Much Ado About Flu


25 Sep 2018

With flu season right around the corner, PHO has been busy reviewing and refreshing the respiratory virus surveillance system. You’ll notice a revised surveillance package for public health units (PHU) and changes to come for an updated Ontario Respiratory Pathogen Bulletin (ORPB)—but that’s not all.  Our Communicable Disease Emergency Preparedness and Response and Laboratory teams gave us a behind-the-scenes look at the planning and preparation that goes into flu season.

Q: What is PHO’s role during flu season?

Throughout the year we monitor influenza and other respiratory virus trends. We post these data weekly on our interactive website. From November to April we amplify this surveillance with a weekly report with data we receive from PHUs, the PHO laboratory, Public Health Agency of Canada (PHAC) and the National Microbiology Laboratory. 

PHO’s Laboratory, via its 11 sites, performs primary diagnostic testing for influenza and other respiratory agents to support both acute care and outbreak management across Ontario. During the influenza season, PHO provides technical expertise to the Ministry of Health and Long-Term Care and respond to numerous science and technical requests from PHUs. This includes consultation support for the management of respiratory infection outbreaks.

Additionally, PHO monitors out-patient influenza vaccine effectiveness through its participation in the Sentinel Practitioner Surveillance Network. If you’re a practitioner interested in contributing to this important surveillance as a sentinel, please contact our coordinator: or 647-792-3187. 

Q: Why is influenza surveillance important?

Influenza is a rapidly changing virus.  It is hard to predict exactly what will be circulating and how severe it will be in terms of causing illness, deaths and outbreaks. Every Fall we monitor for the first signals of local influenza activity.  The data gives us some indications of what might be coming in the months ahead.  In general, seasons with heavy influenza A(H3N2) activity are worse seasons with increased numbers of cases of influenza, hospitalizations, deaths and outbreaks compared to influenza A(H1N1) seasons.

Assessing and reporting on activity levels of influenza throughout the season helps inform health care providers and the community, as well as the public health community. Increasing influenza activity may activate additional control measures or communications to ensure everyone is aware and taking the necessary steps to reduce the burden of influenza illness.

Q: What does it mean when we start seeing influenza cases now?

We provide year round influenza testing in the laboratory, so it is possible to have some cases each week from June to September. In the summer months, many of these will be in people who travelled to other parts of the world where influenza is more common at this time of year.

Once we start detecting a continuous increase in influenza activity among cases who did not travel or start seeing spread in the community—i.e., an influenza outbreak in a long-term care home, we are more alert to this potentially being the start of influenza activity for the season. We report the start of the season on the ORPB webpage based on these surveillance indicators.

For more information about influenza and respiratory infections contact

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Updated 25 Sep 2018