FluWatch report: May 6 to May 12, 2018 (Week 19)

Influenza/Influenza-like Illness Activity (geographic spread)

In week 19, nine regions (ON(5), QC(1), NB(1), NL(1) and NS(1)) reported localized activity. Seventeen regions across nine provinces and territories 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 2018-19

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

Laboratory-Confirmed Influenza Detections

In week 19, the percentage of tests positive for influenza was 5%, a decrease from the previous week. Laboratory detections of influenza are steadily decreasing. In week 19, 176 positive influenza tests were reported, down from 367 tests reported in week 18. Influenza A accounted for 57% of influenza detections in week 19.

Overall, laboratory detections of influenza are below 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 2018-19

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	302	84	29	322
17	214	62	35	238
18	153	51	44	129
19	87	7	10	79

To date this season, 64,040 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 90% 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 2018-19

Reporting provincesTable Figure 3 - Footnote 1	Week (May 6, 2018 to May 12, 2018)					Cumulative (August 27, 2017 to May 12, 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	2	1	1	0	2	2475	516	1515	444	3021	5496
AB	7	5	0	2	9	5667	253	3994	1420	3378	9045
SK	5	0	0	5	3	1755	70	1150	535	1732	3487
MB	0	0	0	0	3	1133	19	378	736	635	1768
ON	18	0	1	17	15	6298	288	3466	2544	4820	11118
QC	31	0	0	31	12	15452	0	0	15452	12329	27781
NB	30	3	5	22	19	1670	31	240	1399	1243	2913
NS	2	0	0	2	7	551	0	0	551	300	851
PE	0	0	0	0	1	146	8	134	4	171	317
NL	5	0	0	5	4	476	0	3	473	433	909
YT	0	0	0	0	0	76	7	48	21	43	119
NT	0	0	0	0	0	130	4	126	0	56	186
NU	0	0	0	0	1	46	6	40	0	4	50
Canada	100	9	7	84	76	35875	1202	11094	23579	28165	64040
PercentageTable figure 3 Footnote 2	57%	9%	7%	84%	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 54,849 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) (57%) and influenza B (46%). 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 (992), 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 52% 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 2018-19

Age groups (years)	Cumulative (August 27, 2017 to May 12, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)table 1 note 1	Total	#	%
0-4	3340	175	690	2475	1623	4963	9%
5-19	2564	145	724	1695	2995	5559	10%
20-44	4587	272	1430	2885	3052	7639	14%
45-64	4967	242	1639	3086	5119	10086	18%
65+	15605	158	5844	9603	10997	26602	49%
Total	31063	992	10327	19744	23786	54849	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 19, 1.4% of visits to healthcare professionals were due to influenza-like illness (ILI).

Number of Sentinels Reporting in Week 19: 154

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 2018-19

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	2.1%	1.5%	1.1%	1.9%
48	2.5%	1.6%	0.8%	2.1%
49	1.7%	1.5%	1.0%	2.5%
50	2.1%	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	4.5%	3.7%	1.7%	5.2%
2	2.7%	3.0%	1.1%	4.5%
3	2.7%	2.5%	1.3%	3.6%
4	2.9%	2.4%	1.7%	3.5%
5	4.0%	2.7%	2.0%	4.4%
6	3.4%	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	1.7%	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	1.3%	1.5%	1.0%	1.9%
17	1.5%	1.5%	0.9%	2.2%
18	1.3%	1.2%	0.8%	1.6%
19	1.4%	1.3%	1.0%	1.7%
20		1.2%	0.9%	1.4%
21		0.9%	0.3%	1.3%
22		0.8%	0.6%	1.0%
23		0.9%	0.6%	1.2%
24		0.7%	0.4%	1.0%
25		1.2%	0.5%	1.6%
26		0.8%	0.4%	1.4%
27		0.8%	0.4%	1.5%
28		1.0%	0.6%	1.9%
29		0.8%	0.5%	1.1%
30		0.5%	0.3%	0.7%
31		0.9%	0.3%	1.4%
32		1.0%	0.6%	1.6%
33		1.2%	0.4%	2.1%
34		0.7%	0.5%	0.9%

Participatory Syndromic Surveillance

FluWatchers is a participatory ILI surveillance system that relies on weekly voluntary submissions of syndromic information from Canadians across Canada.

FluWatchers surveillance has ended for the 2017-18 season.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-18

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
1270	1%	0%	75%	36

Influenza Outbreak Surveillance

In week 19, five laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, two were reported in long-term care facilities (LTC), two in hospitals and one in an other setting.

To date this season, 1,794 influenza/ILI outbreaks have been reported, of which 1,104 (62%) occurred in LTC facilities. Among the 1,532 outbreaks for which the influenza type/subtype was reported, 842 (55%) were associated with influenza A and 618 (40%) were associated with influenza B, and 72 (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 2018-19

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	10	4
17	0	6	3
18	3	4	4
19	2	2	1

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 5,076 influenza-associated hospitalizations were reported by participating provinces and and territories^{Footnote 1}. Among the hospitalizations, 3,382 (67%) were associated with influenza A, and 3,317 cases (65%) were in adults 65 years of age or older.

Additionally, 508 ICU admissions and 295 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 2018-19

Age group	Total
0-4	318
5-19	236
20-44	333
45-64	872
65+	3317

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 19, three laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Pediatric hospitalizations have been on a general decline since week 07. The number of weekly reported hospitalizations are below the seven-season average.

To date this season, 1,068 pediatric hospitalizations have been reported by the IMPACT network, 665 (62%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 403 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 186 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (31%), followed by children aged 5-9 years (26%). Among the ICU cases with available information, 62% 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 2018-19

Age Group	Total
0-5 mo	112
6-23 mo	249
2-4 yr	267
5-9 yr	259
10-16 yr	181

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-18

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 2018-19

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	60	47	7	92
1	57	40	5	75
2	38	35	4	62
3	52	38	4	67
4	93	35	7	47
5	70	40	11	59
6	74	38	15	79
7	83	40	17	120
8	72	47	25	139
9	67	50	13	153
10	60	48	17	135
11	57	41	18	118
12	34	33	13	89
13	28	32	14	67
14	31	24	12	56
15	13	23	13	56
16	9	20	10	41
17	13	16	8	37
18	10	14	4	28
19	3	10	5	18
20		10	4	19
21		5	2	10
22		4	1	8
23		2	0	5
24		2	0	5
25		1	0	3
26		1	0	3
27		1	0	2
28		1	0	2
29		0	0	2
30		0	0	1
31		0	0	0
32		0	0	1
33		0	0	0
34		1	0	2

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,646 influenza viruses [1,509 A(H3N2), 292 A(H1N1)pdm09 and 1,845 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 2018-19

Strain Characterization Results	Count	Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like	300	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	95	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	292	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)	24	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)	54	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)	1767	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, 1,114 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 998 A(H3N2) viruses belonged to genetic group 3C.2a, 114 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 395 influenza A(H3N2) viruses that were antigenically characterized, 274 belonged to genetic group 3C.2a and 26 viruses belonged to subclade 3C.2a1. The 95 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a.

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

Of the 78 influenza B viruses characterized as B/ B/Brisbane/60/2008-like, 24 viruses were antigenically similar to the vaccine strain B/Brisbane/60/2008. Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that 50 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the remaining four virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,565 influenza viruses for resistance to oseltamivir and 1,561 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). The A(H1N1)pdm09 virus resistant to oseltamivir had a H275Y mutation.

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-19

Virus type and subtype	Oseltamivir		Zanamivir
	# tested	# resistant (%)	# tested	# resistant (%)
A (H3N2)	558	1 (0.2%)	554	0 (0%)
A (H1N1)	235	1 (0.4%)	235	0 (0%)
B	772	1 (0.1%)	772	2 (0.3%)
TOTAL	1565	3 (0.2%)	1561	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