FluWatch report: May 7 to May 13, 2017 (week 19)

Overall Summary

  • Overall, influenza activity continues to decline slowly in Canada.
  • In week 19, influenza B accounted for the majority of influenza activity in Canada, with 70% or more of reported 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.
  • To date, 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 19, 16 regions across eight provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 27 regions across nine provinces and territories. Localized activity was reported in ten regions across three provinces. For more details on a specific region, click on the map.

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Organization:

Date published: 2017-05-19

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, Week 19

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 19, 16 regions across eight provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 27 regions across nine provinces and territories. Localized activity was reported in ten regions across three provinces.

Laboratory Confirmed Influenza Detections

In week 19, the number (323) and the percentage (8.3%) of tests positive for influenza decreased from the previous week. Influenza B was the most common type of influenza detected in all jurisdictions in Canada. Since week 16, the percentage of tests positive for influenza B has plateaued (6.6% to 6.9%) and has not yet begun a clear decline. Overall in week 19, influenza B accounted for 80% of total detections. Influenza B detections are within expected levels 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 19

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 9 347
17 113 38 <5 316
18 65 47 <5 283
19 38 28 0 257
20 #N/A #N/A #N/A #N/A
21 #N/A #N/A #N/A #N/A
22 #N/A #N/A #N/A #N/A
23 #N/A #N/A #N/A #N/A
24 #N/A #N/A #N/A #N/A
25 #N/A #N/A #N/A #N/A
26 #N/A #N/A #N/A #N/A
27 #N/A #N/A #N/A #N/A
28 #N/A #N/A #N/A #N/A
29 #N/A #N/A #N/A #N/A
30 #N/A #N/A #N/A #N/A
31 #N/A #N/A #N/A #N/A
32 #N/A #N/A #N/A #N/A
33 #N/A #N/A #N/A #N/A
34 #N/A #N/A #N/A #N/A

To date this season, 38,350 laboratory confirmed influenza detections have been reported, of which 90% 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 19

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 (May 7, 2017 to May 13, 2017) Cumulative (August 28, 2016 to May 13, 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 1 0 0 1 10 5324 43 3297 1984 667 5991
AB 5 0 3 2 37 3802 25 3635 142 599 4401
SK 3 0 1 2 18 1769 4 1029 736 287 2056
MB 1 0 1 0 7 484 0 186 298 117 601
ON 15 0 15 0 67 9740 73 7886 1781 1029 10769
QC 23 0 0 23 74 10854 0 650 10202 862 11716
NB 9 0 4 5 16 1160 3 130 1027 132 1292
NS 2 0 0 2 1 416 0 13 403 30 446
PE 0 0 0 0 0 196 2 194 0 4 200
NL 2 0 0 2 3 446 0 43 403 28 474
YT 0 0 0 0 3 213 0 164 49 21 234
NT 0 0 0 0 3 59 0 58 1 20 79
NU 0 0 0 0 1 85 0 83 2 6 91
Canada 61 0 24 37 240 34548 150 17368 17028 3802 38350
PercentageTable Figure 3 - Footnote 2 20% 0% 39% 61% 80% 90% 0% 50% 49% 10% 100%

To date this season, detailed information on age and type/subtype has been received for 26,447 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 number, 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 19
Age groups (years) Weekly (May 7, 2017 to May 13, 2017) Cumulative (August 28, 2016 to May 13, 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 <5 0 <5 <5 12 2241 17 829 1395 235 2476 9%
5-19 <5 0 0 <5 14 2213 16 1077 1120 444 2657 10%
20-44 <5 0 0 <5 10 3433 34 1801 1598 451 3884 15%
45-64 <5 0 <5 <5 12 3912 27 1952 1933 606 4518 17%
65+ <5 0 0 <5 24 12068 15 5426 6627 844 12912 49%
Total >8 0 <5 8 72 23867 109 11085 12673 2580 26447 100%
PercentageTable 1 - Footnote 2 13% 0% x% x% 87% 90% 0% 46% 53% 10%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 19, 1.0% of visits to healthcare professionals were due to influenza-like illness.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 19

Number of Sentinels Reporting Week 19: 97

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 0.86%
18 0.82%
19 0.99%

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 19, 15 laboratory-confirmed influenza outbreaks were reported. Of the nine outbreaks with known strains or subtypes, two were due to influenza A and seven were due to influenza B. An additional outbreak due to ILI was reported in a school.

To date this season, 1,166 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 82 outbreaks (7%) due to influenza B have been reported. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,710 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 19
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 12 6
18 1 6 6
19 2 10 3

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 19, 52 influenza-associated hospitalizations were reported by participating provinces and territories*, a decrease from 75 hospitalizations reported in the previous week. In week 19, 75% of reported hospitalizations were due to influenza B and 42% occurred in adults 65+. Additionally, less than five intensive care unit (ICU) admissions and five deaths were reported.

To date this season, 6,284 hospitalizations have been reported, of which 90% 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 256 ICU admissions and 366 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 19
Age Groups (years) Cumulative (August 28, 2016 to May 13, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 444 73 517 (8%) 18  7% <5 Table 2 - Footnote x%
5-19 240 79 319 (5%) 20  8% <5 Table 2 - Footnote x%
20-44 293 41 334 (5%) 24  9% 5  1%
45-64 761 112 873 (14%) 76  30% 35 9%
65+ 3909 332 4241 (67%) 118  46% 321 88%
Total 5647 637 6284 (99%) 256  100% 366 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 19, ten laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All hospitalizations were associated with influenza B and 60% were in children over the age of 5 years.

To date this season, 556 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 81% of the reported hospitalizations. Among the 104 hospitalizations due to influenza B, 57 (55%) 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, 95 intensive care unit (ICU) admissions have been reported. A total of 62 ICU cases (65%) 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 19

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 84
6-23 mo 123
2-4 yr 143
5-9 yr 107
10-16 yr 99

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 19

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 49 37 3 75
2 27 36 6 60
3 38 37 2 67
4 35 34 5 47
5 38 39 10 57
6 35 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 10 15 6 28
19 10 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

Surveillance for the 2016-2017 influenza season ended on April 30th, 2017.

This season, 1,535 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 93% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. A total of 141 intensive care unit (ICU) admissions have been reported. Among ICU cases with available data, 120 cases (85%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 71 years. Approximately 84 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 19

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 94
45-64 yr 236
65+ yr 1205

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 19

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= 1535) ICU admissions (n= 141) Deaths (> 84)
- Supressed due to small values
20-44 6.1% 5.7% -
45-64 15.4% 19.1% 5.0%
65+ 78.5% 75.2% 96.6%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,929 influenza viruses [1556 A(H3N2), 40 A(H1N1), 333 influenza B]. All but one influenza A virus (n=1928) and 70 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Two hundred and sixty-three 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 19
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
365 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
1190

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 365 influenza A (H3N2) viruses that underwent HI testing determined that 302 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/4801/20143Table 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 40 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)
70 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)
263 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 1,081 influenza viruses for resistance to oseltamivir, 1,084 influenza viruses for resistance to zanamivir and 228 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 228 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 19
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 743 2 (0.3%) 742 0 (0%) 197 197 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 35 0 (0%) 37 0 (0%) 30 30 (100%)
B 302 0 (0%) 304 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 1081 2 (0.2%) 1084 0 (0%) 228 228 (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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