FluWatch report: January 17, 2016 - January 23, 2016 (week 03)

Overall Summary

  • Overall in week 03, seasonal influenza activity increased from the previous week but remains below expected levels for this time of the year.
  • Hospitalizations among the pediatric population increased in week 03.
  • 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: 2016-01-29

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 03, influenza/ILI activity increased in Canada. A total of 27 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in six regions in Canada (one each in BC, AB and NS, and three in ON).

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 03

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 03, influenza/ILI activity increased in Canada. A total of 27 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in six regions in Canada (one each in BC, AB and NS, and three in ON).

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections continue to increase steadily. The percent positive for influenza increased from 7.0% in week 02 to 12.4% in week 03 (Figure 2). Compared to the previous five seasons, the percent positive (12.4%) reported in week 03 was below the five year average for that week and below expected levels (range 13.2%-29.7%).

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 7.0% in week 02 to 12.4% in week 03.

In week 03, there were 594 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 69% of influenza detections in Canada in week 03. To date, 79% of influenza detections have been influenza A and among those subtyped, the majority have been influenza A(H1N1) [63% (744/1186)].

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 17 to January 23, 2016) Cumulative (August 30, 2015 to January 23, 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 95 39 34 22 98 430 65 192 173 254 684
AB 182 137 7 41 35 552 417 89 46 107 659
SK 17 13 1 3 5 47 33 4 10 11 58
MB 7 3 1 3 1 19 4 10 5 3 22
ON 79 51 11 17 13 434 201 128 105 47 481
QC 44 2 0 42 4 206 5 0 201 24 230
NB 5 0 0 5 0 13 1 0 12 2 15
NS 1 0 0 1 0 12 0 1 11 0 12
PE 4 4 0 0 0 13 13 0 0 0 13
NL 0 0 0 0 0 8 4 2 2 3 11
YT 0 0 0 0 3 4 0 4 0 3 7
NT 1 1 0 0 0 13 1 12 0 0 13
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 435 250 54 134 159 1751 744 442 565 454 2205
Percentage Table Figure 3 - Footnote 2 73.2% 57.5% 12.4% 30.8% 26.8% 79.4% 42.5% 25.2% 32.3% 20.6% 100.0%

To date this season, detailed information on age and type/subtype has been received for 1,435 cases. Adults aged 65 years and older accounted for 27% of reported influenza cases (Table 1). Adults aged 65 years and older also represented 44% of reported A(H3N2) cases. Adults aged 20-44 years represented 26% of reported influenza A(H1N1) cases and 29% of reported influenza B 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 17 to January 23, 2016) Cumulative (August 30, 2015 to January 23, 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 43 12 2 29 7 146 58 30 58 38 184 12.8%
5-19 21 5 1 15 44 107 30 45 32 115 222 15.5%
20-44 63 13 6 44 38 219 66 65 88 117 336 23.4%
45-64 33 5 2 26 13 230 61 89 80 68 298 20.8%
65+ 28 3 8 17 11 316 31 180 105 71 387 27.0%
Unknown 1 1 0 0 0 7 5 2 0 1 8 0.6%
Total 189 39 19 131 113 1025 251 411 363 410 1435 100.0%
PercentageTable 1 - Footnote 2 62.6% 20.6% 10.1% 69.3% 37.4% 71.4% 24.5% 40.1% 35.4% 28.6%    

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 12.5 per 1,000 patient visits in week 02, to 15.6 per 1,000 patient visits in week 03. In week 03, the highest ILI consultation rate was found in those 0-4 years of age (26.9 per 1,000) and the lowest was found in the ≥65 years age group (2.7 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: 26.9; Age 5-19: 25.7; Age 20-64: 14.2; Age 65+: 2.7

Influenza Outbreak Surveillance

In week 03, six new laboratory confirmed influenza outbreaks: four in long-term care facilities (LTCF), one in a hospital and one in an institutional or community setting.  Two outbreaks were due to influenza B, one outbreak was due to influenza A (UnS) and the remainder were unknown. To date this season, 46 outbreaks have been reported (23 of which occurred in LTCFs). In comparison, at week 03 in the 2014-15 season, 941 outbreaks were reported (741 of which occurred in LTCFs) and in the 2013-14 season, 60 outbreaks were reported (33 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

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 03, 24 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 6). Nine hospitalizations were due to influenza A(H1N1) (38%), five were due to influenza B (21%) and the remainder were influenza A (UnS).

To date this season, 94 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by  the IMPACT network. Seventy-one hospitalized cases were due to influenza A and 23 cases were due to influenza B. The majority of hospitalized cases were among children aged 2-4 years (32%). To date, 13 intensive care unit (ICU) admissions have been reported. The majority of ICU admissions were reported in children 2-4 years (46%) and due to influenza A(H1N1) (38%). 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 23 January 2016) 
Influenza A Influenza B
A Total A(H1)
pdm09
A(H3) A (UnS) B Total
0-5m 11 <5 <5 7 5
6-23m 17 9 <5 Table 2 - Footnote x <5
2-4y 24 10 2 12 6
5-9y 10 <5 0 Table 2 - Footnote x 6
10-16y 9 <5 <5 5 <5
Total 71 28 8 35 23

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 13 9
1 16 17
2 14 12
3 24 15

Adult Influenza Hospitalizations and Deaths

In week 03, 15 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS). The majority of hospitalizations were in adults 45-64 years of age (47%) and due to influenza A (73%).

To date this season, 71 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 (77%) and were among adults ≥65 years of age (49%). Five intensive care unit (ICU) admissions have been reported and among those, four (80%) were due to influenza A. No deaths have been reported.

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 16 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 4 1 0 3 7 11 (15%)
45-64 17 3 2 12 5 22 (31%)
65+ 32 2 12 18 3 35 (49%)
Unknown 1 0 0 1 1 2 (3%)
Total 55 7 14 34 16 71
% 77% 13% 25% 62% 23% 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=69) ICU admissions (n=5) Deaths (n=0)
16-20 1.4% 0.0% 0.0%
20-44 15.9% 20.0% 0.0%
45-64 31.9% 60.0% 0.0%
65+ 50.7% 20.0% 0.0%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 03, 51 hospitalizations have been reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (86%) and reported in the 0-4 years age group (35%).

Since the start of the 2015-16 season, 343 laboratory-confirmed influenza-associated hospitalizations have been reported. Two hundred and ninety-nine hospitalizations (87%) were due to influenza A and 44 (13%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 69% (129/187) were influenza A(H1N1). The majority (37%) of hospitalized cases were ≥65 years of age. Thirty-two  ICU admissions have been reported of which 26 (82%) were due to influenza A and 12 (38%) were in the 45-64 age group. A total of 14 deaths have been reported, all due to influenza A.

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=343) ICU admissions (n=32) Deaths (n=14)
0-4 20.4% 12.5% 14.3%
5-19 7.0% 3.1% 0.0%
20-44 14.0% 18.8% 7.1%
45-64 21.9% 37.5% 21.4%
65+ 36.7% 28.1% 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 234 influenza viruses [100 A(H3N2), 94 A(H1N1) and 40 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, twelve 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 88 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): Ninety-four H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: Twenty-five influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. Fifteen 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 222 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to zanamivir and oseltamivir. A total of 161 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) 96 0 96 0 101 100 (99%)
A (H1N1) 85 0 85 0 61 61 (100%)
B 41 0 41 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 222 0 222 0 162 161

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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