FluWatch report: December 9, 2018 to December 15, 2018 (Week 50)

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Organization: Public Health Agency of Canada

Date published: 2018-12-21

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Overall Summary

  • Overall, influenza activity in Canada continued to increase in week 50.
  • 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.
  • This is the last FluWatch report for the 2018 calendar year. The next report will be published on Friday, January 4, 2019 and will contain data for weeks 51 and 52.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 50, influenza activity levels continued to increase (Figure 1):

  • 13 regions reported localized activity: in Alta.(2), Sask.(2), Ont.(3), Que.(2), N.B.(2), N.S.(1), and  N.W.T(1)
  • Sporadic activity was reported by 34 regions:  in B.C.(5), Alta.(4), Sask.(1), Man.(5), Ont.(4), Que.(4), N.B.(5),  N.L.(2), P.E.I.(1), N.W.T(1), Nvt.(1) and Yt.(1).
  • No activity was reported by 6 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-50

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

Laboratory Confirmed Influenza Detections

In week 50, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza continued to increase to 22.8%.
  • 1,869 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 8,245 laboratory-confirmed influenza detections have been reported (Figure 3):

  • 99% have been influenza A.
  • Among the 4,024 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 7,914 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.
  • 66% 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 2018-50

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 1270 33 735 12

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-50

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 9, 2018 to December 15, 2018) Cumulative (August 26, 2018 to December 15, 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 197 84 4 109 3 564 302 62 200 8 572
AB 518 333 6 179 0 3722 2333 52 1337 20 3742
SK 162 103 4 55 0 1165 691 20 454 0 1165
MB 129 16 0 113 0 383 129 3 251 2 385
ON 131 52 17 62 4 446 208 89 149 32 478
QC 580 0 0 580 4 1546 0 0 1546 30 1576
NB 88 7 0 81 1 156 17 0 139 2 158
NS 5 0 0 5 0 18 0 0 18 0 18
PEI 1 1 0 0 0 7 7 0 0 0 7
NL 17 0 0 17 0 31 1 0 30 1 32
YT 3 2 0 1 0 4 2 0 2 0 4
N.W.T 26 26 0 0 0 102 102 0 0 0 102
NU 0 0 0 0 0 6 6 0 0 0 6
Canada 1857 624 31 1202 12 8150 3798 226 4126 95 8245
PercentageTable Figure 3 - Footnote 2 99% 34% 2% 65% 1% 99% 47% 3% 51% 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 2018-50
Age groups (years) Cumulative (August 26, 2018 to December 15, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 1695 865 5 825 10 1705 22%
5-19 1629 818 6 805 19 1648 21%
20-44 1903 898 34 971 13 1916 24%
45-64 1543 726 49 768 11 1554 20%
65+ 1071 414 181 476 20 1091 14%
Total 7841 3721 275 3845 73 7914 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, 1.5% 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 2018-50

Number of Sentinels Reporting in Week 50: 103

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 1.5% 2.1% 1.4% 2.7%

Participatory Syndromic Surveillance

In week 50, 2,210 participants reported to FluWatchers, of which 82 (3.7%) reported symptoms of cough and fever (Figure 5).

Among the 82 participants who reported fever and cough:

  • 15% consulted a healthcare professional;
  • 74% reported days missed from work or school, resulting in a combined total of 180 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-50

Number of Participants Reporting in Week 50: 2,210

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%

Influenza Outbreak Surveillance

In week 50, 13 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (4), acute care facilities (3), schools (1), and other settings (5). One new ILI outbreak was also reported in week 50.

To date this season, 67 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 30 outbreaks were in LTCF, 13 were in schools, 10 in acute care facilities, and 14 were in other settings.
  • All of the 55 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 41 outbreaks for which the influenza A subtype was available:
    • 80% (33) were associated with influenza A(H1N1)pdm09;
    • 20% (8) were associated with A(H3N2),

To date this season, 36 ILI outbreaks have been reported; 26 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 2018-50

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 3 0
49 1 3 3 0 0
50 3 4 5 1 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 864 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99% (861) 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 118 ICU admissions and 22 deaths have been reported.
    • 41% (48) of reported ICU admissions were in adults aged 45-64 years.
    • All reported deaths were associated with influenza A(H1N1)pdm09.
Table 2 – Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2018-50
Age Groups Cumulative (August 26, 2018 to December 15, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 153 0 32.14
5-19 108 0 7.78
20-44 135 0 4.75
45-64 228 0 10.48
65+ 237 3 19.73
Total 861 3  
% 100% 0%  

Pediatric Influenza Hospitalizations and Deaths

In week 50, 45 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, 281 pediatric hospitalizations have been (Figure 8):

  • 99% (278) of cases have been associated with influenza A.
  • Among the 174 cases for which the influenza subtype was available, 172 (98.9%) were associated with A(H1N1)pdm09.

To date this season, 47 ICU admissions, and less than five deaths have been reported.

  • 90% (41) of ICU admissions were in children under the age of 10
  • 98% (46) 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 2018-50

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 45 23 4 47

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 2018-50

Figure 8
Figure 8 - Text description
Age Group Total
0-5 mo 24
6-23 mo 73
2-4 yr 88
5-9 yr 71
10-16 yr 25

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, 55 hospitalizations have been reported:

  • 49 (89%) were associated with influenza A.
  • 29 cases (53%) were adults 65 years of age and older.
  • The most commonly reported comorbidity among hospitalized cases was endocrine disorders, which were reported in 67.2% 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 2018-50

Figure 9
Figure 9 - Text description
Age Group Total
20-34 yr 6
35-49 yr 9
50-64 yr 11
65-79 yr 19
80+ yr 11

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 264 influenza viruses (29 A(H3N2), 221 A(H1N1) and 14 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):

  • Five 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.
  • Two influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Sequencing is pending for the remaining three viruses.

Influenza A(H1N1):

  • 221 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).

  • 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:

221 influenza A (20 A(H3N2) and 195 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 221 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

262 influenza viruses (28 A(H3N2), 220 A(H1N1) and 14 B) were tested for resistance to oseltamivir and it was found that:

  • All 262 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

191 influenza viruses (28 A(H3N2), 150 H1N1 and 13 B) were tested for resistance to zanamivir and it was found that:

  • All 191 influenza viruses were sensitive to zanamivir.
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