FluWatch report:  March 4, 2018 to March 10, 2018 (week 10)

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 2018-10

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

Laboratory-Confirmed Influenza Detections

In week 10, the overall percentage of tests positive for influenza was 27%. The overall percentage of tests positive for influenza has been slowly decreasing from the peak in week 07. Detections of influenza B continue to be greater than those of influenza A. Influenza B accounted for 55% of influenza detections in week 10.

The percentage of influenza A detections for week 10 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 10 continues to be well above expected levels 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 2018-10

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	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	1462	326	51	2058
10	1001	258	75	1669

To date this season, 53,898 laboratory-confirmed influenza detections have been reported, of which 57% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 93% 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 2018-10

Reporting provincesTable Figure 3 - Footnote 1	Week (March 4, 2018 to March 10, 2018)					Cumulative (August 27, 2017 to March 10, 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	130	36	73	21	160	2102	375	1310	417	2497	4599
AB	58	17	21	20	110	5452	152	3936	1364	2872	8324
SK	27	0	8	19	80	1625	43	1109	473	1174	2799
MB	9	0	3	6	43	1106	7	369	730	396	1502
ON	225	16	128	81	194	4970	196	2777	1997	3979	8949
QC	729	0	0	729	868	13627	0	0	13627	10658	24285
NB	93	5	16	72	97	1122	11	202	909	705	1827
NS	37	0	0	37	22	386	0	0	386	172	558
PE	6	0	6	0	11	87	3	84	0	135	222
NL	23	0	0	23	40	256	0	3	253	265	521
YT	2	1	1	0	0	65	7	40	18	41	106
NT	0	0	0	0	2	129	4	125	0	32	161
NU	0	0	0	0	0	42	6	36	0	3	45
Canada	1339	75	256	1008	1627	30969	804	9991	20174	22929	53898
PercentageTable Figure 3 - Footnote 2	45%	6%	19%	75%	55%	57%	3%	32%	65%	43%	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 44,153 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (49%), and among cases of influenza A(H3N2) (58%) and influenza B (47%). 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 (659), the majority of influenza A(H1N1) cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 54% and 32% of cases respectively.

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 2018-10

Age groups (years)	Cumulative (August 27, 2017 to March 10, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)Table 1 Footnote 1	Total	#	%
0-4	2741	118	524	2099	1252	3993	9%
5-19	2068	93	512	1463	2259	4327	10%
20-44	3760	188	1110	2462	2351	6111	14%
45-64	4093	167	1322	2604	3883	7976	18%
65+	13092	93	4792	8207	8654	21746	49%
Total	25754	659	8260	16835	18399	44153	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 10, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease from the previous week.

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 2018-10

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	2.8%	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	3.0%	2.3%	1.9%	2.7%
9	2.8%	2.2%	1.8%	2.7%
10	1.8%	2.1%	1.8%	2.7%

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 10, 1,385 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 22% of these consulted a healthcare professional. Among participants who reported cough and fever, 73% reported days missed from work or school, resulting in a combined total of 74 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-10

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
1385	3%	22%	73%	74

Influenza Outbreak Surveillance

In week 10, 64 laboratory-confirmed outbreaks of influenza were reported, a sharp decrease compared to the previous week. Among the reported influenza outbreaks, 42 were reported in long-term care facilities(LTC), 12 in hospitals, and 10 in other settings. In addition, six ILI outbreaks were reported schools. Among the 52 outbreaks with influenza type/subtype reported, 29 (56%) were associated with influenza A, 23 (44%) were associated with influenza B.

To date this season, 1,508 influenza/ILI outbreaks have been reported, of which 917 (61%) occurred in LTC facilities. Among the 1,294 outbreaks for which the influenza type/subtype was reported, 678 (52%) were associated with influenza A and 500 (39%) were associated with influenza B, and 64 (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 2018-10

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	59	22
9	8	79	16
10	12	42	10

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,086 influenza-associated hospitalizations were reported by participating provinces and territories. Among the hospitalizations, 2,936 (72%) were associated with influenza A, and 2,750 cases (67%) were in adults 65 years of age or older.

Additionally, 394 ICU admissions and 201 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (43%), followed closely by adults aged 20-64 (41%). Adults aged 65 years of age or older accounted the majority of deaths (84%).

Figure 6 - Text Description

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-10

Age Group	Total
0-4 yr	240
5-19 yr	172
20-44 yr	249
45-64 yr	675
65+ yr	2750

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 10, 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 10, 57 hospitalizations were reported of which 33 (58%) were due to influenza A. Pediatric hospitalizations have been decreasing since week 07. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 882 pediatric hospitalizations have been reported by the IMPACT network, 555 (63%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (40%). Among the 327 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 139 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (28%), followed closely by children aged 10-16 years (27%). Among the ICU cases with available information, 65% were due to influenza A and approximately 42% had no reported previous or concurrent medical conditions. All 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 2018-10

Age Group	Total
0-5 mo	96
6-23 mo	202
2-4 yr	230
5-9 yr	203
10-16 yr	151

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 2018-10

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	7	5	1	13
47	13	4	0	9
48	17	9	2	23
49	23	15	3	28
50	26	23	4	47
51	39	32	4	72
52	62	47	7	92
1	57	40	5	75
2	39	35	4	62
3	52	38	4	67
4	93	35	7	47
5	70	40	11	59
6	74	38	15	79
7	89	40	17	120
8	72	47	25	139
9	69	50	13	153
10	57	48	17	135

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 2,367 influenza viruses [1,139 A(H3N2), 155 A(H1N1)pdm09 and 1,073 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 2018-10

Strain Characterization Results	Count	Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like	226	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	45	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	155	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)	10	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)	37	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)	1026	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, 868 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 779 A(H3N2) viruses belonged to genetic group 3C.2a, 87 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 271 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 196 belonged to genetic group 3C.2a and 21 viruses belonged to subclade 3C.2a1. The 45 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the nine remaining 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 36 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the one remaining virus isolate.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 989 influenza viruses for resistance to oseltamivir and 985 viruses for resistance to zanamivir. All but one of the A(H1N1)pdm viruses were sensitive to oseltamivir and all but one influenza B viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-10

Virus type and subtype	Oseltamivir		Zanamivir
	# tested	# resistant (%)	# tested	# resistant (%)
A (H3N2)	454	0 (0%)	450	0 (0%)
A (H1N1)	113	1 (0.9%)	113	0 (0%)
B	422	0 (0%)	422	1 (0.2%)
TOTAL	989	1 (0.1%)	985	1 (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, the subset of 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. 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.