FluWatch report: January 20, 2019 to January 26, 2019 (week 04)

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Organization: Public Health Agency of Canada

Date published: 2019-02-01

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Overall Summary

  • Influenza continues to circulate across Canada with eastern regions reporting higher levels of influenza activity compared to western regions.
  • At the national level, the influenza season appears to be past the peak of activity, with most indicators showing stable or downward trends in week 04.
  • Influenza A is the most common influenza virus circulating in Canada, and the majority of these viruses are A(H1N1)pdm09.
  • Based on a recently published Canadian influenza vaccine effectiveness study, mid-season vaccine effectiveness estimates indicate that this year’s flu shot is approximately 72% effective against the predominant circulating strain. Significant protection was observed in all age groups, especially young children who have been disproportionately affected by influenza this season.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 04, the following influenza activity levels were reported (Figure 1):

  • 2 regions reported widespread activity: in Que.(1) and P.E.I.(1).
  • 19 regions reported localized activity: in Alta.(1), Ont.(6), Que.(3), N.L.(1) N.S.(4) and N.B.(4).
  • 31 regions reported sporadic activity: in B.C.(5), Alta.(4), Sask.(3), Man.(5), Que.(3), N.B.(3), N.L.(3), Nvt.(3), N.W.T.(1) and Y.T.(1).
  • One region reported no activity: in N.W.T.(1).

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-04

Figure 1
Figure 1 - Text description
Province Influenza Surveillance Region Activity Level
N.L. Eastern Sporadic
N.L. Labrador-Grenfell Localized
N.L. Central Sporadic
N.L. Western Sporadic
P.E.I. Prince Edward Island Widespread
N.S. Zone 1 - Western Localized
N.S. Zone 2 - Northern Localized
N.S. Zone 3 - Eastern Localized
N.S. Zone 4 - Central Localized
N.B. Region 1 Localized
N.B. Region 2 Localized
N.B. Region 3 Sporadic
N.B. Region 4 Sporadic
N.B. Region 5 Sporadic
N.B. Region 6 Localized
N.B. Region 7 Localized
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Localized
Que. Centre-du-Québec Localized
Que. Montréal et Laval Localized
Que. Ouest-du-Québec Widespread
Que. Montérégie Sporadic
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 Sporadic
Alta. North Zone Localized
Alta. Edmonton Sporadic
Alta. Central Zone Sporadic
Alta. Calgary Sporadic
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 No Activity
N.W.T. South Sporadic
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq Sporadic
Nvt. Kitimeot Sporadic

Laboratory Confirmed Influenza Detections

In week 04, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza was similar to the previous week at 20.7%.
  • A total 2,270 laboratory detections of influenza were reported, of which 98% were influenza A.

To date this season, 25,764 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 9,479 influenza A viruses subtyped, 93% 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 20,254 laboratory-confirmed influenza cases (Table 1):

  • 86% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
  • 62% 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 2019-04

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 2292 55 903 26
1 2387 58 893 31
2 1985 93 1061 43
3 1613 101 585 40
4 1597 109 516 48

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-04

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 20 to January 26, 2019) Cumulative (August 26, 2018 to January 26, 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 327 218 22 87 2 2987 2096 139 752 16 3003
AB 74 44 10 20 4 5102 3362 105 1635 38 5140
SK 16 9 1 6 0 2113 1325 56 732 1 2114
MB 30 10 20 0 0 919 236 24 659 4 923
ON 437 151 52 234 6 2791 1328 358 1105 61 2852
QC 1,011 0 0 1,011 32 9459 0 0 9459 172 9631
NB 181 20 4 157 0 1420 113 10 1297 2 1422
NS 27 0 0 27 1 129 0 0 129 3 132
PEI 41 41 0 0 0 131 131 0 0 0 131
NL 26 0 0 26 0 213 1 0 212 1 214
YT 11 10 0 1 0 45 37 1 7 0 45
N.W.T 1 1 0 0 0 148 146 2 0 0 148
NU 0 0 0 0 0 9 9 0 0 0 9
Canada 2182 504 109 1569 45 25466 8784 695 15987 298 25764
Table Figure 3 - Footnote 2 98% 23% 5% 72% 2% 99% 34% 3% 63% 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 3

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 2019-04
Age groups (years) Cumulative (August 26, 2018 to January 26, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 4446 1444 23 2979 34 4480 22%
5-19 3035 1220 21 1794 40 3075 15%
20-44 4204 1512 77 2615 28 4232 21%
45-64 4110 1364 89 2657 39 4149 20%
65+ 4213 911 338 2964 105 4318 21%
Total 20008 6451 548 13009 246 20254 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 04, 1.8% 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 2018-19-04

Number of Sentinels Reporting in Week 04: 93

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 1.5% 1.8% 1.0% 2.8%
49 1.6% 1.5% 1.1% 1.8%
50 1.5% 2.1% 1.4% 2.7%
51 1.0% 2.3% 1.6% 3.2%
52 3.2% 3.6% 1.9% 5.0%
01 2.8% 3.8% 1.8% 5.6%
02 1.8% 2.6% 1.3% 3.9%
03 1.3% 2.5% 1.4% 3.6%
04 1.8% 2.5% 1.6% 3.1%

Participatory Syndromic Surveillance

In week 04, 2,207 participants reported to FluWatchers, of which 64 (2.9%) reported symptoms of cough and fever (Figure 5).

Among the 64 participants who reported fever and cough:

  • 25% consulted a healthcare professional;
  • 75% reported days missed from work or school, resulting in a combined total of 147 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-04

Number of Participants Reporting in Week 04: 2,207

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%
02 2.8%
03 2.5%
04 2.9%

Influenza Outbreak Surveillance

In week 04, 27 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (12), acute care facilities (6), schools/daycares (1) and other settings (8). Fourteen new ILI outbreaks in long-term care facilities (3) and  schools/daycares (11) were also reported in week 04.

To date this season, 296 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 175 outbreaks were in LTCF, 23 were in schools, 39 in acute care facilities, and 59 were in other settings.
  • Among the 278 outbreaks for which the influenza type was available 99% (274) were associated with influenza A.
  • Among the 131 outbreaks for which the influenza A subtype was available:
    • 76% (99) were associated with influenza A(H1N1)pdm09;
    • 24% (32) were associated with A(H3N2),

To date this season, 72 ILI outbreaks have been reported; 41 occurred in LTCF, 28 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 2019-04

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 0 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 3 1 0 0
44 0 1 1 2 0
45 0 2 1 3 0
46 2 5 1 3 0
47 2 4 0 1 0
48 2 6 1 5 0
49 1 2 3 1 0
50 3 8 5 4 0
51 3 10 4 2 0
52 4 25 5 0 0
01 5 38 11 0 0
02 8 33 7 0 0
03 3 23 10 0 0
04 6 12 8 1 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1,761 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.7% (1,755) 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 319 ICU admissions and 75 deaths have been reported.
    • 43% (137) of reported ICU admissions were in adults aged 45-64 years.
    • All but one of the reported deaths were associated with influenza A.
    Table 2 - Cumulative number of hospitalizations by age-group and influenza type, reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2019-04
    Age Groups (years) Cumulative (August 26, 2018 to January 26, 2019)
    Influenza A Influenza B Rate per 100,000 population
    Table 2 - Note 1

    Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories.

    Return to Table 2 - Note 1

    0-4  290 2 61.35
    5-19 161 0 11.60
    20-44  243 0 8.54
    45-64  483 1 22.24
    65+  578 3 47.75
    Total 1755 6  
    % 99.7% 0.3%  

    Pediatric Influenza Hospitalizations and Deaths

    In week 04, 65 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, 747 pediatric hospitalizations have been reported (Figure 8):

    • 70% of cases were in children under 5 years of age.
    • 99% (740) of cases have been associated with influenza A.
    • Among the 266 cases for which the influenza subtype was available, 259 (97%) were associated with A(H1N1)pdm09.

    To date this season, 126 ICU admissions, and 10 deaths have been reported.

    • 63% (80) of ICU admissions were in children under 5 years of age.
    • 99% (125) of ICU admissions have been associated with influenza A.
    • 80% (8) of deaths occurred in children 2 to 4 years of age.
    • All deaths 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 2019-04

    Figure 7

    The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

    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 20 3 1 6
    45 34 3 2 4
    46 42 5 1 13
    47 33 4 0 9
    48 47 9 2 23
    49 37 15 3 28
    50 51 23 4 47
    51 82 32 4 72
    52 90 47 7 92
    01 93 40 5 75
    02 59 35 4 62
    03 72 38 4 67
    04 65 35 7 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 2019-04

    Figure 8
    Figure 8 - Text description
    Age Group Total
    0-5 mo 78
    6-23 mo 203
    2-4 yr 238
    5-9 yr 166
    10-16 yr 62

    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, 373 hospitalizations have been reported (Figure 9):

    • 336 (90%) were associated with influenza A.
    • A similar proportion of hospitalizations are reported among adults <65 years of age (45.5%) and adults ≥65 years of age (55.5%).
    • 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 2019-04

    Figure 9
    Figure 9 - Text description
    Age Group Total
    20-34 yr 40
    35-49 yr 43
    50-64 yr 83
    65-79 yr 104
    80+ yr 103

    Influenza Strain Characterizations

    Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 785 influenza viruses (66 A(H3N2), 701 A(H1N1) and 18 B) that were received from Canadian laboratories. 

    Genetic Characterization of Influenza A(H3N2):

    42 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:

    • Seven viruses belonged to genetic group 3C.2a.
    • 34 viruses belonged to subclade 3C.2a1.
    • One isolate could not be sequenced.

    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):

    • 20 influenza A(H3N2) viruses were 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.
    • Four viruses showed reduced titer with ferret antisera 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.
    • 16 influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Two viruses belonged to genetic group 3C.2a and five to 3C.3a. Sequencing is pending for the remaining isolate.

    Influenza A(H1N1):

    • 686 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.
    • 15 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).

    • Three influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine
    • 15 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:

    311 influenza A (44 A(H3N2) and 267 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

    • All 311 influenza A viruses were resistant to amantadine.

    Antiviral Resistance – Oseltamivir:

    601 influenza viruses (52 A(H3N2), 533 A(H1N1) and 16 B) were tested for resistance to oseltamivir and it was found that:

    • All 601 influenza viruses were sensitive to oseltamivir

    Antiviral Resistance – Zanamivir:

    601 influenza viruses (52 A(H3N2), 533 H1N1 and 16 B) were tested for resistance to zanamivir and it was found that:

    • All 601 influenza viruses were sensitive to zanamivir.
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