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FluWatch report: April 23 – April 29, 2017 (week 17)

Overall Summary

  • Overall, influenza activity continues to decline slowly in Canada.
  • In week 17, influenza B accounted for the majority of influenza activity in Canada with 50% or more of 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.
  • 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 17, seven regions across four provinces and territories (NL, NS, NT and NU) reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 33 regions across 12 provinces and territories (all provinces and territories except ON). Localized activity was reported in 13 regions across four provinces (QC, ON, AB and BC). For more details on a specific region, click on the map.

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Organization:

Public Health Agency of Canada

Date published: 2017-05-05

Related Topics

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 17

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 17, seven regions across four provinces and territories (NL, NS, NT and NU) reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 33 regions across 12 provinces and territories (all provinces and territories except ON). Localized activity was reported in 13 regions across four provinces (QC, ON, AB and BC).

Laboratory Confirmed Influenza Detections

In week 17, the number (462) and the percentage (9.8%) of tests positive for influenza decreased from the previous week. Influenza B was the most common type of influenza detected in all but two jurisdictions in Canada (QC and NS). Overall in week 17, influenza B, accounted for 66% of total detections. The number of influenza B detections remains low 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 17

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 9 350
17 114 36 <5 310
18 0 0 0 0
19 0 0 0 0
20 0 0 0 0
21 0 0 0 0
22 0 0 0 0
23 0 0 0 0
24 0 0 0 0
25 0 0 0 0
26 0 0 0 0
27 0 0 0 0
28 0 0 0 0
29 0 0 0 0
30 0 0 0 0
31 0 0 0 0
32 0 0 0 0
33 0 0 0 0
34 0 0 0 0

To date this season, 37,593 laboratory confirmed influenza detections have been reported, of which 91% 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 17

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 (April 23, 2017 to April 29, 2017) Cumulative (August 28, 2016 to April 29, 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 3 0 0 3 24 5319 42 3294 1983 640 5959
AB 0 0 0 0 60 3791 24 3628 139 508 4299
SK 0 0 0 0 0 1749 4 1013 732 193 1942
MB 6 0 1 5 10 476 0 179 297 102 578
ON 33 2 26 5 88 9681 71 7838 1772 879 10560
QC 88 0 0 88 65 10788 0 650 10136 724 11512
NB 9 0 0 9 19 1147 3 126 1018 104 1251
NS 3 0 0 3 0 412 0 13 399 25 437
PE 1 0 1 0 2 196 2 194 0 4 200
NL 1 0 0 1 6 441 0 43 398 20 461
YT 0 0 0 0 4 213 0 164 49 16 229
NT 0 0 0 0 3 59 0 58 1 16 75
NU 0 0 0 0 1 85 0 83 2 5 90
Canada 144 2 28 114 282 34357 146 17283 16926 3236 37593
PercentageTable Figure 3 - Footnote 2 34% 1% 19% 79% 66% 91% 0% 50% 49% 9% 100%

To date this season, detailed information on age and type/subtype has been received for 26,007 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 numbers is mainly affecting individuals less than 65 years of age. Individuals less than 65 years of age accounted for 67% of influenza B detections.

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 17
Age groups (years) Weekly (April 23 to April 29, 2017) Cumulative (August 28, 2016 to April 29, 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 7 0 0 7 16 2229 17 824 1388 200 2429 9%
5-19 5 0 0 5 21 2201 15 1073 1113 384 2585 10%
20-44 <5 0 0 <5 21 3416 34 1795 1587 387 3803 15%
45-64 8 0 0 8 40 3884 27 1941 1916 538 4422 17%
65+ 72 0 5 67 55 12031 15 5414 6602 737 12768 49%
Total >92 0 5 >87 153 23761 108 11047 12606 2246 26007 100%
PercentageTable 1 - Footnote 2 x% x% x% x% x% 91% 0% 46% 53% 9%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 17, 0.9% of visits to healthcare professionals were due to influenza-like illness, a decrease compared to the percentage of visits reported in week 16.

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

Number of Sentinels Reporting Week 17: 113

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 0.87%
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  

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 17, 17 laboratory-confirmed influenza outbreaks were reported, an increase from the previous week. Of the 13 outbreaks with known strains or subtypes: four were due to influenza A and nine were due to influenza B.

To date this season, 1,136 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 68 outbreaks (6%) due to influenza B have been reported.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, week 17
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 11 6
18 0 0 0
19 0 0 0
20 0 0 0
21 0 0 0
22 0 0 0
23 0 0 0
24 0 0 0
25 0 0 0
26 0 0 0
27 0 0 0
28 0 0 0
29 0 0 0
30 0 0 0
31 0 0 0
32 0 0 0
33 0 0 0
34 0 0 0

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 17, 78 influenza-associated hospitalizations were reported by participating provinces and territories*, a decrease from 121 reported in the previous week. In week 17, 60% of hospitalizations occurred in adults 65+ and influenza B accounted for 73% of reported hospitalizations. Additionally, less than five intensive care unit (ICU) admissions and six deaths were reported.

To date this season, 6,110 hospitalizations have been reported, of which 92% 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 68% of the hospitalizations. A total of 242 ICU admissions and 354 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 17
Age Groups (years) Cumulative (August 28, 2016 to April 29, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 440 53 493 (8%) 16  7% <5 Table 2 - Footnote x%
5-19 236 60 296 (5%) 15  6% <5 Table 2 - Footnote x%
20-44 290 26 316 (5%) 23  10% 5  1%
45-64 747 94 841(14%) 72  30% 35  10%
65+ 3882 282 4164 (68%) 116  48% 310  88%
Total 5559 515 6110 (100%) 242  100% 354  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 17, seven laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, of which five were associated with influenza B. Pediatric hospitalizations have been declining since the peak in early January. The number of weekly hospitalizations has been below the six year average since early February (Figure 7).

To date this season, 531 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 38% of hospitalizations and influenza A accounted for 84% of the reported hospitalizations. Among the 84 hospitalizations due to influenza B, 43 (51%) 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, 88 intensive care unit (ICU) admissions have been reported. A total of 60 ICU cases (70%) 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 17

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 81
6-23 mo 121
2-4 yr 138
5-9 yr 100
10-16 yr 91

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

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 26 36 6 60
3 39 37 2 67
4 34 34 5 47
5 38 39 10 57
6 33 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 #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 17, 16 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN), unchanged from the previous week. In week 17, the majority (88%) of hospitalizations occurred in adults 65+ and influenza B accounted for 75% of reported hospitalizations.

To date this season, 1,525 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 79% of hospitalizations. To date, 134 intensive care unit (ICU) admissions have been reported. Among cases with available data, 105 ICU cases (78%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 70 years. Approximately 70 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 17

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 92
45-64 yr 234
65+ yr 1199

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 17

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= 1521) ICU admissions (n= 131) Deaths (n= 73)
20-44 6.0% 6.1% -
45-64 15.4% 20.6% 5.0%
65+ 78.6% 73.3% 96.1%
- Supressed due to small values

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,762 influenza viruses [1530 A(H3N2), 36 A(H1N1), 232 influenza B].  All but one influenza A virus (n=1529) and 54 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and seventy-eight 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 17
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 351 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		 1142

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 351 influenza A (H3N2) viruses that underwent HI testing determined that 288 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 36 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)		 54 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)		 178 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 989 influenza viruses for resistance to oseltamivir, 988 influenza viruses for resistance to zanamivir and 220 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 220 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 17
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 729 2 (0.3%) 728 0 (0%) 190 190 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 35 0 (0%) 34 0 (0%) 29 29 (100%)
B 224 0 (0%) 225 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 989 2 (0.2%) 988 0 (0%) 220 220 (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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