FluWatch report: January 24, 2016 - January 30, 2016 (week 04)

Overall Summary

  • Overall in week 04, seasonal influenza activity increased from the previous week. Laboratory detections remain lower than average but are now within expected levels for this time of the year.
  • An increase in the number of outbreaks was reported in week 04 with the majority due to influenza A.
  • Influenza A(H1N1) is the most common influenza subtype circulating in Canada.
  • Influenza strains characterized by the National Microbiology Laboratory this season appear to be a good match to the World Health Organization’s recommended vaccine strains.
  • For more information on the flu, see our Flu(influenza) web page.

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Organization: Public Health Agency of Canada

Date published: 2016-02-05

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 04, influenza/ILI activity continued to increase in Canada. A total of 17 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 12 regions in Canada (one in YK, two in BC, three in AB, two in MB, three in ON and one in NS).

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 04

Figure 1
Figure 1 Legend

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

In week 04, influenza/ILI activity continued to increase in Canada. A total of 17 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 12 regions in Canada (one in YK, two in BC, three in AB, two in MB, three in ON and one in NS).

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections continued to increase. The percent positive for influenza increased from 12.1% in week 03 to 16.0% in week 04 (Figure 2). Compared to the previous five seasons, the percent positive (16.0%) reported in week 04 was below the five year average for that week but within expected levels (range 12.4%-26.4%).

Figure 2. Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2015-16

Figure 2
Figure 2 - Text Description

The percent positive for influenza increased from 12.1% in week 03 to 16.0% in week 04.

In week 04, there were 895 positive influenza tests reported. Influenza A(H1N1) was the most common subtype detected. The majority of influenza detections were reported from Western Canada, where BC and AB accounted for 58% of influenza detections in Canada in week 04. To date, 79% of influenza detections have been influenza A and among those subtyped, the majority have been influenza A(H1N1) [71% (1202/1704)].

Figure 3. Cumulative numbers of positive influenza specimens by type/subtype and province, Canada, 2015-16

Figure 3

Note: Specimens from NT, YT, and NU are sent to reference laboratories in other provinces. Cumulative data includes updates to previous weeks.

Figure 3 - Text Description
Reporting
provincesTable Figure 3 - Footnote 1
Weekly (January 24 to January 30, 2016) Cumulative (August 30, 2015 to January 30, 2016)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1)pdm09
A
(H3)
A Table Figure 3 - Footnote UnS B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
BC 85 32 21 32 102 520 97 213 210 356 876
AB 280 220 1 64 50 842 676 95 71 160 1002
SK 45 32 5 8 3 114 80 10 24 14 128
MB 4 0 1 3 2 23 7 11 5 5 28
ON 157 87 24 46 23 598 297 154 147 70 668
QC 99 9 0 90 23 305 14 0 291 47 352
NB 3 0 0 3 0 16 1 0 15 2 18
NS 2 0 0 2 0 14 0 1 13 0 14
PE 8 8 0 0 0 21 21 0 0 0 21
NL 0 0 0 0 0 8 4 2 2 3 11
YT 1 0 0 1 3 5 0 4 1 6 11
NT 4 4 0 0 1 17 5 12 0 1 18
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 688 392 52 249 207 2483 1202 502 779 664 3147
Percentage Table Figure 3 - Footnote 2 76.9% 57.0% 7.6% 36.2% 23.1% 78.9% 48.4% 20.2% 31.4% 21.1% 100.0%

To date this season, detailed information on age and type/subtype has been received for 2,056 cases. Adults aged 20-44 years and older accounted for the greatest proportion of influenza cases (Table 1). Adults aged 20-44 and 45-64 years accounted for 51% of reported influenza A(H1N1) cases. Adults aged 65 years and older represented 44% of all reported A(H3N2) cases.

Table 1. Weekly and cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reportingTable 1 - Footnote 1, Canada, 2015-16
Age groups (years) Weekly (January 24 to January 30, 2016) Cumulative (August 30, 2015 to January 30, 2016)
Influenza A B Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A Table 1 - Footnote UnS Total A Total A(H1) pdm09 A(H3) A Table 1 - Footnote UnS Total # %
<5 41 7 2 32 13 207 82 35 90 57 264 12.8%
5-19 43 9 2 32 52 159 48 48 63 183 342 16.6%
20-44 104 10 5 89 47 341 97 73 171 186 527 25.6%
45-64 84 19 7 58 18 342 98 103 141 93 435 21.2%
65+ 46 12 8 26 19 381 54 203 124 95 476 23.2%
Unknown 3 1 2 0 0 11 7 4 0 1 12 0.6%
Total 321 58 26 237 149 1441 386 466 589 615 2056 100.0%
PercentageTable 1 - Footnote 2 68.3% 18.1% 8.1% 73.8% 31.7% 70.1% 26.8% 32.3% 40.9% 29.9%    

For additional data on other respiratory virus detections see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada website.

Influenza-like Illness Consultation Rate

The national ILI consultation rate increased from the previous week from 16.0 per 1,000 patient visits in week 03, to 35.9 per 1,000 patient visits in week 04. In week 04, the highest ILI consultation rate was found in those 0-4 years of age (88.4 per 1,000) and the lowest was found in the ≥65 years age group (19.4 per 1,000) (Figure 4).

Figure 4. Influenza-like-illness (ILI) consultation rates by age group and week, Canada, 2015-16

Figure 4

Delays in the reporting of data may cause data to change retrospectively. In BC, AB, and SK, data are compiled by a provincial sentinel surveillance program for reporting to FluWatch. Not all sentinel physicians report every week.

Figure 4 - Text Description

Influenza-like illness consultation rate by age-group in week 03 for the 2015-16 season:
Age 0-4: 86.6; Age 5-19: 21.0; Age 20-64: 38.9; Age 65+: 19,4

Influenza Outbreak Surveillance

In week 04, 13 new laboratory confirmed influenza outbreaks were reported: six in long-term care facilities (LTCF), four in hospitals and three in an institutional or community setting. Of the outbreaks with known strains or subtypes, two outbreaks were due to Influenza A(H1N1), one was due to Influenza A(H3N2), three outbreaks were due to influenza A (UnS) and one outbreak was due to influenza B. Additionally, four ILI outbreaks were reported in schools.

To date this season, 63 outbreaks have been reported (29 of which occurred in LTCFs). In comparison, at week 04 in the 2014-15 season, 1,146 outbreaks were reported (589 of which occurred in LTCFs) and in the 2013-14 season, 67 outbreaks were reported (37 of which occurred in LTCFs).

Figure 5. Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2015-2016

Figure 5
Figure 5 - Text Description
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 0 0
37 1 1 0
38 0 0 0
39 0 2 0
40 0 2 1
41 0 0 0
42 0 0 0
43 0 1 0
44 1 3 1
45 1 1 0
46 0 0 0
47 0 0 0
48 0 1 0
49 0 1 0
50 0 2 0
51 1 1 0
52 1 0 2
1 0 2 1
2 0 2 0
3 1 4 1
4 4 6 3

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 04, 38 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 6). Nineteen hospitalizations were due to influenza A(H1N1) (50%), one was due to A(H3N2) (2.7%) nine were due to influenza B (24%) and the remainder were influenza A (UnS).

To date this season, 134 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network: 102 hospitalized cases were due to influenza A and 32 cases were due to influenza B. The majority of hospitalized cases were among children aged 2-4 years (34%). To date, 15 intensive care unit (ICU) admissions have been reported. The majority of ICU admissions were reported in children 2-4 years (40%) and due to influenza A(H1N1) (27%). Less than five influenza-associated deaths have been reported.

Table 2 - Cumulative numbers of peadiatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, Canada, 2015-16
Age Groups Cumulative (30 Aug. 2015 to 30 January 2016) 
Influenza A Influenza B
A Total A(H1)
pdm09
A(H3) A (UnS) B Total
0-5m 13 <5 <5 8 5
6-23m 26 15 <5 Table 2 - Footnote x <5
2-4y 36 17 <5 Table 2 - Footnote x 10
5-9y 18 9 Table 2 - Footnote x Table 2 - Footnote x 10
10-16y 9 <5 <5 <5 <5
Total 102 48 9 45 32

Figure 6. Number of cases of influenza reported by sentinel hospital networks, by week, Canada, 2015-16, paediatric and adult hospitalizations (≤16 years of age, IMPACT; ≥16 years of age, CIRN-SOS)

Figure 6

Not included in Table 2 and Figure 6 are two IMPACT cases that were due to co-infections of influenza A and B.

Figure 6 - Text Description
Report week IMPACT CIRN-SOS
35 0 0
36 0 0
37 1 0
38 2 0
39 0 0
40 0 0
41 1 0
42 0 0
43 1 0
44 0 1
45 2 0
46 1 3
47 2 1
48 2 1
49 3 6
50 3 2
51 7 4
52 14 9
1 19 17
2 13 12
3 24 15
4 38 11

Adult Influenza Hospitalizations and Deaths

In week 04, 11 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS). The majority of hospitalizations were in adults 65+ years of age (64%) and due to influenza A (91%).

To date this season, 82 laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations have been reported by CIRN-SOS (Table 3). The majority of hospitalized cases were due to influenza A (79%) and were among adults ≥65 years of age (54%). Six intensive care unit (ICU) admissions have been reported and among those, five (83%) were due to influenza A. Less than five deaths have been reported this season.

Table 3 - Cumulative numbers of adult hospitalizations (≥16 years of age) with influenza reported by the CIRN-SOS network, Canada, 2015-16
Age groups (years) Cumulative (1 Nov. 2015 to 30 Jan. 2016)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
16-20 1 1 0 0 0 1 (1%)
20-44 6 1 0 5 8 14 (17%)
45-64 18 4 2 12 5 23 (28%)
65+ 40 5 12 23 4 44 (54%)
Unknown 0 0 0 0 0 0 (%)
Total 65 11 14 40 17 82
% 79% 17% 22% 62% 21% 100%

Figure 7. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥16 year of age), Canada 2015-16

Figure 7

Note: The number of hospitalizations reported through CIRN-SOS and IMPACT represents a subset of all influenza-associated adult and paediatric hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Figure 7 - Text Description
Age-group (years) Hospitalizations (n=82) ICU admissions (n=6) Deaths (n=1)
16-20 1.2% 0.0% 0.0%
20-44 17.1% 33.3% 0.0%
45-64 28.0% 50.0% 0.0%
65+ 53.7% 16.7% 100.0%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 04, 44 hospitalizations have been reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (82%). The largest proportion of cases reported in week 04 were in children 0-19 years (39%).

Since the start of the 2015-16 season, 421 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 365 hospitalizations (87%) were due to influenza A and 56 (13%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 75% (176/235) were influenza A(H1N1). The majority (34%) of hospitalized cases were ≥65 years of age. Forty-one ICU admissions have been reported of which 35 (85%) were due to influenza A and 15 (37%) were in the 45-64 age group. A total of 14 deaths have been reported, all due to influenza A. The majority of deaths were reported in adults 65+ of age (57%).

Figure 8. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group, Canada 2015-16

Figure 8
Figure 8 - Text Description
Age-group (years) Hospitalizations (n=421) ICU admissions (n=41) Deaths (n=14)
0-4 20.9% 14.6% 14.3%
5-19 7.6% 4.9% 0.0%
20-44 14.7% 22.0% 7.1%
45-64 22.3% 36.6% 21.4%
65+ 34.4% 22.0% 57.1%

See additional data on Reported Influenza Hospitalizations and Deaths in Canada: 2011-12 to 2015-16 on the Public Health Agency of Canada website.

Influenza Strain Characterizations

During the 2015-16 influenza season, the National Microbiology Laboratory (NML) has characterized 282 influenza viruses [106 A(H3N2), 132 A(H1N1) and 44 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 15 H3N2 virus were antigenically characterized as A/Switzerland/9715293/2013-like using antiserum raised against cell-propagated A/Switzerland/9715293/2013.

Sequence analysis was done on 91 H3N2 viruses. All viruses belonged to a genetic group for which most viruses were antigenically related to A/Switzerland/9715293/2013.

A/Switzerland/9715293/2013 is the A(H3N2) component of the 2015-16 Northern Hemisphere's vaccine.

Influenza A (H1N1): One hundred and thrity-two H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: Twenty-seven influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. Seventeen influenza B viruses were characterized as B/Brisbane/60/2008-like, one of the influenza B components of the 2015-16 Northern Hemisphere quadrivalent influenza vaccine.

The recommended components for the 2015-2016 northern hemisphere trivalent influenza vaccine include: an A/California/7/2009(H1N1)pdm09-like virus, an /Switzerland/9715293/2013(H3N2)-like virus, and a B/Phuket/3073/2013 -like virus (Yamagata lineage). For quadrivalent vaccines, the addition of a B/Brisbane/60/2008-like virus (Victoria lineage) is recommended.

The NML receives a proportion of the number of influenza positive specimens from provincial laboratories for strain characterization and antiviral resistance testing. Characterization data reflect the results of haemagglutination inhibition testing compared to the reference influenza strains recommended by WHO.

Antiviral Resistance

During the 2015-16 season, the National Microbiology Laboratory (NML) has tested 275 influenza viruses for resistance to oseltamivir and 274 influenza for resistance to zanamivir. All viruses were sensitive to zanamivir and oseltamivir. A total of 208 influenza A viruses (99%) were resistant to amantadine (Table 4).

Table 4. Antiviral resistance by influenza virus type and subtype, Canada, 2015-16
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 100 0 100 0 107 106 (99.1%)
A (H1N1) 129 0 128 0 102 102 (100%)
B 46 0 46 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 275 0 274 0 209 208

International Influenza Reports


FluWatch definitions for the 2015-2016 season

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).

Influenza-like-illness (ILI): Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which is likely due to influenza. In children under 5, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.

ILI/Influenza outbreaks

Schools:
Greater than 10% absenteeism (or absenteeism that is higher (e.g. >5-10%) than expected level as determined by school or public health authority) which is likely due to ILI.
Note: it is recommended that ILI school outbreaks be laboratory confirmed at the beginning of influenza season as it may be the first indication of community transmission in an area.
Hospitals and residential institutions:
two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case. Institutional outbreaks should be reported within 24 hours of identification. Residential institutions include but not limited to long-term care facilities (LTCF) and prisons.
Workplace:
Greater than 10% absenteeism on any day which is most likely due to ILI.
Other settings:
two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case; i.e. closed communities.

Note that reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions.

Influenza/ILI activity level

1 = No activity: no laboratory-confirmed influenza detections in the reporting week, however, sporadically occurring ILI may be reported

2 = Sporadic: sporadically occurring ILI and lab confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region Footnote

3 = Localized:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance regionFootnote

4 = Widespread:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance regionFootnote

Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.

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