FluWatch report: March 3, 2019 to March 9, 2019 (week 10)

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Organization: Public Health Agency of Canada

Date published: 2019-03-15

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Overall Summary

  • At the national level, most indicators of influenza activity remained similar, or increased slightly, compared to the previous week.
  • Influenza activity continues to be reported in almost all regions in Canada but is circulating at higher levels in eastern regions.
  • Influenza A(H1N1)pdm09 has been the predominant subtype to date this season.
  • Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 56% of subtyped influenza A detections this week.
  • There is currently very little influenza B circulation compared to previous seasons.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 10, the following influenza activity levels were reported (Figure 1):

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

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-10

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern Localized
N.L. Labrador-Grenfell Sporadic
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 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 No Activity
N.B. Region 5 Sporadic
N.B. Region 6 Sporadic
N.B. Region 7 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Localized
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 Sporadic
Ont. North West Sporadic
Ont. South West Localized
Ont. Toronto Localized
Man. Northern Regional No Activity
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern Sporadic
Man. Winnipeg Sporadic
Man. Southern Health Sporadic
Sask. North No Data
Sask. Central No Data
Sask. South No Data
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Sporadic
Alta. Calgary Sporadic
Alta. South Zone Localized
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 10, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

  • The percentage of tests positive for influenza continued to increase slightly to 21.3%.
  • A total 1,803 laboratory detections of influenza were reported, of which 96% were influenza A.
  • Influenza A(H3N2) accounted for 56% of subtyped influenza A detections.
  • Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 308 this week.

To date this season, 36,124 laboratory-confirmed influenza detections have been reported:

  • 98% have been influenza A.
  • Among the 12,329 influenza A viruses subtyped, 85% have been A(H1N1)pdm09.
  • Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 28,283 laboratory-confirmed influenza cases (Table 1):

  • 84% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
  • 60% 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 2019-10

Figure 2. Text equivalent follows.

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 equivalent
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 1483 93 532 48
5 1449 112 433 43
6 1234 118 315 42
7 1116 128 244 33
8 1066 236 216 40
9 1172 285 213 64
10 1243 308 248 71

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-10

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 3 to March 9, 2019) Cumulative (August 26, 2018 to March 9, 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 459 143 145 171 13 4559 2752 620 1187 57 4616
AB 111 23 55 33 19 5593 3517 285 1791 98 5691
SK 9 7 1 1 2 2261 1361 64 836 21 2282
MB 101 2 91 8 0 1022 282 21 719 8 1030
ON 167 39 0 128 10 4676 1912 838 1926 105 4781
QC 619 0 4 615 19 13813 0 0 13813 287 14100
NB 98 13 0 85 2 2197 210 21 1966 5 2202
NS 99 0 5 94 2 494 0 0 494 8 502
PEI 11 11 0 0 0 212 205 7 0 0 212
NL 56 0 1 55 0 452 1 0 451 2 454
YT 2 0 0 2 0 74 50 4 20 0 74
N.W.T 2 2 0 0 1 159 157 2 0 1 160
NU 1 1 0 0 0 20 20 0 0 0 20
Canada 1735 241 302 1192 68 35532 10467 1862 23203 592 36124
PercentageTable Figure 3 - Footnote 2 96% 14% 17% 69% 4% 98% 29% 5% 65% 2% 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 2019-10
Age groups (years) Cumulative (August 26, 2018 to March 9, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 5829 1617 69 4143 83 5912 21%
5-19 4104 1337 131 2636 113 4217 15%
20-44 5506 1802 220 3484 81 5587 20%
45-64 5531 1723 203 3605 59 5590 20%
65+ 6816 1241 905 4670 161 6977 25%
Total 27786 7720 1528 18538 497 28283 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 10, 1.3% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is low compared to previous seasons.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-10

Number of Sentinels Reporting in Week 10: 95

Figure 4. Text equivalent follows.

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 equivalent
Surveillance Week 2018-19 Average Min Max
35 0.6% 0.8% 0.5% 1.2%
36 0.7% 0.8% 0.7% 1.0%
37 0.6% 0.9% 0.7% 1.0%
38 0.5% 1.1% 1.0% 1.4%
39 1.8% 1.1% 0.9% 1.4%
40 0.6% 1.3% 0.9% 1.6%
41 1.1% 1.4% 0.9% 2.4%
42 1.0% 1.4% 1.0% 1.9%
43 0.9% 1.3% 1.0% 1.5%
44 0.8% 1.3% 0.9% 1.6%
45 1.3% 1.3% 1.2% 1.5%
46 1.3% 1.6% 1.0% 2.0%
47 1.3% 1.5% 1.1% 1.9%
48 1.5% 1.6% 0.8% 2.1%
49 1.6% 1.5% 1.0% 2.5%
50 1.5% 2.3% 1.3% 3.7%
51 1.0% 2.5% 1.6% 4.1%
52 3.2% 4.5% 1.7% 7.1%
1 2.8% 3.7% 1.7% 5.2%
2 1.8% 3.0% 1.1% 4.5%
3 1.1% 2.5% 1.3% 3.6%
4 1.3% 2.4% 1.7% 3.5%
5 1.4% 2.7% 2.0% 4.4%
6 0.9% 2.7% 2.1% 3.3%
7 0.9% 2.4% 1.7% 3.0%
8 0.9% 2.3% 1.9% 2.7%
9 1.1% 2.2% 1.8% 2.7%
10 1.3% 2.1% 1.8% 2.7%

Participatory Syndromic Surveillance

In week 10, 2,112 participants reported to FluWatchers, of which 65 (3.1%) reported symptoms of cough and fever (Figure 5).

Among the 65 participants who reported fever and cough:

  • 20% consulted a healthcare professional;
  • 78% reported days missed from work or school, resulting in a combined total of 134 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-10

Number of Participants Reporting in Week 10: 2,112

Figure 5. Text equivalent follows.
Figure 5 - Text equivalent
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%
1 3.4%
2 2.8%
3 2.5%
4 2.9%
5 3.0%
6 2.6%
7 2.7%
8 2.5%
9 2.7%
10 3.1%

Influenza Outbreak Surveillance

In week 10, 30 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (12), acute care facilities (11) and other settings (7).

To date this season, 540 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 314 (58%) outbreaks were in LTCF, 29 were in schools, 83 in acute care facilities, and 114 were in other settings.
  • Among the 481 outbreaks for which the influenza type was available, 98% (473) were associated with influenza A.
  • Among the 206 outbreaks for which the influenza A subtype was available, 56% (116) were associated with influenza A(H1N1)pdm09;

To date this season, 119 ILI outbreaks have been reported; 64 occurred in LTCF, 51 in schools, and four in acute care facilities.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-10

Figure 6. Text equivalent follows.
Figure 6 - Text equivalent
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 12 4 2 0
52 4 24 5 0 0
1 5 40 11 0 0
2 8 38 7 0 0
3 3 27 10 0 0
4 6 18 10 1 0
5 5 22 7 0 0
6 9 20 7 0 0
7 6 18 5 0 0
8 4 26 12 4 0
9 9 21 13 2 0
10 11 12 7 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,351 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.1% (2,329) 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 429 ICU admissions and 109 deaths have been reported.
    • 43% (185) of reported ICU admissions were in adults aged 45-64 years.
    • All but three ICU admissions were associated with influenza A.
    • All but one of the 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 2019-10
Age Groups (years) Cumulative (August 26, 2018 to March 9, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 333 8 71.64
5-19 199 6 14.77
20-44 306 1 10.79
45-64 635 2 29.27
65+ 856 5 70.77
Total 2329 22  
% 99.1% 0.9%  
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 10, 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, 1,015 pediatric hospitalizations have been reported (Figure 8):

  • 68% of cases were in children under 5 years of age.
  • 98% (992) of cases have been associated with influenza A.
  • Among the 311 cases for which the influenza subtype was available, 286 (92%) were associated with A(H1N1)pdm09.

To date this season, 172 ICU admissions, and 10 deaths have been reported.

  • 63% (108) of ICU admissions were in children under 5 years of age.
  • All but two of the 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 2019-10

Figure 7. Text equivalent follows.

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

Figure 7 - Text equivalent
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 5 1 0 4
43 11 1 0 3
44 15 3 1 6
45 37 3 2 4
46 41 5 1 13
47 36 4 0 9
48 43 9 2 23
49 43 15 3 28
50 51 23 4 47
51 85 32 4 72
52 89 47 7 92
1 93 40 5 75
2 60 35 4 62
3 70 38 4 67
4 60 35 7 47
5 51 40 11 59
6 48 38 15 79
7 44 40 17 120
8 44 47 25 139
9 36 50 13 153
10 45 48 17 135

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 2019-10

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 107
6-23 mo 262
2-4 yr 318
5-9 yr 227
10-16 yr 101

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, 694 hospitalizations, 80 ICU admissions and 32 deaths have been reported (Figure 9):

  • 645 (93%) hospitalizations were associated with influenza A.
  • A greater proportion of hospitalizations have been reported among  adults ≥65 years of age (58%) compared to adults <65 years of age (42%).
  • 86% of hospitalized cases reported more than one type of comorbid condition.  
The most commonly reported comorbidity was endocrine disorders, which were reported in 82% 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 2019-10

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 65
35-49 yr 69
50-64 yr 155
65-79 yr 200
80+ yr 205

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,570 influenza viruses (195 A(H3N2), 1,340 A(H1N1) and 35 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

102 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:

  • 17 viruses belonged to genetic group 3C.2a.
  • 82 viruses belonged to subclade 3C.2a1.
  • Two viruses belonged to 3C.3a.
  • 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./p>

Antigenic Characterization:

Influenza A (H3N2):

  • 68 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.
  • 25 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.
  • 53 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 16 viruses belonged to genetic group 3C.2a and 21 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,302 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.
  • 38 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).

  • Nine 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.
  • Seven viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
  • 19 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:

372 influenza A (59 A(H3N2) and 313 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 372 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

961 influenza viruses (93 A(H3N2), 836 A(H1N1) and 32 B) were tested for resistance to oseltamivir and it was found that:

  • All 93 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 836 A(H1N1) viruses tested, 833 were sensitive to oseltamivir and three viruses were resistant to oseltamivir with a H275Y mutation.
  • All 32 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

960 influenza viruses (93 A(H3N2), 835 H1N1 and 32 B) were tested for resistance to zanamivir and it was found that:

  • All 960 influenza viruses were sensitive to zanamivir.
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