FluWatch report: March 11 to March 17, 2018 (week 11)

thumbnail

Download the alternative format
(PDF format, 546 KB, 10 pages)

Organization:

Public Health Agency of Canada

Date published: 2018-03-23

Related Topics
Overall Summary
  • All indicators of influenza activity have either decreased or remained similar to the previous week.
  • The influenza season peaked in mid-February, but influenza activity remains elevated in many parts of the country.
  • Detections of influenza B continue to be greater than those of influenza A.
  • To date this season, the majority of laboratory-confirmed cases, hospitalizations and deaths with influenza have been among adults 65 years of age and older.
  • For more information on the flu, see our Flu(influenza) web page.

On this page

Influenza/Influenza-like Illness Activity (geographic spread)

In week 11, two regions in QC reported widespread activity, and 24 regions (BC(2), AB(1), SK(1), MB(1), ON(7), QC(4), NB(3), NS(2), and NL(3)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-11

Figure 1

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 2018-11
Influenza Surveillance Region Activity Level
Newfoundland - Central Localized
Newfoundland - Eastern Localized
Grenfell Labrador Sporadic
Newfoundland - Western Localized
Prince Edward Island Sporadic
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Sporadic
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 No Activity
New Brunswick - Public Health Region 6 Sporadic
New Brunswick - Public Health Region 7 Sporadic
Nord-est Québec Localized
Québec et Chaudieres-Appalaches Localized
Centre-du-Québec Widespread
Montréal et Laval Localized
Ouest-du-Québec Widespread
Montérégie Localized
Ontario - Central East Localized
Ontario - Central West Localized
Ontario - Eastern Localized
Ontario - North East Localized
Ontario - North West Localized
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 Localized
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone Sporadic
Alberta - Calgary Sporadic
Alberta - South Zone Sporadic
British Columbia - Interior Localized
British Columbia - Fraser Localized
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Sporadic
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Sporadic
Nunavut - Baffin Sporadic
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 11, the overall percentage of tests positive for influenza was 24%, a decrease from the previous week. The overall percentage of tests positive for influenza has been slowly decreasing from the peak in week 07. Detections of influenza B continue to be greater than those of influenza A. Influenza B accounted for 55% of influenza detections in week 11.

The percentage of influenza A detections for week 11 are around the average for this time of year. The percentage of tests positive for influenza B in week 11 continues 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 2018-11

Figure 2

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 2018-11
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 1649 870 80 1912
4 1675 632 57 1802
5 1664 542 54 2125
6 1819 506 49 2383
7 1754 405 63 2443
8 1642 279 51 2354
9 1437 325 51 2057
10 1024 264 80 1713
11 786 242 69 1353

To date this season, 56,284 laboratory-confirmed influenza detections have been reported, of which 57% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 92% 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 2018-11

Figure 3
Figure 3 - Text Description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-11
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 11, 2018 to March 17, 2018) Cumulative (August 27, 2017 to March 17, 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 70 34 26 10 157 2139 411 1335 393 2653 4792
AB 45 13 17 15 90 5500 166 3954 1380 2978 8478
SK 27 0 8 19 80 1625 43 1109 473 1174 2799
MB 7 0 0 7 60 1113 7 369 737 456 1569
ON 272 19 172 81 175 5284 217 2954 2113 4179 9463
QC 538 0 0 538 567 14165 0 0 14165 11225 25390
NB 70 0 0 70 128 1192 11 202 979 833 2025
NS 29 0 0 29 37 415 0 0 415 209 624
PE 15 2 13 0 9 102 5 97 0 144 246
NL 26 0 0 26 30 282 0 3 279 295 577
YT 2 0 2 0 1 67 7 42 18 42 109
NT 0 0 0 0 3 129 4 125 0 38 167
NU 0 0 0 0 0 42 6 36 0 3 45
Canada 1101 68 238 795 1337 32055 877 10226 20952 24229 56284
PercentageTable Figure 3 - Footnote 2 45% 6% 22% 72% 55% 57% 3% 32% 65% 43% 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 46,154 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (49%), and among cases of influenza A(H3N2) (58%) and influenza B (47%). Adults aged 20-64 represent 32% of cases overall and 29% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (720), 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 32% of cases respectively.

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2017-35 to 2018-11
Age groups (years) Cumulative (August 27, 2017 to March 17, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2854 126 530 2198 1327 4181 9%
5-19 2139 106 520 1513 2358 4497 10%
20-44 3889 203 1126 2560 2472 6361 14%
45-64 4234 180 1345 2709 4118 8352 18%
65+ 13524 105 4898 8521 9239 22763 49%
Total 26640 720 8419 17501 19514 46154 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 11, 1.4% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease from the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-11

Number of Sentinels Reporting in Week 11: 167

Figure 4

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2016-17

Figure 4 - Text Description
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-11
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 2.8% 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 4.4% 3.7% 1.7% 5.2%
2 2.8% 3.0% 1.1% 4.5%
3 2.9% 2.5% 1.3% 3.6%
4 3.1% 2.4% 1.7% 3.5%
5 4.0% 2.7% 2.0% 4.4%
6 3.5% 2.7% 2.1% 3.3%
7 3.4% 2.4% 1.7% 3.0%
8 3.0% 2.3% 1.9% 2.7%
9 2.8% 2.2% 1.8% 2.7%
10 1.7% 2.1% 1.8% 2.7%
11 1.4% 2.1% 1.7% 2.7%

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 11, 1,394 participants reported to FluWatchers, of which 2% reported symptoms of cough and fever, and 42% of these consulted a healthcare professional. Among participants who reported cough and fever, 69% reported days missed from work or school, resulting in a combined total of 57 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-11
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
1394 2% 42% 69% 57

Influenza Outbreak Surveillance

In week 11, 57 laboratory-confirmed outbreaks of influenza were reported, a decrease compared to the previous week. Among the reported influenza outbreaks, 43 were reported in long-term care facilities (LTC), 2 in hospitals, and 12 in other settings. Among the 53 outbreaks with influenza type/subtype reported, 26 (49%) were associated with influenza A, 26 (49%) were associated with influenza B and one outbreak was associated with a mix of influenza A and B (2%).

To date this season, 1,570 influenza/ILI outbreaks have been reported, of which 965 (61%) occurred in LTC facilities. Among the 1,352 outbreaks for which the influenza type/subtype was reported, 736 (54%) were associated with influenza A and 551 (41%) were associated with influenza B, and 65 (5%) were associated with a mix of A and B.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-11

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-11
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 65 24
5 9 55 19
6 10 77 31
7 11 58 28
8 8 60 22
9 8 83 16
10 12 42 10
11 2 43 12

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,220 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. Among the hospitalizations, 2,986 (71%) were associated with influenza A, and 2,883 cases (67%) were in adults 65 years of age or older.

Additionally, 412 ICU admissions and 207 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (43%), followed closely by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (84%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-11

Figure 6
Figure 6 - Text Description
Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-11
Age Group Total
0-4 yr 250
5-19 yr 180
20-44 yr 256
45-64 yr 701
65+ yr 2833
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 11, 57 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 57% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07. The number of weekly hospitalizations has been above the seven-season average for the majority of the season.

To date this season, 936 pediatric hospitalizations have been reported by the IMPACT network, 582 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (39%). Among the 354 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (30%).

Additionally, 149 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (30%), followed by children aged 10-16 years (26%). Among the ICU cases with available information, 62% were due to influenza A and approximately 43% had no reported previous or concurrent medical conditions. All reported deaths were among children over the age of two.

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 2018-11

Figure 7
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 2018-11
Age Group Total
0-5 mo 100
6-23 mo 216
2-4 yr 243
5-9 yr 217
10-16 yr 160

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-11

Figure 8
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 2018-11
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 7 5 1 13
47 13 4 0 9
48 17 9 2 23
49 23 15 3 28
50 25 23 4 47
51 39 32 4 72
52 62 47 7 92
1 57 40 5 75
2 38 35 4 62
3 52 38 4 67
4 93 35 7 47
5 71 40 11 59
6 74 38 15 79
7 89 40 17 120
8 72 47 25 139
9 67 50 13 153
10 58 48 17 135
11 58 41 18 118
Figure 8 Footnote 1

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-17

Return to figure 8 note 1 referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 2,514 influenza viruses [1,190 A(H3N2), 164 A(H1N1)pdm09 and 1,160 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition (HI) 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 2018-11
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 243 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 53 These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences
Influenza A (H1N1)pdm09
A/Michigan/45/2015-like 164 Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1)pdm09 component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.
Influenza B
B/Brisbane/60/2008-like (Victoria lineage) 10 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)
40 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)
1,110 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, 894 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 799 A(H3N2) viruses belonged to genetic group 3C.2a, 93 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 296 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 210 belonged to genetic group 3C.2a and 22 viruses belonged to subclade 3C.2a1. The 53 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the 11 remaining 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 37 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the three remaining virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,041 influenza viruses for resistance to oseltamivir and 1,037 viruses for resistance to zanamivir. All but one of the A(H1N1)pdm viruses were sensitive to oseltamivir and all but one influenza B viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-11
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 463 0 (0%) 459 0 (0%)
A (H1N1) 131 1 (0.8%) 131 0 (0%)
B 447 0 (0%) 447 1 (0.2%)
TOTAL 1041 1 (0.1%) 1037 1 (0.1%)

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.

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.

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: