FluWatch report: March 26, 2017 – April 1, 2017 (week 13)

Overall Summary

  • Overall, influenza activity is slowly declining in Canada.
  • All indicators (laboratory detections, influenza-like illness, outbreaks and hospitalizations) have either decreased or remained similar to 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 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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Influenza/Influenza-like Illness Activity (geographic spread)

In week 13, six regions across four provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 22 regions across 11 provinces and territories. Localized activity was reported in 19 regions across six provinces. One region in BC reported widespread activity in week 12. For more details on a specific region, click on the map.

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Organization:

Date published: 2017-04-07

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 13

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 13, six regions across four provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 22 regions across 11 provinces and territories. Localized activity was reported in 19 regions across six provinces. One region in BC reported widespread activity in week 12.

Laboratory Confirmed Influenza Detections

In week 13, the number (902) 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 (67%) of detections. Influenza B detections have been steadily increasing since mid-February. Influenza B detections remain 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 13

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
12 499 258 <5 302
13 381 212 0 304

To date this season, 35,129 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 13

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
Week (March 26, 2016 to April 1, 2017) Cumulative (August 28, 2016 to April 1, 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 53 3 44 6 44 5300 37 3283 1980 510 5810
AB 29 0 19 10 58 3749 24 3586 139 265 4014
SK 12 0 7 5 20 1723 4 996 723 101 1824
MB 17 0 12 5 13 441 0 156 285 67 508
ON 119 2 99 18 96 9428 55 7650 1723 470 9898
QC 219 0 3 216 51 10302 0 650 9650 426 10728
NB 71 0 12 59 6 1029 2 109 918 23 1052
NS 34 0 0 34 0 369 0 13 356 14 383
PE 3 0 3 0 0 192 2 190 0 1 193
NL 25 0 0 25 1 384 0 43 341 7 391
YT 1 0 1 0 1 165 0 164 1 9 174
NT 0 0 0 0 4 58 0 57 1 10 68
NU 9 0 9 0 0 85 0 83 2 1 86
Canada 592 5 209 378 294 33225 124 16980 16119 1904 35129
PercentageTable Figure 3 - Footnote 2 67% 1% 35% 64% 33% 95% 0% 51% 49% 5% 100%

To date, detailed information on age and type/subtype has been received for 24,212 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. 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 13
Age groups (years) Week (March 26, 2017 to April 1, 2017) Cumulative (August 28, 2016 to April 1, 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 >27 0 <5 27 5 2151 15 813 1323 120 2271 9%
5-19 25 0 6 19 15 2136 10 1059 1067 227 2363 10%
20-44 >35 0 <5 35 15 3321 21 1774 1526 229 3550 15%
45-64 >33 0 <5 33 22 3731 19 1906 1806 304 4035 17%
65+ 190 0 19 171 41 11558 9 5310 6239 435 11993 50%
Total 319 0 34 285 98 22897 74 10862 11961 1315 24212 100%
PercentageTable 1 - Footnote 2 76% 0% 11% 89% 24% 95% 0% 47% 52% 5%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 13, 1.2% of visits to healthcare professionals were due to influenza-like illness, which is similar to the percentage of visits reported in week 12.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 13

Number of participants reporting in week 13: 117

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 1.71%
12 1.16%
13 1.18%

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 13, 33 laboratory confirmed influenza outbreaks were reported (three fewer outbreaks than week 12). The majority of outbreaks (73%) occurred in long-term care (LTC) facilities. Of the outbreaks with known strains or subtypes: three were due to influenza A(H3N2), 8 were due to influenza A(UnS), nine outbreaks were due to influenza B and one outbreak was due to A(H3N2) and B. All but one influenza B outbreak occurred in LTC facilities. An additional two outbreaks due to ILI were reported in schools.

To date this season, 1,063 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. A total of 41 outbreaks (4%) due to influenza B have been reported. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,616 outbreaks were reported, of which 74% occurred in LTC facilities and 70 outbreaks (4%) were due to influenza B.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, week 13
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

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 13, 142 influenza-associated hospitalizations were reported by participating provinces and territories*, down from 182 reported in the previous week. Influenza A accounted for 73% 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 (68%). Five intensive care unit (ICU) admissions and nine deaths were reported in week 13.

To date this season, 5,531 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 (2959/2978) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. A total of 208 ICU admissions and 303 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 13
Age Groups (years) Cumulative (August 28, 2016 to April 1, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 421 28 449 (8%) 13  6% <5 Table 2 - Footnote x%
5-19 223 31 254 (5%) 14  7% <5 Table 2 - Footnote x%
20-44 279 11 290 (5%) 22  11% <5 Table 2 - Footnote x%
45-64 705 45 750 (14%) 55  26% 33  11%
65+ 3647 141 3788 (68%) 104  50% 263  87%
Total 5275 256 5531 (100%) 208  100% 303  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 13, 14 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, which is similar to the number of cases reported in week 12. Influenza A and B accounted for an equal number of cases. Fifty percent of the hospitalizations in week 13 occurred in children under the age of 2 years. 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, 484 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 89% (n=431) of the reported hospitalizations. Among the 53 hospitalizations due to influenza B, 28 (47%) 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, 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 13

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 112
2-4 yr 129
5-9 yr 82
10-16 yr 84

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 13

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 27 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 18 45 17 118
12 14 39 14 96
13 14 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 13, 29 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). Influenza A continues to account for the majority of reported hospitalizations (72%). The majority of cases (83%) occurred in adults aged 65+.

To date this season, 1,339 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 96% of hospitalizations. Adults aged 65+ accounted for 79% of hospitalizations. To date, 89 intensive care unit (ICU) admissions have been reported. A total of 65 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 59 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 83 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 13

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 84
45-64 yr 201
65+ yr 1054

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 13

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 = 1339) ICU admissions (n = 89) Deaths (n= >59)
- Supressed due to small values
20-44 6.3% 6.7% -
45-64 15.0% 21.3% 5.0%
65+ 78.7% 71.9% 95.2%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,526 influenza viruses [1362 A(H3N2), 35 A(H1N1), 164 influenza B]. All but one influenza A virus (n=1361) and 42 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and twenty-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 13
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
332 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
994

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 332 influenza A (H3N2) viruses that underwent HI testing determined that  281 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/4801/20143Table 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 35 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)
42 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)
122 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 837 influenza viruses for resistance to oseltamivir, 836 influenza viruses for resistance to zanamivir and 202 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 13
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 682 1 (0.1%) 681 0 (0%) 173 173 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 29 0 (0%) 28 0 (0%) 28 28 (100%)
B 125 0 (0%) 126 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 837 1 (0.1%) 836 0 (0%) 202 202 (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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