FluWatch report: December 31, 2017 to January 6, 2018 (week 1)

Overall Summary
  • Overall, influenza activity in Canada is high and continues to increase. Most indicators of influenza activity increased in week 01, and are in the higher range of expected levels for this time of year.
  • The majority of influenza detections continue to be A(H3N2), although the proportion of detections that are influenza B has been increasing steadily
  • Influenza B is circulating much earlier than usual this season. The number of influenza B detections remains substantially greater this season compared to previous years.
  • To date this season, the majority of lab confirmations, hospitalizations and deaths have been among adults 65 years of age and older.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 01, an increasing number of regions reported localized or widespread influenza activity; nine regions (BC(2), ON(3), QC(3) and PE(1)) reported widespread activity, and 27 regions (BC(2), AB(4), SK(1), MB (4), ON(4), QC(3), NB(5), NS(3) and NT(1)) reported localized activity. 

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Public Health Agency of Canada

Date published: 2018-01-12

Related Topics

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-01

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 2018-01
Influenza Surveillance Region Activity Level
Newfoundland - Central  Sporadic
Newfoundland - Eastern  Sporadic
Grenfell Labrador Sporadic
Newfoundland - Western  No Activity
Prince Edward Island Widespread
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 Localized
New Brunswick - Public Health Region 7 Localized
Nord-est Québec Localized
Québec et Chaudieres-Appalaches Localized
Centre-du-Québec Widespread
Montréal et Laval Widespread
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  Widespread
Ontario - Toronto Localized
Manitoba - Interlake-Eastern  Localized
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Localized
Manitoba - South Localized
Manitoba - Winnipeg Localized
Saskatchewan - North  Sporadic
Saskatchewan - Central Localized
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone  Localized
Alberta - Calgary Localized
Alberta - South Zone  Localized
British Columbia - Interior Sporadic
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Widespread
British Columbia - Vancouver Island Localized
British Columbia - Northern Localized
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Localized
Nunavut - Baffin No Activity
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 01, both influenza A and B detections continued to increase although the rate of increase in influenza A detections was smaller compared to influenza B. The slowing of influenza A detections may indicate that we are approaching the peak of the season for influenza A, at the national level. However, the number of influenza B detections increased 52% compared to the previous week to1,529 in week 01, which is the highest weekly value observed over the past seven seasons.

The proportion of tests positive for influenza increased slightly from 28% in week 52 to 30% in week 01. The proportion of influenza detections that are influenza B has been increasing steadily since week 42. In week 01, 64% of detections were influenza A and 36% influenza B.

The number (2,732) and percentage (19.3%) of influenza A detections for week 01 are within the range of expected levels for this time of year. The number (1,529) and percentage of tests (10.8%) positive for influenza B in week 01 continue to be well above expected levels. Influenza B is circulating much earlier than usual this season. Twenty times the number of influenza B detections have been reported this season compared to the same period during the past seven seasons. 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 2018-01

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 2018-01
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 1130 828 33 1008
1 1731 857 144 1529

To date this season, 15,572 laboratory-confirmed influenza detections have been reported, of which 71% 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 2018-01

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 2018-01
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 17, 2017 to January 6, 2018) Cumulative (August 27, 2017 to January 6, 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 198 31 114 53 218 747 114 432 201 645 1392
AB 441 11 329 101 223 4388 71 3236 1081 1457 5845
SK 109 1 60 48 58 823 20 537 266 206 1029
MB 186 0 31 155 13 521 6 216 299 31 552
ON 344 8 206 130 222 1109 58 649 402 586 1695
QC 1,190 0 0 1,190 617 2919 0 0 2919 1391 4310
NB 80 80 0 0 15 310 80 61 169 37 347
NS 23 0 0 23 8 62 0 0 62 10 72
PE 11 2 9 0 13 40 2 38 0 24 64
NL 12 7 0 5 96 21 7 3 11 101 122
YT 1 0 1 0 4 6 0 6 0 33 39
NT 10 0 10 0 3 84 0 84 0 6 90
NU 1 0 1 0 0 14 0 14 0 1 15
Canada 2606 140 761 1705 1490 11044 358 5276 5410 4528 15572
PercentageTable Figure 3 - Footnote 2 64% 5% 29% 65% 36% 71% 3% 48% 49% 29% 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 14,038 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 47% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults 65 years of age and older represented  52% of cases, compared to 41% and 56% of cases reported in the same period in the 2016-17 and 2014-15 season, respectively. Cases of influenza B this season were distributed more evenly across all age-groups, but the largest proportion of cases was still among adults 65 years of age and older (41%), followed by adults 45-64 years of age (23%).

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 2018-01
Age groups (years) Cumulative (August 27, 2017 to January 6, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 842 48 389 405 211 1053 8%
5-19 868 42 429 397 563 1431 10%
20-44 1710 70 809 831 631 2341 17%
45-64 1719 56 826 837 897 2616 19%
65+ 5001 28 2642 2331 1596 6597 47%
Total 10140 244 5095 4801 3898 14038 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 01, 4.7% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase compared to the previous week, and above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-01

Number of Sentinels Reporting in Week 1: 116

Figure 4

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 2018-01
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 4.7% 3.7% 1.7% 5.2%

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 01, 1,406 participants reported to FluWatchers, of which 5% reported symptoms of cough and fever, and 22% of these consulted a healthcare professional. Among participants who reported cough and fever, 84% reported days missed from work or school, resulting in a combined total of 186 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-01
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
1406 5% 22% 84% 186

Influenza Outbreak Surveillance

In week 01, the number of reported laboratory-confirmed outbreaks of influenza increased compared to the previous week. In week 01, 148 new influenza outbreaks were reported: 98 in long-term care facilities, 12 in hospitals, and 38 in other settings. Among the 120 outbreaks with influenza type/subtype reported, 44 (37%) were associated with influenza B, and 73 were associated with influenza A, of which 20 were influenza A(H3N2) and 53 influenza A(unsubtyped). Three outbreaks were associated with a mix of influenza A and B.

To date this season, 486 influenza/ILI outbreaks have been reported, of which 282 (58%) occurred in LTC facilities. Among the 403 outbreaks for which the influenza type/subtype was reported, 286 were associated with influenza A (of which 153 were A(H3N2), 132 were A(unsubtyped) and one was A(H1N1)pdm09), 101 were associated with influenza B, and 16 were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 01, 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 2018-01

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-01
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 67 23
1 12 98 38

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 01, 128 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. In keeping with the early influenza activity this season, the number of hospitalizations is considerably elevated relative to the same period in the previous two seasons.

To date this season, 1,850 influenza-associated hospitalizations have been reported, 83% of which were associated with influenza A, and 1,254 cases (68%) were in adults 65 years of age or older. To date, 162 ICU admissions and 54 deaths have been reported.

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-01

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 2018-01
Age Group Total
0-4 yr 119
5-19 yr 66
20-44 yr 109
45-64 yr 302
65+ yr 1254
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 01, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network decreased compared to the previous week. In week 01, 46 hospitaliations were reported, of which 25 (54%) were due to influenza A. The proportion of cases associated with influenza B has been increasing over the past three weeks. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 253 pediatric hospitalizations have been reported by the IMPACT network, 177 (70%) of which were associated with influenza A. Forty-one ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 01, the cumulative number of hospitalizations reported this season has been greater than the 2016-17 season, but below the 2014-15 and 2012-13 seasons.

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 2018-01

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 2018-01
Age Group Total
0-5 mo 29
6-23 mo 63
2-4 yr 64
5-9 yr 52
10-16 yr 47

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-01

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 2018-01
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 12 4 0 9
48 18 9 2 23
49 24 15 3 28
50 26 23 4 47
51 39 32 4 72
52 59 47 7 92
1 46 40 5 75
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 351 influenza viruses [229 A(H3N2), 26 A(H1N1)pdm09 and 96 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 2018-01
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 54 Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent vaccine.
Influenza A (H1N1)
A/Michigan/45/2015-like 26 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)
1 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)
5 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)
90 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, 175 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 143 A(H3N2) viruses belonged to genetic group 3C.2a, 31 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.

Additionally, of the 54 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 45 belonged to genetic group 3C.2a and eight viruses belonged to subclade 3C.2a1. Sequencing is pending for the remaining one virus.

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 five viruses had a two amino acids deletion in the HA gene.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 353 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to these neuraminidase inhibitors (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-01
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 230 0 (0%) 230 0 (0%)
A (H1N1) 27 0 (0%) 27 0 (0%)
B 96 0 (0%) 96 0 (0%)
TOTAL 353 0 (0%) 353 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.

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