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FluWatch report: February 26, 2017 – March 4, 2017 (week 9)

Overall Summary

  • Overall, the decline in influenza activity in Canada has been slow compared to previous seasons. Many parts of Canada are still reporting elevated activity in week 09.
  • Widespread or localized influenza activity was reported in 29 regions across 11 provinces.
  • In week 09, laboratory detections, influenza-like illness, outbreaks and hospitalizations from participating provinces and territories and sentinel networks decreased from the previous week.
  • Influenza B activity in Canada is slowly increasing but remain below what has been observed in previous seasons.
  • A(H3N2) continues to be the most common type 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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Organization:

Public Health Agency of Canada

Date published: 2017-03-10

Related Topics

Influenza/Influenza-like Illness Activity (geographic spread)

In week 09, two regions (one each in NB and NT) reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 22 regions across 10 provinces and territories. Localized activity was reported in 25 regions across nine provinces. Widespread activity was reported in four regions (PE, two in BC and one in QC). For more details on a specific region, click on the map.

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 9

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 09, two regions (one each in NB and NT) reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 22 regions across 10 provinces and territories. Localized activity was reported in 25 regions across nine provinces. Widespread activity was reported in four regions (PE, two in BC and one in QC).

Laboratory Confirmed Influenza Detections

In week 09, the number of positive tests (2,072) and the percentage of tests positive for influenza (22%) decreased from the previous week. Peak influenza detections occurred in week 02 at 27%. After a decline from the peak in week 03, detections have remained relatively stable (ranging from 22% to 25% in weeks 03 to 09). Influenza A continues to account for the majority of detections; however, influenza B detections have been steadily increasing for the past few weeks. Influenza B activity is 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 9

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 1346 899 17 128
9 1046 906 7 159

To date, 29,910 laboratory confirmed influenza detections have been reported, of which 97% 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 9

Figure 3
Figure 3 - Text Description
Reporting
provincesTable Figure 3 - Footnote 1		 Weekly (February 26, 2017 to March 4, 2017) Cumulative (August 28, 2016 to March 4, 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 477 7 422 48 48 4499 23 2835 1641 253 4752
AB 69 0 38 31 22 3590 18 3451 121 116 3706
SK 32 0 21 11 2 1563 1 885 677 23 1586
MB 56 0 6 50 6 333 0 115 218 29 362
ON 388 0 330 58 34 8592 45 6942 1605 181 8773
QC 697 0 27 670 43 8804 0 599 8203 234 9038
NB 87 0 0 87 0 686 2 85 599 4 690
NS 24 0 0 24 2 264 0 13 251 4 268
PE 19 0 19 0 0 169 2 167 0 1 170
NL 49 0 0 49 0 226 0 43 183 5 231
YT 5 0 5 0 0 208 0 160 48 2 210
NT 8 0 2 6 0 53 0 47 6 3 56
NU 4 0 4 0 0 67 0 65 2 1 68
Canada 1915 7 874 1034 157 29054 91 15407 13554 856 29910
PercentageTable Figure 3 - Footnote 2 92% 0% 36% 54% 8% 97% 0% 53% 47% 3% 100%

To date, detailed information on age and type/subtype has been received for 20,914 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 46% of cases, followed by adults aged 20-64 (33% of cases). In the previous influenza A(H3N2)-predominant season in 2014-15, adults aged 65+ represented 59% of cases and adults aged 20-64 represented 26% 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 9
Age groups (years) Weekly (February 26 to March 4, 2017) Cumulative (August 28, 2016 to March 4, 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 # %
<5 123 0 11 112 8 2349 10 1028 1311 79 2428 12%
5-19 116 0 27 89 10 2131 9 1127 995 104 2235 11%
20-44 100 0 11 89 10 2654 23 1445 1186 100 2754 13%
45-64 132 0 19 113 14 3523 19 1784 1720 134 3657 17%
65+ 497 0 74 423 41 9634 10 4523 5101 206 9840 47%
Total 968 0 142 826 83 20291 71 9907 10313 623 20914 100%
PercentageTable 1 - Footnote 2 92% 0% 15% 85% 8% 97% 0% 49% 51% 3%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 09, 1.8% of visits to healthcare professionals were due to influenza-like illness, down from 2.2% in the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 9

Number of Sentinels Reporting Week 09: 109

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%

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 09, 43 laboratory confirmed influenza outbreaks were reported (18 less than the previous week). Among the reported outbreaks: 30 were in long-term care (LTC) facilities, four in hospitals and nine in institutional or community (other) settings. Of the outbreaks with known strains or subtypes, 11 were due to influenza A(H3N2), 15 were due to influenza A(UnS) and one outbreak was due to influenza B. An additional outbreak due to ILI was reported in a school.

To date this season, 902 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), 1,436 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 9
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 30 9

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 09, 225 influenza-associated hospitalizations were reported by participating provinces and territories, down slightly from  245 reported in the previous week*. Influenza A accounted for 90% of hospitalizations. The weekly percentage of hospitalizations due to influenza B has been steadily increasing for the past few weeks. The largest proportion of hospitalizations were among adults aged 65+ (67%). A total of nine intensive care unit (ICU) admissions and 15 deaths were reported in week 09.

To date this season, 4,556 hospitalizations have been reported, of which 98% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (2517/2527) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. A total of 168 ICU admissions and 206 deaths have been reported. The majority of deaths 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 9
Age Groups (years) Cumulative (August 28, 2016 to March 4 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 335 14 349 (7%) 10  6% <5 x%
5-19 191 17 208 (5%) 12  7% <5 x%
20-44 244 6 250 (5%) 17  10% <5 x%
45-64 604 17 621 (14%) 45  27% 29 14%
65+ 3076 52 3128 (69%) 84  50% 172 83%
Total 4450 106 4556 (100%) 168  100% 206 100%
Note: Influenza-associated hospitalizations are not reported to PHAC by: BC, NU, and QC. Only hospitalizations that require intensive medical care are reported by SK. ICU admissions
x Supressed to prevent residual disclosure

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 09, 14 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All but two cases were due to influenza A. The number of hospitalizations reported in week 05 is below the six year average for the same time period (Figure 7).

To date this season, 421 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 41% of hospitalizations. Influenza A accounted for 93% (n=386) of the reported hospitalizations, of which 36% (n=138) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 66 intensive care unit (ICU) admissions have been reported. Children aged 0-23 months accounted for 30% of ICU cases followed by children aged 10-16 (26%). A total of 43 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 9

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 72
6-23 mo 95
2-4 yr 111
5-9 yr 71
10-16 yr 68

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 9

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 20 24 4 47
51 17 35 4 71
52 38 47 7 92
1 48 37 3 75
2 28 36 6 60
3 38 37 2 67
4 43 34 5 47
5 28 39 10 57
6 34 38 15 79
7 28 41 15 118
8 34 48 25 134
9 14 59 12 172
10 #N/A 48 17 114
11 #N/A 45 17 118
12 #N/A 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 09, 48 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All but two cases were due to influenza A and the majority of cases  (81%) occurred in adults aged 65+. The number of hospitalizations reported weekly by CIRN have been consistently declining since week 07.

To date this season, 1,100 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 99% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. To date, 66 intensive care unit (ICU) admissions have been reported. A total of 42 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 68 years. Approximately 45 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 9

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 75
45-64 yr 167
65+ yr 858

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 9

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
Age-group (years) Hospitalizations (n = 1100) ICU admissions (n = 66) Deaths (n ≥45)
20-44 6.8% 7.6% 0.0%
45-64 15.2% 22.7% 4.0%
65+ 78.0% 69.7% 95.7%
- Supressed due to small values

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,075 influenza viruses [969 A(H3N2), 25 A(H1N1), 81 influenza B].  All but one influenza A virus (n=993) and 32 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Forty-nine influenza B viruses were similar to the strain which is only included in the quadrivalent vaccine.

The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2017-2018 northern hemisphere influenza season. Trivalent vaccines are recommended to contain: 1) an A/Michigan/45/2015 (H1N1)pdm09-like virus; 2) an A/Hong Kong/4801/2014 (H3N2)-like virus; and 3) a B/Brisbane/60/2008-like virus (Victoria lineage). Quadrivalent vaccines are recommended to contain the above three viruses and a B/Phuket/3073/2013-like virus (Yamagata lineage).

Table 3 – Influenza strain characterizations, Canada, 2016-17, week 9
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 285 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		 683

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 285 influenza A (H3N2) viruses that underwent HI testing determined that 240 viruses belonged to genetic group 3C. 2a and 38 viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining 7 isolates. 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 25 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)		 32 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)		 49 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 562 influenza viruses for resistance to oseltamivir and zanamivir and 158 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 158 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 9
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 548 1 (0.2%) 548 0 (0%) 148 148 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 22 0 (0%) 21 0 (0%) 20 20 (100%)
B 68 0 (0%) 69 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 639 1 (0.2%) 639 0 (0%) 169 169 (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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