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FluWatch report: March 19, 2017 – March 25, 2017 (week 12)

Overall Summary

  • Overall, the slow decline in influenza activity in Canada has continued in week 12. Many parts of Canada are still reporting localized influenza activity in week 12.
  • In week 12, all indicators (laboratory detections, influenza-like illness, outbreaks and hospitalizations) decreased from the previous week.
  • Influenza activity due to influenza B is slowly increasing but is low compared to the same time period in the previous two seasons.
  • Influenza A activity is decreasing; however, influenza A(H3N2) continues to be the most common subtype of influenza affecting Canadians.
  • The majority of laboratory detections, hospitalizations and deaths have been among adults aged 65+ years.
  • 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 12, five regions across four provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 19 regions across eight provinces and territories. Localized activity was reported in 22 regions across seven provinces. No regions reported any widespread activity in week 12. For more details on a specific region, click on the map. 

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Organization:

Public Health Agency of Canada

Date published: 2017-03-31

Related Topics

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 12

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 12, five regions across four provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 19 regions across eight provinces and territories. Localized activity was reported in 22 regions across seven provinces.

Laboratory Confirmed Influenza Detections

In week 12, the number (1,077) and the percentage of tests positive for influenza (15%) decreased slightly from the previous week. Although declining, influenza A continues to account for the majority of detections. Influenza B detections have been steadily increasing for the past few weeks. Influenza B detections are very low compared to the same time period in the previous two 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 12

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
11 645 347 13 242
12 526 248 <5 302

To date this season, 33,816 laboratory confirmed influenza detections have been reported, of which 95% have been influenza A. Influenza A(H3N2) is the most common subtype detected. 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 12

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 (March 19, 2017 to March 25, 2017) Cumulative (August 28, 2016 to March 25, 2017)
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 19 0 1 18 44 4900 34 3238 1628 390 5290
AB 45 0 28 17 40 3720 24 3559 137 207 3927
SK 25 0 15 10 10 1703 4 986 713 70 1773
MB 24 0 8 16 13 424 0 144 280 54 478
ON 182 0 153 29 86 9308 53 7549 1706 374 9682
QC 291 0 9 282 59 10083 0 647 9434 375 10458
NB 94 0 12 82 9 958 2 97 859 17 975
NS 20 0 0 20 4 335 0 13 322 14 349
PE 3 0 3 0 0 189 2 187 0 1 190
NL 46 0 0 46 1 359 0 43 316 6 365
YT 1 0 0 1 4 211 0 162 49 8 219
NT 0 0 0 0 2 58 0 57 1 6 64
NU 8 0 8 0 0 44 0 43 1 1 45
Canada 758 0 237 521 272 32292 119 16725 15446 1523 33815
PercentageTable Figure 3 - Footnote 2 74% 0% 31% 69% 26% 95% 0% 52% 48% 5% 100%

To date, detailed information on age and type/subtype has been received for 23,736 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for almost half of the reported influenza cases. Among cases of influenza A(H3N2), adults aged 65+ represented 49% of cases, followed by adults aged 20-64 (34% of cases). Among cases of influenza B, adults aged 20-64 represented 41% of cases.

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 12
Age groups (years) Weekly (March 19 to March 25, 2017) Cumulative (August 28, 2016 to March 25, 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 # %
<5 >41 0 <5 41 9 2116 14 805 1297 113 2229 9%
5-19 32 0 7 25 18 2112 14 1047 1051 204 2316 10%
20-44 54 0 16 38 26 3292 30 1768 1494 207 3499 15%
45-64 80 0 12 68 39 3686 24 1888 1774 273 3959 17%
65+ 252 0 31 221 52 11354 14 5259 6081 379 11733 49%
Total >459 0 >66 393 144 22560 96 10767 11697 1176 23736 100%
PercentageTable 1 - Footnote 2 76% 0% 15% 85% 24% 95% 0% 48% 52% 5% - -

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 12, 1.2% of visits to healthcare professionals were due to influenza-like illness, compared to 1.7% in the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 12

Number of Sentinels Reporting Week 12: 108

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 1.79%
11 1.72%
12 1.16%

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 12, 36 laboratory confirmed influenza outbreaks were reported (seven fewer outbreaks than week 11). Among the reported outbreaks: 28 were in long-term care (LTC) facilities, two in hospitals and six in institutional or community settings (other). Of the outbreaks with known strains or subtypes: five were due to influenza A(H3N2), 13 were due to influenza A(UnS) and five outbreaks were due to influenza B. Four of the five outbreaks due to influenza B occurred in LTC facilities.

To date this season, 1,028 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,552 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 12
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

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 12, 182 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote *, down from 261 reported in the previous week. Influenza A accounted for 75% of hospitalizations. The weekly percentage of influenza B associated hospitalizations has been steadily increasing since week 02. The largest proportion of hospitalizations were among adults aged 65+ years (67%). Less than five intensive care unit (ICU) admissions and 10 deaths were reported in week 12.

To date this season, 5,377 hospitalizations have been reported, of which 96% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (2886/2903) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. A total of 196 ICU admissions and 292 deaths have been reported. The majority of deaths was 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 12
Age Groups (years) Cumulative (August 28, 2016 to March 25, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 409 22 431 (8%) 11  6% <5 Table 2 - Footnote x%
5-19 222 28 250 (5%) 14  7% <5 Table 2 - Footnote x%
20-44 275 10 285 (5%) 20  10% <5 Table 2 - Footnote x%
45-64 691 38 729 (14%) 52  27% 32  11%
65+ 3563 119 3682 (68%) 99  51% 253  87%
Total 5160 217 5377 (100%) 196  101% 292  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 12, 15 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Nine cases (60%) were due to influenza A. The number of weekly hospitalizations reported since week 05 has been below the six year average for the same time period (Figure 7).

To date this season, 472 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 39% of hospitalizations and influenza A accounted for 90% (n=427) of the reported hospitalizations. Among the 45 hospitalizations due to influenza B, 23 (51%) were in children over the age of 5 years. In comparison, children over the age of 5 years accounted for 32% of influenza A hospitalizations. Additionally, 80 intensive care unit (ICU) admissions have been reported. Children aged 10-16 years accounted for 31% of ICU cases followed by children aged 0-23 months (28%). A total of 56 ICU cases 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 12

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 78
6-23 mo 107
2-4 yr 126
5-9 yr 79
10-16 yr 82

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 12

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 47 37 3 75
2 28 36 6 60
3 38 37 2 67
4 34 34 5 47
5 39 39 10 57
6 33 38 15 79
7 28 41 15 118
8 33 48 25 134
9 19 59 12 172
10 19 48 17 114
11 17 45 17 118
12 15 39 14 96
13 #N/A 33 14 57
14 #N/A 27 12 56
15 #N/A 25 14 56
16 #N/A 22 10 41
17 #N/A 18 9 37
18 #N/A 15 6 28
19 #N/A 10 5 18
20 #N/A 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

In week 12, 47 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). Influenza A accounted for 74% of hospitalizations and the majority of cases (83%) occurred in adults aged 65+. 

To date this season, 1,307 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 97% of hospitalizations. Adults aged 65+ accounted for 79% of hospitalizations. To date, 84 intensive care unit (ICU) admissions have been reported. A total of 60 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 53 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 84 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 12

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 82
45-64 yr 198
65+ yr 1027

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 12

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=1307) ICU admissions (n=84) Deaths (n≥53)
20-44 6.3% 7.1% Table Figure 9 - Footnote -
45-64 15.1% 22.6% 5.0%
65+ 78.6% 70.2% 94.6%

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,461 influenza viruses [1325 A(H3N2), 31 A(H1N1), 136 influenza B].  All but one influenza A virus (n=1324) and 40 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Ninety-six 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 12
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 329 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		 964

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 329 influenza A (H3N2) viruses that underwent HI testing determined that 278 viruses belonged to genetic group 3C.2a and 48 viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining three isolates. The majority of viruses belonging to genetic group 3C.3a are inhibited by antisera raised against A/Hong Kong/4801/2014.Table 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 31 Viruses antigenically similar to A/California/7/2009, the A(H1N1) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)		 40 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)		 96 Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2016-17 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 789 influenza viruses for resistance to oseltamivir and zanamivir and 187 influenza viruses for resistance to amantadine. All but one influenza A(H3N2) virus were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 187 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 12
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 662 1 (0.2%) 662 0 (0%) 161 161 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 25 0 (0%) 24 0 (0%) 25 25 (100%)
B 101 0 (0%) 102 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 789 1 (0.1%) 789 0 (0%) 187 187 (100%)

Provincial and International Influenza Reports

 

 

FluWatch definitions for the 2016-2017 season

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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