FluWatch report: November 18, 2018 to November 24, 2018 (Week 47)

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Organization: Public Health Agency of Canada

Date published: 2018-11-30

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Overall Summary

  • Influenza activity continued to increase in week 47.
  • Influenza A is the most common influenza virus circulating in Canada, and the majority of these viruses are A(H1N1)pdm09.
  • The number of influenza-associated hospitalizations continued to increase in week 47. In particular, the number of pediatric hospitalizations is significantly higher than in recent years.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 47, influenza activity levels increased slightly compared to the previous week (Figure 1):

  • One region reported widespread activity: in Que.(1),
  • Four regions reported localized activity: in Alta.(1), Ont.(2), and N.B.(1),
  • Sporadic activity was reported by 32 regions, in B.C.(5), Alta.(4), Sask.(3), Man.(3), Ont.(3), Que.(5), N.B.(2), N.S.(1), P.E.I.(1), N.L.(2), N.W.T(2) and Nvt.(1).
  • No activity was reported by 16 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-47

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 No Activity
N.S. Zone 2 - Northern No Activity
N.S. Zone 3 - Eastern No Activity
N.S. Zone 4 - Central Sporadic
N.B. Region 1 Sporadic
N.B. Region 2 No Activity
N.B. Region 3 Localized
N.B. Region 4 No Activity
N.B. Region 5 No Activity
N.B. Region 6 No Activity
N.B. Region 7 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Sporadic
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Widespread
Que. Montérégie Sporadic
Ont. Central East Sporadic
Ont. Central West Localized
Ont. Eastern Sporadic
Ont. North East No Activity
Ont. North West No Activity
Ont. South West Sporadic
Ont. Toronto Localized
Man. Northern Regional No Activity
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern No Activity
Man. Winnipeg Sporadic
Man. Southern Health Sporadic
Sask. North Sporadic
Sask. Central Sporadic
Sask. South Sporadic
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 No Activity
N.W.T. North Sporadic
N.W.T. South Sporadic
Nvt. Qikiqtaaluk No Activity
Nvt. Kivalliq No Activity
Nvt. Kitimeot Sporadic

Laboratory Confirmed Influenza Detections

In week 47, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza continued to increase to 15.3% of tests positive.
  • The percentage of tests positive for influenza A is higher for this time of year compared to the same period during the previous eight seasons.
  • In week 47, 950 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 3,176 laboratory-confirmed influenza detections have been reported (Figure 3):

  • 92% have been influenza A.
  • Among the 1,760 influenza A viruses subtyped, 82% have been A(H1N1)pdm09.
  • Provincial and territorial differences in influenza type/subtype distribution are observed (Figure 3).

To date this season, detailed information on age and type/subtype has been received for 3,155 laboratory-confirmed influenza cases (Table 1):

  • 69% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 45 years of age.
  • 70% 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 2018-47

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
46 345 10 404 9
47 445 17 480 8

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-47

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (November 18, 2018 to November 24, 2018) Cumulative (August 26, 2018 to November 24, 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 51 30 5 16 0 162 78 41 43 3 165
AB 539 334 8 197 3 1961 1206 39 716 16 1977
SK 38 0 38 0 58 188 0 188 0 187 375
MB 25 15 0 10 0 100 79 3 18 0 100
ON 28 19 2 7 4 150 64 41 45 26 176
QC 137 0 0 137 1 332 0 0 332 11 343
NB 7 1 0 6 0 12 3 0 9 0 12
NS 1 0 0 1 0 7 0 0 7 0 7
PEI 1 1 0 0 0 4 4 0 0 0 4
NL 0 0 0 0 0 3 1 0 2 1 4
YT 0 0 0 0 0 0 0 0 0 0 0
N.W.T 5 5 0 0 0 9 9 0 0 0 9
NU 1 1 0 0 0 4 4 0 0 0 4
Canada 833 406 53 374 66 2932 1448 312 1172 244 3176
PercentageTable Figure 3 - Footnote 2 93% 49% 6% 45% 7% 92% 49% 11% 40% 8% 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 2018-47
Age groups (years) Cumulative (August 26, 2018 to November 24, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 632 377 3 252 5 637 20%
5-19 650 334 5 311 11 661 21%
20-44 797 399 15 383 9 806 26%
45-64 565 285 32 248 7 572 18
65+ 465 206 131 128 14 479 15%
Total 3109 1601 186 1322 46 3155 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 47, 1.9% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is within expected levels.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-47

Number of Sentinels Reporting in Week 47: 84

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 1.1% 1.4% 0.8% 1.8%
43 1.0% 1.4% 0.7% 1.8%
44 0.8% 1.4% 1.1% 1.6%
45 1.5% 1.5% 1.2% 1.8%
46 1.5% 1.7% 1.1% 2.2%
47 1.9% 1.6% 1.1% 2.2%

Participatory Syndromic Surveillance

In week 47, 2,182 participants reported to FluWatchers, of which 29 (1.3%) reported symptoms of cough and fever (Figure 5).

Among the 29 participants who reported fever and cough:

  • 28% consulted a healthcare professional;
  • 83% reported days missed from work or school, resulting in a combined total of 66 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-47

Number of Participants Reporting in Week 47: 2,182

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%

Influenza Outbreak Surveillance

In week 47, five new laboratory-confirmed influenza outbreaks were reported in long-term care (3) and acute care (2) facilities.

To date this season, 36 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 19 outbreaks were in LTCF, eight were in schools, and five were in other settings.
  • All of the 30 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 21 outbreaks for which the influenza A subtype was available:
    • 17 were associated with influenza A(H1N1)pdm09;
    • Four were associated with A(H3N2);

One new ILI outbreak in a LTCF was reported in week 47.

To date this season, 25 ILI outbreaks have been reported; 23 occurred in LTCF, one in a school, and one in an acute care facility.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2018-47

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 2 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 2 0
47 2 3 0 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, more than 471 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99% (471) were associated with influenza A
  • The highest estimated rates of hospitalization are among children under 5 years of age.

Intensive Care Unit (ICU) cases and deaths:

  • To date this season 49 ICU admissions and nine deaths have been reported.
Table 2 – Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2018-47
Age Groups Cumulative (August 26, 2018 to November 24, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 95 0 7.77
5-19 64 0 2.31
20-44 72 0 1.20
45-64 115 0 2.39
65+ 125 <5 5.18
Total 471 <5
% 99% 1%

Pediatric Influenza Hospitalizations and Deaths

In week 47, 34 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network. Pediatric hospitalizations reported by IMPACT are at levels not normally seen until late December (4-6 weeks earlier than in recent seasons) (Figure 7).

To date this season, 145 pediatric hospitalizations have been reported (Figure 8):

  • All but two cases have been associated with influenza A.
  • Among the 109 cases for which the influenza subtype was available, 108 were associated with A(H1N1)pdm09.

To date this season, 18 ICU admissions, and no deaths have been reported.

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2018-47

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

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 2018-47

Figure 7
Figure 8 - Text description
Age Group Total
0-5 mo 14
6-23 mo 39
2-4 yr 40
5-9 yr 43
10-16 yr 9

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, 17 hospitalizations have been reported, of which 15 were associated with influenza A and 2 with influenza B.

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 101 influenza viruses (11 A(H3N2), 80 A(H1N1) and 10 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A (H3N2):

Ten 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:

  • One virus belonged to genetic group 3C.2a.
  • Nine 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):

  • One 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.
  • The influenza A (H3N2) virus characterized belonged to genetic group 3C.2a1.

Influenza A(H1N1):

  • 80 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.

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).

  • Ten 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:

95 influenza A (18 A(H3N2) and 77 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 95 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

102 influenza viruses (16 A(H3N2), 76 A(H1N1) and 10 B) were tested for resistance to oseltamivir and it was found that:

  • All influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

102 influenza viruses (16 A(H3N2), 76 H1N1 and 10 B) were tested for resistance to zanamivir and it was found that:

  • All influenza viruses were sensitive to zanamivir.
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