FluWatch report: January 27, 2019 to February 2, 2019 (week 05)

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Organization: Public Health Agency of Canada

Date published: 2019-02-08

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Overall Summary

  • Influenza activity in Canada is declining but influenza continues to circulate with eastern regions continuing to report higher levels of influenza activity compared to western regions.
  • At the national level, the influenza season appears to be past the peak of activity, with most indicators showing stable or downward trends in week 05. Influenza A(H1N1)pdm09 continues to be the most common influenza virus circulating in Canada.
  • A report on influenza vaccine coverage in Canada for 2017-18 shows that coverage was low among adults (38%) and highest among seniors (71%). These results are similar to recent seasons.
  • The effectiveness of the influenza vaccine for the 2018-19 season is estimated to be 72% against the predominant circulating strain this season, with significant protection observed in all age groups.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 05, fewer regions reported high levels of activity compared to the previous week. The following influenza activity levels were reported (Figure 1):

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

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-05

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern Sporadic
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 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 Localized
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 Localized
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Localized
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 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 Activity
N.W.T. South No Activity
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq Sporadic
Nvt. Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 05, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

  • The percentage of tests positive for influenza was similar to the previous week at 19.7%.
  • A total 2,002 laboratory detections of influenza were reported, of which 98% were influenza A.

To date this season, 27,645 laboratory-confirmed influenza detections have been reported:

  • 99% have been influenza A.
  • Among the 10,014 influenza A viruses subtyped, 92% 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 21,728 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 2019-05

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 1465 111 519 48
5 1431 107 423 41

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-05

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 27 to February 2, 2019) Cumulative (August 26, 2018 to February 2, 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 232 152 35 45 5 3174 2256 176 742 21 3195
AB 71 43 7 21 8 5184 3412 113 1659 46 5230
SK 8 5 1 2 2 2134 1336 57 741 7 2141
MB 24 13 1 10 1 943 250 24 669 5 948
ON 387 149 62 176 3 3097 1465 420 1212 64 3161
QC 940 0 0 940 22 10399 0 0 10399 194 10593
NB 176 27 1 148 0 1596 140 11 1445 2 1598
NS 32 0 0 32 0 161 0 0 161 3 164
PEI 20 20 0 0 0 151 151 0 0 0 151
NL 38 0 0 38 0 251 1 0 250 1 252
YT 7 4 0 3 0 52 41 1 10 0 52
N.W.T 0 0 0 0 0 149 147 2 0 0 149
NU 2 2 0 0 0 11 11 0 0 0 11
Canada 1937 415 107 1415 41 27302 9210 804 17288 343 27645
PercentageTable Figure 3 - Footnote 2 98% 21% 6% 73% 2% 99% 34% 3% 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 2019-05
Age groups (years) Cumulative (August 26, 2018 to February 2, 2019)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Footnote 1 Total # %
0-4 4775 1493 26 3256 42 4817 22%
5-19 3242 1251 25 1966 46 3288 15%
20-44 4450 1563 87 2800 32 4482 21%
45-64 4367 1418 98 2851 43 4410 20%
65+ 4609 966 384 3259 122 4731 22%
Total 21443 6691 620 14132 285 21728 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 05, 1.5% 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 2019-05

Number of Sentinels Reporting in Week 05: 106

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
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%
1 2.8% 3.8% 1.8% 5.6%
2 1.8% 2.6% 1.3% 3.9%
3 1.2% 2.5% 1.4% 3.6%
4 1.5% 2.5% 1.6% 3.1%
5 1.5% 2.6% 1.9% 4.0%

Participatory Syndromic Surveillance

In week 05, 2,196 participants reported to FluWatchers, of which 66 (3.0%) reported symptoms of cough and fever (Figure 5).

Among the 66 participants who reported fever and cough:

  • 27% consulted a healthcare professional;
  • 83% reported days missed from work or school, resulting in a combined total of 190 missed days of work or school.
  • 68% reported having been vaccinated for influenza this season.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-05

Number of Participants Reporting in Week 05: 2,196

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%

Influenza Outbreak Surveillance

In week 05, 24 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (16), acute care facilities (3), and other settings (5). Ten new ILI outbreaks in long-term care facilities (1) and schools/daycares (9) were also reported in week 05.

To date this season, 322 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 193 (60%) outbreaks were in LTCF, 23 were in schools, 42 in acute care facilities, and 64 were in other settings.
  • Among the 301 outbreaks for which the influenza type was available 98% (296) were associated with influenza A.
  • Among the 140 outbreaks for which the influenza A subtype was available:
    • 74% (104) were associated with influenza A(H1N1)pdm09;
    • 26% (36) were associated with A(H3N2),

To date this season, 82 ILI outbreaks have been reported; 42 occurred in LTCF, 37 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 2019-05

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 10 4 2 0
52 4 24 5 0 0
1 5 39 11 0 0
2 8 35 7 0 0
3 3 23 10 0 0
4 6 12 8 1 0
5 3 16 5 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1,833 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 99.7% (1,828) 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 336 ICU admissions and 77 deaths have been reported.
    • 43% (145) of reported ICU admissions were in adults aged 45-64 years.
    • All but one of the 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 2019-05
Age Groups (years) Cumulative (August 26, 2018 to February 2, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 297 2 62.82
5-19 166 0 11.96
20-44 250 0 8.79
45-64 503 0 23.11
65+ 612 3 50.55
Total 1828 5  
% 99.7% 0.3%  
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 05, 56 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, 802 pediatric hospitalizations have been reported (Figure 8):

  • 69.5% of cases were in children under 5 years of age.
  • 99% (795) of cases have been associated with influenza A.
  • Among the 279 cases for which the influenza subtype was available, 270 (97%) were associated with A(H1N1)pdm09.

To date this season, 135 ICU admissions, and 10 deaths have been reported.

  • 63% (85) of ICU admissions were in children under 5 years of age.
  • All but one 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 2019-05

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 6 1 0 4
43 11 1 0 3
44 19 3 1 6
45 34 3 2 4
46 42 5 1 13
47 33 4 0 9
48 46 9 2 23
49 39 15 3 28
50 52 23 4 47
51 83 32 4 72
52 90 47 7 92
1 93 40 5 75
2 59 35 4 62
3 71 38 4 67
4 65 35 7 47
5 56 40 11 59

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 2019-05

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 84
6-23 mo 219
2-4 yr 254
5-9 yr 178
10-16 yr 67

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, 430 hospitalizations, 47 ICU admissions and 16 deaths have been reported (Figure 9):

  • 388 (90%) hospitalizations were associated with influenza A.
  • A similar proportion of hospitalizations are reported among adults <65 years of age (43.3%) and adults ≥65 years of age (56.7%).
  • Similar to other indicators this season, hospitalizations among adults peaked in week 01, but has been stable over the past three weeks.
  • Among hospitalized cases with available information (367), the most commonly reported comorbidity was endocrine disorders, which were reported in 88% of hospitalized cases. However, 84% of cases reported more than one type of comorbid condition.

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 2019-05

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 45
35-49 yr 49
50-64 yr 92
65-79 yr 124
80+ yr 120

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 972 influenza viruses (69 A(H3N2), 882 A(H1N1) and 21 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

42 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:

  • Seven viruses belonged to genetic group 3C.2a.
  • 34 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):

  • 23 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.
  • Four 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.
  • 17 influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Three viruses belonged to genetic group 3C.2a and five to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 861 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.
  • 21 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).

  • Four 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
  • 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:

322 influenza A (46 A(H3N2) and 276 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 322 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

664 influenza viruses (53 A(H3N2), 593 A(H1N1) and 18 B) were tested for resistance to oseltamivir and it was found that:

  • All 53 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 593 A(H1N1) viruses tested, 592 were sensitive to oseltamivir and one virus was resistant to oseltamivir with a H275Y mutation.
  • All 18 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

664 influenza viruses (53 A(H3N2), 593 H1N1 and 18 B) were tested for resistance to zanamivir and it was found that:

  • All 664 influenza viruses were sensitive to zanamivir.
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