FluWatch report: April 15, 2018 to April 21, 2018 (Week 16)

Influenza/Influenza-like Illness Activity (geographic spread)

In week 16, 14 regions ( ON(7), QC(1), NB(2), NL(2), NS(1) and NT(1)) reported localized activity. Six regions reported no influenza activity.

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 2018-16

Influenza Surveillance Region	Activity Level
Newfoundland - Central	Localized
Newfoundland - Eastern	Localized
Grenfell Labrador	Sporadic
Newfoundland - Western	Sporadic
Prince Edward Island	Sporadic
Nova Scotia - Central (Zone 4)	Localized
Nova Scotia - Western (Zone 1)	Sporadic
Nova Scotia - Northern (Zone 2)	Sporadic
Nova Scotia - Eastern (Zone 3)	Sporadic
New Brunswick - Public Health Region 1	Sporadic
New Brunswick - Public Health Region 2	Localized
New Brunswick - Public Health Region 3	Localized
New Brunswick - Public Health Region 4	No Activity
New Brunswick - Public Health Region 5	No Activity
New Brunswick - Public Health Region 6	Sporadic
New Brunswick - Public Health Region 7	Sporadic
Nord-est Québec	Sporadic
Québec et Chaudieres-Appalaches	Sporadic
Centre-du-Québec	Sporadic
Montréal et Laval	Sporadic
Ouest-du-Québec	Localized
Montérégie	Sporadic
Ontario - Central East	Localized
Ontario - Central West	Localized
Ontario - Eastern	Localized
Ontario - North East	Localized
Ontario - North West	Localized
Ontario - South West	Localized
Ontario - Toronto	Localized
Manitoba - Interlake-Eastern	Sporadic
Manitoba - Northern Regional	Sporadic
Manitoba - Prairie Mountain	Sporadic
Manitoba - South	No Activity
Manitoba - Winnipeg	Sporadic
Saskatchewan - North	No Activity
Saskatchewan - Central	Sporadic
Saskatchewan - South	Sporadic
Alberta - North Zone	Sporadic
Alberta - Edmonton	Sporadic
Alberta - Central Zone	Sporadic
Alberta - Calgary	Sporadic
Alberta - South Zone	Sporadic
British Columbia - Interior	Sporadic
British Columbia - Fraser	Sporadic
British Columbia - Vancouver Coastal	Sporadic
British Columbia - Vancouver Island	Sporadic
British Columbia - Northern	No Activity
Yukon	No Activity
Northwest Territories - North	Sporadic
Northwest Territories - South	Localized
Nunavut - Baffin	No Data
Nunavut - Kivalliq	No Data
Nunavut - Kitimeot	No Data

Laboratory-Confirmed Influenza Detections

In week 16, the overall percentage of tests positive for influenza was 12%, a decrease from the previous week. Overall, laboratory detections of influenza are steadily decreasing. In week 16, 719 positive influenza tests were reported, down from 955 tests reported in week 15. Influenza A accounted for 57% of influenza detections in week 16.

Overall, laboratory detections of influenza are around the average for this time of year. For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report.

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 2018-16

Report Week	A(Unsubtyped)	A(H3N2)	A(H1N1)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	1836	925	60	1539
2	1987	808	49	1730
3	1649	870	80	1912
4	1675	632	57	1802
5	1664	542	54	2125
6	1819	506	49	2383
7	1754	405	63	2443
8	1642	279	51	2354
9	1437	325	51	2057
10	1023	265	80	1714
11	807	246	73	1387
12	551	189	76	966
13	458	183	40	767
14	436	143	49	661
15	370	127	57	500
16	306	79	29	318

To date this season, 62,933 laboratory-confirmed influenza detections have been reported, of which 56% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 91% 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 - Text description

Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-16

Reporting provincesTable Figure 3 - Footnote 1	Week (April 15, 2018 to April 21, 2018)					Cumulative (August 27, 2017 to April 21, 2018)
	Influenza A				B	Influenza A				B	A & B
	A Total	A(H1N1)pdm09	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A Total	A(H1N1)pdm09	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	Total
BC	16	6	9	1	15	2437	503	1497	437	2992	5429
AB	12	7	3	2	40	5617	226	3988	1403	3319	8936
SK	4	1	1	2	17	1722	63	1149	510	1707	3429
MB	2	2	0	0	16	1131	18	377	736	613	1744
ON	118	11	55	52	66	6178	276	3410	2492	4722	10900
QC	128	0	0	128	77	15276	0	0	15276	12250	27526
NB	89	0	9	80	57	1511	22	216	1273	1155	2666
NS	13	0	0	13	4	518	0	0	518	286	804
PE	2	0	2	0	4	129	7	121	1	165	294
NL	27	0	0	27	11	449	0	3	446	403	852
YT	0	0	0	0	0	75	7	47	21	43	118
NT	0	0	0	0	1	130	4	126	0	56	186
NU	0	0	0	0	0	46	6	40	0	3	49
Canada	411	27	79	305	308	35219	1132	10974	23113	27714	62933
PercentageTable figure 3 Footnote 2	57%	7%	19%	74%	43%	56%	3%	31%	66%	44%	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 50,729 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (50%), and among cases of influenza A(H3N2) (59%) and influenza B (48%). Adults aged 20-64 represent 32% of cases overall and 29% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (898), the majority of influenza A(H1N1)pdm09 cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 54% and 30% of cases respectively.

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 2018-16

Age groups (years)	Cumulative (August 27, 2017 to April 21, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)table 1 note 1	Total	#	%
0-4	3099	148	556	2395	1461	4560	9%
5-19	2273	125	538	1610	2536	4809	9%
20-44	4179	251	1183	2745	2732	6911	14%
45-64	4605	231	1432	2942	4628	9233	18%
65+	14791	143	5392	9256	10425	25216	50%
Total	28947	898	9101	18948	21782	50729	100%
Table 1 Notes Table 1 Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available Return to table 1 note 1 referrer

Syndromic/Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Syndromic Surveillance

In week 16, 1.7% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease from the previous week.

Number of participants in week 16: 158

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2016-17

Figure 4 - Text description

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-15

Semaine de déclaration	2017-18	Moyenne	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	4.4%	3.7%	1.7%	5.2%
2	2.8%	3.0%	1.1%	4.5%
3	2.9%	2.5%	1.3%	3.6%
4	3.1%	2.4%	1.7%	3.5%
5	4.0%	2.7%	2.0%	4.4%
6	3.5%	2.7%	2.1%	3.3%
7	3.4%	2.4%	1.7%	3.0%
8	3.1%	2.3%	1.9%	2.7%
9	2.8%	2.2%	1.8%	2.7%
10	1.7%	2.1%	1.8%	2.7%
11	1.2%	2.1%	1.7%	2.7%
12	1.6%	1.8%	1.1%	2.7%
13	1.7%	1.7%	1.2%	2.6%
14	0.9%	1.8%	1.3%	2.4%
15	1.3%	1.6%	0.9%	1.9%
16	1.7%	1.5%	1.0%	1.9%

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 16, 1,314 participants reported to FluWatchers, of which 1% reported symptoms of cough and fever, and 19% of these consulted a healthcare professional. Among participants who reported cough and fever, 88% reported days missed from work or school, resulting in a combined total of 43 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-16

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
1314	1%	19%	88%	43

Influenza Outbreak Surveillance

In week 16, 14 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, nine were reported in long-term care facilities (LTC), one in a hospital, and four in other settings. In addition, one ILI outbreak was reported in a school. Among the 11 outbreaks with influenza type/subtype reported, eight (73%) were associated with influenza A and three (27%) were associated with influenza B.

To date this season, 1,767 influenza/ILI outbreaks have been reported, of which 1,091 (62%) occurred in LTC facilities. Among the 1,512 outbreaks for which the influenza type/subtype was reported, 834 (55%) were associated with influenza A and 609 (40%) were associated with influenza B, and 69 (5%) were associated with a mix of A and B.

Figure 5 - Text description

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-16

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	72	23
1	12	110	38
2	18	99	48
3	14	84	45
4	13	65	24
5	9	55	19
6	10	77	31
7	11	58	28
8	8	60	22
9	8	84	16
10	12	46	10
11	2	44	12
12	8	32	10
13	5	30	8
14	9	18	8
15	3	31	10
16	1	9	4

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,928 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 1}. Among the hospitalizations, 3,305 (67%) were associated with influenza A, and 3,232 cases (66%) were in adults 65 years of age or older.

Additionally, 496 ICU admissions and 271 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (44%), followed by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (85%).

Figure 6 - Text description

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-16

Age group	Total
0-4	308
5-19	224
20-44	321
45-64	843
65+	3232

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 16, seven laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 57% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07. The number of weekly reported hospitalizations has finally fallen to levels that are below the seven-season average.

To date this season, 1,040 pediatric hospitalizations have been reported by the IMPACT network, 645 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (40%). Among the 395 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 177 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (29%), followed by children aged 5-9 years (30%). Among the ICU cases with available information, 25% were due to influenza A and approximately 46% had no reported previous or concurrent medical conditions. All but one reported deaths were among children over the age of two.

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 2018-16

Age Group	Total
0-5 mo	111
6-23 mo	245
2-4 yr	262
5-9 yr	246
10-16 yr	176

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-17

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 2018-15

Report week	2017-18	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	7	5	1	13
47	13	4	0	9
48	17	9	2	23
49	23	15	3	28
50	25	23	4	47
51	38	32	4	72
52	59	47	7	92
1	57	40	5	75
2	38	35	4	62
3	52	38	4	67
4	94	35	7	47
5	69	40	11	59
6	75	38	15	79
7	84	40	17	120
8	72	47	25	139
9	68	50	13	153
10	58	48	17	135
11	57	41	18	118
12	34	33	13	89
13	29	32	14	67
14	30	24	12	56
15	13	23	13	56
16	7	20	10	41

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,317 influenza viruses [1,420 A(H3N2), 247 A(H1N1)pdm09 and 1,650 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition (HI) 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 2018-16

Strain Characterization Results	Count	Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like	287	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	82	These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences
Influenza A (H1N1)pdm09
A/Michigan/45/2015-like	247	Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1)pdm09 component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.
Influenza B
B/Brisbane/60/2008-like (Victoria lineage)	20	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)	49	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)	1581	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, 1,051 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 942 A(H3N2) viruses belonged to genetic group 3C.2a, 107 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 369 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 251 belonged to genetic group 3C.2a and 26 viruses belonged to subclade 3C.2a1. The 82 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the remaining 10 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 48 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the remaining virus isolate.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,379 influenza viruses for resistance to oseltamivir and 1,376 viruses for resistance to zanamivir. All but three viruses (1 A(H1N1)pdm09,1 A(H3N2) and 1 influenza B) were sensitive to oseltamivir and all but two influenza B viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-16

Virus type and subtype	Oseltamivir		Zanamivir
	# tested	# resistant (%)	# tested	# resistant (%)
A (H3N2)	522	1 (0.2%)	518	0 (0%)
A (H1N1)	199	1 (0.5%)	200	0 (0%)
B	658	1 (0.2%)	658	2 (0.3%)
TOTAL	1379	3 (0.2%)	1376	2 (0.1%)
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, all but eight influenza A viruses that were tested for resistance to amantadine were resistant.

Provincial and International Influenza Reports

FluWatch Surveillance System Description and Definitions, 2017-18

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.

Influenza/Influenza-like Illness (ILI) Activity

Influenza/ILI activity levels, as represented on the map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, primary care consultations for ILI and reported outbreaks. ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls, and the determination of an increase is based on the assessment of the provincial/territorial epidemiologist. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.

Influenza/ILI Activity Level definitions

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†

3 = Localized:

(1) evidence of increased ILI*; (2) lab confirmed influenza detection(s); (3) outbreaks in schools, hospitals, residential
institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance region†

4 = Widespread:

(1) evidence of increased ILI*; (2) lab confirmed influenza detection(s);(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 region†;

* More than just sporadic as determined by the provincial/territorial epidemiologist. †Influenza surveillance regions within the province or territory as defined by the provincial/territorial epidemiologist

Laboratory-Confirmed Influenza Detections

Provincial, regional and some hospital laboratories report the weekly number of tests and detections of influenza and other respiratory viruses. Provincial public health laboratories submit demographic information for cases of influenza. This case-level data represents a subset of influenza detections reported through aggregate reporting. Specimens from NT, YT, and NU are sent to reference laboratories in the provinces for testing. Cumulative data includes updates to previous weeks. Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Syndromic/Influenza-like Illness Surveillance

FluWatch maintains a network of primary care practitioners who report the weekly proportion of ILI cases seen in their practice. Independent sentinel networks in BC, AB, and SK compile their data for reporting to FluWatch. Not all sentinel physicians report every week.

Definition of 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 years of age, gastrointestinal symptoms may also be present. In patients under 5 or 65 years and older, fever may not be prominent.

Influenza Outbreak Surveillance

Outbreaks of influenza or ILI are reported from all provinces and territories, according to the definitions below. However, reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions. All provinces and territories with the exception of NU report influenza outbreaks in long-term care facilities. All provinces and territories with the exception of NU and QC report outbreaks in hospitals.

Outbreak definitions:

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.

Hospitals and residential institutions:

two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza. Residential institutions include but are 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 of influenza; i.e. closed communities.

Serious Outcome Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

Influenza-associated hospitalizations and deaths are reported by 8 Provincial and Territorial Ministries of Health (excluding BC, NU, ON and QC). The hospitalization or death does not have to be attributable to influenza, a positive laboratory test is sufficient for reporting. Only hospitalizations that require intensive medical care are reported by SK.

Due to changes in participating provinces and territories, comparisons to previous years should be done with caution.

Pediatric Influenza Hospitalizations and Deaths

The Immunization Monitoring Program Active (IMPACT) network reports the weekly number of hospitalizations with influenza among children admitted to one of the 12 participating paediatric hospitals in 8 provinces. These represent a subset of all influenza-associated pediatric hospitalizations in Canada.

Influenza Strain Characterizations and Antiviral Resistance

Provincial public health laboratories send a subset of influenza virus isolates to the National Microbiology Laboratory for strain characterization and antiviral resistance. These represent a subset of all influenza detections in Canada and the proportion of isolates of each type and subtype is not necessarily representative of circulating viruses.

Antigenic strain characterization data reflect the results of hemagglutination inhibition (HI) testing compared to the reference influenza strains recommended by WHO. Genetic strain characterization data are based on analysis of the sequence of the viral hemagglutinin (HA) gene.

Antiviral resistance testing is conducted by phenotypic and genotypic methods on influenza virus isolates submitted to the National Microbiology Laboratory. All isolates are tested for oseltamivir and zanamivir and a subset are tested for resistance to amantadine.

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).

This report is available on the Government of Canada Influenza webpage.

We would like to thank all the FluWatch surveillance partners who are participating in this year's influenza surveillance program.