FluWatch report: February 10 to 16, 2019 (Week 07)

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Organization: Public Health Agency of Canada

Date published: 2019-02-22

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Overall Summary

  • Influenza activity in Canada continues to decline slowly. Influenza activity is past the peak in most regions in western Canada, but continues to circulate in eastern regions.
  • At the national level, most indicators of influenza activity declined in week 07.
  • Influenza A(H1N1)pdm09 continues to be the most common influenza virus circulating in Canada. There is currently very little influenza B circulation compared to previous seasons.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 07, levels of influenza activity were similar to the previous week. The following influenza activity levels were reported (Figure 1):

  • 15 regions reported localized activity: in Alta.(1), Ont.(6), Que.(2), N.S.(4) and N.B.(2).
  • 32 regions reported sporadic activity: in B.C.(5), Alta.(4), Man.(4), Ont.(1), Que.(4), N.B.(5), N.L.(4), P.E.I.(1), Nvt.(2), N.W.T(1), and Y.T.(1).
  • Three regions: in Man.(1), N.W.T(1), and Nvt.(1) reported no activity.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-07

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern Sporadic
N.L. Labrador-Grenfell Sporadic
N.L. Central Sporadic
N.L. Western Sporadic
P.E.I. Prince Edward Island Sporadic
N.S. Zone 1 - Western Localized
N.S. Zone 2 - Northern Localized
N.S. Zone 3 - Eastern Localized
N.S. Zone 4 - Central Localized
N.B. Region 1 Localized
N.B. Region 2 Localized
N.B. Region 3 Sporadic
N.B. Region 4 Sporadic
N.B. Region 5 Sporadic
N.B. Region 6 Sporadic
N.B. Region 7 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Localized
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Localized
Que. Montérégie Sporadic
Ont. Central East Localized
Ont. Central West Localized
Ont. Eastern Localized
Ont. North East Localized
Ont. North West Sporadic
Ont. South West Localized
Ont. Toronto Localized
Man. Northern Regional Sporadic
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern No Activity
Man. Winnipeg Sporadic
Man. Southern Health Sporadic
Sask. North No Data
Sask. Central No Data
Sask. South No Data
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Sporadic
Alta. Calgary Localized
Alta. South Zone Sporadic
B.C. Interior Sporadic
B.C. Fraser Sporadic
B.C. Vancouver Coastal Sporadic
B.C. Vancouver Island Sporadic
B.C. Northern Sporadic
Y.T. Yukon Sporadic
N.W.T. North No Activity
N.W.T. South Sporadic
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq No Activity
Nvt. Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 07, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

  • The percentage of tests positive for influenza was similar to the previous week at 17.9%.
  • A total 1,565 laboratory detections of influenza were reported, of which 98% were influenza A.

To date this season, 30,981 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 10,778 influenza A viruses subtyped, 91% have been A(H1N1)pdm09.
  • Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 24,187 laboratory-confirmed influenza cases (Table 1):

  • 85% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
  • 62% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

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 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-07

Figure 2. Text equivalent follows.

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.

Figure 2 - Text equivalent
Surveillance Week A(Unsubtyped) A(H3) A(H1)pdm09 Influenza B
35 3 2 7 0
36 4 7 4 0
37 3 2 3 1
38 6 3 2 3
39 11 5 1 3
40 16 7 29 3
41 27 6 21 3
42 40 19 55 2
43 83 23 128 4
44 169 13 214 6
45 244 18 295 15
46 346 10 404 9
47 449 17 507 8
48 679 29 632 10
49 851 35 785 16
50 1368 35 828 14
51 1890 54 953 21
52 2292 55 903 26
1 2387 58 893 31
2 1985 93 1061 43
3 1613 101 585 40
4 1483 93 532 48
5 1449 112 433 43
6 1241 113 313 42
7 1205 109 220 31

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-07

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (February 10, 2019 to February 16, 2019) Cumulative (August 26, 2018 to February 16, 2019)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1N1)pdm09
A
(H3N2)
A(UnS)Table Figure 3 - Footnote 3 B
Total
A
Total
A
(H1N1)pdm09
A
(H3N2)
A(UnS)Table Figure 3 - Footnote 3 B
Total
BC 195 52 21 122 5 3481 2386 220 875 28 3509
AB 60 26 17 17 9 5309 3457 151 1701 64 5373
SK 6 3 1 2 1 2173 1349 60 764 10 2183
MB 11 4 0 7 0 982 270 6 706 6 988
ON 315 96 69 150 4 3839 1723 560 1556 77 3916
QC 734 0 0 734 10 11949 0 0 11949 225 12174
NB 110 23 0 87 0 1831 183 13 1635 2 1833
NS 58 0 0 58 1 260 0 0 260 4 264
PEI 11 11 0 0 0 183 183 0 0 0 183
NL 26 0 0 26 0 325 1 0 324 2 327
YT 5 2 0 3 0 63 47 1 15 0 63
N.W.T 0 0 0 0 0 151 149 2 0 0 151
NU 1 1 0 0 0 17 17 0 0 0 17
Canada 1532 218 108 1206 30 30563 9765 1013 19785 418 30981
PercentageTable Figure 3 - Footnote 2 98% 14% 7% 79% 2% 99% 32% 3% 65% 1% 100%
Table Figure 3 - Footnote 1

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces.

Return to Table Figure 3 - Footnote 1 referrer

Table Figure 3 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table Figure 3 - Footnote 2 referrer

Table Figure 3 - Footnote 3

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to first Table Figure 3 - Footnote 3 referrer

Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Cumulative data includes updates to previous weeks.

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2018-35 to 2019-07
Age groups (years) Cumulative (August 26, 2018 to February 16, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 5269 1552 36 3681 54 5323 22%
5-19 3575 1284 38 2253 63 3638 15%
20-44 4859 1655 110 3094 49 4908 20%
45-64 4808 1541 118 3149 48 4856 20%
65+ 5327 1062 487 3778 135 5462 23%
Total 23838 7094 789 15955 349 24187 100%
Table 1 - Note 1

UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to Table 1 - Note 1

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 07, 1.1% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is low compared to previous seasons.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-07

Number of Sentinels Reporting in Week 07: 81

Figure 4. Text equivalent follows.

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18

Figure 4 - Text equivalent
Surveillance Week 2018-19 Average Min Max
35 0.6% 0.6% 0.4% 0.9%
36 0.7% 0.8% 0.5% 1.0%
37 0.6% 0.9% 0.7% 1.1%
38 0.5% 1.0% 0.7% 1.4%
39 1.8% 1.1% 0.8% 1.5%
40 0.6% 1.6% 0.9% 3.4%
41 1.1% 1.6% 1.1% 2.1%
42 1.0% 1.4% 0.8% 1.8%
43 0.9% 1.4% 0.7% 1.8%
44 0.8% 1.4% 1.1% 1.6%
45 1.3% 1.5% 1.2% 1.8%
46 1.3% 1.7% 1.1% 2.2%
47 1.3% 1.6% 1.1% 2.2%
48 1.5% 1.8% 1.0% 2.8%
49 1.6% 1.5% 1.1% 1.8%
50 1.5% 2.1% 1.4% 2.7%
51 1.0% 2.3% 1.6% 3.2%
52 3.2% 3.6% 1.9% 5.0%
1 2.8% 3.8% 1.8% 5.6%
2 1.8% 2.6% 1.3% 3.9%
3 1.1% 2.5% 1.4% 3.6%
4 1.3% 2.5% 1.6% 3.1%
5 1.4% 2.6% 1.9% 4.0%
6 1.0% 2.7% 2.1% 3.5%
7 1.1% 2.7% 1.9% 3.4%

Participatory Syndromic Surveillance

In week 07, 2,131 participants reported to FluWatchers, of which 57 (2.7%) reported symptoms of cough and fever (Figure 5).

Among the 57 participants who reported fever and cough:

  • 19% consulted a healthcare professional;
  • 68% reported days missed from work or school, resulting in a combined total of 102 missed days of work or school.
  • 69% reported having been vaccinated for influenza this season.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-07

Number of Participants Reporting in Week 07: 2,131

Figure 5. Text equivalent follows.
Figure 5 - Text equivalent
Surveillance week % cough and fever
40 2.6%
41 2.5%
42 1.7%
43 1.5%
44 1.3%
45 1.7%
46 2.0%
47 1.3%
48 2.4%
49 2.0%
50 3.7%
51 3.9%
52 3.6%
1 3.4%
2 2.8%
3 2.5%
4 2.9%
5 3.0%
6 2.6%
7 2.7%

Influenza Outbreak Surveillance

In week 07, 21 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (13), acute care facilities (4), and other settings (4). Four new ILI outbreaks in schools/daycares were also reported in week 07. The number of new outbreaks reported each week continues to decline from the peak in week 01.

To date this season, 398 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 244 (61%) outbreaks were in LTCF, 23 were in schools, 52 in acute care facilities, and 79 were in other settings.
  • Among the 369 outbreaks for which the influenza type was available 98% (363) were associated with influenza A.
  • Among the 163 outbreaks for which the influenza A subtype was available, 67% (110) were associated with influenza A(H1N1)pdm09;

To date this season, 94 ILI outbreaks have been reported; 44 occurred in LTCF, 47 in schools, and three in acute care facilities.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-07

Figure 6. Text equivalent follows.
Figure 6 - Text equivalent
Surveillance Week Acute Care Facilities Long Term Care Facilities Other Schools and Daycares Remote and/or Isolated Communities
35 0 0 0 0 0
36 0 0 0 0 0
37 0 0 0 0 0
38 0 0 0 0 0
39 0 0 0 0 0
40 0 2 0 1 0
41 0 0 0 0 0
42 0 1 1 0 0
43 0 3 1 0 0
44 0 1 1 2 0
45 0 2 1 3 0
46 2 5 1 3 0
47 2 4 0 1 0
48 2 6 1 5 0
49 1 2 3 1 0
50 3 8 5 4 0
51 3 12 4 2 0
52 4 24 5 0 0
1 5 40 11 0 0
2 8 38 7 0 0
3 3 26 10 0 0
4 6 17 10 1 0
5 4 21 8 0 0
6 5 19 6 0 0
7 4 13 4 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,004 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.7% (1,997) were associated with influenza A
  • The highest estimated rate of hospitalization is among children under 5 years of age.

Intensive Care Unit (ICU) cases and deaths:

  • To date this season 368 ICU admissions and 87 deaths have been reported.
    • 43% (157) of reported ICU admissions were in adults aged 45-64 years.
    • All the ICU admissions, and all but one of the deaths were associated with influenza A.
Table 2 - Cumulative number of hospitalizations by age-group and influenza type, reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2019-07
Age Groups (years) Cumulative (August 26, 2018 to February 16, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 307 2 64.92
5-19 177 1 12.83
20-44 274 0 9.63
45-64 558 1 25.69
65+ 681 3 56.22
Total 1997 7  
% 99.7% 0.3%  
Table 2 - Note 1

Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories.

Return to Table 2 - Note 1

Pediatric Influenza Hospitalizations and Deaths

In week 07, 44 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7).

To date this season, 884 pediatric hospitalizations have been reported (Figure 8):

  • 69% of cases were in children under 5 years of age.
  • 99% (874) of cases have been associated with influenza A.
  • Among the 290 cases for which the influenza subtype was available, 276 (95%) were associated with A(H1N1)pdm09.

To date this season, 147 ICU admissions, and 10 deaths have been reported.

  • 63% (93) of ICU admissions were in children under 5 years of age.
  • All but one of the ICU admissions have been associated with influenza A.
  • 80% (8) of deaths occurred in children 2 to 4 years of age.
  • All deaths have been associated with influenza A.

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-07

Figure 7. Text equivalent follows.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Figure 7 - Text equivalent
Surveillance week 2018-19 Average Min Max
35 0 0 0 0
36 0 0 0 1
37 0 0 0 2
38 0 0 0 2
39 0 1 0 3
40 0 0 0 2
41 1 1 0 2
42 5 1 0 4
43 11 1 0 3
44 15 3 1 6
45 37 3 2 4
46 41 5 1 13
47 36 4 0 9
48 46 9 2 23
49 39 15 3 28
50 51 23 4 47
51 85 32 4 72
52 89 47 7 92
1 94 40 5 75
2 59 35 4 62
3 70 38 4 67
4 61 35 7 47
5 51 40 11 59
6 48 38 15 79
7 44 40 17 120

Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-07

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 89
6-23 mo 231
2-4 yr 287
5-9 yr 196
10-16 yr 81

Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.

To date this season, 538 hospitalizations, 59 ICU admissions and 18 deaths have been reported (Figure 9):

  • 493 (92%) hospitalizations were associated with influenza A.
  • A greater proportion of hospitalizations have been reported among adults ≥65 years of age (57.3%) compared to adults <65 years of age (42.8%).
  • Hospitalizations among adults peaked in week 01 then declined to week 04, and have increased in weeks 05 to 07.
  • Among hospitalized cases with available information (481), the most commonly reported comorbidity was endocrine disorders, which were reported in 78% of hospitalized cases. However, 84% of cases reported more than one type of comorbid condition.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-07

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 53
35-49 yr 57
50-64 yr 120
65-79 yr 158
80+ yr 150

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,287 influenza viruses (119 A(H3N2), 1,142 A(H1N1) and 26 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

61 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.

Sequence analysis of the HA gene of the viruses showed that:

  • 10 viruses belonged to genetic group 3C.2a.
  • 50 viruses belonged to subclade 3C.2a1.
  • One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.

Antigenic Characterization:

Influenza A (H3N2):

  • 43 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
  • 15 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
  • A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 27 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. Nine viruses belonged to genetic group 3C.2a and nine to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,112 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 30 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:

Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

  • Eight influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
  • One virus showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
  • 17 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

Antiviral Resistance – Amantadine:

351 influenza A (51 A(H3N2) and 300 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 351 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

793 influenza viruses (71 A(H3N2), 697 A(H1N1) and 25 B) were tested for resistance to oseltamivir and it was found that:

  • All 71 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 697 A(H1N1) viruses tested, 696 were sensitive to oseltamivir and one virus was resistant to oseltamivir with a H275Y mutation.
  • All 25 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

794 influenza viruses (71 A(H3N2), 698 H1N1 and 25 B) were tested for resistance to zanamivir and it was found that:

  • All 794 influenza viruses were sensitive to zanamivir.
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