FluWatch report: December 16, 2018 to December 29, 2018 (Week 51-52)

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Organization: Public Health Agency of Canada

Date published: 2019-01-04

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Overall Summary

  • Overall, influenza activity in Canada continued to increase in weeks 51 and 52.
  • All indicators have increased or remained similar compared to the previous week.
  • Influenza A is the most common influenza virus circulating in Canada, and the majority of these viruses are A(H1N1)pdm09.
  • The majority of lab confirmations and hospitalizations have been among individuals under the age of 65.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 52, influenza activity levels continued to increase (Figure 1):

  • 7 regions reported localized activity: in Alta.(1), Ont.(4), B.C.(1), and N.B.(1)
  • Sporadic activity was reported by 31 regions:  in B.C.(4), Alta.(4), Sask.(3), Man.(5), Ont.(2), N.B.(6),  N.S.(3), N.L.(2), P.E.I.(1), and Yt.(1).
  • No activity was reported by 3 regions.
  • No data was reported by 12 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-52

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

Laboratory Confirmed Influenza Detections

In weeks 51 and 52, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza continued to increase from 25.1% in week 51 to  29.4% in week 52.
  • A total 3,387 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 13,796 laboratory-confirmed influenza detections have been reported (Figure 3):

  • 99% have been influenza A.
  • Among the 6,007 influenza A viruses subtyped, 94% have been A(H1N1)pdm09.
  • Provincial and territorial differences in influenza type/subtype distribution are observed.

To date this season, detailed information on age and type/subtype has been received for 11,531 laboratory-confirmed influenza cases (Table 1):

  • 68% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 45 years of age.
  • 63% 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 2018-52

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 period of seasonal influenza activity.

Figure 2 - Text description
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 1833 34 681 21
52 1554 40 733 13

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-52

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 16, 2018 to December 29, 2018) Cumulative (August 26, 2018 to December 29, 2018)
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 785 486 5 294 1 1472 816 67 589 9 1481
AB 737 576 15 146 6 4519 2954 68 1497 26 4545
SK 27 0 2 25 0 1723 1060 51 612 0 1723
MB 239 43 0 196 0 622 176 3 443 2 624
ON 572 241 52 279 7 1023 459 141 423 40 1063
QC 1,919 0 0 1,919 20 3475 0 0 3475 51 3526
NB 391 25 1 365 0 547 42 1 504 2 549
NS 14 0 0 14 0 32 0 0 32 0 32
PEI 14 14 0 0 0 21 21 0 0 0 21
NL 49 0 0 49 0 80 1 0 79 1 81
YT 5 3 0 2 0 9 5 0 4 0 9
N.W.T 23 22 1 0 0 135 133 2 0 0 135
NU 1 1 0 0 0 7 7 0 0 0 7
Canada 4776 1411 76 3289 34 13665 5674 333 7658 131 13796
PercentageTable Figure 3 - Footnote 2 99% 30% 2% 69% 1% 99% 42% 2% 56% 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 UnS

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 2018-52
Age groups (years) Cumulative (August 26, 2018 to December 29, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 2512 1058 12 1442 18 2530 22%
5-19 2149 968 9 1172 23 2172 19%
20-44 2634 1118 46 1470 16 2650 23%
45-64 2302 935 60 1307 18 2320 20%
65+ 1830 568 214 1048 29 1859 16%
Total 11427 4647 341 6439 104 11531 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 50, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). In weeks 51 and 52, an insufficient number of sentinels reported ILI activity. Data will be updated in the report for week 01.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-50

Number of Sentinels Reporting in Week 50: 115

Figure 4

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 description
Report 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 1.6% 1.8% 1.0% 2.8%
49 1.8% 1.5% 1.1% 1.8%
50 1.6% 2.1% 1.4% 2.7%
51 N/A 2.3% 1.6% 3.2%
52 N/A 3.6% 1.9% 5.0%

Participatory Syndromic Surveillance

In week 52, 1,947 participants reported to FluWatchers, of which 70 (4%) reported symptoms of cough and fever (Figure 5).

Among the 70 participants who reported fever and cough:

  • 27% consulted a healthcare professional;
  • 63% reported days missed from work or school, resulting in a combined total of 150 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-52

Number of Participants Reporting in Week 52: 1,947

Figure 5
Figure 5 - Text description
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%

Influenza Outbreak Surveillance

In weeks 51 and 52, 15 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (4), acute care facilities (6), schools (1), and other settings (4).

To date this season, 86 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 37 outbreaks were in LTCF, 17 were in schools, 14 in acute care facilities, and 18 were in other settings.
  • All of the 73 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 50 outbreaks for which the influenza A subtype was available:
    • 82% (41) were associated with influenza A(H1N1)pdm09;
    • 18% (9) were associated with A(H3N2),

To date this season, 38 ILI outbreaks have been reported; 28 occurred in LTCF, seven 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 2018-52

Figure 6
Figure 6 - Text description
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 1 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 2 1 0 0
44 0 1 1 2 0
45 0 2 1 3 0
46 2 5 1 3 0
47 2 3 0 0 0
48 2 6 1 4 0
49 1 3 3 1 0
50 3 5 5 2 0
51 2 2 1 1 0
52 2 4 3 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1046 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.6% (1042) 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 119 ICU admissions and 24 deaths have been reported.
    • 44% (52) of reported ICU admissions were in adults aged 45-64 years.
    • All reported deaths were associated with influenza A.
Table 2 – Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2018-52
Age Groups Cumulative (August 26, 2018 to December 29, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 179 1 37.82
5-19 124 0 8.94
20-44 164 0 5.76
45-64 272 0 12.50
65+ 303 3 25.15
Total 1042 4  
% 99.6 0.4  

Pediatric Influenza Hospitalizations and Deaths

In weeks 51 and 52, 133 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, 414 pediatric hospitalizations have been reported (Figure 8):

  • 99% (408) of cases have been associated with influenza A.
  • Among the 203 cases for which the influenza subtype was available, 199 (98%) were associated with A(H1N1)pdm09.

To date this season, 71 ICU admissions, and less than five deaths have been reported.

  • 85% (60) of ICU admissions were in children under the age of 10
  • 99% (69) of ICU admissions 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 2018-52

Figure 7
Figure 7 - Text description
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 6 1 0 4
43 11 1 0 3
44 19 3 1 6
45 32 3 2 4
46 42 5 1 13
47 34 4 0 9
48 46 9 2 23
49 39 15 3 28
50 49 23 4 47
51 68 32 4 72
52 66 47 7 92

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 2018-52

Figure 8
Figure 8 - Text description
Age Group Total
0-5 mo 37
6-23 mo 105
2-4 yr 139
5-9 yr 98
10-16 yr 35

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, 115 hospitalizations have been reported (Figure 9):

  • 108 (94%) were associated with influenza A.
  • 58 cases (50%) were adults 65 years of age and older.
  • The most commonly reported comorbidity among hospitalized cases was endocrine disorders, which were reported in 84% of hospitalized cases.

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 2018-52

Figure 9
Figure 9 - Text description
Age Group Total
20-34 yr 16
35-49 yr 17
50-64 yr 24
65-79 yr 35
80+ yr 23

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 395 influenza viruses (30 A(H3N2), 350 A(H1N1) and 15 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A (H3N2):

24 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:

  • Three viruses belonged to genetic group 3C.2a.
  • 21 viruses belonged to subclade 3C.2a1.

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):

  • Six influenza A(H3N2) virus was 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.
  • A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • Four influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Sequencing is pending for the remaining three viruses.

Influenza A(H1N1):

  • 345 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.
  • Five 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).

  • One influenza B virus was characterized as B/Colorado/06/2017, which belongs to the Victoria lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine
  • 14 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:

274 influenza A (35 A(H3N2) and 239 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 274 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

263 influenza viruses (28 A(H3N2), 221 A(H1N1) and 14 B) were tested for resistance to oseltamivir and it was found that:

  • All 263 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

263 influenza viruses (28 A(H3N2), 221 H1N1 and 14 B) were tested for resistance to zanamivir and it was found that:

  • All 263 influenza viruses were sensitive to zanamivir.

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