FluWatch report: November 25, 2018 to December 1, 2018 (Week 48)

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Organization: Public Health Agency of Canada

Date published: 2018-12-07

Overall Summary

Influenza activity continued to increase in week 48.
Influenza A is the most common influenza virus circulating in Canada, and the majority of these viruses are A(H1N1)pdm09.
The number of influenza-associated hospitalizations continued to increase in week 48. In particular, the number of pediatric hospitalizations is significantly higher than in recent years.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 48, influenza activity levels continued to increase (Figure 1):

Nine regions reported localized activity: in Alta.(2), Sask.(1), Man.(1), Ont.(2), Que.(1), N.B.(1) and N.S.(1).
Sporadic activity was reported by 29 regions in Alta.(3), Sask.(2), Man.(4), Ont.(5), Que.(5), N.B.(3), N.S.(1), N.L.(2), N.W.T(2), Nvt.(1) and Yt.(1).
No activity was reported by 10 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-48

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Sporadic
N.L.	Labrador-Grenfell	Sporadic
N.L.	Central	No Activity
N.L.	Western	No Activity
P.E.I.	Prince Edward Island	No Activity
N.S.	Zone 1 - Western	Localized
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	Sporadic
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	Localized
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	Sporadic
Ont.	Central West	Sporadic
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	Localized
Man.	Southern Health	Sporadic
Sask.	North	Localized
Sask.	Central	Sporadic
Sask.	South	Sporadic
Alta.	North Zone	Sporadic
Alta.	Edmonton	Localized
Alta.	Central Zone	Sporadic
Alta.	Calgary	Localized
Alta.	South Zone	Sporadic
B.C.	Interior	No Data
B.C.	Fraser	No Data
B.C.	Vancouver Coastal	No Data
B.C.	Vancouver Island	No Data
B.C.	Northern	No Data
Y.T.	Yukon	Sporadic
N.W.T.	North	Sporadic
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	No Activity
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	Sporadic

Laboratory Confirmed Influenza Detections

In week 48, the following results were reported from sentinel laboratories across Canada (Figure 2):

The percentage of tests positive for influenza continued to increase to 18.1% of tests positive.
The percentage of tests positive for influenza A is higher for this time of year compared to the same period during the previous eight seasons.
In week 48, 1,301 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 4,485 laboratory-confirmed influenza detections have been reported (Figure 3):

99% have been influenza A.
Among the 2,384 influenza A viruses subtyped, 93% have been A(H1N1)pdm09.

To date this season, detailed information on age and type/subtype has been received for 4,409 laboratory-confirmed influenza cases (Table 1):

70% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 45 years of age.
70% 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.

Figure 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2018-48

Surveillance Week	A(Unsubtyped)	A(H3)	A(H1)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	463	17	506	8
48	691	28	572	10

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-48

Reporting provinces^{Table Figure 3 - Footnote 1}	Week (November 25, 2018 to December 1, 2018)	Cumulative (August 26, 2018 to December 1, 2018)
BC	94	49	2	43	0	260	127	43	90	3	263
AB	549	334	3	212	2	2548	1568	42	938	18	2566
SK	109	73	2	34	0	557	309	8	240	0	557
MB	74	15	0	59	0	180	91	3	86	0	180
ON	71	28	20	23	1	221	92	61	68	27	248
QC	246	0	0	246	7	578	0	0	578	18	596
NB	13	0	0	13	0	25	3	0	22	0	25
NS	3	0	0	3	0	10	0	0	10	0	10
PEI	0	0	0	0	0	4	4	0	0	0	4
NL	0	0	0	0	0	3	1	0	2	1	4
YT	0	0	0	0	0	0	0	0	0	0	0
N.W.T	17	17	0	0	0	27	27	0	0	0	27
NU	1	1	0	0	0	5	5	0	0	0	5
Canada	1177	517	27	633	10	4418	2227	157	2034	67	4485
Percentage^{Table Figure 3 - Footnote 2}	99%	44%	2%	54%	1%	99%	50%	4%	46%	1%	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 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 Table Figure 3 - Footnote UnS Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to first Table Figure 3 - Footnote 3 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 2018-48
Age groups (years)	Cumulative (August 26, 2018 to December 1, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)^{Footnote 1}	Total	#	%
0-4	908	517	3	388	6	914	21%
5-19	925	467	5	453	13	938	21%
20-44	1100	551	17	532	12	1112	25%
45-64	816	392	38	386	9	825	19%
65+	604	259	149	196	16	620	14%
Total	4353	2186	212	1955	56	4409	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 48, 2.3% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is slightly above expected levels.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-48

Number of Sentinels Reporting in Week 48: 86

Report week	2018-19	Average	Min	Max
35	0.6%	0.6%	0.4%	0.9%
36	0.7%	0.8%	0.5%	1.0%
37	0.6%	0.9%	0.7%	1.1%
38	0.5%	1.0%	0.7%	1.4%
39	1.8%	1.1%	0.8%	1.5%
40	0.8%	1.6%	0.9%	3.4%
41	1.7%	1.6%	1.1%	2.1%
42	1.5%	1.4%	0.8%	1.8%
43	1.4%	1.4%	0.7%	1.8%
44	1.1%	1.4%	1.1%	1.6%
45	2.1%	1.5%	1.2%	1.8%
46	1.9%	1.7%	1.1%	2.2%
47	2.4%	1.6%	1.1%	2.2%
48	2.3%	1.8%	1.0%	2.8%

Participatory Syndromic Surveillance

In week 48, 2,226 participants reported to FluWatchers, of which 53 (2.3%) reported symptoms of cough and fever (Figure 5).

Among the 53 participants who reported fever and cough:

21% consulted a healthcare professional;
64% reported days missed from work or school, resulting in a combined total of 89 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-48

Number of Participants Reporting in Week 48: 2,226

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%

Influenza Outbreak Surveillance

In week 48, seven new laboratory-confirmed influenza outbreaks were reported in long-term care (4), acute care facilities (2) and other settings (1).

To date this season, 44 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

23 outbreaks were in LTCF, nine were in schools, six in acute care facilities, and six were in other settings.
All of the 36 outbreaks for which the influenza type was available were associated with influenza A.
Among the 27 outbreaks for which the influenza A subtype was available:
- 21 were associated with influenza A(H1N1)pdm09;
- 6 were associated with A(H3N2),

Three new ILI outbreaks were reported in week 48.

To date this season, 31 ILI outbreaks have been reported; 25 occurred in LTCF, three in schools, and three in acute care facilities.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2018-48

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares
35	0	0	0	0
36	0	0	0	0
37	0	2	0	0
38	0	1	0	0
39	0	0	0	0
40	0	2	0	1
41	0	0	0	0
42	0	1	1	0
43	0	2	1	0
44	0	1	1	2
45	0	2	1	3
46	2	5	1	3
47	2	3	0	0
48	2	4	1	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, more than 588 influenza-assocaited hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

99% (588) were associated with influenza A
The highest estimated rate of hospitalization is among children under 5 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 65 ICU admissions and 9 deaths have been reported.

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 2018-48
Age Groups	Cumulative (August 26, 2018 to December 1, 2018)
Age Groups	Influenza A	Influenza B	Rate per 100,000 population
0-4	108	0	22.69
5-19	75	0	5.41
20-44	91	0	3.20
45-64	149	0	6.85
65+	165	<5	13.81
Total	588	<5
%	99%	1%
Table 2 - Footnote 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 - Footnote 1

Pediatric Influenza Hospitalizations and Deaths

In week 48, 44 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network. Pediatric hospitalizations reported by IMPACT are at levels not normally seen until late December (approximately 4 weeks earlier than in recent seasons) (Figure 7).

To date this season, 189 pediatric hospitalizations have been reported (Figure 8):

All but three cases have been associated with influenza A.
Among the 132 cases for which the influenza subtype was available, 130 (98.5%) were associated with A(H1N1)pdm09.

To date this season, 28 ICU admissions, and no deaths have been reported.

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2018-48

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	6	1	0	4
43	11	1	0	3
44	19	3	1	6
45	32	3	2	4
46	42	5	1	13
47	34	4	0	9
48	44	9	2	23

Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2018-48

Age Group	Total
0-5 mo	17
6-23 mo	51
2-4 yr	53
5-9 yr	54
10-16 yr	14

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, 23 hospitalizations have been reported:

20 (87%) were associated with influenza A and 3 with influenza B.
11 of the 23 cases (48%) were adults 65 years of age and older.

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 142 influenza viruses (20 A(H3N2), 112 A(H1N1) and 10 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A (H3N2):

19 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:

Two viruses belonged to genetic group 3C.2a.
17 viruses belonged to subclade 3C.2a1.

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):

One influenza A(H3N2) virus was 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.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
The influenza A (H3N2) virus characterized belonged to genetic group 3C.2a1.

Influenza A(H1N1):

112 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.

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).

Ten 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:

130 influenza A (20 A(H3N2) and 110 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

All 130 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

138 influenza viruses (18 A(H3N2), 110 A(H1N1) and 10 B) were tested for resistance to oseltamivir and it was found that:

All 138 influenza viruses were sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

138 influenza viruses (18 A(H3N2), 110 H1N1 and 10 B) were tested for resistance to zanamivir and it was found that:

All 138 influenza viruses were sensitive to zanamivir.

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Date modified:: 2021-05-10

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