Data Notes
Many cases of influenza are not diagnosed or reported to the Halton Region Health Department because infected individuals may not seek medical attention, or when physicians are visited they often do not order laboratory confirmation because it is unnecessary in uncomplicated situations when influenza is known to be circulating. Data provided in this report reflect only those cases that had laboratory confirmation of influenza infection. The actual number of cases in the community is likely to be much higher than the number presented in this report.
In contrast to the common cold, symptoms of influenza are more sudden in onset and more severe (fever, sore throat, headache, muscle ache, profound fatigue, cough), especially in the very young or old, or individuals with compromised immune systems. In children, nausea, vomiting, and diarrhea are not uncommon. Symptoms usually resolve in five to seven days, however, monitoring influenza is important due to how quickly epidemics evolve the widespread morbidity, and the seriousness of complications, notably viral and bacterial pneumonias.
Influenza Activity Level Definitions:
No activity – no laboratory-confirmed cases of influenza reported and no ongoing laboratory-confirmed institutional influenza outbreaks
Sporadic – at least one laboratory-confirmed case of influenza with no ongoing laboratory-confirmed institutional influenza outbreaks
Localized – at least one ongoing laboratory-confirmed influenza outbreak in an institution
Widespread – multiple ongoing laboratory-confirmed influenza outbreaks in institutions separated by some geographic distance, in other words, non-adjacent areas
Comparisons to previous flu seasons:
Variability between flu seasons exists for many reasons, including: the strains of influenza that are circulating; how well matched the flu vaccine was to the circulating strains; which age groups are most affected; and the severity of illness resulting from infection. In addition, many cases of influenza go unreported, laboratory confirmation is not necessary in uncomplicated cases, and changes to laboratory testing algorithms over time may have altered the percent of samples that are tested for influenza. Recent changes have also occurred in the requirements for laboratory-confirmed influenza case follow up. For the 2017/18 season, there is no longer a provincial requirement for PHU's to follow up any laboratory-confirmed influenza cases. For these reasons it is not recommended to compare the current flu season to previous flu seasons.
Data Source
iPHIS - This report uses data from iPHIS. iPHIS is a dynamic disease reporting system which allows ongoing updates to data previously entered. As a result, data extracted from iPHIS represent a snapshot at the time of extraction and may differ from previous or subsequent reports.
ACES - This report uses emergency department visit data from the Acute Care Enhanced Surveillance (ACES) Application.
For more information on influenza activity in Ontario please visit the Influenza-Like Illness (ILI) Mapper and the Ontario Respiratory Pathogen Bulletin.
Last updated: Tuesday, March 20, 2018
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