FluWatch report: January 29, 2017 to February 4, 2017 (week 5)

Overall Summary

  • Influenza activity continues to be reported across Canada and two regions are reporting widespread influenza activity.
  • A slight increase in the percent of tests positive for influenza and number of laboratory confirmed influenza outbreaks was observed in week 5. 
  • In week 05, 56 laboratory confirmed outbreaks were reported (up from 54 in the previous week), the majority in long-term care facilities and due to influenza A.
  • A(H3N2) 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.
  • Canadian study reported an interim estimate of vaccine effectiveness of 42% against influenza A(H3N2) in Canada. The estimate is greater than the estimate for the previous A(H3N2) dominated season where no vaccine protection was found. The results of the study are consistent with expected vaccine effectiveness estimates for influenza A(H3N2). .
  • For more information on the flu, see our Flu(influenza) web page.

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Date published: 2017-02-10

Influenza/Influenza-like Illness Activity (geographic spread)

In week 05, all but two regions (one each in NB and MB) are reporting influenza or influenza-like illness activity. Sporadic influenza activity was reported in 24 regions across ten provinces and territories. Localized activity was reported in 24 regions across ten provinces. Widespread activity was reported in two provinces (one region each in BC and QC). For more details on a specific region, click on the map. 

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 5

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 05, all but two regions (one each in NB and MB) are reporting influenza or influenza-like illness activity. Sporadic influenza activity was reported in 24 regions across ten provinces and territories. Localized activity was reported in 24 regions across ten provinces. Widespread activity was reported in two provinces (one region each in BC and QC).

Laboratory Confirmed Influenza Detections

In week 05, the percentage of tests positive for influenza remained similar to the previous week from 23.5 to 24.3%. 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 5

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 1357 1413 0 47
4 1341 1312 <5 49
5 1208 1385 8 64
6 0 0 0 0
7 0 0 0 0
8 0 0 0 0
9 0 0 0 0
10 0 0 0 0
11 0 0 0 0
12 0 0 0 0
13 0 0 0 0
14 0 0 0 0
15 0 0 0 0
16 0 0 0 0
17 0 0 0 0
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

Nationally in week 05, 2,547 positive influenza tests were reported, fewer than the 2,586 tests reported in week 04. Western and Central-Eastern regions of Canada (BC, AB and ON) reported lower influenza detections in week 05 while a total of three provinces in the Central-Eastern and Atlantic regions of Canada reported higher influenza detections (QC, NB and NL). To date, 19,377 laboratory confirmed influenza detections have been reported, of which 98% have been influenza A. Influenza A(H3N2) is the most common subtype detected, representing over 99% of subtyped influenza A detections (10817/10866). 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 5

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 (January 29, 2017 to Febuary 4, 2017) Cumulative (August 28, 2016 to Febuary 4, 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 596 4 560 32 30 3177 7 1678 1492 102 3279
AB 176 0 112 64 6 3152 8 3012 132 60 3212
SK 0 0 0 0 0 0 0 0 0 0 0
MB 52 0 9 43 0 152 0 56 96 10 162
ON 663 3 524 136 9 6563 31 5292 1240 73 6636
QC 837 0 70 766 14 5098 0 361 4735 121 5219
NB 86 0 14 72 0 266 1 42 223 3 269
NS 31 0 0 31 1 156 0 13 143 1 157
PE 17 1 16 0 0 90 2 88 0 1 91
NL 13 0 0 13 0 66 0 45 21 5 71
YT 5 0 5 0 1 194 0 147 47 2 196
NT 5 0 4 1 0 32 0 31 1 0 32
NU 5 0 5 0 0 52 0 52 0 1 53
Canada 2486 8 1319 1158 61 18998 49 10817 8130 379 19377
PercentageTable Figure 3 - Footnote 2 98% 0% 53% 47% 2% 98% 0% 57% 43% 2% 100%

To date, detailed information on age and type/subtype has been received for over 14,347 laboratory confirmed influenza cases. Among cases with reported age and type/subtype information, almost half of the reported influenza cases and the largest proportion (47%) of influenza A (H3N2) cases were in adults aged 65+. 

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 5
Age groups (years) Weekly (January 29 to February 4, 2017) Cumulative (August 28, 2016 to February 4, 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 # %
<5 123 0 30 93 <5 >1150 <5 519 631 49 >1199 8%
5-19 136 0 37 99 <5 >1392 <5 745 647 44 >1436 10%
20-44 199 0 70 129 <5 >2175 <5 1199 976 40 >2215 15%
45-64 223 0 78 145 5 2395 6 1241 1148 53 2448 17%
65+ 632 0 191 441 8 >6967 <5 3256 3711 82 >7049 49%
Total 1313 0 406 907 >13 >14079 15 6960 7113 268 >14347 100%
PercentageTable 1 - Footnote 2 99% 0% 31% 69% 1% 98% 0% 49% 50% 2%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 05, 2.4% of visits to healthcare professionals were due to influenza-like illness, up slightly from 2.0% in the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 5

Number of Sentinels Reporting Week 05: 118

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 2.37%

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 05, 56 laboratory confirmed influenza outbreaks were reported, two more than the previous week: 32 in long-term care (LTC) facilities, 13 in hospitals and 11 in institutional or community (other) settings. All but one outbreak were due to influenza A. Of the outbreaks with known strains or subtypes, 12 were due to influenza A(H3N2) and 22 were due to influenza A(UnS). An additional four outbreaks due to ILI were reported in schools.

To date this season, 662 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,225 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 5
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 80 24
3 19 44 9
4 8 38 8
5 13 31 11

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 05, 336 influenza-associated hospitalizations were reported by participating provinces and territories, down from  423 reported in the previous week*. Influenza A accounted for nearly all of hospitalizations (99%). The largest proportion of hospitalizations (66% were among adults aged 65+. A total of six intensive care unit (ICU) admissions and 21 deaths were reported in week 05.

To date this season, 3,349 hospitalizations have been reported, of which 99% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (1932/1947) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. One hundred and twelve ICU admissions and greater than 130 deaths have been reported. The majority of deaths 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 5
Age Groups (years) Cumulative (August 28, 2016 to Feb. 4 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
Note: Influenza-associated hospitalizations are not reported to PHAC by: BC, NU, and QC. Only hospitalizations that require intensive medical care are reported by SK. ICU admissions
x Supressed to prevent residual disclosure
0-4 234 8 242 (7%) 7  6% 0 x%
5-19 144 8 152 (5%) 8  7% <5 x%
20-44 181 <5 >181 (x%) 10  9% 0 x%
45-64 448 <5 >448 (x%) 35  31% 21 x%
65+ 2294 26 2320 (69%) 53  47% 109 x%
Total 3301 48 3349 (99%) 113  100% >130 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 05, 29 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All cases but four were due to influenza A. The number of hospitalizations reported in week 04 is below the six year average for the same time period (Figure 7).

To date this season, 314 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 40% of hospitalizations. Influenza A accounted for 93% (n=292) of the reported hospitalizations, of which 41% (n=119) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 55 intensive care unit (ICU) admissions have been reported, of which the largest proportion (27%) was reported in children 0-23 months. A total of 36 ICU cases reported at least one underlying condition or comorbidity. No deaths have been reported this season.

In 2014-15, the previous influenza A(H3N2)-predominant season, there were 489 hospitalizations, 56 ICU admissions and less than five deaths reported as of week 05. 

 

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 5

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 50
6-23 mo 65
2-4 yr 89
5-9 yr 54
10-16 yr 55

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 5

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 8 5 1 13
47 1 5 0 9
48 7 10 1 22
49 10 15 2 28
50 21 24 4 47
51 18 35 4 71
52 38 47 7 92
1 48 37 3 75
2 28 36 6 60
3 38 37 2 67
4 43 34 5 47
5 29 39 10 57
6 #N/A 38 15 79
7 #N/A 41 15 118
8 #N/A 48 25 134
9 #N/A 59 12 172
10 #N/A 48 17 114
11 #N/A 45 17 118
12 #N/A 39 14 96
13 #N/A 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 05, 109 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All  but three cases were due to influenza A and the majority of cases  (74%) occurred in adults aged 65+.

To date this season, 736 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. All but eight hospitalized cases were due to influenza A. Adults aged 65+ accounted for 77% of hospitalizations. To date, 39 intensive care unit (ICU) admissions have been reported. A total of 25 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 67 years. A total of 23 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 82 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 5

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 58
45-64 yr 110
65+ yr 568

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 5

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= 736) ICU admissions (n=39) Deaths (n= 23)
- Supressed due to small values
20-44 7.9% - -
45-64 14.9% 25.6% x%
65+ 77.2% 66.7% x%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 560 influenza viruses [516 A(H3N2), 10 A(H1N1), 34 influenza B].  All but one influenza A virus (n=515) and all 34 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Nineteen influenza B viruses were similar to the strain which is included only in the quadrivalent vaccine.

Table 3 – Influenza strain characterizations, Canada, 2016-17, week 5
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
167 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
348

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 XX influenza A (H3N2) viruses that underwent HI testing determined that  XX viruses belonged to genetic group 3C.2a and XX viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining XX isolates. 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 10 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)
15 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)
19 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 391 influenza viruses for resistance to oseltamivir, amantadine. All viruses were sensitive to oseltamivir and zanamivir. All 138 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 5
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 348 0 (0%) 348 0 (0%) 129 129 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 10 0 (0%) 9 0 (0%) 8 8 (100%)
B 32 0 (0%) 33 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 391 0 (0%) 391 0 (0%) 138 138 (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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