FluWatch report: December 30, 2018 to January 5, 2019 (Week 1)

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Organization: Public Health Agency of Canada

Date published: 2019-01-11

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Overall Summary

  • In week 01, laboratory detections declined from the previous week suggesting that nationally the influenza season may have reached peak levels in the last week of December.
  • Overall, influenza activity remains high in Canada.
  • 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 01, all regions reported some level of influenza activity (Figure 1):

  • 1 region reported widespread activity: in Que.(1)
  • 15 regions reported localized activity: in Alta.(2), Sask.(1), Ont.(6), Que.(2), N.L.(1) and N.B.(3)
  • 31 regions reported sporadic activity: in B.C.(5), Alta.(3), Sask.(2), Man.(5), Ont.(1), Que.(3), N.B.(4),  N.S.(4), N.L.(3), P.E.I.(1), Nvt.(3), N.W.T.(2) and Yt.(1).

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-01

Figure 1
Figure 1 - Text description
Province Influenza Surveillance Region Activity Level
N.L. Eastern Localized
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 Sporadic
N.S. Zone 2 - Northern Sporadic
N.S. Zone 3 - Eastern Sporadic
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 Localized
Que. Nord-est Localized
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Widespread
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
Que. Montérégie Localized
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 Sporadic
Man. Winnipeg Sporadic
Man. Southern Health Sporadic
Sask. North Sporadic
Sask. Central Sporadic
Sask. South Localized
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Localized
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 Sporadic
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq Sporadic
Nvt. Kitimeot Sporadic

Laboratory Confirmed Influenza Detections

In week 01, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza decreased to 25.6% in week 01.
  • A total 3,153 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 17,743 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 6,775 influenza A viruses subtyped, 94% 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 14,897 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.
  • 61% 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 2019-01

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 1890 54 953 21
52 2239 55 892 26
01 2508 55 849 28

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-01

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 30, 2018 to Januray 5, 2019) Cumulative (August 26, 2018 to January 5, 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 407 192 8 207 1 1840 1010 75 755 10 1850
AB 226 178 5 43 3 4745 3132 73 1540 29 4774
SK 0 0 0 0 0 1723 1060 51 612 0 1723
MB 121 13 0 108 1 681 192 3 486 3 684
ON 445 242 36 167 2 1478 752 180 546 42 1520
QC 1 627 0 0 1 627 17 5974 0 0 5974 81 6055
NB 211 0 0 211 0 758 42 1 715 2 760
NS 20 0 0 20 1 52 0 0 52 1 53
PEI 17 17 0 0 0 38 38 0 0 0 38
NL 34 0 0 34 0 114 1 0 113 1 115
YT 14 11 1 2 0 23 16 1 6 0 23
N.W.T 5 5 0 0 0 140 138 2 0 0 140
NU 1 1 0 0 0 8 8 0 0 0 8
Canada 3128 659 50 2419 25 17574 6389 386 10799 169 17743
PercentageTable Figure 3 - Footnote 2 99% 21% 2% 77% 1% 99% 36% 2% 61% 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 2019-01
Age groups (years) Cumulative (August 26, 2018 to January 5, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 3175 1239 15 1921 24 3199 21%
5-19 2498 1108 15 1375 26 2524 17%
20-44 3277 1294 55 1928 20 3297 22%
45-64 3020 1077 70 1873 22 3042 20%
65+ 2792 673 246 1873 43 2835 19%
Total 14762 5391 401 8970 135 14897 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 1, 3.9% 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 2019-01

Number of Sentinels Reporting in Week 01: 77

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 1.2% 2.3% 1.6% 3.2%
52 3.7% 3.6% 1.9% 5.0%
01 3.9% 3.8% 1.8% 5.6%

Participatory Syndromic Surveillance

In week 01, 2,240 participants reported to FluWatchers, of which 77 (3.4%) reported symptoms of cough and fever (Figure 5).

Among the 77 participants who reported fever and cough:

  • 13% consulted a healthcare professional;
  • 77% reported days missed from work or school, resulting in a combined total of 159 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-01

Number of Participants Reporting in Week 01: 2,240

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%
01 3.4%

Influenza Outbreak Surveillance

In week 01, 37 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (24), acute care facilities (4), and other settings (9). One new ILI outbreak in a LTCF was also reported reported in week 01.

To date this season, 152 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 79 outbreaks were in LTCF, 22 were in schools, 21 in acute care facilities, and 30 were in other settings.
  • All of the 119 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 76 outbreaks for which the influenza A subtype was available:
    • 86% (65) were associated with influenza A(H1N1)pdm09;
    • 14% (11) were associated with A(H3N2),

To date this season, 39 ILI outbreaks have been reported; 29 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 2019-01

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 3 10 4 2 0
52 4 12 3 0 0
01 4 24 9 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1348 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.6% (1342) 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 196 ICU admissions and 37 deaths have been reported.
    • 41% (80) 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 2019-01
Age Groups Cumulative (August 26, 2018 to January 5, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 225 2 47.69
5-19 139 0 10.02
20-44 194 0 6.82
45-64 360 0 16.54
65+ 424 4 35.18
Total 1342 6 -
% 94.6% 0.4% -

Pediatric Influenza Hospitalizations and Deaths

In week 01, 87 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, 540 pediatric hospitalizations have been reported (Figure 8):

  • 99% (535) of cases have been associated with influenza A.
  • Among the 228 cases for which the influenza subtype was available, 222 (97%) were associated with A(H1N1)pdm09.

To date this season, 95 ICU admissions, and six deaths have been reported.

  • 88% (83) of ICU admissions were in children under the age of 10
  • 99% (93) of ICU admissions have been associated with influenza A.
  • All deaths occurred in children under the age of 10

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-01

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 79 32 4 72
52 89 47 7 92
01 87 40 5 75

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 2019-01

Figure 8
Figure 8 - Text description
Age Group Total
0-5 mo 53
6-23 mo 147
2-4 yr 177
5-9 yr 121
10-16 yr 42

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, 223 hospitalizations have been reported (Figure 9):

  • 212 (95%) were associated with influenza A.
  • The distribution of cases among adults <65 years of age is similar to adults ≥65 years of age
  • The most commonly reported comorbidity among hospitalized cases was endocrine disorders, which were reported in 70% 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 2019-01

Figure 9
Figure 9 - Text description
Age Group Total
20-34 yr 26
35-49 yr 31
50-64 yr 54
65-79 yr 59
80+ yr 55

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 481 influenza viruses (45 A(H3N2), 420 A(H1N1) and 16 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

33 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:

  • Five viruses belonged to genetic group 3C.2a.
  • 27 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):

  • 12 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):

  • 415 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).

  • Two 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:

278 influenza A (37 A(H3N2) and 241 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 278 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

403 influenza viruses (40 A(H3N2), 348 A(H1N1) and 15 B) were tested for resistance to oseltamivir and it was found that:

  • All 403 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

403 influenza viruses (40 A(H3N2), 348 H1N1 and 15 B) were tested for resistance to zanamivir and it was found that:

  • All 403 influenza viruses were sensitive to zanamivir.
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