FluWatch report: March 24, 2019 to March 30, 2019 (week 13)

Figure 1 - Text equivalent

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Localized
N.L.	Labrador-Grenfell	Sporadic
N.L.	Central	Localized
N.L.	Western	Localized
P.E.I.	Prince Edward Island	Localized
N.S.	Zone 1 - Western	Localized
N.S.	Zone 2 - Northern	Localized
N.S.	Zone 3 - Eastern	No Activity
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	Localized
N.B.	Region 7	Sporadic
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Localized
Que.	Centre-du-Québec	Localized
Que.	Montréal et Laval	Sporadic
Que.	Ouest-du-Québec	Sporadic
Que.	Montérégie	Sporadic
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	No Activity
Man.	Prairie Mountain	Sporadic
Man.	Interlake-Eastern	No Activity
Man.	Winnipeg	Sporadic
Man.	Southern Health	Sporadic
Sask.	North	Sporadic
Sask.	Central	Sporadic
Sask.	South	Sporadic
Alta.	North Zone	Sporadic
Alta.	Edmonton	Sporadic
Alta.	Central Zone	Localized
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	Localized
N.W.T.	North	Sporadic
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	No Activity
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	No Activity

Laboratory-Confirmed Influenza Detections

In week 13, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza remained steady at 22%.
• A total 1,579 laboratory detections of influenza were reported, of which 91% were influenza A.
• Influenza A(H3N2) accounted for 76% of subtyped influenza A detections.
• Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 358 this week.

To date this season, 41,372 laboratory-confirmed influenza detections have been reported:

• 98% have been influenza A.
• Among the 13,859 influenza A viruses subtyped, 79% 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 31,770 laboratory-confirmed influenza cases (Table 1):

• 83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
• 58% 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(H3N2)	A(H1N1)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	1066	236	216	40
9	1172	285	213	64
10	1243	308	248	71
11	990	357	197	90
12	1264	358	143	131
13	1160	359	114	164

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (March 24 to March 30, 2019)					Cumulative (August 26, 2018 to March 23, 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	499	59	147	293	38	6065	2981	1065	2019	143	6208
AB	178	21	100	57	21	6088	3572	549	1967	163	6251
SK	13	5	3	5	12	2273	1373	82	818	60	2333
MB	13	1	9	3	7	1058	293	43	722	18	1076
ON	188	21	89	78	6	5342	2016	1122	2204	136	5478
QC	428	0	0	428	30	15163	0	0	15163	360	15523
NB	101	0	0	101	49	2540	230	34	2276	82	2622
NS	39	0	0	39	1	667	0	0	667	11	678
PEI	12	1	10	1	0	255	217	37	1	0	255
NL	97	0	0	97	0	673	1	0	672	3	676
YT	7	0	0	7	0	81	50	4	27	0	81
N.W.T	4	4	0	0	0	170	168	2	0	1	171
Nvt.	0	0	0	0	0	20	20	0	0	0	20
Canada	1579	112	358	1109	164	40395	10921	2938	26536	977	41372
PercentageTable Figure 3 - Footnote 2	91%	7%	23%	70%	9%	98%	27%	7%	66%	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 2019-13

Age groups (years)	Cumulative (August 26, 2018 to March 30, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)Table 1 - Note 1	Total	#	%
0-4	6148	1644	127	4377	130	6278	20%
5-19	4537	1366	281	2890	202	4739	15%
20-44	6059	1910	332	3817	137	6196	20%
45-64	6079	1832	345	3902	76	6155	19%
65+	8224	1360	1479	5385	178	8402	26%
Total	31047	8112	2564	20371	723	31770	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 13, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018

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	0.8%	2.4%	1.7%	3.0%
8	0.9%	2.3%	1.9%	2.7%
9	1.0%	2.2%	1.8%	2.7%
10	1.0%	2.1%	1.8%	2.7%
11	0.8%	2.1%	1.7%	2.7%
12	1.2%	1.8%	1.1%	2.7%
13	1.6%	1.7%	1.2%	2.6%

Participatory Syndromic Surveillance

In week 13, 2,041 participants reported to FluWatchers, of which 49 (2.4%) reported symptoms of cough and fever (Figure 5).

Among the 49 participants who reported fever and cough:

• 16% consulted a healthcare professional;
• 67% reported days missed from work or school, resulting in a combined total of 110 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%
10	3.1%
11	2.6%
12	2.4%
13	2.4%

Influenza Outbreak Surveillance

In week 13, 31 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (13), acute care facilities (7) and other settings (11). Three new ILI outbreaks (LTCF (2) and schools and daycares (1)) were also reported in week 13. Among the outbreaks with available subtype information (8), all (8) were associated with influenza A(H3N2).

To date this season, 664 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

• 385 (58%) outbreaks were in LTCF, 30 were in schools and daycares, 102 in acute care facilities, and 147 were in other settings.
• Among the 603 outbreaks for which the influenza type was available, 98% (590) were associated with influenza A.
• Among the 262 outbreaks for which the influenza A subtype was available, 51% (128) were associated with influenza A(H3N2);

To date this season, 137 ILI outbreaks have been reported; 77 occurred in LTCF, 56 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	9	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	19	10	1	0
5	5	23	7	0	0
6	9	21	7	0	0
7	6	20	6	0	0
8	5	29	11	4	0
9	9	23	13	2	0
10	12	26	8	1	0
11	2	22	13	0	0
12	8	19	11	0	0
13	7	13	11	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,701 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 98.4% (2,659) were associated with influenza A
• Among the 1,629 cases for which the influenza subtype was available, 1,380 (85%) were associated with A(H1N1)pdm09.
• The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

• To date this season 474 ICU admissions and 139 deaths have been reported.
  • 43% (202) of reported ICU admissions were in adults aged 45-64 years.
  • All but four ICU admissions were associated with influenza A.
  • All but one of the deaths were associated with influenza A.

Table 2 - Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territories^{Footnote 1}, Canada, weeks 2018-35 to 2019-13

Age Groups (years)	Cumulative (August 26, 2018 to March 30, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	361	15	79.00
5-19	218	13	16.65
20-44	327	4	11.63
45-64	704	4	32.53
65+	1049	6	86.71
Total	2659	42
%	98.4%	1.6%
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 13, 30 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 30 hospitalizations, 27 (90%) were due to influenza A.

To date this season, 1,116 pediatric hospitalizations have been reported (Figure 8):

• 67% of cases were in children under 5 years of age.
• 96% (1,076) of cases have been associated with influenza A.
• Among the 330 cases for which the influenza subtype was available, 289 (89%) were associated with A(H1N1)pdm09.

To date this season, 197 ICU admissions, and 10 deaths have been reported.

• 60% (119) of ICU admissions were in children under 5 years of age.
• All but six 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	12	1	0	3
44	15	3	1	6
45	37	3	2	4
46	41	5	1	13
47	36	4	0	9
48	40	9	2	23
49	46	15	3	28
50	51	23	4	47
51	84	32	4	72
52	89	47	7	92
1	91	40	5	75
2	62	35	4	62
3	70	38	4	67
4	61	35	7	47
5	50	40	11	59
6	48	38	15	79
7	44	40	17	120
8	43	47	25	139
9	35	50	13	153
10	45	48	17	135
11	42	41	18	118
12	42	33	13	89
13	30	32	14	67

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	119
6-23 mo	288
2-4 yr	343
5-9 yr	244
10-16 yr	122

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, 812 hospitalizations, 98 ICU admissions and 43 deaths have been reported (Figure 9):

• 757 (93%) hospitalizations were associated with influenza A.
• A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
• Among the 169 cases for which the influenza subtype was available, 105 (62%) were associated with A(H1N1)pdm09.
• 88% of hospitalized cases reported more than one type of comorbid condition.
• The most commonly reported comorbidity was endocrine disorders, which were reported in 83% of hospitalized cases.

Figure 9 - Text equivalent

Age Group	Total
20-34 yr	77
35-49 yr	78
50-64 yr	176
65-79 yr	241
80+ yr	240

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,745 influenza viruses (244 A(H3N2), 1,445 A(H1N1) and 56 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

130 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:

• 18 viruses belonged to genetic group 3C.2a.
• 108 viruses belonged to subclade 3C.2a1.
• Three 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):

• 85 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.
• 29 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.
• 64 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,404 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.
• 41 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).

• 15 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.
• 19 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
• 22 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:

412 influenza A (71 A(H3N2) and 341 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 412 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,057 influenza viruses (109 A(H3N2), 903 A(H1N1) and 45 B) were tested for resistance to oseltamivir and it was found that:

• All 109 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 903 A(H1N1) viruses tested, 899 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
• All 45 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,056 influenza viruses (109 A(H3N2), 902 H1N1 and 45 B) were tested for resistance to zanamivir and it was found that:

• All 1,056 influenza viruses were sensitive to zanamivir.