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FluWatch report: January 13, 2019 to January 19, 2019 (week 03)

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Organization: Public Health Agency of Canada

Date published: 2019-01-25

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Overall Summary

  • In week 03, laboratory detections continued to decline from the previous week.Overall, influenza continues to circulate across Canada but the Eastern region is reporting higher levels of influenza activity than the rest of the country.
  • 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.
  • 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. The study confirmed that significant protection was observed in all age groups, especially young children who have been disproportionately affected by influenza this season.

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Influenza/Influenza-like Illness Activity (geographic spread)

During week 03, the following influenza activity levels were reported  (Figure 1):

  • 23 regions reported localized activity: in Alta.(1), Ont.(6), Que.(4), N.L.(2) N.S.(4) P.E.I.(1) and N.B.(5).
  • 26 regions reported sporadic activity: in B.C.(5), Alta.(4), Sask.(3), Man.(5), Que.(2), N.B.(2), N.L.(2), Nvt.(2), and N.W.T.(1).
  • Three regions reported no activity: in Ont.(1), N.W.T.(1) and Nvt.(1).
  • No data was reported by one region: in Y.T.(1).

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-03

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

Laboratory Confirmed Influenza Detections

In week 03, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza decreased to 20.8% in week 03.
  • A total 2,313 laboratory detections of influenza were reported, of which 98% were influenza A.

To date this season 20,753 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 7,565 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 18,923 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 2019-03

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 2032 92 1060 43
3 1701 99 533 40

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-03

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1		 Week (January 13 to January 19, 2019) Cumulative (August 26, 2018 to January 19, 2019)
Influenza A B Influenza A B A & B
Total
A
Total		 A
(H1N1)pdm09		 A
(H3N2)		 Table Figure 3 - Footnote Table Figure 3 - Footnote 3 B
Total		 A
Total		 A
(H1N1)pdm09		 A
(H3N2)		 Table Figure 3 - Footnote Table Figure 3 - Footnote 3 B
Total
BC 299 193 13 93 3 1958 1069 77 812 10 1968
AB 94 59 12 23 1 4915 3250 82 1583 33 4948
SK 31 21 1 9 0 2079 1307 55 717 1 2080
MB 59 10 1 48 1 830 211 3 616 3 833
ON 419 165 69 185 7 1893 977 236 680 48 1941
QC 1,051 0 0 1,051 25 7387 0 0 7387 115 7502
NB 214 25 3 186 0 1025 68 3 954 2 1027
NS 17 0 0 17 1 85 0 0 85 1 86
PEI 32 32 0 0 0 58 58 0 0 0 58
NL 52 0 0 52 0 135 1 0 134 1 136
YT 6 6 0 0 0 23 16 1 6 0 23
N.W.T 1 1 0 0 0 142 140 2 0 0 142
NU 0 0 0 0 0 9 9 0 0 0 9
Canada 2275 512 99 1664 38 20539 7106 459 12974 214 20753
Table Figure 3 - Footnote 2 98% 23% 4% 73% 2% 99% 35% 2% 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 2019-03
Age groups (years) Cumulative (August 26, 2018 to January 19, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 4072 1412 22 2638 32 4104 22%
5-19 2884 1198 21 1665 34 2918 15%
20-44 3975 1482 73 2420 26 4001 21%
45-64 3887 1325 85 2477 33 3920 21%
65+ 3896 883 334 2679 84 3980 21%
Total 18714 6300 535 11879 209 18923 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 03, 1.4% 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 2018-19-03

Number of Sentinels Reporting in Week 03: 99

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 1.4% 2.5% 1.4% 3.6%

Participatory Syndromic Surveillance

In week 03, 2,211 participants reported to FluWatchers, of which 55 (2.5%) reported symptoms of cough and fever (Figure 5).

Among the 55 participants who reported fever and cough:

  • 13% consulted a healthcare professional;
  • 73% reported days missed from work or school, resulting in a combined total of 108 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-03

Number of Participants Reporting in Week 03: 2,211

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%

Influenza Outbreak Surveillance

In week 03, 31 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (19), acute care facilities (3), and other settings (9). Thirteen new ILI outbreaks in long-term care facilities (5) and  schools (8) were also reported in week 03.

To date this season, 254 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 148 outbreaks were in LTCF, 22 were in schools, 33 in acute care facilities, and 51 were in other settings.
  • Among the 239 outbreaks for which the influenza type was available 99% (236) were associated with influenza A.
  • Among the 115 outbreaks for which the influenza A subtype was available:
    • 77% (89) were associated with influenza A(H1N1)pdm09;
    • 23% (26) were associated with A(H3N2),

To date this season, 58 ILI outbreaks have been reported; 38 occurred in LTCF, 17 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 2019-03

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 7 5 4 0
51 3 10 4 2 0
52 4 24 5 0 0
01 5 34 11 0 0
02 8 28 8 0 0
03 3 19 9 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1,637 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.6% (1,512) 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 262 ICU admissions and 56 deaths have been reported.
    • 43% (113) of reported ICU admissions were in adults aged 45-64 years
    • All 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 2019-03
Age Groups (years) Cumulative (August 26, 2018 to January 19, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4  274 3 58.20
5-19 156 0 11.24
20-44  228 0 8.01
45-64  444 0 20.40
65+  529 3 43.73
Total 1631 6  
% 99.6% 0.4%  
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

Pediatric Influenza Hospitalizations and Deaths

In week 03, 68 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, 677 pediatric hospitalizations have been reported (Figure 8):

  • 81% of cases were in children 6 months to 9 years of age.
  • 99% (670) of cases have been associated with influenza A.
  • Among the 256 cases for which the influenza subtype was available, 250 (98%) were associated with A(H1N1)pdm09.

To date this season, 98 ICU admissions, and 10 deaths have been reported.

  • 87% (100) of ICU admissions were in children 6 months to 9 years of age.
  • 99% (114) 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 2019-03

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 39 15 3 28
50 51 23 4 47
51 82 32 4 72
52 89 47 7 92
01 93 40 5 75
02 59 35 4 62
03 68 38 4 67

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 2019-03

Figure 8
Figure 8 - Text description
Age Group Total
0-5 mo 73
6-23 mo 184
2-4 yr 218
5-9 yr 149
10-16 yr 53

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, 324 hospitalizations have been reported (Figure 9):

  • 299 (92%) were associated with influenza A.
  • A similar proportion of hospitalizations are reported among adults <65 years of age and adults ≥65 years of age
  • The most commonly reported comorbidity among hospitalized cases was endocrine disorders, which were reported in 68% 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 2019-03

Figure 9
Figure 9 - Text description
Age Group Total
20-34 yr 33
35-49 yr 38
50-64 yr 79
65-79 yr 92
80+ yr 82

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 728 influenza viruses (57 A(H3N2), 654 A(H1N1) and 17 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

40 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:

  • Six viruses belonged to genetic group 3C.2a.
  • 33 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):

  • 17 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.
  • A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 13 influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Two viruses belonged to genetic group 3C.2a and two to 3C.3a.

Influenza A(H1N1):

  • 641 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.
  • 13 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
  • 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:

304 influenza A (42 A(H3N2) and 262 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 304 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

539 influenza viruses (48 A(H3N2), 475 A(H1N1) and 16 B) were tested for resistance to oseltamivir and it was found that:

  • All 539 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

537 influenza viruses (48 A(H3N2), 473 H1N1 and 16 B) were tested for resistance to zanamivir and it was found that:

  • All 537 influenza viruses were sensitive to zanamivir.

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