FluWatch report: December 8 to 14, 2019 (week 50)

Influenza/Influenza-like Illness (ILI) Activity (geographic spread)

During week 50, both the number of regions reporting influenza activity and the level of activity reported increased compared to the previous week (Figure 1).

• Activity was reported across the country, in 11 provinces and territories.
• 74% of regions reported influenza activity; among these 72% reporting sporadic activity and 28% reported localized activity

Figure 1 - Text equivalent

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

Laboratory-Confirmed Influenza Detections

In week 50, the number of detections of influenza continued to increase, with an equal proportion of influenza A and B detections. The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza was 15.6%. This is similar to the average (15.3%) for week 50 over the past five seasons.
• A total of 1,272 laboratory detections of influenza were reported, of which 50.2% (638) were influenza A. The proportion of detections that are influenza B has been increasing since week 44 (October 27 to November 2), to 49.8% in week 50.
• The percentage of tests positive for influenza B (7.8%) is higher than the average (1.5%) for this time of year. The current level of influenza B activity is not normally seen until February or March.
• Among subtyped influenza A detections, a mix of A(H1N1) and A(H3N2) were detected; 60% (87 out of 145) were influenza A(H3N2).

To date this season (weeks 35 to 50), 3,762 laboratory detections of influenza were reported:

• 61% (2,291) were influenza A. The percentage of tests positive for influenza B to date this season is following a similar trend to the 2017-18 season, when influenza A and B circulated in almost equal proportions.
• Among subtyped influenza A detections (790), 68% were influenza A(H3N2).

Detailed information on age and type/subtype has been received for 3,241 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 50):

• Among cases of influenza A(H3N2) (397), the largest proportion were in adults 65 years of age and older (45%).
• Cases of influenza B (1,357) were primarily in younger age groups; 63% of cases were under 20 years of age and 30% between 20 and 44 years of age.
• Among cases of influenza A(H1N1) (215), 35% of cases were in adults between 45 and 64 years of age, and 23% between 20 and 44 years of age.

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	Percent Positive A	Percent Positive B
35	10	16	0	2	1.3	0.1
36	11	13	2	2	1.1	0.1
37	5	17	2	5	0.9	0.2
38	11	15	3	6	1.0	0.2
39	11	21	2	3	1.0	0.1
40	34	9	1	2	1.2	0.1
41	34	18	0	5	1.4	0.1
42	54	12	1	14	1.6	0.3
43	44	13	7	17	1.6	0.3
44	43	23	16	17	1.8	0.3
45	57	57	20	39	2.2	0.7
46	82	43	23	77	2.7	1.4
47	118	49	33	124	3.1	1.9
48	225	67	42	223	4.9	3.2
49	281	79	41	336	5.3	4.2
50	472	87	58	634	7.8	7.8

Footnote *

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces.

Return to footnote * referrer

Figure 3 - Text equivalent

Provinces Table Figure 3 - Footnote 1	Cumulative (August 25, 2019 to December 14, 2019)
	A Total	A(H1N1)	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A & B Total
B.C.	302	30	101	74	88	390
Alta.	568	102	292	174	644	1212
Sask.	84	0	0	84	23	107
Man.	76	9	29	38	118	194
Ont.	359	99	83	177	114	473
Que.	820	0	0	820	468	1288
N.B.	29	5	4	20	10	39
N.S.	2	0	0	2	2	4
P.E.I.	4	0	0	4	2	6
N.L.	25	0	21	4	2	27
Y.T.	14	0	8	6	0	14
N.W.T	8	6	1	1	0	8
Nvt.	0	0	0	0	0	0
Canada	2291	251	539	1404	1471	3762
PercentageTable Figure 3 - Footnote 2	61%	11%	24%	61%	39%	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 Table Figure 3 - Footnote 3 referrer

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age group reported through case-based laboratory reporting, Canada, weeks 2019-35 to 2019-50

Age groups (years)	Cumulative (August 25, 2019 to December 14, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped)1	Total	#	%
0-4	265	40	59	166	222	487	15%
5-19	226	11	64	151	632	858	26%
20-44	344	49	74	221	402	746	23%
45-64	376	76	82	218	48	424	13%
65+	673	39	225	409	53	726	22%
Total	1884	215	504	1165	1357	3241	100%
Table 1 Footnote 1 Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Table 1 Return to footnote 1 referrer

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 50, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI) which is slightly above the average for this time of year (1.5%) (Figure 4).

Number of participants reporting in week 50: 83

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2014-2015 to 2018-2019

Figure 4 - Text equivalent

Surveillance Week	2019-20	Average	Min	Max
35	0.6%	0.6%	0.4%	0.9%
36	0.4%	0.6%	0.4%	0.9%
37	0.7%	0.7%	0.5%	1.0%
38	1.1%	0.7%	0.6%	1.0%
39	0.8%	0.9%	0.5%	1.2%
40	1.0%	1.2%	0.8%	1.7%
41	0.9%	1.7%	0.8%	2.8%
42	1.1%	1.6%	1.2%	2.1%
43	0.7%	1.2%	0.8%	1.7%
44	0.9%	1.2%	0.7%	1.7%
45	0.8%	1.2%	0.9%	1.5%
46	1.2%	1.4%	1.2%	1.8%
47	1.4%	1.6%	1.1%	2.2%
48	1.1%	1.5%	1.1%	2.2%
49	1.1%	1.7%	1.0%	2.8%
50	1.8%	1.5%	1.1%	1.7%

FluWatchers

In week 50, 3,088 participants reported to FluWatchers, of which 2.1% (65) reported symptoms of cough and fever (Figure 5).

Among the 65 participants who reported cough and fever:

• 28% consulted a healthcare professional;
• 71% reported days missed from work or school, resulting in a combined total of 108 missed days of work or school.
• 70% reported having been vaccinated for influenza this season.

If you are interested in becoming a FluWatcher, sign up today.

Number of Participants Reporting in Week 50: 3,088

Figure 5 - Text equivalent

Surveillance Week	% cough and fever
40	2.2%
41	1.8%
42	1.7%
43	2.2%
44	1.6%
45	1.4%
46	1.2%
47	1.5%
48	1.7%
49	2.2%
50	2.1%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2019-50

Click on the map to access the link

Influenza Outbreak Surveillance

In week 50, 14 new laboratory-confirmed outbreaks were reported: six in long term care facilities, three in an acute care facility, one in a school/daycare and four in a facility categorized as 'other', which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6). One new ILI outbreak in a school was reported.

To date this season, a total of 62 laboratory-confirmed influenza outbreaks have been reported; 33 in long-term care facilities, five in schools/daycares, nine in acute care facilities and 15 in facilities categorized as 'other'. Of the outbreaks where influenza type was reported (58), 85% (49) were due to influenza A. Among the 26 outbreaks for which the influenza A subtype was reported, 25 were associated with A(H3N2) and one was associated with A(H1N1). Four ILI outbreaks in schools/daycares have also been reported.

Number of provinces and territories reporting in week 50: 13 out of 13

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	1	0	0	0
39	0	1	0	0	0
40	0	2	0	0	0
41	0	2	1	0	0
42	1	0	0	0	0
43	0	0	1	0	0
44	0	0	1	0	0
45	0	2	4	0	0
46	1	4	0	0	0
47	0	2	1	1	0
48	1	6	2	2	0
49	3	7	1	1	0
50	3	6	4	1	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 274 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 1}.

• 69% of the cases were influenza A.
• Of the cases for which subtype was reported (164), 76% were associated with influenza A(H3N2).
• The greatest proportion of hospitalizations (40%) were among adults ≥ 65 years of age.

Thirty-one ICU admissions and three deaths have been reported.

Number of provinces and territories reporting in week 50: 9 out of 9

Pediatric Influenza Hospitalizations and Deaths

In week 50, 35 pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). This is slightly above the average (29) for week 50 over the previous five seasons.

To date this season, 104 pediatric hospitalizations have been reported by the IMPACT network; 55% (57) of cases were associated with influenza B and 45 % (47) with influenza A. The largest proportion of hospitalizations (63%) were among children under 5 years of age (Figure 8).

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2014-15 to 2018-19

Figure 7 - Text equivalent

Surveillance week	2019-2020	Average	Min	Max
35	0	0	0	1
36	2	0	0	1
37	0	1	0	2
38	0	1	0	2
39	1	1	0	3
40	0	1	0	2
41	2	1	0	3
42	2	2	0	5
43	1	5	2	12
44	2	5	1	15
45	1	10	2	37
46	6	13	1	41
47	6	13	2	36
48	22	18	2	40
49	24	22	3	47
50	35	29	4	50

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	13
6-23 mo	30
2-4 yr	22
5-9 yr	23
10-16 yr	16

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 1st for the 2019-20 season. To date this season, 38 hospitalizations and less than 5 intensive care unit admissions and deaths have been reported. The majority of hospitalizations have been due to influenza A (80%) and in adults 65 years of age and older (61%).

Influenza Strain Characterizations

From September 1 to December 19, 2019, the National Microbiology Laboratory (NML) has characterized 159 influenza viruses (78 A(H3N2), 45 A(H1N1) and 36 influenza B) that were received from Canadian laboratories.

Influenza A(H3N2)

Over recent years, circulating strains of A(H3N2) have evolved, and are increasingly difficult to characterize by hemagglutination inhibition (HI) assay. Genetic characterization is established by sequencing the hemagglutinin (HA) gene of the influenza viruses to compare their genetic properties.

Antigenic Characterization:

Among the 20 influenza A(H3N2) viruses antigenically characterized to date, the majority (85%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017 (Figure 9a).

Genetic Characterization:

Nearly all (96%) of the 78 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Three viruses belonged to the genetic group 3C.3a (Figure 10).

Group 3C.2a1b viruses analysed represent:

• 85% (17 out of 20) viruses that were also antigenically characterized.
• 100% (58 out of 58) viruses which did not grow to sufficient hemagglutination titer for antigenic characterization by HI assay.

A/Kansas/14/2017 belongs to genetic group 3C.3a and is the influenza A(H3N2) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza A(H1N1)

Among the 45 A(H1N1) viruses characterized to date, all were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 9b).

A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza B

Among the 36 influenza B viruses antigenically characterized this season, all belonged to the B/Victoria lineage, and the majority (78%) showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 9c).

Sequence analysis showed that 96% (27) of the viruses showing reduced titre had a three amino acid deletion (162-164) in the HA gene. Sequence is pending for one isolate.

The recommended influenza B components for the 2019-20 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage). B/Phuket/3073/2013 is included in the quadrivalent influenza vaccine.

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir:

157 influenza viruses (74 A(H3N2), 44 A(H1N1) and 39 B) were tested for resistance to oseltamivir:

• All influenza viruses tested were sensitive to oseltamivir.

Zanamivir:

158 influenza viruses (75 A(H3N2), 44 A(H1N1) and 39 B) were tested for resistance to zanamivir:

• All influenza viruses tested were sensitive to zanamivir.

Amantadine:

High levels of resistance to amantadine persist among influenza A(H1N1) and influenza A(H3N2) viruses. All viruses tested this season were resistant.

Vaccine Monitoring

Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and effectiveness.

Vaccine Coverage

Influenza vaccine coverage estimates for the 2019-20 season are anticipated to be available in February or March 2020.

Vaccine Effectiveness

Influenza vaccine effectiveness estimates for the 2019-20 season are anticipated to be available in February or March 2020.