FluWatch report: November 25, 2018 to December 1, 2018 (Week 48)

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Organization: Public Health Agency of Canada

Date published: 2018-12-07

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Overall Summary

  • Influenza activity continued to increase in week 48.
  • 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 48. In particular, the number of pediatric hospitalizations is significantly higher than in recent years.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 48, influenza activity levels continued to increase (Figure 1):

  • Nine regions reported localized activity: in Alta.(2), Sask.(1), Man.(1), Ont.(2), Que.(1), N.B.(1) and N.S.(1).
  • Sporadic activity was reported by 29 regions in Alta.(3), Sask.(2), Man.(4), Ont.(5), Que.(5), N.B.(3), N.S.(1), N.L.(2), N.W.T(2), Nvt.(1) and Yt.(1).
  • No activity was reported by 10 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-48

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 No Activity
N.S. Zone 1 - Western Localized
N.S. Zone 2 - Northern No Activity
N.S. Zone 3 - Eastern Sporadic
N.S. Zone 4 - Central No Activity
N.B. Region 1 Sporadic
N.B. Region 2 No Activity
N.B. Region 3 Sporadic
N.B. Region 4 No Activity
N.B. Region 5 No Activity
N.B. Region 6 Sporadic
N.B. Region 7 Localized
Que. Nord-est Localized
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Sporadic
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
Que. Montérégie Sporadic
Ont. Central East Sporadic
Ont. Central West Sporadic
Ont. Eastern Localized
Ont. North East Sporadic
Ont. North West Sporadic
Ont. South West Sporadic
Ont. Toronto Localized
Man. Northern Regional Sporadic
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern Sporadic
Man. Winnipeg Localized
Man. Southern Health Sporadic
Sask. North Localized
Sask. Central Sporadic
Sask. South Sporadic
Alta. North Zone Sporadic
Alta. Edmonton Localized
Alta. Central Zone Sporadic
Alta. Calgary Localized
Alta. South Zone Sporadic
B.C. Interior No Data
B.C. Fraser No Data
B.C. Vancouver Coastal No Data
B.C. Vancouver Island No Data
B.C. Northern No Data
Y.T. Yukon Sporadic
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 48, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza continued to increase to 18.1% 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 48, 1,301 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 4,485 laboratory-confirmed influenza detections have been reported (Figure 3):

  • 99% have been influenza A.
  • Among the 2,384 influenza A viruses subtyped, 93% have been A(H1N1)pdm09.

To date this season, detailed information on age and type/subtype has been received for 4,409 laboratory-confirmed influenza cases (Table 1):

  • 70% 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 2018-48

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
47 463 17 506 8
48 691 28 572 10

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-48

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (November 25, 2018 to December 1, 2018) Cumulative (August 26, 2018 to December 1, 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 94 49 2 43 0 260 127 43 90 3 263
AB 549 334 3 212 2 2548 1568 42 938 18 2566
SK 109 73 2 34 0 557 309 8 240 0 557
MB 74 15 0 59 0 180 91 3 86 0 180
ON 71 28 20 23 1 221 92 61 68 27 248
QC 246 0 0 246 7 578 0 0 578 18 596
NB 13 0 0 13 0 25 3 0 22 0 25
NS 3 0 0 3 0 10 0 0 10 0 10
PEI 0 0 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 17 17 0 0 0 27 27 0 0 0 27
NU 1 1 0 0 0 5 5 0 0 0 5
Canada 1177 517 27 633 10 4418 2227 157 2034 67 4485
PercentageTable Figure 3 - Footnote 2 99% 44% 2% 54% 1% 99% 50% 4% 46% 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 2018-48
Age groups (years) Cumulative (August 26, 2018 to December 1, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 908 517 3 388 6 914 21%
5-19 925 467 5 453 13 938 21%
20-44 1100 551 17 532 12 1112 25%
45-64 816 392 38 386 9 825 19%
65+ 604 259 149 196 16 620 14%
Total 4353 2186 212 1955 56 4409 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 48, 2.3% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is slightly above expected levels.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-48

Number of Sentinels Reporting in Week 48: 86

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 0.8% 1.6% 0.9% 3.4%
41 1.7% 1.6% 1.1% 2.1%
42 1.5% 1.4% 0.8% 1.8%
43 1.4% 1.4% 0.7% 1.8%
44 1.1% 1.4% 1.1% 1.6%
45 2.1% 1.5% 1.2% 1.8%
46 1.9% 1.7% 1.1% 2.2%
47 2.4% 1.6% 1.1% 2.2%
48 2.3% 1.8% 1.0% 2.8%

Participatory Syndromic Surveillance

In week 48, 2,226 participants reported to FluWatchers, of which 53 (2.3%) reported symptoms of cough and fever (Figure 5).

Among the 53 participants who reported fever and cough:

  • 21% consulted a healthcare professional;
  • 64% reported days missed from work or school, resulting in a combined total of 89 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-48

Number of Participants Reporting in Week 48: 2,226

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%

Influenza Outbreak Surveillance

In week 48, seven new laboratory-confirmed influenza outbreaks were reported in long-term care (4), acute care facilities (2) and other settings (1).

To date this season, 44 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 23 outbreaks were in LTCF, nine were in schools, six in acute care facilities, and six were in other settings.
  • All of the 36 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 27 outbreaks for which the influenza A subtype was available:
    • 21 were associated with influenza A(H1N1)pdm09;
    • 6 were associated with A(H3N2),

Three new ILI outbreaks were reported in week 48.

To date this season, 31 ILI outbreaks have been reported; 25 occurred in LTCF, three 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 2018-48

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 3 0
47 2 3 0 0 0
48 2 4 1 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, more than 588 influenza-assocaited hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99% (588) 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 65 ICU admissions and 9 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 2018-48
Age Groups Cumulative (August 26, 2018 to December 1, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 108 0 22.69
5-19 75 0 5.41
20-44 91 0 3.20
45-64 149 0 6.85
65+ 165 <5 13.81
Total 588 <5
% 99% 1%

Pediatric Influenza Hospitalizations and Deaths

In week 48, 44 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 (approximately 4 weeks earlier than in recent seasons) (Figure 7).

To date this season, 189 pediatric hospitalizations have been reported (Figure 8):

  • All but three cases have been associated with influenza A.
  • Among the 132 cases for which the influenza subtype was available, 130 (98.5%) were associated with A(H1N1)pdm09.

To date this season, 28 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 2018-48

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 44 9 2 23

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 2018-48

Figure 7
Figure 8 - Text description
Age Group Total
0-5 mo 17
6-23 mo 51
2-4 yr 53
5-9 yr 54
10-16 yr 14

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, 23 hospitalizations have been reported:

  • 20 (87%) were associated with influenza A and 3 with influenza B.
  • 11 of the 23 cases (48%) were adults 65 years of age and older.

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 142 influenza viruses (20 A(H3N2), 112 A(H1N1) and 10 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A (H3N2):

19 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:

  • Two viruses belonged to genetic group 3C.2a.
  • 17 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):

  • 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.

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:

130 influenza A (20 A(H3N2) and 110 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 130 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

138 influenza viruses (18 A(H3N2), 110 A(H1N1) and 10 B) were tested for resistance to oseltamivir and it was found that:

  • All 138 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

138 influenza viruses (18 A(H3N2), 110 H1N1 and 10 B) were tested for resistance to zanamivir and it was found that:

  • All 138 influenza viruses were sensitive to zanamivir.
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