Summary of Weekly Influenza Report: Week 45 (Nov 5 to Nov 11 2017)
prepared by Toronto Public Health’s Communicable Disease Surveillance Unit (CDSU)

Indicator Activity Level* Description
Laboratory-Confirmed Influenza Cases Comparable Five new laboratory-confirmed cases of influenza were reported in week 45, comparable to the four cases reported in week 44. To date this season, 36 cases have been reported, higher than the previous 5-season mean of 23 cases.
Influenza Strains for Ontario Cases ‡  No report

The Ontario Respiratory Pathogen Bulletin for week 44 did not report additional characterizations of isolates for Ontario cases since the last report. Since September 1, 2017, the following isolates were characterized:

·        A/H1N1 strain antigenically similar to A/Michigan/45/2015 (n=5)

·        A/H3N2 strain antigenically characterized as A/Hong Kong/4801/2014-like (n=2)

 Institutional Influenza Outbreaks  No report  No institutional influenza outbreaks have been reported for the 2017/18 season.
 Overall  Comparable Influenza activity in Toronto for week 45 was comparable to the activity in week 44.


*May not reflect statistically significant changes, but describes overall observed trends and compares to the previous surveillance week.Starting in the 2017/18 season, the Ontario Ministry of Health and Long-Term Care advised public health units that they were no longer required to do any additional investigation to collect information beyond what has already been reported in the initial laboratory report. No changes were made to investigation of institutional influenza outbreaks. As a result, subtype information will be available for a smaller proportion of laboratory-confirmed cases, and hospitalization and death information will be underestimated. Therefore, comparisons between the current season and prior seasons should be made with caution. Please refer to the technical notes for details.Data on influenza strains for Ontario cases are obtained from the Ontario Respiratory Pathogen Bulletin published the week preceding the current Weekly Influenza News for Toronto (e.g. for the Weekly Influenza News for week 34, the influenza strains data are obtained from the Ontario Respiratory Pathogen Bulletin published for week 33).