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GAS - Group A Streptococcus - Outbreak
Specimen Type:


Purity plates (fresh subcultures) of group A streptococcus (GAS) isolates are the preferred specimen. Swabs of isolates are also accepted.


If swabs are used to send isolates, send in Amies charcoal transport medium (GC kit). Swab should be received within 3 days of collection.

Collection information:

PHOL does not provide swabs for performance of primary GAS outbreak screening.

Minimum volume required:



​Complete all fields of the General Test Requisition Form. The outbreak number MUST appear in the space provided.



Preparation prior to transport:

​Label the container with two identifiers and place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to PHOL on ice packs.

Special Instructions:



Isolates are regrown on bacterial culture medium for confirmation prior to typing.


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

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 PHOL 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.
  • The microbiologist or designate approves outbreak -level testing which includes Pulsed Field Gel Electrophoresis (PFGE) performed at PHOL and emm-typing performed at the National Microbiology Laboratory (NML).
Process for approved outbreaks: 

  • PHOL does not perform isolation from primary specimens for GAS or invasive GAS (iGAS). Primary swabs received by PHOL will be discarded.
  • PHOL 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 PHOL.
  • It is recommended that the health unit review the PHOL 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 PHOL.
  • 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 PHOL in conjunction with the approval of investigational-level testing.
​Additional Public Health Ontario Laboratories GAS-related Test Information Sheets:


Isolates are confirmed as GAS prior to further investigation.

Emm typing: up to two weeks for outbreak specimens.

PFGE: up to two weeks.


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

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Page updated on [date/time] 2016-06-01 8:58 AM
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