Summary of the Timing of the Annual Influenza A Epidemic across Canada and the United States.

<p>Weeks are numbered according to the calendar year with week 1 corresponding to the 1^st week of January and week 52 is one week earlier. Weeks run from Sunday to Saturday, and run continuously so that each week covers a 7 day period. The influenza season starts at week 35 or the 1st week of September and runs for a full year. Week 53 was not included in the legend as it only occurred in 2 out of 6 seasons. Only seasons where over 80% of the influenza strains characterized were antigenically similar are included in the summaries, namely, seasons shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021471#pone-0021471-g001" target="_blank">Figure 1:</a> 1997/98, 1998/99, 1999/2000, 2000/01, 2001/02, and 2003/04. a) The average week of peak activity; b) The earliest week of peak influenza activity by Canadian province and American influenza surveillance region; c) The latest week of peak influenza A activity by Canadian province and American influenza surveillance region.</p

Degree of Synchronization¹ between the Major City² in each Province and other Communities.³

1<p>Includes seasons where over 80% of the influenza strains were antigenically similar.</p>2<p>The major city for each province was identified as the CMA reporting the most cases.</p>3<p>Communities (geographic units) which confirmed at least 50 positive cases in one season.</p>4<p>Cases from the rural area of each province and communities with less than 50 positive cases per season were combined into one local epidemic curve. Cases from rural areas accounted for the majority of cases in the ‘rest of the province’ epidemic curve.</p>5<p>The number of local epidemics meeting the inclusion criteria over the study period of 6 seasons. To compare sub-provincial synchronization at least 2 geographic units from one province must meet the inclusion criteria for the same season; that is at least 1 CMA/CA and one other community from the same province or the ‘rest of province’ aggregate must meet the criteria in the same season. Over the 6 seasons, 114 pairs were available to assess the degree of synchronization.</p><p>The Chi-squared value for a test of association is 2.3 on 4 degrees of freedom for a p-value of 0.67. Note that cell counts are given in cumulative format in this table and the categories of 3 weeks and 4 or more weeks were combined in the test of association due to small numbers.</p

Timing of the Annual Influenza A Epidemic across Canada and the United States, by Season.

<p>The temporal midpoint of each influenza A season where over 80% of the influenza strains were antigenically similar by Canadian province and American influenza surveillance region is shown in the chloropleth maps. The region reaching its midpoint first was identified as the reference region. In three out of the six seasons the epidemic appeared first in Canada. Considerable variability in the timing and direction of spread is noted.</p

Reference Region: Region with the Earliest Epidemic.

<p>Reference Region: Region with the Earliest Epidemic.</p

Strain type and composition.

<p>Seasons where over 80% influenza A strains were antigenically similar are shown in <b>BOLD</b>.</p

ICD-10-CA codes for COVID-19.

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Charlson comorbidity index.

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Prevalence (%) of chronic conditions among adults (aged 20+ years) during first acute care hospitalizations with a confirmed or suspected COVID-19 diagnosis in Canada by life-course age group.

Includes acute care hospitalizations ending by March 31, 2021 in Canada, excluding Quebec. For detailed estimates see Table 2. COVID-19 = coronavirus disease 2019.</p

Health condition definitions.

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Associations between demographic, temporal and health characteristics and death in hospital among adults (aged 20+ years) during first acute care hospitalizations with a confirmed COVID-19 diagnosis in Canada by life-course age group.

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