FluWatch report: February 25 to March 3, 2018 (week 9)

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 2018-09

Influenza Surveillance Region	Activity Level
Newfoundland - Central	Localized
Newfoundland - Eastern	Localized
Grenfell Labrador	Sporadic
Newfoundland - Western	Localized
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	Localized
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	Widespread
Québec et Chaudieres-Appalaches	Widespread
Centre-du-Québec	Widespread
Montréal et Laval	Localized
Ouest-du-Québec	Widespread
Montérégie	Localized
Ontario - Central East	Widespread
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	Sporadic
Manitoba - Northern Regional	No Activity
Manitoba - Prairie Mountain	Localized
Manitoba - South	Sporadic
Manitoba - Winnipeg	Localized
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	Sporadic
British Columbia - Interior	Sporadic
British Columbia - Fraser	Widespread
British Columbia - Vancouver Coastal	Localized
British Columbia - Vancouver Island	Widespread
British Columbia - Northern	Sporadic
Yukon	Sporadic
Northwest Territories - North	Sporadic
Northwest Territories - South	No Activity
Nunavut - Baffin	Sporadic
Nunavut - Kivalliq	Sporadic
Nunavut - Kitimeot	Sporadic

Laboratory-Confirmed Influenza Detections

In week 09, the overall percentage of tests positive for influenza was 30%. For the past two weeks, the percentage of tests positive for influenza B has decreased. This indicates that the peak for influenza B detections occurred in week 07. This also suggests that the peak for the influenza season occurred week 07.

The percentage of influenza A detections for week 09 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 09 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 2018-09

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	1644	277	51	2354
9	1412	323	48	1991

To date this season, 50,912 laboratory-confirmed influenza detections have been reported, of which 58% 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 2018-09

Reporting provincesTable Figure 3 - Footnote 1	Week (February 25, 2018 to March 3, 2018)					Cumulative (August 27, 2017 to March 3, 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	25	11	14	0	22	1968	339	1237	392	2337	4305
AB	463	13	318	132	122	5393	134	3915	1344	2749	8142
SK	27	0	8	19	80	1625	43	1109	473	1174	2799
MB	25	2	22	1	1	1097	7	365	725	353	1450
ON	44	4	27	13	20	4697	178	2646	1873	3732	8429
QC	80	0	0	80	22	12892	0	0	12892	9790	22682
NB	11	0	3	8	0	1029	6	186	837	608	1637
NS	2	0	0	2	0	349	0	0	349	150	499
PE	1	0	1	0	0	81	3	78	0	124	205
NL	0	0	0	0	0	233	0	3	230	225	458
YT	0	0	0	0	2	63	6	39	18	41	104
NT	0	0	0	0	0	128	4	124	0	29	157
NU	5	0	5	0	0	42	6	36	0	3	45
Canada	683	30	398	255	269	29597	726	9738	19133	21315	50912
PercentageTable Figure 3 - Footnote 2	72%	4%	58%	37%	28%	58%	2%	33%	65%	42%	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 41,767 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 30% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (596), 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 2018-09

Age groups (years)	Cumulative (August 27, 2017 to March 3, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)Table 1 Footnote 1	Total	#	%
0-4	2569	106	507	1956	1159	3728	9%
5-19	1971	87	499	1385	2135	4106	10%
20-44	3610	170	1086	2354	2229	5839	14%
45-64	3926	150	1286	2490	3596	7522	18%
65+	12593	83	4615	7895	7979	20572	49%
Total	24669	596	7993	16080	17098	41767	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 09, 3.2% of visits to healthcare professionals were due to influenza-like illness (ILI); similar to the previous week, and above the 5-year average.

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 2018-09

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	2.8%	2.5%	1.3%	3.6%
4	3.1%	2.4%	1.7%	3.5%
5	4.1%	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	3.2%	2.3%	1.9%	2.7%
9	3.2%	2.2%	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 09, 1,419 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 14% of these consulted a healthcare professional. Among participants who reported cough and fever, 69% reported days missed from work or school, resulting in a combined total of 90 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-09

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
1419	3%	14%	69%	90

Influenza Outbreak Surveillance

In week 09, 103 laboratory-confirmed outbreaks of influenza were reported, an increase compared to the previous week. Among the reported influenza outbreaks, 79 were reported in long-term care facilities, eight in hospitals, and 16 in other settings. In addition, seven ILI outbreaks were reported schools. Among the 87 outbreaks with influenza type/subtype reported, 48 (55%) were associated with influenza B, 37 (43%) were associated with influenza A and two outbreaks were associated with a mix of influenza A and B (2%).

To date this season, 1,428 influenza/ILI outbreaks have been reported, of which 865 (61%) occurred in LTC facilities. Among the 1,232 outbreaks for which the influenza type/subtype was reported, 672 (54%) were associated with influenza A and 498 (40%) were associated with influenza B, and 62 (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 2018-09

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	63	24
5	9	54	19
6	10	75	31
7	11	55	28
8	8	57	22
9	8	79	16

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 3,892 influenza-associated hospitalizations were reported by participating provinces and territories1. Among the hospitalizations, 2,861 (74%) were associated with influenza A, and 2,629 cases (68%) were in adults 65 years of age or older.

Additionally, 377 ICU admissions and 189 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 (42%). 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 2018-09

Age Group	Total
0-4 yr	227
5-19 yr	164
20-44 yr	236
45-64 yr	636
65+ yr	2629

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 09, 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 09, 58 hospitalizations were reported of which 36 (62%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 811 pediatric hospitalizations have been reported by the IMPACT network, 516 (64%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 295 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (30%).

Additionally, 135 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 43% 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 2018-09

Age Group	Total
0-5 mo	90
6-23 mo	184
2-4 yr	214
5-9 yr	182
10-16 yr	141

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 2018-09

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	8	5	1	13
47	13	4	0	9
48	16	9	2	23
49	23	15	3	28
50	26	23	4	47
51	39	32	4	72
52	60	47	7	92
1	57	40	5	75
2	39	35	4	62
3	50	38	4	67
4	93	35	7	47
5	67	40	11	59
6	88	40	17	120
7	88	40	17	120
8	69	47	25	139
9	58	50	13	153

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 2,085 influenza viruses [1,040 A(H3N2), 123 A(H1N1)pdm09 and 922 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition 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 2018-09

Strain Characterization Results	Count	Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like	207	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	30	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	123	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)	8	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)	36	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)	878	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, 803 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 719 A(H3N2) viruses belonged to genetic group 3C.2a, 82 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 237 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 176 belonged to genetic group 3C.2a and 21 viruses belonged to subclade 3C.2a1. The 30 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the 10 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 28 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the eight remaining virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 913 influenza viruses for resistance to oseltamivir and 909 viruses for resistance to zanamivir. All but one of the A(H1N1) 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 2018-09

Virus type and subtype	Oseltamivir		Zanamivir
	# tested	# resistant (%)	# tested	# resistant (%)
A (H3N2)	435	0 (0%)	431	0 (0%)
A (H1N1)	89	1 (1.1%)	89	0 (0%)
B	389	0 (0%)	389	1 (0.3%)
TOTAL	913	1 (0.1%)	909	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.