FluWatch report: December 1 to 7, 2019 (week 49)

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

During week 49, the number of regions reporting influenza activity and the level of activity reported both increased compared to the previous week (Figure 1).

• Activity was reported across the country, in 10 provinces and territories.
• 64% of regions reported influenza activity; among these 76% reporting sporadic activity and 24% 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	No Activity
N.S.	Zone 1 - Western	No Activity
N.S.	Zone 2 - Northern	No Activity
N.S.	Zone 3 - Eastern	Sporadic
N.S.	Zone 4 - Central	No Activity
N.B.	Region 1	Sporadic
N.B.	Region 2	No Activity
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	No Activity
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
Que.	Montréal et Laval	Localized
Que.	Ouest-du-Québec	Localized
Que.	Montérégie	Sporadic
Ont.	Central East	Sporadic
Ont.	Central West	Sporadic
Ont.	Eastern	Localized
Ont.	North East	Sporadic
Ont.	North West	No Activity
Ont.	South West	Sporadic
Ont.	Toronto	Localized
Man.	Northern Regional	Sporadic
Man.	Prairie Mountain	No Activity
Man.	Interlake-Eastern	Sporadic
Man.	Winnipeg	Localized
Man.	Southern Health	Sporadic
Sask.	North	Localized
Sask.	Central	Sporadic
Sask.	South	Sporadic
Alta.	North Zone	Localized
Alta.	Edmonton	Sporadic
Alta.	Central Zone	Sporadic
Alta.	Calgary	Sporadic
Alta.	South Zone	Sporadic
B.C.	Interior	Localized
B.C.	Fraser	Sporadic
B.C.	Vancouver Coastal	Sporadic
B.C.	Vancouver Island	No Activity
B.C.	Northern	Sporadic
Y.T.	Yukon	Sporadic
N.W.T.	North	No Activity
N.W.T.	South	No Activity
Nvt.	Qikiqtaaluk	No Activity
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	No Activity

Laboratory-Confirmed Influenza Detections

In week 49, the number of detections of influenza continued to increase. The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza was 9.1%. This is slightly below the average (13.7%) for week 49 over the past five seasons.
• A total of 724 laboratory detections of influenza were reported, of which 56.5% (409) were influenza A. The proportion of detections that are influenza B has been increasing over the past four weeks, to 43.5% in week 49.
• The percentage of tests positive for influenza B (4.0%) is higher than the average (1.1%) for this time of year. The current level of influenza B activity is not normally seen until January or February.
• Among subtyped influenza A detections, a mix of A(H1N1) and A(H3N2) were detected; 65% (60 out of 93) were influenza A(H3N2).

To date this season (weeks 35 to 49), 2,494 laboratory detections of influenza were reported:

• 67% (1,673) 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 (612), 70% were influenza A(H3N2).

Detailed information on age and type/subtype has been received for 2,104 laboratory-confirmed influenza cases (Table 1).

To date this season (weeks 35 to 49):

• Among cases of influenza A(H3N2) (397), the largest proportion were in adults 65 years of age and older (44%).
• Cases of influenza B (753) were primarily in younger age groups; 61% of cases were under 20 years of age and 31% between 20 and 44 years of age.
• Among cases of influenza A(H1N1) (161), 34% 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	227	62	41	221	4.8	3.2
49	291	60	33	315	5.1	4.0

Footnote *

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces. However, data on laboratory-confirmed detections of influenza from Nunavut are not currently available

Return to footnote * referrer

Figure 3 - Text equivalent

Provinces Table Figure 3 - Footnote 1	Cumulative (August 25, 2019 to December 7, 2019)
	A Total	A(H1N1)	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A & B Total
B.C.	254	23	80	78	35	289
Alta.	435	86	221	128	393	828
Sask.	61	0	0	61	10	71
Man.	52	7	26	19	91	143
Ont.	269	60	69	140	78	347
Que.	537	0	0	537	205	742
N.B.	19	4	3	12	5	24
N.S.	2	0	0	2	1	3
P.E.I.	3	0	0	3	2	5
N.L.	24	0	21	3	1	25
Y.T.	12	0	8	4	0	12
N.W.T	5	4	0	1	0	5
Nvt.	0	0	0	0	0	0
Canada	1673	184	428	988	821	2494
PercentageTable Figure 3 - Footnote 2	67%	11%	26%	59%	33%	100%
Table Figure 3 - Footnote 1 Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces. However, data on laboratory-confirmed detections of influenza from Nunavut are not currently available. 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 2019-49

Age groups (years)	Cumulative (August 25, 2019 to December 7, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped)1	Total	#	%
0-4	185	32	46	107	127	312	15%
5-19	158	10	50	98	331	489	23%
20-44	241	37	61	143	236	477	23%
45-64	272	55	67	150	32	304	14%
65+	495	27	173	295	27	522	25%
Total	1351	161	397	793	753	2104	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 49, 1.3% of visits to healthcare professionals were due to influenza-like illness (ILI) which is slightly below the average for this time of year (1.5%) (Figure 4).

Number of participants reporting in week 49: 81

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	1.3%	1.7%	1.0%	2.8%

FluWatchers

In week 49, 3,092 participants reported to FluWatchers, of which 2.0% (62) reported symptoms of cough and fever (Figure 5).

Among the 62 participants who reported cough and fever:

• 31% consulted a healthcare professional;
• 79% reported days missed from work or school, resulting in a combined total of 136 missed days of work or school.
• 68% 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 49: 3,092

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	2.0%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2019-49

Click on the map to access the link

Influenza Outbreak Surveillance

In week 49, ten new laboratory-confirmed outbreaks were reported: seven in long term care facilities, one in an acute care facility, one in a school/daycare and one in a facility categorized as ‘other’, which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6). Two new ILI outbreaks in schools were reported.

To date this season, a total of 45 laboratory-confirmed influenza outbreaks have been reported; 26 in long-term care facilities, four in schools/daycares, four in acute care facilities and 11 in a facilities categorized as ‘other’. Of the outbreaks where influenza type was reported (42), 86%(36) were due to influenza A. Among the 18 outbreaks for which the influenza A subtype was reported, all were associated with A(H3N2). Three ILI outbreaks in schools/daycares have also been reported.

Number of provinces and territories reporting in week 49: 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	5	2	2	0
49	1	7	1	1	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season. 200 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 1}.

• 75% of the cases were influenza A.
• Of the cases for which subtype was reported (129), 77% were associated with influenza A(H3N2).
• The greatest proportion of hospitalizations (42%) were among adults ≥ 65 years of age.

Twenty-eight ICU admissions and one death have been reported.

Number of provinces and territories reporting in week 49: 9 out of 9

Pediatric Influenza Hospitalizations and Deaths

In week 49, 24 pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). This is close to  the average (22) for week 49 over the previous five seasons.

To date this season, 69 pediatric hospitalizations have been reported by the IMPACT network; 51% (35) of cases were associated with influenza A and 49 % (34) with influenza B. Among the 13 cases for which the influenza A subtype was reported, 54% (7) were associated with A(H1N1). The largest proportion of hospitalizations (61%) 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

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	10
6-23 mo	21
2-4 yr	14
5-9 yr	16
10-16 yr	13

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, 24 hospitalizations, no ICU admissions, and less than 5 deaths have been reported.

Influenza Strain Characterizations

From September 1 to December 12, 2019, the National Microbiology Laboratory (NML) has characterized 133 influenza viruses (65 A(H3N2), 35 A(H1N1) and 33 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 18 influenza A(H3N2) viruses antigenically characterized to date, the majority (83%) 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 (95%) of the 64 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:

• 82% (14 out of 17) viruses that were also antigenically characterized. Sequence is pending for one isolate.
• 100% (47 out of 47) 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 35 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 33 influenza B viruses antigenically characterized this season, all belonged to the B/Victoria lineage, and the majority (79%) 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 100% (25) 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:

123 influenza viruses (63 A(H3N2), 28 A(H1N1) and 32 B) were tested for resistance to oseltamivir:

• All influenza viruses tested were sensitive to oseltamivir.

Zanamivir:

123 influenza viruses (63 A(H3N2), 28 A(H1N1) and 32 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.