FluWatch report: February 24, 2019 to March 2, 2019 (week 09)

Figure 1 - Text equivalent

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Localized
N.L.	Labrador-Grenfell	Localized
N.L.	Central	Sporadic
N.L.	Western	NoActivity
P.E.I.	Prince Edward Island	Sporadic
N.S.	Zone 1 - Western	Localized
N.S.	Zone 2 - Northern	Sporadic
N.S.	Zone 3 - Eastern	Localized
N.S.	Zone 4 - Central	Localized
N.B.	Region 1	Localized
N.B.	Region 2	Localized
N.B.	Region 3	Sporadic
N.B.	Region 4	Sporadic
N.B.	Region 5	Sporadic
N.B.	Region 6	Sporadic
N.B.	Region 7	Sporadic
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
Que.	Montréal et Laval	Localized
Que.	Ouest-du-Québec	Sporadic
Que.	Montérégie	Localized
Ont.	Central East	Localized
Ont.	Central West	Localized
Ont.	Eastern	Localized
Ont.	North East	Localized
Ont.	North West	Sporadic
Ont.	South West	Localized
Ont.	Toronto	Localized
Man.	Northern Regional	NoData
Man.	Prairie Mountain	NoData
Man.	Interlake-Eastern	NoData
Man.	Winnipeg	NoData
Man.	Southern Health	NoData
Sask.	North	No Activity
Sask.	Central	Sporadic
Sask.	South	Sporadic
Alta.	North Zone	Sporadic
Alta.	Edmonton	Sporadic
Alta.	Central Zone	Sporadic
Alta.	Calgary	Localized
Alta.	South Zone	Sporadic
B.C.	Interior	Sporadic
B.C.	Fraser	Sporadic
B.C.	Vancouver Coastal	Sporadic
B.C.	Vancouver Island	Sporadic
B.C.	Northern	Sporadic
Y.T.	Yukon	Sporadic
N.W.T.	North	Sporadic
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	Sporadic
Nvt.	Kivalliq	Sporadic
Nvt.	Kitimeot	Sporadic

Laboratory-Confirmed Influenza Detections

In week 09, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza continued to increase slightly to 20.1%.
• A total 1,692 laboratory detections of influenza were reported, of which 96% were influenza A.
• Influenza A(H3N2) accounted for 58% of subtyped influenza A detections.
• Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 271 this week.

To date this season, 34,267 laboratory-confirmed influenza detections have been reported:

• 98% have been influenza A.
• Among the 11,749 influenza A viruses subtyped, 87% have been A(H1N1)pdm09.
• Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 26,890 laboratory-confirmed influenza cases (Table 1):

• 84% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
• 61% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

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.

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 equivalent

Surveillance Week	A(Unsubtyped)	A(H3)	A(H1)pdm09	Influenza B
35	3	2	7	0
36	4	7	4	0
37	3	2	3	1
38	6	3	2	3
39	11	5	1	3
40	16	7	29	3
41	27	6	21	3
42	40	19	55	2
43	83	23	128	4
44	169	13	214	6
45	244	18	295	15
46	346	10	404	9
47	449	17	507	8
48	679	29	632	10
49	851	35	785	16
50	1368	35	828	14
51	1890	54	953	21
52	2292	55	903	26
1	2387	58	893	31
2	1985	93	1061	43
3	1613	101	585	40
4	1483	93	532	48
5	1449	112	433	43
6	1234	118	315	42
7	1116	128	244	33
8	1067	235	216	40
9	1189	271	198	63

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (February 24 to March 2, 2019)					Cumulative (August 26, 2018 to March 2, 2019)
	Influenza A				B	Influenza A				B	A & B Total
	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
BC	408	114	124	170	11	4068	2596	467	1005	44	4112
AB	81	9	42	30	4	5471	3494	224	1753	78	5549
SK	10	2	1	7	4	2244	1353	62	829	18	2262
MB	18	5	7	6	2	1012	280	21	711	8	1020
ON	264	55	91	118	11	4418	1868	745	1805	95	4513
QC	601	0	0	601	28	13198	0	0	13198	268	13466
NB	128	0	2	126	1	2095	197	17	1881	3	2098
NS	64	0	0	64	0	400	0	0	400	6	406
PEI	11	9	2	0	0	196	194	2	0	0	196
NL	40	0	0	40	0	397	1	0	396	2	399
YT	3	0	2	1	0	71	50	3	18	0	71
N.W.T	3	3	0	0	0	156	154	2	0	0	156
NU	0	0	0	0	0	19	19	0	0	0	19
Canada	1631	197	271	1163	61	33745	10206	1543	21996	522	34267
PercentageTable Figure 3 - Footnote 2	96%	12%	17%	71%	4%	98%	30%	4%	65%	2%	100%
Table Figure 3 - Footnote 1 Specimens from NWT, YT, and Nvt 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.

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2018-35 to 2019-09

Age groups (years)	Cumulative (August 26, 2018 to March 2, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)Footnote 1	Total	#	%
0-4	5671	1594	58	4019	72	5743	21%
5-19	3892	1321	79	2492	90	3982	15%
20-44	5286	1743	174	3369	69	5355	20%
45-64	5307	1653	168	3486	54	5361	20%
65+	6292	1173	752	4367	157	6449	24%
Total	26448	7484	1231	17733	442	26890	100%
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

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 09, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is low compared to previous seasons.

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18

Figure 4 - Text equivalent

Surveillance Week	2018-19	Average	Min	Max
35	0.6%	0.8%	0.5%	1.2%
36	0.7%	0.8%	0.7%	1.0%
37	0.6%	0.9%	0.7%	1.0%
38	0.5%	1.1%	1.0%	1.4%
39	1.8%	1.1%	0.9%	1.4%
40	0.6%	1.3%	0.9%	1.6%
41	1.1%	1.4%	0.9%	2.4%
42	1.0%	1.4%	1.0%	1.9%
43	0.9%	1.3%	1.0%	1.5%
44	0.8%	1.3%	0.9%	1.6%
45	1.3%	1.3%	1.2%	1.5%
46	1.3%	1.6%	1.0%	2.0%
47	1.3%	1.5%	1.1%	1.9%
48	1.5%	1.6%	0.8%	2.1%
49	1.6%	1.5%	1.0%	2.5%
50	1.5%	2.3%	1.3%	3.7%
51	1.0%	2.5%	1.6%	4.1%
52	3.2%	4.5%	1.7%	7.1%
1	2.8%	3.7%	1.7%	5.2%
2	1.8%	3.0%	1.1%	4.5%
3	1.1%	2.5%	1.3%	3.6%
4	1.3%	2.4%	1.7%	3.5%
5	1.4%	2.7%	2.0%	4.4%
6	0.9%	2.7%	2.1%	3.3%
7	0.9%	2.4%	1.7%	3.0%
8	1.1%	2.3%	1.9%	2.7%
9	1.6%	2.2%	1.8%	2.7%

Participatory Syndromic Surveillance

In week 09, 2,101 participants reported to FluWatchers, of which 57 (Figure 5).

Among the 57 participants who reported fever and cough:

• 16% consulted a healthcare professional;
• 74% reported days missed from work or school, resulting in a combined total of 118 missed days of work or school.

Figure 5 - Text equivalent

Surveillance week	% cough and fever
40	2.6%
41	2.5%
42	1.7%
43	1.5%
44	1.3%
45	1.7%
46	2.0%
47	1.3%
48	2.4%
49	2.0%
50	3.7%
51	3.9%
52	3.6%
1	3.4%
2	2.8%
3	2.5%
4	2.9%
5	3.0%
6	2.6%
7	2.7%
8	2.5%
9	2.7%

Influenza Outbreak Surveillance

In week 09, 37 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (18), acute care facilities (8), schools and daycares (1) and other settings (10). Among the outbreaks with available subtype information (12), 92% (11) were associated with influenza A(H3N2).

To date this season, 491 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

• 292 (59%) outbreaks were in LTCF, 28 were in schools, 71 in acute care facilities, and 100 were in other settings.
• Among the 444 outbreaks for which the influenza type was available, 98% (436) were associated with influenza A.
• Among the 194 outbreaks for which the influenza A subtype was available, 59% (114) were associated with influenza A(H1N1)pdm09;

To date this season, 107 ILI outbreaks have been reported; 56 occurred in LTCF, 47 in schools, and four in acute care facilities.

Figure 6 - Text equivalent

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares	Remote and/or Isolated Communities
35	0	0	0	0	0
36	0	0	0	0	0
37	0	0	0	0	0
38	0	0	0	0	0
39	0	0	0	0	0
40	0	2	0	1	0
41	0	0	0	0	0
42	0	1	1	0	0
43	0	3	1	0	0
44	0	1	1	2	0
45	0	2	1	3	0
46	2	5	1	3	0
47	2	4	0	1	0
48	2	6	1	5	0
49	1	2	3	1	0
50	3	8	5	4	0
51	3	12	4	2	0
52	4	24	5	0	0
1	5	40	11	0	0
2	8	38	7	0	0
3	3	27	10	0	0
4	6	18	10	1	0
5	5	22	7	0	0
6	9	20	7	0	0
7	6	18	5	0	0
8	4	21	10	4	0
9	8	18	10	1	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,214 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 99.5% (2,202) were associated with influenza A
• The highest estimated rate of hospitalization is among children under 5 years of age.

Intensive Care Unit (ICU) cases and deaths:

• To date this season 403 ICU admissions and 93 deaths have been reported.
  • 42% (163) of reported ICU admissions were in adults aged 45-64 years.
  • All but two ICU admissions were associated with influenza A.
  • All but one of the deaths were associated with influenza A.

Table 2 - Cumulative number of hospitalizations by age-group and influenza type, reported by participating provinces and territories^{Footnote 1}, Canada, weeks 2018-35 to 2019-09

Age Groups (years)	Cumulative (August 26, 2018 to March 2, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	323	4	68.70
5-19	189	2	13.76
20-44	294	0	10.33
45-64	610	2	28.12
65+	786	4	64.93
Total	2202	12
%	99.5%	0.5%
Table 2 - Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 - Note 1

Pediatric Influenza Hospitalizations and Deaths

In week 09, 30 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7).

To date this season, 964 pediatric hospitalizations have been reported (Figure 8):

• 69% of cases were in children under 5 years of age.
• 98% (947) of cases have been associated with influenza A.
• Among the 301 cases for which the influenza subtype was available, 283 (94%) were associated with A(H1N1)pdm09.

To date this season, 167 ICU admissions, and 10 deaths have been reported.

• 63% (106) of ICU admissions were in children under 5 years of age.
• All but two of the ICU admissions have been associated with influenza A.
• 80% (8) of deaths occurred in children 2 to 4 years of age.
• All deaths have been associated with influenza A.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Figure 7 - Text equivalent

Surveillance week	2018-19	Average	Min	Max
35	0	0	0	0
36	0	0	0	1
37	0	0	0	2
38	0	0	0	2
39	0	1	0	3
40	0	0	0	2
41	1	1	0	2
42	5	1	0	4
43	11	1	0	3
44	15	3	1	6
45	37	3	2	4
46	41	5	1	13
47	36	4	0	9
48	43	9	2	23
49	43	15	3	28
50	51	23	4	47
51	85	32	4	72
52	89	47	7	92
1	93	40	5	75
2	60	35	4	62
3	70	38	4	67
4	60	35	7	47
5	51	40	11	59
6	48	38	15	79
7	44	40	17	120
8	46	47	25	139
9	30	50	13	153

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	101
6-23 mo	250
2-4 yr	310
5-9 yr	212
10-16 yr	91

Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1^st for the 2018-19 season.

To date this season, 641 hospitalizations, 71 ICU admissions and 25 deaths have been reported (Figure 9):

• 594 (93%) hospitalizations were associated with influenza A.
• A greater proportion of hospitalizations have been reported among  adults ≥65 years of age (58%) compared to adults <65 years of age (42%).
• 85% of hospitalized cases reported more than one type of comorbid condition.  
• The most commonly reported comorbidity was endocrine disorders, which were reported in 81% of hospitalized cases.

Figure 9 - Text equivalent

Age Group	Total
20-34 yr	60
35-49 yr	64
50-64 yr	145
65-79 yr	187
80+ yr	185

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,495 influenza viruses (174 A(H3N2), 1,289 A(H1N1) and 32 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

87 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.

Sequence analysis of the HA gene of the viruses showed that:

• 16 viruses belonged to genetic group 3C.2a.
• 68 viruses belonged to subclade 3C.2a1.
• Two viruses belonged to 3C.3a.
• One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.

Antigenic Characterization:

Influenza A (H3N2):

• 65 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
• 22 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
• A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
• 44 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 15 viruses belonged to genetic group 3C.2a and 11 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,253 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
• 36 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:

Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

• Nine influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
• Four viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
• 19 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

Antiviral Resistance – Amantadine:

365 influenza A (55 A(H3N2) and 310 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 365 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

891 influenza viruses (81 A(H3N2), 783 A(H1N1) and 27 B) were tested for resistance to oseltamivir and it was found that:

• All 81 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 783 A(H1N1) viruses tested, 780 were sensitive to oseltamivir and three viruses were resistant to oseltamivir with a H275Y mutation.
• All 27 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

890 influenza viruses (81 A(H3N2), 782 H1N1 and 27 B) were tested for resistance to zanamivir and it was found that:

• All 890 influenza viruses were sensitive to zanamivir.