Influenza cases rise in second week of flu season, swine flu most prominent

Influenza cases were on the rise during the second week of the annual flu season, according to the Public Health Agency of Canada, with swine flu being the most detected subtype.

"At the national level, influenza activity has continued to increase," the agency said in its weekly FluWatch report. "Most surveillance indicators are increasing but remain within expected levels typical of this time of year."

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According to the latest FluWatch report, laboratory detections reached 3,077 during the week of Nov. 26 to Dec. 2, up from 2,143 the week prior. The positive test rate increased to 9.9 per cent from 7.5 per cent. There were also 202 new influenza-associated hospitalizations and six associated deaths.

The vast majority of cases this season have involved influenza A, and particularly the influenza A(H1N1) subtype, which is more commonly known as swine flu. Out of 1,129 influenza A detections that underwent further analysis last week, 90 per cent were determined to be the swine flu subtype.

When influenza subtype information was available, swine flu was also associated with 91 per cent of all outbreaks and 94 per cent of all hospitalizations since Aug. 27.

Influenza activity was most widespread in Alberta, according to available data. Localized influenza activity was also reported across much of New Brunswick, Saskatchewan, southern Ontario and southwestern British Columbia.

"The proportion of regions reporting influenza activity and the intensity of reported activity is increasing," the FluWatch report stated.

There were 19 laboratory-confirmed outbreaks during the week, bringing the total since August to 81. Most outbreaks have occurred in long-term and acute care facilities. While those aged zero to 19 are the most likely to get infected, representing 34 per cent of all detections since August, adults aged 65 and older have accounted for 30 per cent of all hospitalizations.