FluWatch report: February 17 to 23, 2019 (Week 08)

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Organization: Public Health Agency of Canada

Date published: 2019-03-01

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Overall Summary

  • Influenza activity is past the peak in most regions in western Canada, but continues to circulate at higher levels in eastern regions.
  • At the national level, most indicators of influenza activity remained similar, or increased slightly, compared to the previous week.
  • Influenza A(H1N1)pdm09 continues to be the most common influenza virus circulating in Canada. There is currently very little influenza B circulation compared to previous seasons.
  • The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2019-2020 northern hemisphere influenza season. The recommended strain was changed for the A(H1N1)pdm09 component.The recommendation for the A(H3N2) component has been postponed.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 08, the following influenza activity levels were reported (Figure 1):

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

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-08

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
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 Sporadic
N.S. Zone 2 - Northern Localized
N.S. Zone 3 - Eastern Localized
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 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Localized
Que. Centre-du-Québec Sporadic
Que. Montréal et Laval Localized
Que. Ouest-du-Québec Localized
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 Sporadic
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern No Activity
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 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 08, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

  • The percentage of tests positive for influenza was 17.9%.
  • A total 1,535 laboratory detections of influenza were reported, of which 98% were influenza A.
  • Influenza  A(H1N1)pdm09 and A(H3N2) accounted for equal proportions of subtyped influenza A detections.
  • Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 199 this week.

To date this season, 32,429 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 11,210 influenza A viruses subtyped, 89% 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 25,393 laboratory-confirmed influenza cases (Table 1):

  • 85% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
  • 61% 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 2019-08

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 1091 123 234 31
8 1105 199 200 39

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-08

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (February 17, 2019 to February 23, 2019) Cumulative (August 26, 2018 to February 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 300 83 101 116 5 3678 2473 329 876 33 3711
AB 72 28 27 17 10 5382 3485 178 1719 74 5456
SK 0 0 0 0 0 2173 1349 60 764 10 2183
MB 12 0 2 10 0 994 270 8 716 6 1000
ON 268 67 66 135 4 4119 1800 637 1682 81 4200
QC 594 0 0 594 15 12544 0 0 12544 240 12784
NB 136 14 2 120 0 1967 197 15 1755 2 1969
NS 76 0 0 76 2 336 0 0 336 6 342
PEI 2 2 0 0 0 185 185 0 0 0 185
NL 32 0 0 32 0 357 1 0 356 2 359
YT 5 3 0 2 0 68 50 1 17 0 68
N.W.T 1 1 0 0 0 153 151 2 0 0 153
NU 1 1 0 0 0 19 19 0 0 0 19
Canada 1499 199 198 1102 36 31975 9980 1230 20765 454 32429
PercentageTable Figure 3 - Footnote 2 98% 13% 13% 74% 2% 99% 31% 4% 65% 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 2019-08
Age groups (years) Cumulative (August 26, 2018 to February 23, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 5452 1570 42 3840 62 5514 22%
5-19 3724 1300 58 2366 70 3794 15%
20-44 5064 1699 139 3226 55 5119 20%
45-64 5018 1597 139 3282 49 5067 20%
65+ 5755 1110 596 4049 144 5899 23%
Total 25013 7276 974 16763 380 25393 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 08, 1.2% 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 2019-08

Number of Sentinels Reporting in Week 08: 117

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% 0.6% 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%
1 2.8% 3.8% 1.8% 5.6%
2 1.8% 2.6% 1.3% 3.9%
3 1.1% 2.5% 1.4% 3.6%
4 1.3% 2.5% 1.6% 3.1%
5 1.4% 2.6% 1.9% 4.0%
6 0.9% 2.7% 2.1% 3.5%
7 0.9% 2.7% 1.9% 3.4%
8 1.2% 2.6% 2.1% 3.1%

Participatory Syndromic Surveillance

In week 08, 2,131 participants reported to FluWatchers, of which 53 (2.5%) reported symptoms of cough and fever (Figure 5).

Among the 53 participants who reported fever and cough:

  • 9% consulted a healthcare professional;
  • 74% reported days missed from work or school, resulting in a combined total of 102 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-08

Number of Participants Reporting in Week 08: 2,131

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%

Influenza Outbreak Surveillance

In week 08, 37 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (20), acute care facilities (4), schools and daycares (4) and other settings (9). Two new ILI outbreaks in long-term care facilities were also reported in week 08.

To date this season, 446 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 269 (60%) outbreaks were in LTCF, 27 were in schools, 61 in acute care facilities, and 89 were in other settings.
  • Among the 408 outbreaks for which the influenza type was available, 99% (402) were associated with influenza A.
  • Among the 177 outbreaks for which the influenza A subtype was available, 63% (112) were associated with influenza A(H1N1)pdm09;

To date this season, 107 ILI outbreaks have been reported; 56 occurred in LTCF, 47 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 2019-08

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 26 10 0 0
4 6 17 10 1 0
5 4 20 8 0 0
6 8 20 6 0 0
7 6 18 5 0 0
8 4 20 9 4 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,093 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.6% (2,085) 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 384 ICU admissions and 93 deaths have been reported.
    • 42% (163) of reported ICU admissions were in adults aged 45-64 years.
    • All the ICU admissions, and 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 2019-08
Age Groups (years) Cumulative (August 26, 2018 to February 23, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 316 2 66.81
5-19 179 2 13.04
20-44 287 0 10.09
45-64 581 1 26.74
65+ 722 3 59.59
Total 2085 8  
% 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 08, 43 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, 928 pediatric hospitalizations have been reported (Figure 8):

  • 69% of cases were in children under 5 years of age.
  • 98% (914) of cases have been associated with influenza A.
  • Among the 295 cases for which the influenza subtype was available, 280 (95%) were associated with A(H1N1)pdm09.

To date this season, 159 ICU admissions, and 10 deaths have been reported.

  • 63% (101) 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 2019-08

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 47 9 2 23
49 39 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 43 47 25 139

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 2019-08

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 94
6-23 mo 238
2-4 yr 305
5-9 yr 204
10-16 yr 87

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, 590 hospitalizations, 65 ICU admissions and 22 deaths have been reported (Figure 9):

  • 543 (92%) 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%).
  • 84% of hospitalized cases reported more than one type of comorbid condition.  
  • The most commonly reported comorbidity was endocrine disorders, which were reported in 80% 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 2019-08

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 57
35-49 yr 58
50-64 yr 134
65-79 yr 172
80+ yr 169

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,412 influenza viruses (150 A(H3N2), 1,234 A(H1N1) and 28 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

79 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:

  • 15 viruses belonged to genetic group 3C.2a.
  • 63 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):

  • 55 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.
  • 16 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.
  • 33 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 15 viruses belonged to genetic group 3C.2a and 11 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,201 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.
  • 33 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.
  • Two viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
  • 17 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:

356 influenza A (51 A(H3N2) and 305 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 356 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

842 influenza viruses (76 A(H3N2), 740 A(H1N1) and 26 B) were tested for resistance to oseltamivir and it was found that:

  • All 76 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 740 A(H1N1) viruses tested, 738 were sensitive to oseltamivir and two viruses were resistant to oseltamivir with a H275Y mutation.
  • All 26 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

841 influenza viruses (76 A(H3N2), 739 H1N1 and 26 B) were tested for resistance to zanamivir and it was found that:

  • All 841 influenza viruses were sensitive to zanamivir.
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