FluWatch report: January 19 to 25, 2020 (week 04)

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

During week 04, influenza activity was reported in all provinces and territories and in almost all regions (51). Among these regions, 45% reported sporadic activity, 53% reported localized activity, and 2% reported widespread activity (Figure 1). Elevated influenza activity (localized and widespread activity) is being reported in many regions in provinces across the country. Sporadic influenza activity is being reported in the territories.

Figure 1 - Text equivalent

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

Laboratory-Confirmed Influenza Detections

In week 04, the percentage of laboratory tests positive for influenza increased compared to recent weeks. Influenza A and B continue to co-circulate, with an increased proportion of influenza B detections.

The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• Following a plateau around 26% over the previous three weeks the percentage of tests positive for influenza increased to 28% in week 04. This is slightly higher than the average (23%) for week 04 over the past five seasons, and consistent with the usual period of high influenza activity in Canada.
• The percentage of tests positive for influenza A has remained similar over the past four weeks, and was 15% in week 04.
• The percentage of tests positive for influenza B increased from 10% in week 03 to 13% in week 04. This continues to be three times greater than the average (3.7%) for this time of year.
• Among subtyped influenza A detections, the proportion of A(H1N1) has been similar over the past 3 weeks, at approximately 75%.

To date this season (weeks 35 to 04), 24,448 laboratory detections of influenza were reported:

• 59% (14,344) were influenza A.
• Among subtyped influenza A detections (3 957), A(H1N1) is now the predominant subtype overall this season (59%), due to the increase in A(H1N1) detections in recent weeks.

Detailed information on age and type/subtype has been received for 18,766 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 04):

• Among cases of influenza A(H3N2) (1,446), the largest proportion were in adults 65 years of age and older (47%).
• Cases of influenza B (8,470) were primarily in younger age groups; 56% of cases were under 20 years of age and 32% between 20 and 44 years of age.
• Among cases of influenza A(H1N1) (1,531), 32% of cases were in adults 65 years of age and older, with equal proportions in adults 20-44 years and 45-64 years (25%).

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	4.1
50	463	100	73	654	7.7	8.0
51	794	149	169	1094	10.6	10.4
52	1223	267	197	1439	15.0	12.7
1	1620	261	431	1533	15.8	10.3
2	1690	165	493	1463	15.8	9.4
3	1589	131	412	1406	16.3	10.3
4	1675	116	348	1863	15.2	12.6

Footnote *

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

Return to footnote * referrer

Figure 3 - Text equivalent

ProvincesTable Figure 3 - Footnote 1	Cumulative (August 25, 2019 to January 25, 2020)
	A Total	A(H1N1)	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A & B Total
B.C.	1079	150	231	249	770	1849
Alta.	2084	494	991	599	2291	4375
Sask.	618	0	0	618	179	797
Man.	569	78	68	423	638	1207
Ont.	3936	1536	297	2103	916	4852
Que.	5674	0	0	5674	4928	10602
N.B.	197	23	14	160	269	466
N.S.	38	0	0	38	31	69
P.E.I.	15	0	0	15	15	30
N.L.	56	4	24	28	45	101
Y.T.	29	4	8	17	4	33
N.W.T	36	27	8	1	15	51
Nvt.	13	0	0	13	3	16
Canada	14344	2316	1641	9938	10104	24448
PercentageTable Figure 3 - Footnote 2	59%	16%	11%	69%	41%	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 2020-01 to 2020-04

Age groups (years)	Cumulative (August 25, 2019 to January 25, 2020)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped)Table 1 Footnote 1	Total	#	%
0-4	1561	170	142	1249	1850	3411	18%
5-19	997	99	183	715	2852	3849	21%
20-44	2021	397	216	1408	2685	4706	25%
45-64	1923	392	224	1307	466	2389	13%
65+	3794	503	681	2610	617	4411	24%
Total	10296	1561	1446	7289	8470	18766	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 04, 1.5% of visits to healthcare professionals were due to influenza-like illness (ILI) which is below the average for this time of year (Figure 4).

Number of Sentinels Reporting in Week 04: 109

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	0.7%	1.2%	0.9%	1.5%
46	1.1%	1.4%	1.2%	1.8%
47	1.2%	1.6%	1.1%	2.2%
48	0.9%	1.5%	1.1%	2.2%
49	1.0%	1.7%	1.0%	2.8%
50	1.4%	1.5%	1.1%	1.7%
51	1.2%	1.9%	1.4%	2.7%
52	2.6%	2.0%	1.0%	3.1%
1	2.9%	3.4%	1.9%	5.4%
2	1.6%	3.4%	1.8%	5.7%
3	1.9%	2.3%	1.3%	3.7%
4	1.5%	2.0%	1.1%	2.9%

FluWatchers

The proportion of FluWatchers participants reporting symptoms of cough and fever decreased slightly in week 04 compared to the previous week. In week 04, 3,190 participants reported to FluWatchers, of which 3.0% (97) reported symptoms of cough and fever (Figure 5).

Among the 97 participants who reported cough and fever:

• 20% consulted a healthcare professional;
• 77% reported days missed from work or school, resulting in a combined total of 256 missed days of work or school.
• 72% 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 04: 3,190

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%
51	2.6%
52	4.1%
1	4.3%
2	3.1%
3	3.3%
4	3.0%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2020-04

Click on the map to access the link

Influenza Outbreak Surveillance

In week 04, the number of new laboratory-confirmed influenza outbreaks was the same as the previous week. A total of 53 outbreaks were reported: 38 in long term care facilities, 5 in acute care facilities, and 10 in facilities categorized as 'other', which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6). In addition, 26 ILI outbreaks in schools/daycares were reported.

To date this season, a total of 493 laboratory-confirmed influenza outbreaks have been reported; 61% (302) in long-term care facilities, 26% (128) in facilities categorized as 'other', 12% (58) in acute care facilities, and 1% (5) in schools/daycares. Of the 464 outbreaks where influenza type was reported, 89% (413) were due to influenza A. Among the 217 outbreaks for which the influenza A subtype was reported, 55% (119) were associated with A(H3N2). To date this season, 34 ILI outbreaks in schools/daycares have also been reported.

Number of provinces and territories reporting in week 04: 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
36	0	0	0	0
37	0	0	0	0
38	0	1	0	0
39	0	1	0	0
40	0	2	0	0
41	0	2	1	0
42	1	0	0	0
43	0	0	1	0
44	0	0	1	0
45	0	2	4	0
46	1	4	0	0
47	0	2	1	1
48	1	6	2	2
49	2	8	1	1
50	3	10	4	1
51	4	14	11	0
52	4	35	15	0
1	16	59	38	0
2	11	79	35	0
3	10	39	4	0
4	5	38	10	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 1,115 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote †}.

• 66% of the cases were associated with influenza A.
• Of the 568 cases for which subtype was reported, 71% were associated with influenza A(H3N2).
• The highest cumulative hospitalization rates up to week 04 were adults 65 years of age and older (36/100,000 population) and among children under 5 years of age (36/100,000 population).

112 ICU admissions and 26 deaths have been reported.

• 58% of the ICU admissions and 65% of the deaths were associated with influenza A.

Number of provinces and territories reporting in week 04: 8 out of 9

Footnote ‡

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.

Return to footnote 1 referrer

Figure 7 - Text equivalent

Surveillance Week	0-4 yrs	5-19 yrs	20-44 yrs	45-64 yrs	65+ yrs
35	0.0	0.0	0.0	0.0	0.0
36	0.0	0.0	0.0	0.0	0.2
37	0.0	0.0	0.0	0.1	0.2
38	0.0	0.0	0.0	0.1	0.4
39	0.2	0.0	0.0	0.1	0.6
40	0.2	0.0	0.0	0.1	0.8
41	0.4	0.2	0.1	0.2	1.1
42	0.8	0.2	0.1	0.2	1.3
43	1.0	0.2	0.2	0.3	1.6
44	1.5	0.2	0.2	0.5	2.1
45	1.9	0.4	0.4	0.8	2.8
46	1.9	0.4	0.6	1.1	3.3
47	3.1	0.6	0.8	1.5	4.6
48	5.0	1.1	1.0	1.6	5.7
49	7.1	1.9	1.3	1.9	7.5
50	11.1	3.0	1.8	2.2	10.0
51	14.3	3.7	2.5	3.4	13.3
52	18.5	5.6	3.7	4.5	18.9
1	27.3	6.2	4.5	6.3	27.0
2	31.3	7.3	5.2	7.6	31.5
3	33.8	7.8	5.9	8.2	34.3
4	36.0	8.3	6.3	9.1	36.3

Pediatric Influenza Hospitalizations and Deaths

In week 04, 93 pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 8). The weekly number of cases increased compared to the previous week which is the same as the 5-year maximum in week 04.

The elevated number of cases in recent weeks is likely due to the concurrent circulation of influenza A and B this season. The number of influenza A-associated pediatric hospitalizations is slighly above the average for this time of year. The number of hospitalizations with influenza B is well above average compared to previous seasons, and occurring earlier in the season.

To date this season (weeks 35 to 04):

• 658 pediatric hospitalizations have been reported by the IMPACT network, of which 51% (338) were associated with influenza B and 49% (320) with influenza A.
• The largest proportion of hospitalizations (65%) were among children under 5 years of age (Figure 9).
• Among cases in children under 5 years of age (425), 54% were associated with influenza A, compared to cases in children 5 to 16 years of age (233), among whom 62% of cases were associated with influenza B.
• 87 ICU admissions were reported, of which 51% (47) were associated with influenza A.
• Less than five pediatric deaths have been reported.

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

Figure 8 - 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	3	10	2	37
46	6	13	1	41
47	6	13	2	36
48	26	18	2	40
49	23	22	3	47
50	39	29	4	50
51	60	41	5	84
52	97	54	14	89
1	110	55	21	94
2	99	40	12	63
3	83	44	28	64
4	93	53	34	93

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. In week 04, the number of cases decreased for the third consecutive week.

To date this season, 411 hospitalizations, 22 intensive care unit admissions, and nine deaths have been reported (Figure 10).

• The majority of hospitalizations have been due to influenza A (87%), and among those subtyped (98) 91% were influenza A(H1N1).
• The largest proportion of hospitalizations are in adults 65-79 years of age (34%) and adults 80 years of age and older (31%) (Figure 11).
• 65% of hospitalized cases reported at least one type of comorbid condition.

Influenza Strain Characterizations

From September 1, 2019 to January 23, 2020, the National Microbiology Laboratory (NML) has characterized 456 influenza viruses (142 A(H3N2), 190 A(H1N1) and 124 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 38 influenza A(H3N2) viruses antigenically characterized to date, the majority (89%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017. Four viruses were characterized as A Kansas/14/2017-like (Figure 12 a).

Genetic Characterization:

Nearly all (98%) of the 135 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 13).

Group 3C.2a1b viruses analysed represent:

• 74% (28 out of 31) viruses that were also antigenically characterized.
• 100% (104 out of 104) 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 190 A(H1N1) viruses characterized to date, 62% were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 12 b).

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

Influenza B

Among the 124 influenza B viruses antigenically characterized this season, the vast majority (122) belonged to the B/Victoria lineage. Two viruses were antigenically characterized as similar to B/Phuket/3073/2013 (B/Yamagata lineage).

The majority (89%, 108) of B/Victoria lineage viruses showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 12 c).

Sequence analysis showed that 100% of the 105 B/Victoria lineage viruses showing reduced titre to B/Colorado/06/2017 had a three amino acid deletion (162-164) in the HA gene. Sequencing is pending for the remaining three viruses.

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. From September 1, 2019 to January 23, 2020, the following results were reported:

Oseltamivir:

277 influenza viruses (118 A(H3N2), 72 A(H1N1) and 87 B) were tested for resistance to oseltamivir:

• All influenza A(H3N2) and B viruses were sensitive to oseltamivir.
• Among the A(H1N1) viruses tested, 71 (99%) were sensitive to oseltamivir and one virus was resistant to oseltamivir with the H275Y mutation in the neuraminidase gene.

Zanamivir:

277 influenza viruses (118 A(H3N2), 72 A(H1N1) and 87 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.