FluWatch report: March 25 to March 31, 2018 (week 13)

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 2018-13

Influenza Surveillance Region	Activity Level
Newfoundland - Central	Localized
Newfoundland - Eastern	Localized
Grenfell Labrador	No Activity
Newfoundland - Western	Sporadic
Prince Edward Island	Localized
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	No Activity
New Brunswick - Public Health Region 6	Sporadic
New Brunswick - Public Health Region 7	Localized
Nord-est Québec	Localized
Québec et Chaudieres-Appalaches	Sporadic
Centre-du-Québec	Widespread
Montréal et Laval	Sporadic
Ouest-du-Québec	Localized
Montérégie	Localized
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	Sporadic
Manitoba - Winnipeg	Sporadic
Saskatchewan - North	Sporadic
Saskatchewan - Central	Sporadic
Saskatchewan - South	Localized
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	Localized
British Columbia - Vancouver Coastal	Widespread
British Columbia - Vancouver Island	Localized
British Columbia - Northern	Sporadic
Yukon	Sporadic
Northwest Territories - North	Sporadic
Northwest Territories - South	Sporadic
Nunavut - Baffin	No Data
Nunavut - Kivalliq	No Data
Nunavut - Kitimeot	No Data

Laboratory-Confirmed Influenza Detections

In week 13, the overall percentage of tests positive for influenza was 19%, a decrease from the previous week. Overall, laboratory detections of influenza are steadily decreasing. Influenza B accounted for 54% of influenza detections in week 13.

The percentage of influenza A detections for week 13 is around the average for this time of year. The percentage of tests positive for influenza B in week 13 is above average but within the expected range 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 2018-13

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	1437	325	51	2057
10	1023	265	80	1714
11	807	246	73	1387
12	551	189	76	966
13	431	176	35	739

To date this season, 59,699 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 2018-13

Reporting provincesTable Figure 3 - Footnote 1	Week (March 25, 2018 to March 31, 2018)					Cumulative (August 27, 2017 to March 31, 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	61	12	41	8	85	2321	471	1431	419	2860	5181
AB	24	12	5	7	63	5557	191	3976	1390	3150	8707
SK	13	3	5	5	53	1677	47	1136	494	1493	3170
MB	2	0	1	1	37	1120	9	374	737	542	1662
ON	163	7	99	57	114	5665	237	3157	2271	4446	10111
QC	226	0	0	226	264	14722	0	0	14722	11843	26565
NB	66	2	5	59	48	1308	13	207	1088	945	2253
NS	33	0	0	33	31	475	0	0	475	257	732
PE	15	0	14	1	6	123	6	116	1	154	277
NL	27	0	0	27	25	350	0	3	347	355	705
YT	0	0	0	0	0	72	7	44	21	42	114
NT	0	0	0	0	4	129	4	125	0	44	173
NU	2	0	2	0	0	46	6	40	0	3	49
Canada	632	36	172	424	730	33565	991	10609	21965	26134	59699
PercentageTable Figure 3 - Footnote 2	46%	6%	27%	67%	54%	56%	3%	32%	65%	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 48,582 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) (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 (814), 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 53% and 32% 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 2018-13

Age groups (years)	Cumulative (August 27, 2017 to March 31, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)Table 1 Footnote 1	Total	#	%
0-4	2991	136	544	2311	1406	4397	9%
5-19	2216	121	532	1563	2474	4690	10%
20-44	4048	227	1164	2657	2613	6661	14%
45-64	4426	207	1395	2824	4413	8839	18%
65+	14100	123	5135	8842	9895	23995	49%
Total	27781	814	8770	18197	20801	48582	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 Practitioners Sentinel Syndromic Surveillance

In week 13, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase 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 2016-17

Figure 4 - Text Description

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-13

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	1.7%	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	1.8%	1.7%	1.2%	2.6%

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 13, 1,287 participants reported to FluWatchers, of which 2% reported symptoms of cough and fever, and 16% of these consulted a healthcare professional. Among participants who reported cough and fever, 76% reported days missed from work or school, resulting in a combined total of 44 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-13

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
1287	2%	16%	76%	44

Influenza Outbreak Surveillance

In week 13, 42 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, 29 were reported in long-term care facilities (LTC), five in hospitals, and eight in other settings. Among the 32 outbreaks with influenza type/subtype reported, 18 (56%) were associated with influenza A, 13 (41%) were associated with influenza B and one outbreak was associated with a mix of influenza A and B (3%).

To date this season, 1,663 influenza/ILI outbreaks have been reported, of which 1,025 (62%) occurred in LTC facilities. Among the 1,427 outbreaks for which the influenza type/subtype was reported, 781 (55%) were associated with influenza A and 579 (41%) were associated with influenza B, and 67 (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 2018-13

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	83	16
10	12	42	10
11	2	43	12
12	8	31	10
13	5	29	8

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,500 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 1}. Among the hospitalizations, 3,116 (69%) were associated with influenza A, and 2,990 cases (66%) were in adults 65 years of age or older.

Additionally, 439 ICU admissions and 230 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (44%), followed closely by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (83%).

Figure 6 - Text Description

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-13

Age Group	Total
0-4 yr	266
5-19 yr	203
20-44 yr	286
45-64 yr	755
65+ yr	2990

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 13, 26 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 62% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07.

To date this season, 995 pediatric hospitalizations have been reported by the IMPACT network, 619 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (41%). Among the 376 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 159 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 by children aged 10-16 years (26%). Among the ICU cases with available information, 64% were due to influenza A and approximately 48% 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 2018-13

Age Group	Total
0-5 mo	108
6-23 mo	234
2-4 yr	251
5-9 yr	232
10-16 yr	170

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 2018-13

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	25	23	4	47
51	38	32	4	72
52	62	47	7	92
1	57	40	5	75
2	38	35	4	62
3	52	38	4	67
4	94	35	7	47
5	70	40	11	59
6	74	38	15	79
7	89	40	17	120
8	72	47	25	139
9	68	50	13	153
10	58	48	17	135
11	57	41	18	118
12	35	33	13	89
13	26	32	14	67

Figure 8 Footnote 1

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

Return to figure 8 note 1 referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 2,856 influenza viruses [1,287 A(H3N2), 200 A(H1N1)pdm09 and 1,369 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 2018-13

Strain Characterization Results	Count	Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like	256	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	65	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	200	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)	14	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)	43	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)	1312	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, 965 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 862 A(H3N2) viruses belonged to genetic group 3C.2a, 101 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 322 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 232 belonged to genetic group 3C.2a and 24 viruses belonged to subclade 3C.2a1. The 65 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the remaining one isolate.

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 43 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 1,103 influenza viruses for resistance to oseltamivir and 1,099 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 2018-13

Virus type and subtype	Oseltamivir		Zanamivir
	# tested	# resistant (%)	# tested	# resistant (%)
A (H3N2)	474	0 (0%)	471	0 (0%)
A (H1N1)	143	1 (0.7%)	143	0 (0%)
B	486	0 (0%)	485	1 (0.2%)
TOTAL	1103	1 (0.1%)	1099	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.