laboratory does not perform isolation from primary specimens for GAS or invasive GAS (iGAS). Primary swabs received by PHO laboratory will be discarded.
  • PHO laboratory does not supply swabs for collection of specimens that will be tested by another laboratory.
  • Submit purity plates of identified isolates. Swabs of isolates are also acceptable but are discouraged. Swabs will delay turnaround time by at least 24 hours.
  • Only submit a purity plate from one isolate per person (NOT per site).
  • Requisitions and purity plates should be labeled with the outbreak number.
  • All isolates will be confirmed as GAS, sent to NML for emm-typing, and have PFGE performed at PHO laboratory.
  • It is recommended that the health unit review the PHO laboratory submission process with the laboratory performing primary culture.

Follow up submissions:

Follow-up submissions of one isolate per person if GAS is found in re-screening performed 14 days or greater following treatment from persons previously identified with the outbreak strain are permitted and will receive confirmation, emm-typing and PFGE. Notify PHOL Customer Service Center in advance of follow-up submissions at 416-235-6556/1-877-604-4567.

Cluster-related (non-outbreak) isolates:

  • Cluster related emm-typing of isolates and PFGE from non-sterile sites is only performed in the following scenarios. This testing requires microbiologist approval:
    • A nosocomial cluster of iGAS
    • Suspected increase in iGAS in a geographic area. These requests should be made by the health unit involved after confirming there is a true increase in iGAS.
    • Suspicion of an outbreak in an institution which does not meet ID Protocol Appendix B requirements to be declared as an outbreak.
  • This testing is only performed on isolates received from another laboratory.
  • All isolates will be confirmed as GAS, sent to NML for emm-typing, and have PFGE performed by PHO laboratory.
  • It is recommended that an investigation number be used to track the samples from non-outbreak settings accepted for testing. Investigation numbers should appear on the requisition and submitted purity plates. Investigation numbers will be assigned by PHO laboratory in conjunction with the approval of investigational-level testing.
Mis à jour le 25 sept. 2019