FluWatch report:  June 18 to July 22, 2017 (weeks 25-29)

Overall Summary

  • Influenza activity is at interseasonal levels across the country, with a few regions reporting sporadic or localized activity.
  • In weeks 25-29, influenza A and B viruses circulated at interseasonal levels in Canada. The majority of subtyped influenza A viruses were A(H3N2).
  • FluWatch will publish monthly reports over the summer. The next report will be published on August 25, 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 25-29, influenza or influenza-like illness activity levels continued to decline and the majority of regions reported no activity. In week 29, one region in Ontario reported localized activity, and seven regions across five provinces reported sporadic activity. For more details on a specific region, click on the map. 

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Organization:

Date published: 2017-07-28

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, Week 29

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 25-29, influenza or influenza-like illness activity levels continued to decline and the majority of regions reported no activity. In week 29, one region in Ontario reported localized activity, and seven regions across five provinces reported sporadic activity.

Laboratory Confirmed Influenza Detections

In weeks 25-29, the number of tests positive for influenza remained at interseasonal levels, although slightly higher than in the previous six seasons. The percentage of tests positive was low, around 2% during weeks 25-29. Detections of influenza A and B were nearly equal in weeks 25-29, and 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 29

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 7 15 <5 <5

To date this season, 39,235 laboratory-confirmed influenza detections have been reported, of which 89% 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 29

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 (June 18, 2017 to July 22, 2017) Cumulative (August 28, 2016 to July 22, 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 20 4 15 1 9 5365 48 3325 1992 722 6087
AB 24 3 17 4 25 3843 33 3665 145 763 4606
SK 4 1 2 1 8 1795 5 1047 743 363 2158
MB 0 0 0 0 3 484 1 189 294 136 620
ON 20 1 14 5 12 9801 79 7923 1799 1208 11009
QC 20 0 0 20 9 10894 0 650 10242 981 11875
NB 2 0 0 2 6 1166 3 131 1032 162 1328
NS 0 0 0 0 1 417 0 13 404 34 451
PE 0 0 0 0 0 196 2 194 0 5 201
NL 0 0 0 0 3 447 0 43 404 62 509
YT 5 0 3 2 1 172 0 168 4 25 197
NT 0 0 0 0 0 59 0 58 1 23 82
NU 0 0 0 0 8 85 0 83 2 27 112
Canada 95 9 51 35 85 34724 171 17489 17062 4511 39235
PercentageTable Figure 3 - Footnote 2 53% 9% 54% 37% 47% 89% 0% 50% 49% 11% 100%

To date this season, detailed information on age and type/subtype has been received for 27,258 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+ 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. 

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 29
Age groups (years) Weeks 25-29 (June 18, 2017 to July 22, 2017) Cumulative (August 28, 2016 to July 22, 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 <5 <5 <5 9 2253 22 833 1398 298 2551 9%
5-19 5 0 <5 <5 9 2225 18 1080 1127 555 2780 10%
20-44 >10 <5 5 5 8 3460 43 1810 1607 551 4011 15%
45-64 16 <5 10 5 9 3952 34 1971 1947 740 4692 17%
65+ 34 <5 18 15 24 12141 21 5470 6650 1083 13224 49%
Total 71 6 36 29 59 24031 138 11164 12729 3227 27258 100%
PercentageTable 1 - Footnote 2 55% 8% 51% 41% 45% 88% 1% 46% 53% 12%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In weeks 25-29, overall, the proportion of visits to healthcare professionals due to influenza-like illness was low. The weekly percentage varied between 0.5% and 1.9% due to a large proportion of visits for ILI reported by a single sentinel practitioner.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 29

Number of Sentinels Reporting Week 29: 94

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%

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 25-29, four laboratory-confirmed influenza outbreaks were reported, of which three were in long-term care facilities, and one was in an institutional or community (other) setting.

To date this season, 1,194 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 1,732 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 29
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

Provincial/Territorial Influenza Hospitalizations and Deaths

During the period of weeks 25-29, the number of weekly influenza-associated hospitalizations reported by participating provinces and territoriesTable 1 - Footnote * decreased to low levels. In weeks 25-29, 37 hospitalizations were reported, of which 21 were associated with influenza A and 65% occurred in adults 65+. Four intensive care unit (ICU) admissions and two deaths were reported.

To date this season, 6,527 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 273 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 29
Age Groups (years) Cumulative (August 28, 2016 to July 22, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 447 94 541 (8%) 20  7% <5 x%
5-19 241 99 340 (5%) 20  7% <5 x%
20-44 296 52 348 (5%) 27  10% 5  1%
45-64 765 143 908 (14%) 83  30% 37  10%
65+ 3964 426 4390 (67%) 123  45% 340  88%
Total 5713 814 6527 (99%) 273  99% 387 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In weeks 25-29, nine laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Six of the nine hospitalizations were associated with influenza B.

To date this season, 595 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 29

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 89
6-23 mo 132
2-4 yr 152
5-9 yr 116
10-16 yr 106

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 29

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

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 2,307 influenza viruses [1,628 A(H3N2), 59 A(H1N1), 620 influenza B].  All seasonal influenza A viruses and 20% of influenza B viruses characterized 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 29
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
1232

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 395 influenza A (H3N2) viruses that underwent HI testing determined that 329 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 59 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)
125 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)
495 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 1,250 influenza viruses for resistance to oseltamivir, 1,250 influenza viruses for resistance to zanamivir and 272 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 272 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 29
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 757 2 (0.3%) 756 0 (0%) 218 218 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 52 1 (1.9%) 51 0 (0%) 53 53 (100%)
B 440 0 (0%) 442 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 1250 3 (0.2%) 1250 0 (0%) 272 272 (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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