FluWatch report: March 17, 2019 to March 23, 2019 (week 12)

Figure 1 - Text equivalent

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Localized
N.L.	Labrador-Grenfell	Sporadic
N.L.	Central	Sporadic
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	Sporadic
N.S.	Zone 4 - Central	Localized
N.B.	Region 1	Sporadic
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	Localized
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
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	Sporadic
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	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	No Data
N.W.T.	South	No Data
Nvt.	Qikiqtaaluk	Sporadic
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	No Activity

Laboratory-Confirmed Influenza Detections

In week 12, 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 21.8%.
• A total 1,735 laboratory detections of influenza were reported, of which 93% were influenza A.
• Influenza A(H3N2) accounted for 72% of subtyped influenza A detections.
• Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 342 this week.

To date this season, 39,297 laboratory-confirmed influenza detections have been reported:

• 98% have been influenza A.
• Among the 13,414 influenza A viruses subtyped, 81% 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 30,844 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.
• 57% 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	1037	295	219	64
10	1085	335	268	71
11	990	354	195	89
12	1261	342	132	129

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (March 17 to 23, 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	539	59	125	355	22	5288	2937	934	1417	105	5393
AB	159	22	87	50	22	5899	3551	439	1909	142	6041
SK	12	1	4	7	13	2240	1368	78	794	48	2288
MB	11	2	3	6	3	1045	290	39	716	11	1056
ON	230	24	100	106	11	5134	1992	1038	2104	127	5261
QC	423	0	0	423	26	14735	0	0	14735	330	15065
NB	120	13	6	101	24	2439	230	34	2175	33	2472
NS	77	0	0	77	2	628	0	0	628	10	638
PEI	14	5	9	0	0	243	216	27	0	0	243
NL	78	0	0	78	1	576	1	0	575	3	579
YT	0	0	0	0	0	74	50	4	20	0	74
N.W.T	3	3	0	0	0	166	164	2	0	1	167
NU	0	0	0	0	0	20	20	0	0	0	20
Canada	1666	129	334	1203	124	38487	10819	2595	25073	810	39297
PercentageTable Figure 3 - Footnote 2	93%	8%	20%	72%	7%	98%	28%	7%	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 2019-12

Age groups (years)	Cumulative (August 26, 2018 to March 23, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)Table 1 - Note 1	Total	#	%
0-4	6093	1639	106	4348	115	6208	20%
5-19	4425	1359	240	2826	176	4601	15%
20-44	5905	1882	298	3725	117	6022	20%
45-64	5915	1800	292	3823	70	5985	19%
65+	7852	1320	1265	5267	176	8028	26%
Total	30190	8000	2201	19989	654	30844	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 12, 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 2013-14 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	0.8%	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	1.6%	1.8%	1.1%	2.7%

Participatory Syndromic Surveillance

In week 12, 2,056 participants reported to FluWatchers, of which 50 (2.4%) reported symptoms of cough and fever (Figure 5).

Among the 50 participants who reported fever and cough:

• 30% consulted a healthcare professional;
• 92% reported days missed from work or school, resulting in a combined total of 136 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%

Influenza Outbreak Surveillance

In week 12, 38 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (19), acute care facilities (8) and other settings (11). Eleven new ILI outbreaks (LTCF (8) and schools and daycares (3)) were also reported in week 12. Among the outbreaks with available subtype information (12), 92% (11) were associated with influenza A(H3N2).

To date this season, 633 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

• 371 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 94 in acute care facilities, and 138 were in other settings.
• Among the 563 outbreaks for which the influenza type was available, 98% (550) were associated with influenza A.
• Among the 243 outbreaks for which the influenza A subtype was available, 55% (125) were associated with influenza A(H1N1)pdm09;

To date this season, 134 ILI outbreaks have been reported; 75 occurred in LTCF, 55 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	18	10	1	0
5	5	23	7	0	0
6	9	20	8	0	0
7	6	20	6	0	0
8	4	28	11	4	0
9	9	23	13	2	0
10	12	23	9	1	0
11	2	21	12	0	0
12	8	19	11	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,592 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 98.7% (2,558) were associated with influenza A
• Among the 1,555 cases for which the influenza subtype was available, 1,366 (88%) 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 464 ICU admissions and 127 deaths have been reported.
  • 43% (199) 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 2019-12

Age Groups (years)	Cumulative (August 26, 2018 to March 23, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	354	12	76.89
5-19	210	10	15.85
20-44	317	4	11.28
45-64	688	3	31.75
65+	989	5	81.70
Total	2558	34
%	98.7%	1.3%
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 12, 41 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 41 hospitalizations, 34 (83%) were due to influenza A.

To date this season, 1,089 pediatric hospitalizations have been reported (Figure 8):

• 67% of cases were in children under 5 years of age.
• 97% (1,054) of cases have been associated with influenza A.
• Among the 324 cases for which the influenza subtype was available, 289 (89%) were associated with A(H1N1)pdm09.

To date this season, 194 ICU admissions, and 10 deaths have been reported.

• 60% (117) 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	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	41	33	13	89

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	115
6-23 mo	281
2-4 yr	337
5-9 yr	240
10-16 yr	117

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, 773 hospitalizations, 90 ICU admissions and 40 deaths have been reported (Figure 9):

• 718 (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 167 cases for which the influenza subtype was available, 103 (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	72
35-49 yr	75
50-64 yr	168
65-79 yr	228
80+ yr	230

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,700 influenza viruses (233 A(H3N2), 1,415 A(H1N1) and 52 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

124 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.
• 102 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):

• 82 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.
• 27 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.
• 63 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):

• 1,375 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.
• 40 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).

• 18 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.
• 12 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:

388 influenza A (64 A(H3N2) and 324 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 388 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,017 influenza viruses (103 A(H3N2), 879 A(H1N1) and 35 B) were tested for resistance to oseltamivir and it was found that:

• All 103 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 879 A(H1N1) viruses tested, 875 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
• All 35 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,016 influenza viruses (103 A(H3N2), 878 H1N1 and 35 B) were tested for resistance to zanamivir and it was found that:

• All 1,016 influenza viruses were sensitive to zanamivir.