FluWatch report: March 12, 2017 – March 18, 2017 (week 11)

Overall Summary

  • Overall, the slow decline in influenza activity in Canada has continued in week 11.However, many parts of Canada, particulary the Eastern and Atlantic regions are still reporting elevated activity in week 11.
  • In week 11, the number of laboratory detections, outbreaks and the number of geographic regions with influenza activity, decreased from the previous week.
  • Although adult sentinel hospitalizations decreased from the previous week, the number of hospitalizations and deaths reported by participating provinces and territories increased.
  • Influenza B detections and outbreaks in Canada are slowly increasing.
  • Although declining for most indicators, 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 11, one region in NL, reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 29 regions across 11 provinces and territories. Localized activity was reported in 21 regions across nine provinces.No regions reported any widespread activity in week 11. For more details on a specific region, click on the map. 

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Organization:

Date published: 2017-03-24

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 11

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 11, one region in NL, reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 29 regions across 11 provinces and territories. Localized activity was reported in 21 regions across nine provinces.No regions reported any widespread activity in week 11.

Laboratory Confirmed Influenza Detections

In week 11, the number (1,197) and the percentage of tests positive for influenza (16%) decreased from the previous week. Peak influenza detections occurred in week 02 at 27%. Although declining, 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 11

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
10 804 724 14 203
11 651 331 9 235

To date this season, 32,836 laboratory confirmed influenza detections have been reported, of which 96% 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 11

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 12, 2017 to March 18, 2017) Cumulative (August 28, 2016 to March 18, 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 46 1 28 17 78 4883 34 3238 1611 405 5288
AB 36 1 24 11 28 3676 20 3527 129 164 3840
SK 47 1 39 7 9 1663 3 960 700 48 1711
MB 42 0 13 29 3 400 0 136 264 41 441
ON 231 6 192 33 63 9113 53 7383 1677 288 9401
QC 411 0 11 400 35 9792 0 638 9152 316 10108
NB 90 0 0 90 4 864 2 85 777 8 872
NS 29 0 0 29 3 315 0 13 302 10 325
PE 12 0 12 0 0 186 2 184 0 1 187
NL 29 0 0 29 0 313 0 43 270 5 318
YT 0 0 0 0 0 210 0 162 48 4 214
NT 0 0 0 0 1 58 0 57 1 4 62
NU 0 0 0 0 0 68 0 66 2 1 69
Canada 973 9 319 645 224 31541 114 16492 14933 1295 32836
PercentageTable Figure 3 - Footnote 2 81% 1% 33% 66% 19% 96% 0% 52% 47% 4% 100%

To date, detailed information on age and type/subtype has been received for 23,013 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). In the previous influenza A(H3N2)-predominant season in 2014-15, adults aged 65+ represented 58% of cases and adults aged 20-64 represented 27% 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 11
Age groups (years) Weekly (March 12 to March 18, 2017) Cumulative (August 28, 2016 to March 18, 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 >87 <5 10 77 7 2068 14 799 1255 102 2170 9%
5-19 >24 0 <5 24 21 2076 13 1038 1025 172 2248 10%
20-44 64 0 7 57 32 3233 27 1751 1455 177 3410 15%
45-64 85 0 17 68 19 3595 23 1871 1701 210 3805 17%
65+ >321 <5 64 257 43 11063 13 5204 5846 317 11380 49%
Total 586 <5 >98 483 122 22035 90 10663 11282 978 23013 100%
PercentageTable 1 - Footnote 2 83% x% x% 82% 17% 96% 0% 48% 51% 4%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 11, 1.7% of visits to healthcare professionals were due to influenza-like illness, compared to 1.8% in the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 11

Number of Sentinels Reporting Week 11: 101

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%

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 11, 42 laboratory confirmed influenza outbreaks were reported (three less than the previous week). Among the reported outbreaks: 21 were in long-term care (LTC) facilities, seven in hospitals and  12 in institutional or community (other) settings. Of the outbreaks with known strains or subtypes, 11 were due to influenza A(H3N2), eight were due to influenza A(UnS) and seven outbreaks were due to influenza B. An additional two outbreaks due to ILI were reported in a school.

To date this season, 991 outbreaks have been reported and the majority (66%) 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 11
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 21 12

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 11, 261 influenza-associated hospitalizations were reported by participating provinces and territories, up from  254 reported in the previous week *. Influenza A accounted for 88% of hospitalizations. The weekly percentage of influenza B associated hospitalizations has been steadily increasing for the past few weeks (from 1.2% in week 02 to 11.5% in week 11). The largest proportion of hospitalizations were among adults aged 65+ years (71%). A total of ten intensive care unit (ICU) admissions were reported in week 11. An increase in the number of deaths was reported in week 11, with 35 deaths reported. All deaths were reported in adults aged 65+ years. 

To date this season, 5,139 hospitalizations have been reported, of which 97% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (2770/2787) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. A total of 193 ICU admissions and 277 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 11
Age Groups (years) Cumulative (August 28, 2016 to March 18 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %

* 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 are not distinguished among hospital admissions reported from ON. The hospitalization or death does not have to be attributable to influenza, a positive laboratory test is sufficient for reporting.
x Supressed to prevent residual disclosure
0-4 395 17 412 (8%) 11  6% <5 x%
5-19 217 21 238 (5%) 13  7% <5 x%
20-44 263 8 271 (5%) 18  9% <5 x%
45-64 666 30 696 (14%) 52  27% 32  12%
65+ 3433 89 3522 (68%) 99  51% 238  86%
Total 4974 165 5139 (100%) 193  100% 277  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 11, 17 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All but three cases were due to influenza A. The number of weekly hospitalizations reported since week 05 have been below the six year average for the same time period (Figure 7).

To date this season, 458 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 39% of hospitalizations. Influenza A accounted for 91% (n=419) of the reported hospitalizations, of which 34% (n=141) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 74 intensive care unit (ICU) admissions have been reported. Children aged 10-16 years accounted for 30% of ICU cases followed by children aged 0-23 months (27%). A total of 47 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 11

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 77
6-23 mo 102
2-4 yr 122
5-9 yr 78
10-16 yr 79

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 11

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 48 37 3 75
2 28 36 6 60
3 38 37 2 67
4 43 34 5 47
5 30 39 10 57
6 33 38 15 79
7 28 41 15 118
8 34 48 25 134
9 19 59 12 172
10 19 48 17 114
11 17 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 11, 42 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All but nine cases were due to influenza A and the majority of cases  (69%) occurred in adults aged 65+. The number of hospitalizations due to influenza B has been increasing since week 05.

To date this season, 1,222 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 98% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. To date, 81 intensive care unit (ICU) admissions have been reported. A total of 55 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 51 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 11

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 79
45-64 yr 188
65+ yr 955

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 11

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 = 1222) ICU admissions (n = 81) Deaths (n ≥51)
- Supressed due to small values
20-44 6.5% 7.4% 0.0%
45-64 15.4% 22.2% 4.0%
65+ 78.2% 70.4% 96.2%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,420 influenza viruses [1272 A(H3N2), 28 A(H1N1), 120 influenza B].  All but one influenza A virus (n=1271) and 40 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Eighty 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 11
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
319 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
952

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 319 influenza A (H3N2) viruses that underwent HI testing determined that  272 viruses belonged to genetic group 3C.2a and 47 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 28 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)
80 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 760 influenza viruses for resistance to oseltamivir and zanamivir and 180 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 180 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 11
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 635 1 (0.2%) 635 0 (0%) 155 155 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 25 0 (0%) 24 0 (0%) 24 24 (100%)
B 99 0 (0%) 100 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 760 1 (0.1%) 760 0 (0%) 180 180 (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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