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FluWatch report: January 21, 2018 to January 27, 2018 (week 4)

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Organization:

Public Health Agency of Canada

Date published:

2018-02-02

Flu (influenza)

Influenza surveillance

Overall, influenza activity in Canada remains at peak levels but there are signs that activity is starting to slow down in parts of the country.

The majority of influenza detections continue to be A(H3N2), although 40% of detections were influenza B in week 04.

To date this season, the majority of lab confirmations, hospitalizations and deaths have been among adults 65 years of age and older.

A

Canadian study

reported a mid-season estimate of influenza vaccine effectiveness of 42% overall. The study confirmed an anticipated low vaccine effectiveness of 17% against the A(H3N2) strain and moderate vaccine effectiveness against influenza B of 55%, which is circulating at high levels in Canada this season.

For more information on the flu, see our

Flu(influenza)

web page.

On this page

Influenza/ILI Activity (geographic spread)

Laboratory Confirmed Influenza Detections

Syndromic/Influenza-like Illness Surveillance

Influenza Outbreak Surveillance

Severe Outcomes Influenza Surveillance

Influenza Strain Characterizations

Antiviral Resistance

Provincial and International Influenza Reports

FluWatch Surveillance System Description and Definitions, 2017-18

Influenza/Influenza-like Illness Activity (geographic spread)

In week 04, a similar number of regions reported localized or widespread influenza activity compared to the previous week. Among the 53 regions reporting data for week 04, 6 regions (BC(1), ON(2), QC(3)) reported widespread activity, and 21 regions (BC(1), AB(1), MB(1), ON(5), QC(3), NB(4), NS(3), NL(2), and NT(1)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-04

Note:

Influenza/ILI activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates and reported outbreaks. Please refer to detailed definitions at the end of the report. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the

Weekly Influenza Reports

.

Figure 1 - Text Description

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-04

Influenza Surveillance Region

Activity Level

Newfoundland - Central

Sporadic

Newfoundland - Eastern

Localized

Grenfell Labrador

No Activity

Newfoundland - Western

Localized

Prince Edward Island

Localized

Nova Scotia - Central (Zone 4)

Localized

Nova Scotia - Western (Zone 1)

Localized

Nova Scotia - Northern (Zone 2)

Sporadic

Nova Scotia - Eastern (Zone 3)

Localized

New Brunswick - Public Health Region 1

Localized

New Brunswick - Public Health Region 2

Localized

New Brunswick - Public Health Region 3

Localized

New Brunswick - Public Health Region 4

Sporadic

New Brunswick - Public Health Region 5

Sporadic

New Brunswick - Public Health Region 6

Sporadic

New Brunswick - Public Health Region 7

Sporadic

Nord-est Québec

Localized

Québec et Chaudieres-Appalaches

Widespread

Centre-du-Québec

Widespread

Montréal et Laval

Localized

Ouest-du-Québec

Widespread

Montérégie

Localized

Ontario - Central East

Widespread

Ontario - Central West

Localized

Ontario - Eastern

Localized

Ontario - North East

Localized

Ontario - North West

Widespread

Ontario - South West

Localized

Ontario - Toronto

Localized

Manitoba - Interlake-Eastern

Sporadic

Manitoba - Northern Regional

Sporadic

Manitoba - Prairie Mountain

Sporadic

Manitoba - South

Sporadic

Manitoba - Winnipeg

Localized

Saskatchewan - North

Sporadic

Saskatchewan - Central

Sporadic

Saskatchewan - South

Sporadic

Alberta - North Zone

Sporadic

Alberta - Edmonton

Sporadic

Alberta - Central Zone

Sporadic

Alberta - Calgary

Localized

Alberta - South Zone

Sporadic

British Columbia - Interior

Sporadic

British Columbia - Fraser

Widespread

British Columbia - Vancouver Coastal

Localized

British Columbia - Vancouver Island

Sporadic

British Columbia - Northern

Sporadic

Yukon

Sporadic

Northwest Territories - North

No Activity

Northwest Territories - South

Localized

Nunavut - Baffin

No Activity

Nunavut - Kivalliq

Sporadic

Nunavut - Kitimeot

Sporadic

Laboratory-Confirmed Influenza Detections

In week 04, the overall percentage of tests positive for influenza remained similar to the previous week at 31%. Since week 02, the percentage of tests positive for influenza A has remained stable at 18%. This suggests that the peak for influenza A detections occurred in week 01 (19%). The percentage of tests positive for influenza B remained similar to the previous week.

The percentage of influenza A detections for week 04 is average for this time of year. The percentage of tests positive for influenza B in week 04 continue to be well above expected levels for this time of year. For data on other respiratory virus detections, see 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 2017-35 to 2018-04

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

Figure 2 - Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2017-35 to 2018-04

Report Week

A(Unsubtyped)

A(H3)

A(H1)pdm09

Influenza B

35

3

20

6

5

36

7

28

1

3

37

7

14

13

4

38

18

31

3

5

39

18

53

1

8

40

24

41

1

5

41

32

50

0

11

42

27

73

1

15

43

44

107

3

21

44

52

114

3

30

45

71

153

7

47

46

113

187

13

75

47

157

272

13

112

48

259

417

33

190

49

370

544

16

274

50

523

633

16

473

51

800

864

51

719

52

1105

856

33

1008

1

1836

925

60

1539

2

1987

808

49

1730

3

1727

869

79

1914

4

1636

570

52

1640

To date this season, 28,729 laboratory-confirmed influenza detections have been reported, of which 66% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 94% of subtyped influenza A detections. 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 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-04

Figure 3 - Text Description

Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-04

Reporting

provinces

Table Figure 3 - Footnote

1

Week (January 21, 2018 to January 27, 2018)

Cumulative (August 27, 2017 to January 27, 2018)

Influenza A

B

Influenza A

B

A & B

Total

A

Total

A

(H1)pdm09

A

(H3)

A(UnS)

Table Figure 3 - Footnote

3

B

Total

A

Total

A

(H1)pdm09

A

(H3)

A(UnS)

Table Figure 3 - Footnote

3

B

Total

BC

169

24

112

33

172

1570

221

958

391

1494

3064

AB

143

6

101

36

140

5004

88

3690

1226

1939

6943

SK

67

2

53

12

69

1300

36

914

350

473

1773

MB

78

0

11

67

25

975

7

327

641

102

1077

ON

428

16

223

189

352

2501

96

1423

982

1780

4281

QC

1241

0

0

1241

800

6540

0

0

6540

3705

10245

NB

0

0

0

0

0

549

0

84

465

125

674

NS

39

0

0

39

13

191

0

0

191

43

234

PE

6

1

5

0

4

53

3

50

0

70

123

NL

11

0

0

11

12

53

0

3

50

31

84

YT

15

1

8

6

2

33

2

19

12

37

70

NT

2

0

2

0

3

116

1

115

0

18

134

NU

3

0

3

0

0

25

0

25

0

2

27

Canada

2202

50

518

1634

1592

18910

454

7608

10848

9819

28729

Percentage

Table Figure 3 - Footnote

2

58%

2%

24%

74%

42%

66%

2%

40%

57%

34%

100%

Table Figure 3 - Footnote 1

Specimens from NT, YT, and NU 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.

To date this season, detailed information on age and type/subtype has been received for 25,244 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (50%), and among cases of influenza A(H3N2) (54%) and influenza B (46%). Adults aged 20-64 represent 33% of cases overall and 31% of influenza A(H3N2) and 36% of influenza B cases. Although much smaller in numbers (402), the majority of influenza A(H1N1) cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 53% and 33% of cases respectively.

Table 1 - Weekly and cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2017-35 to 2018-04

Age groups (years)

Cumulative (August 27, 2017 to January 27, 2018)

Influenza A

B

Influenza A and B

A Total

A(H1) pdm09

A(H3)

A (UnS)

Table 1 Footnote

1

Total

#

%

0-4

1461

72

505

884

496

1957

8%

5-19

1302

62

550

690

1038

2340

9%

20-44

2690

114

1093

1483

1175

3865

15%

45-64

2761

100

1156

1505

1813

4574

18%

65+

8715

54

3839

4822

3793

12508

50%

Total

16929

402

7143

9384

8315

25244

100%

Table 1 Footnote 1

UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available;

Return to table 1 footnote

1

referrer

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 04, 3% of visits to healthcare professionals were due to influenza-like illness (ILI); a slight increase compared to the previous week, and slightly above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-04

Number of Sentinels Reporting in Week 04: 140

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2017-18

Figure 4 - Text Description

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-04

Report week

2017-18

Average

Min

Max

35

0.4%

0.8%

0.5%

1.2%

36

0.5%

0.8%

0.7%

1.0%

37

0.7%

0.9%

0.7%

1.0%

38

0.7%

1.1%

1.0%

1.4%

39

1.1%

1.1%

0.9%

1.4%

40

1.3%

1.3%

0.9%

1.6%

41

1.7%

1.4%

0.9%

2.4%

42

1.2%

1.4%

1.0%

1.9%

43

1.6%

1.3%

1.0%

1.5%

44

1.5%

1.3%

0.9%

1.6%

45

1.8%

1.3%

1.2%

1.5%

46

1.7%

1.6%

1.0%

2.0%

47

2.2%

1.5%

1.1%

1.9%

48

2.7%

1.6%

0.8%

2.1%

49

1.7%

1.5%

1.0%

2.5%

50

2.2%

2.3%

1.3%

3.7%

51

2.6%

2.5%

1.6%

4.1%

52

4.0%

4.5%

1.7%

7.1%

1

4.7%

3.7%

1.7%

5.2%

2

3.2%

3.0%

1.1%

4.5%

3

3.0%

2.5%

1.3%

3.6%

4

3.3%

2.4%

1.7%

3.5%

Participatory Syndromic Surveillance

FluWatchers is a participatory ILI surveillance system that relies on weekly voluntary submissions of syndromic information from Canadians across Canada.

In week 04, 1,479 participants reported to FluWatchers, of which 4% reported symptoms of cough and fever, and 29% of these consulted a healthcare professional. Among participants who reported cough and fever, 73% reported days missed from work or school, resulting in a combined total of 123 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-04

Number of Participants Reporting

Percentage participants reporting Cough and Fever

Percentage of participants with cough and fever who consulted a healthcare professional

Percentage of participants with cough and fever who reported missed days from work or school

Number of missed days from work or school

1479

4%

29%

73%

123

Influenza Outbreak Surveillance

In week 04, the number of reported laboratory-confirmed outbreaks of influenza decreased compared to the previous week. In week 04, 97 new influenza outbreaks were reported: 60 in long-term care facilities, 13 in hospitals, and 24 in other settings. In addition, six ILI outbreaks were reported schools. Among the 87 outbreaks with influenza type/subtype reported, 39 (45%) were associated with influenza B, and 44 were associated with influenza A. Four outbreaks were associated with a mix of influenza A and B.

To date this season, 916 influenza/ILI outbreaks have been reported, of which 542 (59%) occurred in LTC facilities. Among the 794 outbreaks for which the influenza type/subtype was reported, 483 (61%) were associated with influenza A) and 276 (35%) were associated with influenza B, and 34 (4%) were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 04, the number of cumulative outbreaks reported this season has been greater than during the 2016-17 and 2012-13 seasons, and lower compared to the 2014-15 season.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-04

Figure 5 - Text Description

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-04

Report week

Hospitals

Long Term Care Facilities

Other

35

0

0

0

36

0

1

0

37

0

0

0

38

0

2

0

39

0

1

1

40

1

0

0

41

0

0

1

42

0

2

1

43

3

1

1

44

0

1

0

45

3

1

4

46

0

2

5

47

0

2

5

48

9

11

7

49

4

14

12

50

9

31

16

51

11

48

28

52

5

72

23

1

12

110

38

2

18

99

48

3

14

84

45

4

13

60

24

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 04, 130 influenza-associated hospitalizations were reported by participating provinces and territories1. To date this season, 3,018 influenza-associated hospitalizations have been reported, 79% of which were associated with influenza A, and 2,078 cases (69%) were in adults 65 years of age or older. To date, 271 ICU admissions and 120 deaths have been reported.

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories

figure 6 note

1

, weeks 2017-35 to 2018-04

Figure 6 - Text Description

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-04

Age Group

Total

0-4 yr

176

5-19 yr

113

20-44 yr

185

45-64 yr

466

65+ yr

2078

Figure 6 note 1

Influenza-associated hospitalizations are reported by NL, PE, NS, NB, MB, AB, YT and NT. Only hospitalizations that require intensive medical care are reported by SK.

Return to figure 6 note

1

referrer

Pediatric Influenza Hospitalizations and Deaths

In week 04, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network increased compared to the previous week. In week 04, 88 hospitaliations were reported of which influenza A and B made up almost equal proportion of cases. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 446 pediatric hospitalizations have been reported by the IMPACT network, 299 (67%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A cases (40%) and the smallest propotion of influenza B cases (22%). Among the 147 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (29%).

Additionally, 71 ICU admissions and five deaths have been reported to date. Seventy percent of ICU cases were due to influenza A. Children aged 0-23 months and 10-16 years each accounted for 31% of ICU cases.

Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-04

Figure 7 - Text Description

Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-04

Age Group

Total

0-5 mo

52

6-23 mo

101

2-4 yr

118

5-9 yr

97

10-16 yr

78

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-04

Figure 8 - Text Description

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-04

Report Week

2017-2018

Average

Min

Max

35

0

0

0

0

36

1

0

0

1

37

0

0

0

2

38

1

0

0

2

39

2

1

0

3

40

0

0

0

2

41

3

1

0

2

42

1

1

0

4

43

7

1

0

3

44

1

3

1

6

45

4

3

2

4

46

8

5

1

13

47

13

4

0

9

48

16

9

2

23

49

23

15

3

28

50

26

23

4

47

51

39

32

4

72

52

60

47

7

92

1

56

40

5

75

2

39

35

4

62

3

49

38

4

67

4

88

35

7

47

Figure 8 Footnote 1

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

Return to figure 8 note

1

referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 874 influenza viruses [467 A(H3N2), 51 A(H1N1)pdm09 and 356 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition assay during the

2017-18 season,

most viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.

Table 3 - Influenza antigenic strain characterizations, Canada, weeks 2017-35 to 2018-04

Strain Characterization Results

Count

Description

Influenza A (H3N2)

A/Hong Kong/4801/2014-like

118

Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's

trivalent

and

quadrivalent

vaccine.

Reduced titer to A/Hong Kong/4801/2014

4

These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences.

Influenza A (H1N1)

A/Michigan/45/2015-like

51

Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1) component of the 2017-18 Northern Hemisphere's

trivalent

and

quadrivalent

influenza vaccine.

Influenza B

B/Brisbane/60/2008-like

(Victoria lineage)

5

Viruses antigenically similar to B/Brisbane/60/2008.

B/Brisbane/60/2008 is the influenza B component of the 2017-18 Northern Hemisphere's

trivalent

and

quadrivalent

influenza vaccine.

Reduced titer to B/Brisbane/60/2008

(Victoria lineage)

10

These B/Victoria lineage viruses reacted poorly with antisera raised against cell-propagated B/Brisbane/60/2008, suggesting some antigenic differences.

B/Phuket/3073/2013-like

(Yamagata lineage)

341

Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2017-18 Northern Hemisphere

quadrivalent

influenza vaccine.

Genetic Characterization of A(H3N2) viruses

During the 2017-18 season, 349 A(H3N2) viruses did not grow to sufficient titers for antigenic characterization by HI assay. Therefore, genetic characterization was performed to determine to which genetic group they belong. Sequence analysis showed that 295 A(H3N2) viruses belonged to genetic group 3C.2a, 53 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.

Additionally, of the 118 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 75 belonged to genetic group 3C.2a and 12 viruses belonged to subclade 3C.2a1. The four viruses that showed reduced titer belonged to genetic clade 3C.3a. Sequencing is pending for the remaining 27 virus isolates.

A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A/H3N2 component of the 2017-18 Northern Hemisphere influenza vaccine.

Genetic Characterization of Influenza B viruses

Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that all 10 viruses had a two amino acid deletion in the HA gene.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 589 influenza viruses for resistance to oseltamivir and 586 viruses for resistance to zanamivir. All but one of the A(H1N1) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-04

Virus type and subtype

Oseltamivir

Zanamivir

# tested

# resistant (%)

# tested

# resistant (%)

A (H3N2)

324

0 (0%)

321

0 (0%)

A (H1N1)

42

1 (2.4%)

42

0 (0%)

B

223

0 (0%)

223

0 (0%)

TOTAL

589

1 (0.2%)

586

0 (0%)

Note: Since the 2009 pandemic, all circulating influenza A viruses have been resistant to amantadine, and it is therefore not currently recommended for use in the treatment of influenza. During the 2017-18 season, the subset of influenza A viruses that were tested for resistance to amantadine were resistant.

Provincial and International Influenza Reports

Provincial Influenza Reports

Alberta - Influenza Surveillance Report

British Columbia - Influenza Surveillance

Manitoba - Seasonal Influenza Reports

New Brunswick - Influenza Surveillance Reports

Newfoundland and Labrador - Surveillance and Disease Reports

Nova Scotia - Respiratory Watch Report

Ontario - Respiratory Pathogen Bulletin

Prince Edward Island - Influenza Summary

Saskatchewan - Influenza Reports

Québec - Flash Grippe

International Influenza Reports

Australia - Influenza Surveillance Report

European Centre for Disease Prevention and Control - Surveillance reports and disease data on seasonal influenza

New Zealand - Influenza Weekly Update

Public Health England - Weekly national flu reports

Pan-American Health Organization - Influenza Situation Report

United States Centres for Disease Control and Prevention - Weekly Influenza Surveillance Report

World Health Organization - Influenza update

World Health Organization - FluNet

FluWatch Surveillance System Description and Definitions, 2017-18

The FluWatch report is compiled from a number of data sources. Surveillance information contained in this report is a reflection of the surveillance data available to FluWatch at the time of production. Delays in reporting of data may cause data to change retrospectively. For a description of FluWatch surveillance components and definitions, see

System Description and Definitions

.

Abbreviations:

Newfoundland/Labrador (NL), Prince Edward Island (PE), New Brunswick (NB), Nova Scotia (NS), Quebec (QC), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB), British Columbia (BC), Yukon (YT), Northwest Territories (NT), Nunavut (NU).

We would like to thank all the FluWatch surveillance partners who are participating in this year's influenza surveillance program.

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2018-02-02