FluWatch report: January 6, 2019 to January 12, 2019 (week 02)

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Organization: Public Health Agency of Canada

Date published: 2019-01-18

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Overall Summary

  • In week 02, laboratory detections continued to decline sharply from the previous week confirming that the influenza season reached peak levels in the last week of December (week 52).
  • Overall, the Central and Eastern regions are 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.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 02, the following influenza activity levels were reported (Figure 1):

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

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-02

Figure 1
Figure 1 - Text description
Province Influenza Surveillance Region Activity Level
N.L. Eastern Localized
N.L. Labrador-Grenfell Localized
N.L. Central Localized
N.L. Western Sporadic
P.E.I. Prince Edward Island Sporadic
N.S. Zone 1 - Western Localized
N.S. Zone 2 - Northern Sporadic
N.S. Zone 3 - Eastern Sporadic
N.S. Zone 4 - Central Localized
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 Localized
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 Widespread
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 Sporadic
Alta. North Zone Sporadic
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 Sporadic
N.W.T. South Sporadic
Nvt. Qikiqtaaluk No Activity
Nvt. Kivalliq Sporadic
Nvt. Kitimeot No Activity

Laboratory Confirmed Influenza Detections

In week 02, the following results were reported from sentinel laboratories across Canada (Figure 2):

  • The percentage of tests positive for influenza decreased to 20.5% in week 02.
  • A total 2,486 laboratory detections of influenza were reported, of which 98% were influenza A.

To date this season 20,494 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 7,523 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 17,295 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.
  • 63% 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 2019-02

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
01 2563 58 893 31
02 1986 66 443 42

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-02

Figure 3
Figure 3 - Text description
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 6, 2018 to Januray 12, 2019) Cumulative (August 26, 2018 to January 12, 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 98 31 1 66 0 1958 1069 77 812 10 1968
AB 147 102 7 38 3 4915 3250 82 1583 33 4948
SK 26 14 0 12 0 2034 1266 54 714 1 2035
MB 89 15 0 74 0 830 211 3 616 3 833
ON 409 213 56 140 6 1893 977 236 680 48 1941
QC 1 334 0 0 1 334 32 7387 0 0 7387 115 7502
NB 267 26 2 239 0 1025 68 3 954 2 1027
NS 33 0 0 33 0 85 0 0 85 1 86
PEI 20 20 0 0 0 58 58 0 0 0 58
NL 21 0 0 21 0 135 1 0 134 1 136
YT 0 0 0 0 0 23 16 1 6 0 23
N.W.T 0 0 0 0 0 142 140 2 0 0 142
NU 1 1 0 0 0 9 9 0 0 0 9
Canada 2445 422 66 1957 41 20494 7065 458 12971 214 20708
PercentageTable Figure 3 - Footnote 2 98% 17% 3% 80% 2% 99% 34% 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 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 2019-02
Age groups (years) Cumulative (August 26, 2018 to January 12, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 3679 1351 18 2310 28 3707 21%
5-19 2698 1168 17 1513 29 2727 16%
20-44 3676 1412 62 2202 24 3700 21%
45-64 3601 1253 76 2272 29 3630 21%
65+ 3464 816 294 2354 67 3531 20%
Total 17118 6000 467 10651 177 17295 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 02, 2.5% 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 2019-02

Number of Sentinels Reporting in Week 02: 97

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 3.4% 3.6% 1.9% 5.0%
01 3.3% 3.8% 1.8% 5.6%
02 2.5% 2.6% 1.3% 3.9%

Participatory Syndromic Surveillance

In week 02, 2,259 participants reported to FluWatchers, of which 64 (2.8%) reported symptoms of cough and fever (Figure 5).

Among the 64 participants who reported fever and cough:

  • 19% consulted a healthcare professional;
  • 72% reported days missed from work or school, resulting in a combined total of 142 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-02

Number of Participants Reporting in Week 02: 2,259

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%

Influenza Outbreak Surveillance

In week 02, 33 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (21), acute care facilities (4), and other settings (8). Two new ILI outbreaks in schools were also reported in week 02.
To date this season, 206 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 116 outbreaks were in LTCF, 22 were in schools, 26 in acute care facilities, and 42 were in other settings.
  • All of the 194 outbreaks for which the influenza type was available were associated with influenza A.
  • Among the 93 outbreaks for which the influenza A subtype was available:
    • 80% (74) were associated with influenza A(H1N1)pdm09;
    • 20% (19) were associated with A(H3N2),

To date this season, 44 ILI outbreaks have been reported; 32 occurred in LTCF, nine 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 2019-02

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 30 11 0 0
02 4 21 8 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1,518 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 227 ICU admissions and 47 deaths have been reported.
    • 42% (97) 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 2019-02
Age Groups Cumulative (August 26, 2018 to January 12, 2018)
Influenza A Influenza B Rate per 100,000 population
0-4 252 2 53,36
5-19 152 0 10,95
20-44 213 0 7,49
45-64 413 0 18,98
65+ 482 4 39,95
Total 1512 6 -
  99.6% 0.4% -

Pediatric Influenza Hospitalizations and Deaths

In week 02, 57 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, 603 pediatric hospitalizations have been reported (Figure 8):

  • 99% (598) of cases have been associated with influenza A.
  • Among the 240 cases for which the influenza subtype was available, 234 (98%) were associated with A(H1N1)pdm09.

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

  • 85% (84) of ICU admissions were in children 6 months to 9 years of age
  • 99% (97) 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 2019-02

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 20 3 1 6
45 32 3 2 4
46 42 5 1 13
47 33 4 0 9
48 47 9 2 23
49 39 15 3 28
50 52 23 4 47
51 79 32 4 72
52 89 47 7 92
01 93 40 5 75
02 57 35 4 62

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 2019-02

Figure 8
Figure 8 - Text description
Age Group Total
0-5 mo 64
6-23 mo 171
2-4 yr 192
5-9 yr 129
10-16 yr 47

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, 278 hospitalizations have been reported (Figure 9):

  • 262 (94%) 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 2019-02

Figure 9
Figure 9 - Text description
Age Group Total
20-34 yr 29
35-49 yr 37
50-64 yr 69
65-79 yr 74
80+ yr 69

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 571 influenza viruses (49 A(H3N2), 506 A(H1N1) and 16 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

39 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.
  • 32 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):

  • 495 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.
  • 11 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 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:

290 influenza A (41 A(H3N2) and 249 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 290 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

467 influenza viruses (47 A(H3N2), 404 A(H1N1) and 16 B) were tested for resistance to oseltamivir and it was found that:

  • All 467 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

466 influenza viruses (47 A(H3N2), 403 H1N1 and 16 B) were tested for resistance to zanamivir and it was found that:

  • All 466 influenza viruses were sensitive to zanamivir.
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