FluWatch report:  July 23 – August 19, 2017 (weeks 30-33)

Overall Summary

  • Influenza activity remains at interseasonal levels across the country, with a few regions reporting sporadic or localized activity.
  • In weeks 30-33, circulation of influenza B continued to decline. The majority of detections were influenza A(H3N2) with slightly more detections reported than in previous seasons.
  • FluWatch will publish the last report of the 2016-17 season on September 1, 2017. We continue to monitor influenza and other respiratory infections via the RVDSS report, published every Thursday.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In weeks 30-33, influenza or influenza-like illness activity levels remained at low levels and the majority of regions reported no activity. In week 33, one region in Ontario and one region in Quebec reported localized activity, and seven regions in Ontario (1), Alberta (4) and British Columbia (2) reported sporadic activity. For more details on a specific region, click on the map. 

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Organization:

Date published: 2017-08-25

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, Week 33

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 weeks 30-33, influenza or influenza-like illness activity levels remained at low levels and the majority of regions reported no activity. In week 33, one region in Ontario and one region in Quebec reported localized activity, and seven regions in Ontario (1), Alberta (4) and British Columbia (2) reported sporadic activity.

Laboratory Confirmed Influenza Detections

In weeks 30-33, the number of tests positive for influenza remained at interseasonal levels. The percentage of tests positive was low, around 1.6% during weeks 30-33, although slightly higher than in the previous six seasons. The number of detections of influenza A was stable compared to the previous month, while influenza B detections continued to decline. The majority of influenza A viruses subtyped were A(H3N2). 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 33

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 6 <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 45 200 0 9
48 91 272 <5 7
49 141 414 <5 12
50 297 467 <5 18
51 535 750 <5 17
52 852 1064 <5 33
1 1438 1360 <5 38
2 1510 2118 10 39
3 1350 1412 0 47
4 1334 1220 <5 47
5 1222 1290 7 62
6 1200 1225 9 81
7 1291 1141 11 97
8 1344 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
17 112 39 <5 316
18 62 49 0 283
19 36 30 0 259
20 13 26 <5 228
21 13 12 0 168
22 9 14 7 94
23 13 8 <5 75
24 0 <5 <5 48
25 7 <5 <5 29
26 9 <5 <5 21
27 9 23 <5 21
28 0 8 0 12
29 6 16 <5 <5
30 7 13 <5 <5
31 7 16 <5 6
32 0 9 <5 <5
33 16 9 0 <5

To date this season, 39,339 laboratory-confirmed influenza detections have been reported, of which 88% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing over 99% of influenza A detections. 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 33

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
Weeks (July 23, 2017 to August 19, 2017) Cumulative (August 28, 2016 to August 19, 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 18 1 13 4 4 5386 49 3338 1999 726 6112
AB 27 1 19 7 0 3871 34 3685 152 763 4634
SK 3 0 2 1 0 1798 5 1049 744 363 2161
MB 1 0 1 0 1 485 1 190 294 137 622
ON 19 4 11 4 3 9820 83 7934 1803 1211 11031
QC 11 0 0 11 4 10905 0 650 10253 985 11890
NB 2 0 0 2 0 1168 3 131 1034 162 1330
NS 0 0 0 0 0 417 0 13 404 34 451
PE 0 0 0 0 0 196 2 194 0 5 201
NL 1 0 0 1 0 448 0 43 405 62 510
YT 2 0 1 1 1 174 0 169 5 26 200
NT 0 0 0 0 0 59 0 58 1 23 82
NU 0 0 0 0 3 85 0 83 2 30 115
Canada 84 6 47 31 16 34812 177 17537 17096 4527 39339
PercentageTable Figure 3 - Footnote 2 84% 7% 56% 37% 16% 88% 1% 50% 49% 12% 100%

To date this season, detailed information on age and type/subtype has been received for 27,323 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for nearly half of the reported influenza cases. Adults aged 65+ accounted for 51% of influenza A detections; however the majority of influenza B cases were among those less than 65 years of age.

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 33
Age groups (years) weeks 30-33 (July 23, 2017 to August 19, 2017) Cumulative (August 28, 2016 to August 19, 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 6 <5 <5 <5 <5 2259 23 837 1399 299 2558 9%
5-19 0 0 0 0 <5 2225 18 1080 1127 557 2782 10%
20-44 13 0 8 5 0 3473 43 1818 1612 551 4024 15%
45-64 13 0 11 <5 <5 3965 34 1982 1949 742 4707 17%
65+ 25 <5 9 15 <5 12166 22 5479 6665 1086 13252 49%
Total >55 <5 32 23 8 24088 140 11196 12752 3235 27323 100%
PercentageTable 1 - Footnote 2 88% 4% 56% 40% 12% 88% 1% 46% 53% 12%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In weeks 30-33, the proportion of visits to healthcare professionals due to influenza-like illness increased from 0.6% in week 30 to 1.8% in week 33.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 33

Number of Sentinels Reporting Week 33: 99

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 0.81%
19 0.96%
20 0.85%
21 0.94%
22 0.64%
23 0.89%
24 0.43%
25 1.48%
26 0.49%
27 1.49%
28 1.93%
29 1.12%
30 0.63%
31 1.37%
32 1.57%
33 1.79%

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

During the period of weeks 30-33, four laboratory-confirmed influenza outbreaks were reported, of which three were in long-term care (LTC) facilities, and one was in a hospital. Two outbreaks in LTC facilities were associated with influenza B (the influenza type of the third outbreak is not known), and the hospital outbreak was associated with influenza A (subtype unknown).

To date this season, 1,198 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. Fewer outbreaks were reported this season compared to the same period in the most recent previous A(H3N2)-predominant season (2014-15) when 1,735 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 33
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
20 0 6 3
21 0 4 1
22 2 2 0
23 1 1 2
24 0 1 0
25 0 0 0
26 0 0 0
27 0 1 1
28 0 1 0
29 0 1 0
30 0 0 0
31 0 1 0
32 0 1 0
33 1 1 0

Provincial/Territorial Influenza Hospitalizations and Deaths

During the period of weeks 30-33, the number of weekly influenza-associated hospitalizations reported by participating provinces and territoriesTable 1 - Footnote * remained at low levels. In weeks 30-33, 13 hospitalizations were reported, of which 11 were associated with influenza A and 7 (54%) occurred in adults 65+. Two intensive care unit (ICU) admissions and no deaths were reported.

To date this season, 6,542 hospitalizations have been reported, of which 88% 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 67% of the hospitalizations. A total of 274 ICU admissions and 387 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 33
Age Groups (years) Cumulative (August 28, 2016 to August 19, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 448 95 543 (8%) 20 7% <5 x%
5-19 241 100 341 (5%) 20 7% <5 x%
20-44 298 53 351 (5%) 27 10% 5 1%
45-64 766 143 909 (14%) 83 30% 37 10%
65+ 3971 427 4398 (67%) 124 45% 340 88%
Total 5724 818 6542 (99%) 274 99% 387 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In weeks 30-33, one laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalization associated with influenza A(H1N1)pdm09 was reported by the Immunization Monitoring Program Active (IMPACT) network.

To date this season, 597 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 37% of hospitalizations and influenza A accounted for 78% of the reported hospitalizations. Among the 132 hospitalizations due to influenza B, 69 (52%) were in children 5 to 16 years of age. In comparison, children over the age of 5 years accounted for 33% of influenza A hospitalizations. Additionally, 100 intensive care unit (ICU) admissions have been reported. A total of 67 ICU cases (67%) 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 33

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 88
6-23 mo 132
2-4 yr 153
5-9 yr 119
10-16 yr 105

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 33

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 15 35 4 71
52 39 47 7 92
1 49 37 3 75
2 28 36 6 60
3 37 37 2 67
4 36 34 5 47
5 38 39 10 57
6 34 38 15 79
7 30 41 15 118
8 32 48 25 134
9 21 59 12 172
10 20 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 10 22 10 41
17 8 18 9 37
18 11 15 6 28
19 10 10 5 18
20 13 9 4 18
21 5 6 2 10
22 6 4 1 7
23 3 2 0 4
24 0 2 0 5
25 2 1 0 3
26 3 1 0 2
27 2 0 0 2
28 2 1 0 1
29 0 0 0 2
30 1 0 0 0
31 0 0 0 0
32 0 0 0 1
33 0 0 0 0

Adult Influenza Hospitalizations and Deaths

Surveillance for the 2016-2017 influenza season ended on April 30th, 2017 (week 20).

This season, 1,535 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by the Canadian Immunization Research Network (CIRN). Influenza A accounted for 92% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. A total of 143 intensive care unit (ICU) admissions have been reported. Among ICU cases with available data, 126 cases (88%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 71 years. Approximately 86 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 20

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 237
65+ yr 1204

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 20

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= 143) Deaths (> 86)
- Supressed due to small values
20-44 6.1% 6.3% -
45-64 15.4% 18.9% 5.0%
65+ 78.4% 74.8% 96.6%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 2,341 influenza viruses [1,652 A(H3N2), 61 A(H1N1), 627 influenza B]. Among viruses characterized during the 2016-17 season, all seasonal influenza A viruses and 20% of influenza B viruses were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Eighty percent of influenza B viruses characterized were similar to the strain which is only included in the quadrivalent vaccine.

Table 3 – Influenza strain characterizations, Canada, 2016-17, Week 33
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
395 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
1255

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, one virus belonged to genetic group 3C.3a. Genetic characterization of the 396 influenza A (H3N2) viruses that underwent HI testing determined that 331 viruses belonged to genetic group 3C.2a and 65 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 61 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)
126 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)
501 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 1,255 influenza viruses for resistance to oseltamivir, 1,255 influenza viruses for resistance to zanamivir and 288 influenza viruses for resistance to amantadine. All but two influenza A(H3N2) viruses and one of the A(H1N1) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 288 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 33
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 760 2 (0.3%) 759 0 (0%) 232 232 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 52 1 (1.9%) 51 0 (0%) 55 55 (100%)
B 442 0 (0%) 444 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 1255 3 (0.2%) 1255 0 (0%) 288 288 (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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