FluWatch report: January 7, 2018 to January 13, 2018 (week 2)

Overall Summary
  • Overall, influenza activity in Canada remains high.
  • Most indicators have slowed their increase, remained similar, or declined compared to the previous week, suggesting that we may be nearing the peak of the season at the national level.
  • Most indicators remain in the higher range of expected levels for this time of year.
  • The majority of influenza detections continue to be A(H3N2), although 37% of detections were influenza B in week 02.
  • Influenza B began 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 02, a similar number of regions reported localized or widespread influenza activity compared to the previous week. Among the 48 regions reporting data for week 02, nine regions (BC(2), ON(5), and QC(2)) reported widespread activity, and 24 regions (BC(1), AB(5), SK(2), ON(2), QC(4), NB(5), NS(1), NL(2), PE(1) and NT(1)) reported localized activity.

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Public Health Agency of Canada

Date published: 2018-01-19

Related Topics

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-02

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 2018-02
Influenza Surveillance Region Activity Level
Newfoundland - Central  No Activity
Newfoundland - Eastern  Localized
Grenfell Labrador No Activity
Newfoundland - Western  Localized
Prince Edward Island Localized
Nova Scotia - Central (Zone 4) Sporadic
Nova Scotia - Western (Zone 1) Sporadic
Nova Scotia - Northern (Zone 2) No Activity
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 Localized
Montérégie  Localized
Ontario - Central East Widespread
Ontario - Central West Widespread
Ontario - Eastern Localized
Ontario - North East Widespread
Ontario - North West  Widespread
Ontario - South West  Widespread
Ontario - Toronto Localized
Manitoba - Interlake-Eastern  No Data
Manitoba - Northern Regional No Data
Manitoba - Prairie Mountain No Data
Manitoba - South No Data
Manitoba - Winnipeg No Data
Saskatchewan - North  Sporadic
Saskatchewan - Central Localized
Saskatchewan - South Localized
Alberta - North Zone Localized
Alberta - Edmonton Localized
Alberta - Central Zone  Localized
Alberta - Calgary Localized
Alberta - South Zone  Localized
British Columbia - Interior Widespread
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Localized
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Localized
Nunavut - Baffin Sporadic
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 02, 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. The increase in the number of influenza B detections slowed slightly, increasing 11% compared to the previous week, to1,713 in week 02. Influenza B detections to date are higher than has been observed over the past seven seasons.

The proportion of tests positive for influenza increased slightly from 29% in week 01 to 30% in week 02. The proportion of influenza detections that are influenza B has been increasing since week 43. In week 02, 63% of detections were influenza A and 37% influenza B.

The number (2,952) and percentage (19.0%) of influenza A detections for week 02 are within the range of expected levels for this time of year. The number (1,713) and percentage of tests (11.0%) positive for influenza B in week 02 continue to be well above expected levels for this time of year. 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 average over the same period during the past seven seasons. However, the percentage of tests positive for influenza B at week 02 is within the range of levels usually observed in March-April. 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 2018-02

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 2018-02
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 1839 928 60 1538
2 2163 745 44 1713

To date this season, 20,349 laboratory-confirmed influenza detections have been reported, of which 69% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 95% 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 2018-02

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 2018-02
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 7, 2018 to January 13, 2018) Cumulative (August 27, 2017 to January 13, 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 343 29 145 169 312 1113 143 577 393 992 2105
AB 191 4 148 39 109 4617 77 3411 1129 1597 6214
SK 98 6 73 19 41 1032 28 704 300 276 1308
MB 237 0 40 197 27 756 6 293 457 58 814
ON 462 4 222 236 403 1632 63 899 670 1023 2655
QC 1261 0 0 1261 738 4180 0 0 4180 2129 6309
NB 154 0 23 131 20 464 0 84 380 57 521
NS 50 0 0 50 7 112 0 0 112 17 129
PE 2 0 2 0 15 42 2 40 0 39 81
NL 17 0 0 17 7 33 0 3 30 17 50
YT 6 0 2 4 0 12 0 8 4 33 45
NT 4 0 4 0 1 95 0 95 0 7 102
NU 1 0 1 0 0 15 0 15 0 1 16
Canada 2826 43 660 2123 1680 14103 319 6129 7655 6246 20349
PercentageTable Figure 3 - Footnote 2 63% 2% 23% 75% 37% 69% 2% 43% 54% 31% 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 17,495 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 49% 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 53% of cases, compared to 43% and 58% 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 (45%), followed by adults 45-64 years of age (23%).

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 2018-02
Age groups (years) Cumulative (August 27, 2017 to January 13, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 1005 59 429 517 291 1296 7%
5-19 953 45 461 447 654 1607 9%
20-44 1983 83 890 1010 784 2767 16%
45-64 2074 66 937 1071 1187 3261 19%
65+ 6214 35 3048 3131 2350 8564 49%
Total 12229 288 5765 6176 5266 17495 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 02, 3.2% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease 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 2018-02

Number of Sentinels Reporting in Week 02: 144

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 2018-02
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%

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 02, 1,443 participants reported to FluWatchers, of which 4% reported symptoms of cough and fever, and 20% of these consulted a healthcare professional. Among participants who reported cough and fever, 74% reported days missed from work or school, resulting in a combined total of 135 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-02
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
1443 4% 20% 74% 135

Influenza Outbreak Surveillance

In week 02, the number of reported laboratory-confirmed outbreaks of influenza increased slightly compared to the previous week. In week 02, 163 new influenza outbreaks were reported: 97 in long-term care facilities, 18 in hospitals, and 48 in other settings. In addition, one ILI outbreak was reported in a school. Among the 149 outbreaks with influenza type/subtype reported, 71 (48%) were associated with influenza B, and 73 were associated with influenza A, of which 17 were influenza A(H3N2) and 56 influenza A(unsubtyped). Five outbreaks were associated with a mix of influenza A and B.

To date this season, 663 influenza/ILI outbreaks have been reported, of which 392 (59%) occurred in LTC facilities. Among the 566 outbreaks for which the influenza type/subtype was reported, 364 were associated with influenza A (of which 175 were A(H3N2), 188 were A(unsubtyped) and one was A(H1N1)pdm09), 179 were associated with influenza B, and 23 were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 02, 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 2018-02

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-02
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 69 23
1 12 109 38
2 18 97 48

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 02, 133 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1, a similar number compared to the previous week. 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, 2,168 influenza-associated hospitalizations have been reported, 81% of which were associated with influenza A, and 1,480 cases (68%) were in adults 65 years of age or older. To date, 202 ICU admissions and 82 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 2018-02

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 2018-02
Age Group Total
0-4 yr 134
5-19 yr 72
20-44 yr 133
45-64 yr 349
65+ yr 1480
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 02, 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 02, 40 hospitaliations were reported, of which 25 (63%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45, but following seasonal patterns.

To date this season, 303 pediatric hospitalizations have been reported by the IMPACT network, 209 (69%) of which were associated with influenza A. Forty-eight ICU admissions and fewer than five deaths have been reported. Compared to the cumulative number of pediatric hospitalizations reported up to week 02 during recent influenza A(H3N2)-dominant seasons, the cumulative number of pediatric 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 2018-02

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 2018-02
Age Group Total
0-5 mo 38
6-23 mo 75
2-4 yr 81
5-9 yr 58
10-16 yr 51

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-02

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 2018-02
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 61 47 7 92
1 55 40 5 75
2 40 35 4 62
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 482 influenza viruses [299 A(H3N2), 34 A(H1N1)pdm09 and 149 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 2018-02
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 72 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 1 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 34 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)
6 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)
142 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, 227 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 185 A(H3N2) viruses belonged to genetic group 3C.2a, 41 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.

Additionally, of the 72 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 57 belonged to genetic group 3C.2a and 10 viruses belonged to subclade 3C.2a1. The virus that showed reduced titer belonged to genetic clade 3C.3a. Sequencing is pending for the remaining 5 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 six 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 423 influenza viruses for resistance to oseltamivir and 424 viruses for resistance to 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 2018-02
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 255 0 (0%) 255 0 (0%)
A (H1N1) 32 0 (0%) 33 0 (0%)
B 136 0 (0%) 136 0 (0%)
TOTAL 423 0 (0%) 424 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.

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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