FluWatch report: November 11, 2018 to November 17, 2018 (Week 46)

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Organization: Public Health Agency of Canada

Date published: 2018-11-23

Overall Summary

Influenza activity continued to increase in week 46. The influenza season has started earlier than in recent years.The number of regions in Canada reporting localized influenza activity in week 46 increased slightly compared to the previous week.
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 46. In particular, the number of pediatric hospitalizations is significantly higher than in recent years.
The number of influenza outbreaks remains within expected levels. However, the settings in which outbreaks have been reported this season suggests that younger age-groups are being affected more than in previous seasons.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 46, the following influenza activity levels increased slightly compared to the previous week (Figure 1):

Five regions reported localized activity in Alta. (2) and Ont. (2), and Que. (1).
Sporadic activity was reported by 25 regions, in B.C.(5), Alta.(3), Sask.(3), Man.(2), Ont.(2), Que.(5), N.B.(1), P.E.I.(1), N.L.(1), N.W.T(1) and Nvt.(1).
No activity was reported by 23 regions.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2018-46

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	No Activity
N.L.	Labrador-Grenfell	No Activity
N.L.	Central	No Activity
N.L.	Western	Sporadic
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	No Activity
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	No Activity
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	Sporadic
Que.	Ouest-du-Québec	Localized
Que.	Montérégie	Sporadic
Ont.	Central East	Sporadic
Ont.	Central West	Localized
Ont.	Eastern	No Activity
Ont.	North East	No Activity
Ont.	North West	No Activity
Ont.	South West	Sporadic
Ont.	Toronto	Localized
Man.	Northern Regional	No Activity
Man.	Prairie Mountain	Sporadic
Man.	Interlake-Eastern	No Activity
Man.	Winnipeg	Sporadic
Man.	Southern Health	No Activity
Sask.	North	Sporadic
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	Sporadic
B.C.	Fraser	Sporadic
B.C.	Vancouver Coastal	Sporadic
B.C.	Vancouver Island	Sporadic
B.C.	Northern	Sporadic
Y.T.	Yukon	No Activity
N.W.T.	North	No Activity
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	No Activity
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	Sporadic

Laboratory Confirmed Influenza Detections

In week 46, the following results were reported from sentinel laboratories across Canada (Figure 2):

The percentage of tests positive for influenza continued to increase to 13.8% 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 46, 642 laboratory detections of influenza were reported, of which 99% were influenza A.

To date this season 2,063 laboratory-confirmed influenza detections have been reported (Figure 3):

98% have been influenza A
Among the 1,203 influenza A viruses subtyped, 91% have been A(H1N1)pdm09

To date this season, detailed information on age and type/subtype has been received for 2,069 laboratory-confirmed influenza cases (Table 1):

Adults 20-44 years of age represent the largest proportion of cases (25%), followed by individuals 5-19 years of age (20%).

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, 2018-35 to 2018-46

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	170	13	213	6
45	201	17	276	15
46	249	10	375	8

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2018-46

Reporting provinces^{Table Figure 3 - Footnote 1}	Week (November 11, 2018 to November 17, 2018)	Cumulative (August 26, 2018 to November 17, 2018)
BC	19	13	0	6	1	111	47	36	28	3	114
AB	451	293	3	155	1	1354	846	31	477	12	1366
SK	0	0	0	0	0	140	78	3	59	0	140
MB	18	9	0	9	0	75	62	3	10	0	75
ON	23	13	7	3	3	121	45	39	37	22	143
QC	70	0	0	70	3	190	0	0	190	10	200
NB	1	1	0	0	0	5	2	0	3	0	5
NS	1	0	0	1	0	6	0	0	6	0	6
PEI	1	1	0	0	0	3	3	0	0	0	3
NL	1	0	0	1	0	3	1	0	2	1	4
YT	0	0	0	0	0	0	0	0	0	0	0
N.W.T	4	4	0	0	0	4	4	0	0	0	4
NU	1	1	0	0	0	3	3	0	0	0	3
Canada	590	335	10	245	8	2015	1091	112	812	48	2063
Percentage^{Table Figure 3 - Footnote 2}	99%	57%	2%	42%	1%	98%	54%	6%	40%	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 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 2018-46
Age groups (years)	Cumulative (August 26, 2018 to November 17, 2018)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)^{Footnote 1}	Total	#	%
0-4	387	246	3	138	5	392	19%
5-19	411	213	4	194	7	418	20%
20-44	519	272	12	235	8	527	25%
45-64	371	195	28	148	7	378	18%
65+	342	140	124	78	12	354	17%
Total	2034	1066	171	793	39	2069	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 46, 1.7% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is within expected levels.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-46

Number of Sentinels Reporting in Week 46: 84

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	0.6%	1.6%	0.9%	3.4%
41	1.1%	1.6%	1.1%	2.1%
42	1.2%	1.4%	0.8%	1.8%
43	1,0%	1,4%	0,7%	1,8%
44	0,9%	1,4%	1,1%	1,6%
45	1,8%	1,5%	1,2%	1,8%
46	1,7%	1,7%	1,1%	2,2%

Participatory Syndromic Surveillance

In week 46, 2,183 participants reported to FluWatchers, of which 43 (2.0%) reported symptoms of cough and fever (Figure 5).

Among the 43 participants who reported fever and cough:

16% consulted a healthcare professional
79% reported days missed from work or school, resulting in a combined total of 87 missed days of work or school.

Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-46

Number of Participants Reporting in Week 46: 2,183

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%

Influenza Outbreak Surveillance

In week 46, five new laboratory-confirmed influenza outbreaks were reported in long-term care (3) and acute care (2) facilities.

To date this season, 26 influenza outbreaks have been reported (Figure 6):

14 outbreaks were in LTCF, five were in schools, and four were in other settings.
All of the 23 outbreaks for which the influenza type was available were associated with influenza A.
Among the 15 outbreaks for which the influenza A subtype was available:
- Eight were associated with influenza A(H1N1)pdm09, reported from schools, acute care facilities and other settings;
- Four were associated with A(H3N2), reported from LTCF and other settings;
- Three were associated with both A(H1N1)pdm09 and A(H3N2), reported from LTCF.
Compared to previous seasons, a greater proportion of outbreaks have been reported in settings other than LTCF, suggesting an increased burden of disease in younger age-groups.

No new ILI outbreaks were reported in week 46.

To date this season, 23 ILI outbreaks have been reported; 21 occurred in LTCF, one in a school, and one in an acute care facility.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2018-46

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	0	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	0	1	1
45	0	3	1	3
46	2	3	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 46, 62 influenza-associated hospitalizations were reported, which is a slight increase compared to the previous week.

To date this season, mothe than 300 influenza-assocaited hospitalizations have been reported by participating provinces and territories^Footnote 1.

Hospitalizations (Table 2):

99% (310) were associated with influenza A
The highest estimated rates of hospitalization are among children under 5 years of age, and adults 65 years of age and older.

Intensive Care Unit (ICU) cases and deaths:

To date this season 36 ICU admissions and <5 deaths have been reported.

Table 2 – Cumulative number of hospitalizations by age-group reported by participating provinces and territories^{Footnote 1}, Canada, weeks 2018-35 to 2018-46
Age Groups	Cumulative (August 26, 2018 to November 17, 2018)
Age Groups	Influenza A	Influenza B	Rate per 100,000 population
0-4	61	10	7.77
5-19	39	0	2.31
20-44	47	0	1.20
45-64	79	0	2.39
65+	84	<5	5.18
Total	310	<5
%	99%	1%
Table 2 - Footnote 1 Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. 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

TIn week 46, 39 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 (4-6 weeks earlier than in recent seasons)(Figure 7).

To date this season, 108 pediatric hospitalizations have been reported (Figure 8):

All but one case have been associated with influenza A.
Among the 83 cases for which the influenza subtype was available, 82 were associated with A(H1N1)pdm09.
91 of the 108 cases (84%) were between 6 months and 9 years of age.

To date this season, 10 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 2018-46

Surveillance week	2018-19	Average	Min	Max
35	0	0	0	1
36	0	0	0	1
37	0	0	0	2
38	0	1	0	2
39	0	1	0	3
40	1	0	0	2
41	1	1	0	3
42	6	1	0	4
43	11	1	0	3
44	19	3	1	6
45	32	3	2	4
46	39	5	1	13

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 2018-46

Age Group	Total
0-5 mo	11
6-23 mo	30
2-4 yr	29
5-9 yr	32
10-16 yr	6

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, seven hospitalizations have been reported, of which six were associated with influenza A and one with influenza B.

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 60 influenza viruses (11 A(H3N2), 48 A(H1N1) and one B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A (H3N2):

Ten 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:

One virus belonged to genetic group 3C.2a.
Nine 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):

48 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).

One influenza B viruses was 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:

59 influenza A (11 A(H3N2) and 48 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

The 11 A(H3N2) viruses tested were resistant to amantadine.
The 48 A(H1N1) viruses tested were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

59 influenza viruses (10 A(H3N2), 48 A(H1N1) and 1 B) were tested for resistance to oseltamivir and it was found that:

The 10 A(H3N2) viruses tested were sensitive to oseltamivir
The 48 A(H1N1) viruses tested were sensitive to oseltamivir
The B virus was sensitive to oseltamivir

Antiviral Resistance – Zanamivir:

59 influenza viruses (10 A(H3N2), 48 H1N1 and 1 B) were tested for resistance to zanamivir and it was found that:

The 10 A(H3N2) viruses were sensitive to zanamivir.
The 48 A(H1N1) viruses were sensitive to zanamivir.
The B virus was sensitive to zanamivir.

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Date modified:: 2021-05-10

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