FluWatch report: March 17, 2019 to March 23, 2019 (week 12)

thumbnail

Download the alternative format
(PDF format, 900 KB, 9 pages)

Organization: Public Health Agency of Canada

Date published: 2019-03-29

Related Topics

Overall Summary

  • Influenza activity continues to be reported in almost all regions in Canada but is circulating at higher levels in some eastern regions.
  • Though A(H1N1) peaked at end of December, over the past four weeks a second smaller wave, dominated by A(H3N2), is being observed in most regions of the country.
  • Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 72% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
  • Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 12, the following influenza activity levels were reported (Figure 1):

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

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-12

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 Sporadic
N.L. Western Localized
P.E.I. Prince Edward Island Localized
N.S. Zone 1 - Western Localized
N.S. Zone 2 - Northern Localized
N.S. Zone 3 - Eastern Sporadic
N.S. Zone 4 - Central Localized
N.B. Region 1 Sporadic
N.B. Region 2 Localized
N.B. Region 3 Sporadic
N.B. Region 4 Sporadic
N.B. Region 5 Sporadic
N.B. Region 6 Sporadic
N.B. Region 7 Localized
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Sporadic
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
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 No Activity
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 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 No Data
N.W.T. South No Data
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq No Activity
Nvt. Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 12, 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 21.8%.
  • A total 1,735 laboratory detections of influenza were reported, of which 93% were influenza A.
  • Influenza A(H3N2) accounted for 72% of subtyped influenza A detections.
  • Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 342 this week.

To date this season, 39,297 laboratory-confirmed influenza detections have been reported:

  • 98% have been influenza A.
  • Among the 13,414 influenza A viruses subtyped, 81% 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 30,844 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.
  • 57% 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 2019-12

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(H3N2) A(H1N1)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 1037 295 219 64
10 1085 335 268 71
11 990 354 195 89
12 1261 342 132 129

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-12

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 17 to 23, 2019) Cumulative (August 26, 2018 to March 23, 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 539 59 125 355 22 5288 2937 934 1417 105 5393
AB 159 22 87 50 22 5899 3551 439 1909 142 6041
SK 12 1 4 7 13 2240 1368 78 794 48 2288
MB 11 2 3 6 3 1045 290 39 716 11 1056
ON 230 24 100 106 11 5134 1992 1038 2104 127 5261
QC 423 0 0 423 26 14735 0 0 14735 330 15065
NB 120 13 6 101 24 2439 230 34 2175 33 2472
NS 77 0 0 77 2 628 0 0 628 10 638
PEI 14 5 9 0 0 243 216 27 0 0 243
NL 78 0 0 78 1 576 1 0 575 3 579
YT 0 0 0 0 0 74 50 4 20 0 74
N.W.T 3 3 0 0 0 166 164 2 0 1 167
NU 0 0 0 0 0 20 20 0 0 0 20
Canada 1666 129 334 1203 124 38487 10819 2595 25073 810 39297
PercentageTable Figure 3 - Footnote 2 93% 8% 20% 72% 7% 98% 28% 7% 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 2019-12
Age groups (years) Cumulative (August 26, 2018 to March 23, 2019)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)Table 1 - Note 1 Total # %
0-4 6093 1639 106 4348 115 6208 20%
5-19 4425 1359 240 2826 176 4601 15%
20-44 5905 1882 298 3725 117 6022 20%
45-64 5915 1800 292 3823 70 5985 19%
65+ 7852 1320 1265 5267 176 8028 26%
Total 30190 8000 2201 19989 654 30844 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 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 12, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-12

Number of Sentinels Reporting in Week 12: 86

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 0.8% 2.4% 1.7% 3.0%
8 0.9% 2.3% 1.9% 2.7%
9 1.0% 2.2% 1.8% 2.7%
10 1.0% 2.1% 1.8% 2.7%
11 0.8% 2.1% 1.7% 2.7%
12 1.6% 1.8% 1.1% 2.7%

Participatory Syndromic Surveillance

In week 12, 2,056 participants reported to FluWatchers, of which 50 (2.4%) reported symptoms of cough and fever (Figure 5).

Among the 50 participants who reported fever and cough:

  • 30% consulted a healthcare professional;
  • 92% reported days missed from work or school, resulting in a combined total of 136 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-12

Number of Participants Reporting in Week 12: 2,056

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%
11 2.6%
12 2.4%

Influenza Outbreak Surveillance

In week 12, 38 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (19), acute care facilities (8) and other settings (11). Eleven new ILI outbreaks (LTCF (8) and schools and daycares (3)) were also reported in week 12. Among the outbreaks with available subtype information (12), 92% (11) were associated with influenza A(H3N2).

To date this season, 633 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 371 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 94 in acute care facilities, and 138 were in other settings.
  • Among the 563 outbreaks for which the influenza type was available, 98% (550) were associated with influenza A.
  • Among the 243 outbreaks for which the influenza A subtype was available, 55% (125) were associated with influenza A(H1N1)pdm09;

To date this season, 134 ILI outbreaks have been reported; 75 occurred in LTCF, 55 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 2019-12

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 9 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 23 7 0 0
6 9 20 8 0 0
7 6 20 6 0 0
8 4 28 11 4 0
9 9 23 13 2 0
10 12 23 9 1 0
11 2 21 12 0 0
12 8 19 11 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,592 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 98.7% (2,558) were associated with influenza A
  • Among the 1,555 cases for which the influenza subtype was available, 1,366 (88%) were associated with A(H1N1)pdm09.
  • The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

  • To date this season 464 ICU admissions and 127 deaths have been reported.
    • 43% (199) of reported ICU admissions were in adults aged 45-64 years.
    • All but four ICU admissions were associated with influenza A.
    • All but one of the 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 2019-12
Age Groups (years) Cumulative (August 26, 2018 to March 23, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 354 12 76.89
5-19 210 10 15.85
20-44 317 4 11.28
45-64 688 3 31.75
65+ 989 5 81.70
Total 2558 34  
% 98.7% 1.3%  
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 12, 41 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 41 hospitalizations, 34 (83%) were due to influenza A.

To date this season, 1,089 pediatric hospitalizations have been reported (Figure 8):

  • 67% of cases were in children under 5 years of age.
  • 97% (1,054) of cases have been associated with influenza A.
  • Among the 324 cases for which the influenza subtype was available, 289 (89%) were associated with A(H1N1)pdm09.

To date this season, 194 ICU admissions, and 10 deaths have been reported.

  • 60% (117) 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 2019-12

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 12 1 0 3
44 15 3 1 6
45 37 3 2 4
46 41 5 1 13
47 36 4 0 9
48 40 9 2 23
49 46 15 3 28
50 51 23 4 47
51 84 32 4 72
52 89 47 7 92
1 91 40 5 75
2 62 35 4 62
3 70 38 4 67
4 61 35 7 47
5 50 40 11 59
6 48 38 15 79
7 44 40 17 120
8 43 47 25 139
9 35 50 13 153
10 45 48 17 135
11 42 41 18 118
12 41 33 13 89

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 2019-12

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 115
6-23 mo 281
2-4 yr 337
5-9 yr 240
10-16 yr 117

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, 773 hospitalizations, 90 ICU admissions and 40 deaths have been reported (Figure 9):

  • 718 (93%) hospitalizations were associated with influenza A.
  • A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
  • Among the 167 cases for which the influenza subtype was available, 103 (62%) were associated with A(H1N1)pdm09.
  • 88% of hospitalized cases reported more than one type of comorbid condition.
  • The most commonly reported comorbidity was endocrine disorders, which were reported in 83% 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 2019-12

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 72
35-49 yr 75
50-64 yr 168
65-79 yr 228
80+ yr 230

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,700 influenza viruses (233 A(H3N2), 1,415 A(H1N1) and 52 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

124 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:

  • 18 viruses belonged to genetic group 3C.2a.
  • 102 viruses belonged to subclade 3C.2a1.
  • Three 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.

Antigenic Characterization:

Influenza A (H3N2):

  • 82 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.
  • 27 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.
  • 63 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,375 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.
  • 40 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).

  • 18 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.
  • 12 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
  • 22 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:

388 influenza A (64 A(H3N2) and 324 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 388 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,017 influenza viruses (103 A(H3N2), 879 A(H1N1) and 35 B) were tested for resistance to oseltamivir and it was found that:

  • All 103 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 879 A(H1N1) viruses tested, 875 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
  • All 35 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,016 influenza viruses (103 A(H3N2), 878 H1N1 and 35 B) were tested for resistance to zanamivir and it was found that:

  • All 1,016 influenza viruses were sensitive to zanamivir.
Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: