FluWatch report: May 14 to May 20, 2017 (week 20)

Overall Summary

  • Overall, influenza activity continues to decline slowly in Canada.
  • In week 20, influenza B accounted for the majority of influenza activity in Canada, with 75% or more of reported influenza laboratory detections, hospitalizations and outbreaks due to influenza B.
  • This increase in influenza B activity is expected as influenza B often appears later in the flu season.
  • To date, the majority of laboratory detections, hospitalizations and deaths have been among adults aged 65+ years.
  • The current FluWatch report is the last weekly report for the 2016-2017 season. During the summer, monthly reports will be published starting on June 23, 2017. We will continue to monitor influenza and other respiratory infections via the RVDSS report, published every Thursday.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 20, 19 regions across eight provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 25 regions across 11 provinces and territories. Localized activity was reported in nine regions across five provinces. For more details on a specific region, click on the map. 

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Organization:

Date published: 2017-05-26

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, Week 20

Figure 1
Figure 1 Legend

Note: Influenza/ILI activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates and reported outbreaks. Please refer to detailed definitions at the end of the report. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.

Figure 1 - Text Description

In week 20, 19 regions across eight provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 25 regions across 11 provinces and territories. Localized activity was reported in nine regions across five provinces.

Laboratory Confirmed Influenza Detections

In week 20, the number (245) and the percentage (6.8%) of tests positive for influenza decreased from the previous week. Influenza B was the most common type of influenza detected in all jurisdictions in Canada. Since week 16, the percentage of tests positive for influenza B has plateaued (6.0% to 6.9%) and has not yet begun a clear decline.  Overall in week 20, influenza B accounted for 86% of total detections. Influenza B detections are within expected levels compared to the same time period in recent seasons. For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada (PHAC) website. 

Figure 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2016-17, week 20

Figure 2

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the start and end of seasonal influenza activity.

Figure 2 - Text Description
Figure 2 - Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2016-17
Report Week A(Unsubtyped) A(H3) A(H1)pdm09 Influenza B
35 0 <5 0 0
36 <5 0 <5 9
37 <5 17 0 <5
38 11 28 <5 <5
39 14 41 <5 7
40 0 47 <5 <5
41 10 31 0 <5
42 14 49 <5 6
43 16 76 <5 <5
44 19 110 <5 9
45 31 150 <5 11
46 52 140 <5 7
47 54 200 0 9
48 91 272 <5 7
49 148 414 <5 12
50 305 467 <5 18
51 535 750 <5 17
52 857 1064 <5 33
1 1444 1360 <5 38
2 1516 2118 10 39
3 1354 1412 0 47
4 1336 1220 <5 47
5 1222 1290 7 62
6 1200 1225 9 81
7 1291 1141 11 97
8 1345 899 17 128
9 977 935 7 159
10 802 726 14 203
11 629 347 13 242
12 498 259 <5 302
13 369 221 0 309
14 273 134 6 365
15 216 73 0 321
16 167 59 9 347
17 113 38 <5 316
18 64 47 0 283
19 36 30 0 259
20 13 24 <5 219

To date this season, 38,570 laboratory confirmed influenza detections have been reported, of which 90% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season. For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, 2016-17, week 20

Figure 3
Figure 3 - Text Description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, 2016-17
Reporting
provincesTable Figure 3 - Footnote 1
Weekly (May 14, 2017 to May 20, 2017) Cumulative (August 28, 2016 to May 20, 2016)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
BC 5 0 5 0 10 5329 43 3302 1984 677 6006
AB 0 0 0 0 50 3802 25 3637 140 649 4451
SK 9 0 9 0 7 1778 4 1042 736 308 2086
MB 0 0 0 0 5 484 1 186 297 122 606
ON 11 2 6 3 51 9751 75 7892 1784 1080 10831
QC 9 0 0 9 66 10863 2 650 10211 930 11793
NB 1 0 0 1 6 1161 3 130 1028 138 1299
NS 0 0 0 0 1 416 0 13 403 31 447
PE 0 0 0 0 1 196 2 194 0 5 201
NL 0 0 0 0 9 446 0 43 403 37 483
YT 0 0 0 0 2 172 0 164 8 23 195
NT 0 0 0 0 1 59 0 58 1 21 80
NU 0 0 0 0 1 85 0 83 2 7 92
Canada 35 2 20 13 210 34542 155 17394 16997 4028 38570
PercentageTable Figure 3 - Footnote 2 14% 6% 57% 37% 86% 90% 0% 50% 49% 10% 100%

To date this season, detailed information on age and type/subtype has been received for 26,534 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for half of the reported influenza cases. Adults aged 65+ have predominantly been affected by influenza A accounting for 51% of influenza A detections. Influenza B, while much smaller in number, is mainly affecting individuals less than 65 years of age. 

Table 1 - Weekly and cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reportingTable 1 - Footnote 1, Canada, 2016-17, Week 20
Age groups (years) Weekly (May 14, 2017 to May 20, 2017) Cumulative (August 28, 2016 to May 20, 2017)
Influenza A B Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) ATable 1 - Footnote UnS Total A Total A(H1) pdm09 A(H3) ATable 1 - Footnote UnS Total # %
0-4 5 0 <5 <5 <5 2235 15 830 1390 246 2481 9%
5-19 0 0 0 0 15 2196 11 1077 1108 473 2669 10%
20-44 <5 0 0 <5 13 3406 23 1801 1582 480 3886 15%
45-64 <5 0 0 <5 24 3893 21 1954 1918 645 4538 17%
65+ >9 0 9 <5 42 12060 10 5441 6609 900 12960 49%
Total >21 0 >9 12 >94 23790 80 11103 12607 2744 26534 100%
PercentageTable 1 - Footnote 2 18% 0% 0% 0% 82% 90% 0% 47% 53% 10%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 20, 0.9% of visits to healthcare professionals were due to influenza-like illness.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 20

Number of Sentinels Reporting Week 20: 94

Figure 4

Delays in the reporting of data may cause data to change retrospectively. In BC, AB, and SK, data are compiled by a provincial sentinel surveillance program for reporting to FluWatch. Not all sentinel physicians report every week.

Figure 4 - Text Description
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17
Report week % Visits for ILI
35 0.96%
36 0.96%
37 0.98%
38 0.96%
39 0.94%
40 1.03%
41 2.41%
42 1.04%
43 1.01%
44 1.39%
45 1.32%
46 0.97%
47 1.11%
48 1.07%
49 1.08%
50 1.30%
51 1.73%
52 2.83%
1 1.96%
2 2.22%
3 1.92%
4 2.02%
5 2.31%
6 3.13%
7 1.73%
8 2.19%
9 1.82%
10 1.77%
11 1.70%
12 1.13%
13 1.18%
14 1.31%
15 0.88%
16 0.98%
17 0.86%
18 0.82%
19 0.99%
20 0.88%

Are you a primary healthcare practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel?
Please visit our Influenza Sentinel page for more details.

Influenza Outbreak Surveillance

In week 20, nine laboratory-confirmed influenza outbreaks were reported. Of the four outbreaks with known strains or subtypes, three were due to influenza B and one was due to influenza A(H3N2). An additional outbreak due to ILI was reported in a school.

To date this season, 1,176 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 82 outbreaks (7%) due to influenza B have been reported. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,724 outbreaks were reported, of which 74% occurred in LTC facilities.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, week 20
Figure 5
Figure 5 - Text Description
Figure 5 - Overall number of new laboratory-confirmed influenza outbreaks by report week, Canada, 2016-17
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 0 0
37 0 2 0
38 1 1 1
39 1 3 1
40 0 0 0
41 0 3 0
42 0 3 1
43 0 3 0
44 2 5 2
45 1 1 0
46 2 6 0
47 1 8 0
48 0 2 0
49 1 14 3
50 4 15 4
51 5 32 13
52 7 65 18
1 15 84 22
2 13 83 24
3 19 44 9
4 8 39 8
5 13 36 11
6 4 46 20
7 8 38 8
8 5 39 17
9 4 32 9
10 3 32 9
11 7 22 12
12 2 28 6
13 1 24 8
14 0 11 7
15 1 14 6
16 2 8 1
17 0 12 6
18 1 6 6
19 2 10 3
20 0 0 0

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 20, 46 influenza-associated hospitalizations were reported by participating provinces and territories*, a slight decrease from 52 hospitalizations reported in the previous week. In week 20, 80% of reported hospitalizations were due to influenza B and 61% occurred in adults 65+. Additionally, less than five intensive care unit (ICU) admissions and five deaths were reported.

To date this season, 6,335 hospitalizations have been reported, of which 89% were due to influenza A. Among cases for which the subtype of influenza A was reported, 99% were influenza A(H3N2). Adults 65+ accounted for 88% of the hospitalizations. A total of 259 ICU admissions and 371 deaths have been reported. The majority of deaths (88%) were reported in adults aged 65+ years. 

Table 2 - Cumulative number of hospitalizations, ICU admissions and deaths by age and influenza type reported by participating provinces and territories, Canada 2016-17, week 20
Age Groups (years) Cumulative (August 28, 2016 to May 20, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 444 80 524 (8%) 18 7% <5 Table 2 - Footnote x%
5-19 240 83 323 (5%) 20 8% <5 Table 2 - Footnote x%
20-44 294 43 337 (5%) 24 9% 5 1%
45-64 761 118 879 (14%) 78 30% 35 9%
65+ 3917 355 4272 (68%) 119 46% 326 88%
Total 5656 679 6335 (100%) 259 100% 371 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 20, 13 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All hospitalizations were associated with influenza B and 69% were in children over the age of 5 years.

To date this season, 569 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 37% of hospitalizations and influenza A accounted for 79% of the reported hospitalizations. Among the 117 hospitalizations due to influenza B, 64 (54%) were in children over the age of 5 years. In comparison, children over the age of 5 years accounted for 33% of influenza A hospitalizations. Additionally, 93 intensive care unit (ICU) admissions have been reported. A total of 64 ICU cases (69%) reported at least one underlying condition or comorbidity. Less than five deaths have been reported this season. 

Figure 6 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2016-17, week 20

Figure 6
Figure 6 - Text Description
Figure 6 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2016-17
Age Group Total
0-5 mo 86
6-23 mo 125
2-4 yr 145
5-9 yr 110
10-16 yr 103

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 20

Figure 7

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2015-16.

The number of hospitalizations reported through IMPACT represents a subset of all influenza-associated pediatric and adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Figure 7 - Text Description
Figure 7 - Number of pediatric (≤16 years of age) hospitalizations reported by IMPACT sentinel hospital network, by week, Canada, 2016-17
Report week 2016-17 Average Min Max
35 0 0 0 0
36 1 0 0 0
37 0 1 0 2
38 0 1 0 2
39 3 0 0 1
40 2 0 0 1
41 0 1 0 2
42 4 1 0 1
43 3 1 0 3
44 6 2 1 4
45 3 3 2 4
46 5 5 1 13
47 3 5 0 9
48 7 10 1 22
49 10 15 2 28
50 19 24 4 47
51 17 35 4 71
52 38 47 7 92
1 49 37 3 75
2 27 36 6 60
3 38 37 2 67
4 35 34 5 47
5 38 39 10 57
6 35 38 15 79
7 29 41 15 118
8 33 48 25 134
9 20 59 12 172
10 17 48 17 114
11 19 45 17 118
12 13 39 14 96
13 14 33 14 57
14 14 27 12 56
15 15 25 14 56
16 11 22 10 41
17 7 18 9 37
18 10 15 6 28
19 10 10 5 18
20 13 9 4 18
21 #N/A 6 2 10
22 #N/A 4 1 7
23 #N/A 2 0 4
24 #N/A 2 0 5
25 #N/A 1 0 3
26 #N/A 1 0 2
27 #N/A 0 0 2
28 #N/A 1 0 1
29 #N/A 0 0 2
30 #N/A 0 0 0
31 #N/A 0 0 0
32 #N/A 0 0 1
33 #N/A 0 0 0
34 #N/A 1 0 2

Adult Influenza Hospitalizations and Deaths

Surveillance for the 2016-2017 influenza season ended on April 30th, 2017.

This season, 1,535 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 92% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. A total of 143 intensive care unit (ICU) admissions have been reported. Among ICU cases with available data, 126 cases (88%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 71 years. Approximately 86 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 85 years. 

Figure 8 - Cumulative numbers of adult hospitalizations (≥20 years of age) with influenza by type and age-group reported by CIRN, Canada, 2016-17, week 20

Figure 8
Figure 8 - Text Description
Figure 8 - Cumulative numbers of adult hospitalizations (≥20 years of age) with influenza by type and age-group reported by the CIRN network, Canada, 2016-17
Age Group Total
20-44 yr 94
45-64 yr 237
65+ yr 1204

Figure 9 – Percentage of hospitalizations, ICU admissions and deaths with influenza by age-group (≥20 years of age) reported by CIRN, Canada 2016-17, week 20

Figure 9

The number of hospitalizations reported through CIRN represents a subset of all influenza-associated adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Figure 9 - Text Description
Figure 9 - Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥20 year of age), CIRN, Canada, 2016-17
Age-group (years) Hospitalizations (n= 1535) ICU admissions (n= 143) Deaths (> 86)
- Supressed due to small values
20-44 6.1% 6.3% -
45-64 15.4% 18.9% 5.0%
65+ 78.4% 74.8% 96.6%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 2,050 influenza viruses [1565 A(H3N2), 48 A(H1N1), 437 influenza B].  All but one influenza A virus (n=1613) and 95 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Three hundred and forty-two influenza B viruses were similar to the strain which is only included in the quadrivalent vaccine.

Table 3 – Influenza strain characterizations, Canada, 2016-17, Week 20
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
369 Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.
GeneticallyTable 3 - Footnote 2
A/Hong Kong/4801/2014-like
1195

Viruses belonging to genetic group 3C.2a. A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.

Additionally, genetic characterization of the 369 influenza A (H3N2) viruses that underwent HI testing determined that 306 viruses belonged to genetic group 3C.2a and 63 viruses belonged to genetic group 3C.3a. The majority of viruses belonging to genetic group 3C.3a are inhibited by antisera raised against A/Hong Kong/4801/2014Table 3 - Footnote 3.

Antigenically
A/Indiana/10/2011-likeTable 3 - Footnote 4
1

Viruses antigenically similar to A/Indiana/10/2011, a candidate H3N2v vaccine virus.

Influenza A (H1N1)
A/California/7/2009-like 48 Viruses antigenically similar to A/California/7/2009, the A(H1N1) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)
95 Viruses antigenically similar to B/Brisbane/60/2008, the influenza B component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent influenza vaccine
B/Phuket/3073/2013-like
(Yamagata lineage)
342 Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2016-17 Northern Hemisphere quadrivalent influenza vaccine.

During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 1,122 influenza viruses for resistance to oseltamivir, 1,124 influenza viruses for resistance to zanamivir and 247 influenza viruses for resistance to amantadine. All but two influenza A(H3N2) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 228 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 20
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 748 2 (0.3%) 747 0 (0%) 206 206 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 42 0 (0%) 41 0 (0%) 40 40 (100%)
B 331 0 (0%) 335 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 1122 2 (0.2%) 1124 0 (0%) 247 247 (100%)

Abbreviations: Newfoundland/Labrador (NL), Prince Edward Island (PE), New Brunswick (NB), Nova Scotia (NS), Quebec (QC), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB), British Columbia (BC), Yukon (YT), Northwest Territories (NT), Nunavut (NU).

Influenza-like-illness (ILI): Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which is likely due to influenza. In children under 5, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.

ILI/Influenza outbreaks

Schools:
Greater than 10% absenteeism (or absenteeism that is higher (e.g. >5-10%) than expected level as determined by school or public health authority) which is likely due to ILI.
Note: it is recommended that ILI school outbreaks be laboratory confirmed at the beginning of influenza season as it may be the first indication of community transmission in an area.
Hospitals and residential institutions:
two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case. Institutional outbreaks should be reported within 24 hours of identification. Residential institutions include but not limited to long-term care facilities (LTCF) and prisons.
Workplace:
Greater than 10% absenteeism on any day which is most likely due to ILI.
Other settings:
two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case; i.e. closed communities.

Note that reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions.

Influenza/ILI activity level

1 = No activity: no laboratory-confirmed influenza detections in the reporting week, however, sporadically occurring ILI may be reported

2 = Sporadic: sporadically occurring ILI and lab confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region Footnote

3 = Localized:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance regionFootnote

4 = Widespread:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance regionFootnote

Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.


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