Seasonal Influenza in Alberta 2016/2017 Season

Unlike other recent seasons, the characteristics of the season varied between the zones, with Calgary Zone experiencing a more intense season with the highest number of lab- confirmed cases since the 2009 pandemic and high numbers of outbreaks in long-term care facilities and supportive living sites. [...] Introduction The predominant circulating strain in Canada was influenza A (H3N2); 98 per cent of influenza A isolates analyzed by the National Microbiology Laboratory (NML) were influenza A(H3N2) isolates that were considered genetically or antigenically similar to the vaccine strain1 2. Of the 608 influenza B isolates analyzed, 20 per cent were of the same lineage as what was recommended for the [...] The other 80 per cent were of the Yamagata lineage and thus mismatched to the trivalent vaccine, but similar to the strain recommended in the quadravalent vaccine. [...] The first estimate utilized was the median of the previous five seasons, week 2. The seasonal threshold was estimated as the average number of cases reported per week, in weeks considered outside of the influenza season (i.e., pre-season weeks). [...] The start of the influenza epidemic was defined as the week in which the per cent positivity of influenza A laboratory tests at ProvLab were ≥10 per cent of all respiratory laboratory tests ordered that week2.