FluWatch report: January 31, 2016 - February 6, 2016 (week 05)

Overall Summary

  • Overall in week 05, several seasonal influenza indicators increased from the previous week.
  • Laboratory detections reached expected levels for this time of the year.
  • An increase in the number of outbreaks was reported in week 05 with the majority due to influenza A.
  • In the past 3 weeks young/middle age adults are accounting for an increasing proportion of hospitalizations as reported by participating provinces and territories.
  • Influenza A(H1N1) is the most common influenza subtype circulating in Canada.
  • For more information on the flu, see our Flu(influenza) web page.

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Organization: Public Health Agency of Canada

Date published: 2016-02-12

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 05, influenza/ILI activity continued to increase in Canada. A total of 32 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 8 regions in Canada and widespread activity was reported in 2 regions of NL.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 05

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 05, influenza/ILI activity continued to increase in Canada. A total of 32 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 8 regions in Canada and widespread activity was reported in 2 regions of NL.

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections are on the rise in Canada. The percent positive for influenza increased from 16.0% in week 04 to 20.4% in week 05 (Figure 2). Compared to the previous five seasons, the percent positive (20.4%) reported in week 05 was above the five year average for that week but remained within expected levels (range 13.2%-24.4%).

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 16.0% in week 04 to 20.4% in week 05.

In week 05, there were 1,271 positive influenza tests reported. Influenza A(H1N1) was the most common subtype detected. The majority of influenza detections were reported in the provinces of AB, ON and QC. To date, 80% of influenza detections have been influenza A and among those subtyped, the majority have been influenza A(H1N1) [77% (1834/2390)].

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 31 to February 6, 2016) Cumulative (August 30, 2015 to February 6, 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 94 53 24 17 109 619 150 237 232 465 1084
AB 388 286 2 105 47 1231 1016 101 114 207 1438
SK 85 47 0 38 8 223 133 10 80 29 252
MB 21 8 5 8 2 44 16 17 11 7 51
ON 204 126 15 63 29 802 435 170 197 99 901
QC 193 14 1 178 17 498 28 1 469 64 562
NB 32 7 1 24 0 48 8 1 39 2 50
NS 10 0 0 10 0 24 0 1 23 0 24
PE 2 2 0 0 0 23 23 0 0 0 23
NL 4 3 0 1 0 12 7 2 3 3 15
YT 9 8 0 1 6 14 8 4 2 12 26
NT 11 5 0 6 0 28 10 12 6 1 29
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 1,053 559 48 451 218 3566 1834 556 1176 889 4455
Percentage Table Figure 3 - Footnote 2 82.8% 53.1% 4.6% 42.8% 17.2% 80.0% 51.4% 15.6% 33.0% 20.0% 100.0%

To date this season, detailed information on age and type/subtype has been received for 3,694 cases. Adults aged 20-44 years accounted for the greatest proportion of influenza cases (Table 1). Adults aged 20-44 and 45-64 years accounted for 57% of reported influenza A(H1N1) cases. Children 5-19 years and adults 20-44 years accounted for 60% of all influenza B cases reported.

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 31 to February 6, 2016) Cumulative (August 30, 2015 to February 6, 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 # %
<5 114 55 0 59 10 469 294 37 138 70 539 14.6%
5-19 74 39 2 33 24 339 208 52 79 214 553 15.0%
20-44 208 100 0 108 22 838 530 78 230 212 1050 28.4%
45-64 220 97 6 117 10 760 421 112 227 106 866 23.4%
65+ 86 42 2 42 16 558 196 205 157 112 670 18.1%
Unknown 4 2 2 0 0 15 9 6 0 1 16 0.4%
Total 706 335 12 359 82 2979 1658 490 831 715 3694 100.0%
PercentageTable 1 - Footnote 2 89.6% 47.5% 1.7% 50.8% 10.4% 80.6% 55.7% 16.4% 27.9% 19.4%    

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 35.9 per 1,000 patient visits in week 04, to 75.4 per 1,000 patient visits in week 05. In week 05, the highest ILI consultation rate was found in those 0-4 years of age (136.4 per 1,000) and the lowest was found in the ≥65 years age group (11.2 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 05 for the 2015-16 season:
Age 0-4: 136.4; Age 5-19: 119.0; Age 20-64: 69.9; Age 65+: 11.2

Influenza Outbreak Surveillance

In week 05, the number of outbreaks reported continued to increase. A total of 16 new laboratory confirmed influenza outbreaks were reported: nine 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, one outbreak was due to Influenza A(H1N1). Additionally, one ILI outbreak was reported in a school.

To date this season, 80 outbreaks have been reported. In comparison, at week 05 in the 2014-15 season, 1,225 outbreaks were reported and in the 2013-14 season, 82 outbreaks were reported.

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
5 8 5 3

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 05, 41 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 6). Eighteen hospitalizations were due to influenza A(H1N1) (44%), one was due to A(H3N2) (2.4%), eight were due to influenza B (20%) and the remainder were influenza A (UnS).

To date this season, 175 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network: 135 hospitalized cases were due to influenza A and 40 cases were due to influenza B. The highest proportion of hospitalizations was among children aged 2-4 years (34%). To date, 20 intensive care unit (ICU) admissions have been reported. The highest proportion of ICU admissions was reported in children 2-4 years (30%). Among ICU admissions for which the subtype of influenza A was reported, 75% were due to influenza A(H1N1). 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 6 February 2016) 
Influenza A Influenza B
A Total A(H1)
pdm09
A(H3) A (UnS) B Total
0-5m 15 <5 <5 8 6
6-23m 33 20 <5 Table 2 - Footnote x 5
2-4y 47 22 <5 Table 2 - Footnote x 12
5-9y 30 18 0 12 13
10-16y 10 5 <5 <5 <5

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 05, 38 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 (58%) and have been due to influenza A (82%).

To date this season, 128 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 (80%) and were among adults ≥65 years of age (54%). Ten intensive care unit (ICU) admissions have been reported and among those, nine (90%) 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 6 Feb. 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 11 2 0 9 10 21 (16%)
45-64 32 8 2 22 5 37 (29%)
65+ 59 10 13 36 10 69 (54%)
Unknown 0 0 0 0 0 0 (%)
Total 103 21 15 67 25 128
% 80% 20% 15% 65% 20% 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=128) ICU admissions (n=10) Deaths (n=0)
16-20 0.8% 0.0% 0.0%
20-44 16.4% 30.0% 0.0%
45-64 28.9% 40.0% 0.0%
65+ 53.9% 30.0% 0.0%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 05, 171 hospitalizations have been reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (93%). The largest proportion of cases reported in week 05 were in adults 20-64 years (44%).

Since the start of the 2015-16 season, 675 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 599 hospitalizations (89%) were due to influenza A and 76 (11%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 83% (329/395) were influenza A(H1N1). The highest proportion (32%) of hospitalized cases of were among those aged ≥65 years. Sixty-eight ICU admissions have been reported of which 58 (85%) were due to influenza A and 29 (43%) were in the 45-64 age group. A total of 19 deaths have been reported, all due to influenza A. The majority of deaths were reported in adults 65+ of age (53%).

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=675) ICU admissions (n=68) Deaths (n=19)
0-4 19.9% 10.3% 10.5%
5-19 8.3% 2.9% 0.0%
20-44 14.5% 23.5% 5.3%
45-64 25.6% 42.6% 31.6%
65+ 31.7% 20.6% 52.6%

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 330 influenza viruses [107 A(H3N2), 152 A(H1N1) and 71 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 92 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 fifty-two H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza 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-two influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. Thirty-nine 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 327 influenza viruses for resistance to oseltamivir, 326 to zanamivir and 257 for resistance to amantadine. All viruses were sensitive to zanamivir. All but one virus were sensitive to oseltamivir and a total of 256 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) 109 0 109 0 111 110 (99.1%)
A (H1N1) 150 1 149 0 146 146 (100%)
B 68 0 68 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 327 1 326 0 257 256

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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