FluWatch report: March 10, 2019 to March 16, 2019 (week 11)

Figure 1 - Text equivalent

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

Laboratory-Confirmed Influenza Detections

In week 11, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza continued to increase slightly to 21.4%.
• A total 1,721 laboratory detections of influenza were reported, of which 95% were influenza A.
• Influenza A(H3N2) accounted for 64% of subtyped influenza A detections.
• Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 339 this week.

To date this season, 37,610 laboratory-confirmed influenza detections have been reported:

• 98% have been influenza A.
• Among the 12,926 influenza A viruses subtyped, 83% have been A(H1N1)pdm09.
• Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 29,558 laboratory-confirmed influenza cases (Table 1):

• 84% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
• 59% 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.

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(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	449	17	507	8
48	679	29	632	10
49	851	35	785	16
50	1368	35	828	14
51	1890	54	953	21
52	2292	55	903	26
1	2387	58	893	31
2	1985	93	1061	43
3	1613	101	585	40
4	1483	93	532	48
5	1449	112	433	43
6	1234	118	315	42
7	1116	128	244	33
8	1066	236	216	40
9	1037	295	219	64
10	1060	339	267	70
11	1152	341	191	88

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (March 10 to March 16, 2019)					Cumulative (August 26, 2018 to March 16, 2019)
	Influenza A				B	Influenza A				B	A & B Total
	A Total	A (H1N1)pdm09	A (H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A Total	A (H1N1)pdm09	A (H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total
BC	522	106	168	248	27	4879	2878	811	1190	84	4963
AB	119	9	58	52	20	5717	3526	344	1847	118	5835
SK	10	2	3	5	7	2230	1365	69	796	32	2262
MB	12	3	8	1	0	1034	288	35	711	8	1042
ON	228	52	84	92	11	4903	1966	933	2004	116	5019
QC	499	0	0	499	17	14312	0	0	14312	304	14616
NB	122	7	7	108	4	2319	217	28	2074	9	2328
NS	57	0	0	57	0	551	0	0	551	8	559
PEI	17	6	11	0	0	229	211	18	0	0	229
NL	46	0	0	46	0	498	1	0	497	2	500
YT	0	0	0	0	0	74	50	4	20	0	74
N.W.T	3	3	0	0	0	162	160	2	0	1	163
NU	0	0	0	0	0	20	20	0	0	0	20
Canada	1635	188	339	1108	86	36928	10682	2244	24002	682	37610
PercentageTable Figure 3 - Footnote 2	95%	11%	21%	68%	5%	98%	29%	6%	65%	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 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 first Table Figure 3 - Footnote 3 referrer 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 2019-11

Age groups (years)	Cumulative (August 26, 2018 to March 16, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1) pdm09	A(H3)	A (UnS)Footnote 1	Total	#	%
0-4	5965	1632	91	4242	95	6060	21%
5-19	4255	1348	175	2732	134	4389	15%
20-44	5709	1845	268	3596	98	5807	20%
45-64	5722	1774	236	3712	67	5789	20%
65+	7344	1288	1097	4959	169	7513	25%
Total	28995	7887	1867	19241	563	29558	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 11, 0.7% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is low compared to previous seasons.

Number of Sentinels Reporting in Week 11: 75

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18

Figure 4 - Text equivalent

Surveillance Week	2018-19	Average	Min	Max
35	0.6%	0.8%	0.5%	1.2%
36	0.7%	0.8%	0.7%	1.0%
37	0.6%	0.9%	0.7%	1.0%
38	0.5%	1.1%	1.0%	1.4%
39	1.8%	1.1%	0.9%	1.4%
40	0.6%	1.3%	0.9%	1.6%
41	1.1%	1.4%	0.9%	2.4%
42	1.0%	1.4%	1.0%	1.9%
43	0.9%	1.3%	1.0%	1.5%
44	0.8%	1.3%	0.9%	1.6%
45	1.3%	1.3%	1.2%	1.5%
46	1.3%	1.6%	1.0%	2.0%
47	1.3%	1.5%	1.1%	1.9%
48	1.5%	1.6%	0.8%	2.1%
49	1.6%	1.5%	1.0%	2.5%
50	1.5%	2.3%	1.3%	3.7%
51	1.0%	2.5%	1.6%	4.1%
52	3.2%	4.5%	1.7%	7.1%
1	2.8%	3.7%	1.7%	5.2%
2	1.8%	3.0%	1.1%	4.5%
3	1.1%	2.5%	1.3%	3.6%
4	1.3%	2.4%	1.7%	3.5%
5	1.4%	2.7%	2.0%	4.4%
6	0.9%	2.7%	2.1%	3.3%
7	0.9%	2.4%	1.7%	3.0%
8	0.9%	2.3%	1.9%	2.7%
9	1.0%	2.2%	1.8%	2.7%
10	1.1%	2.1%	1.8%	2.7%
11	0.7%	2.1%	1.7%	2.7%

Participatory Syndromic Surveillance

In week 11, 2,066 participants reported to FluWatchers, of which 54 (2.7%) reported symptoms of cough and fever (Figure 5).

Among the 54 participants who reported fever and cough:

• 13% consulted a healthcare professional;
• 75% reported days missed from work or school, resulting in a combined total of 124 missed days of work or school.

Number of Participants Reporting in Week 11: 2,066

Figure 5 - Text equivalent

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%
49	2.0%
50	3.7%
51	3.9%
52	3.6%
1	3.4%
2	2.8%
3	2.5%
4	2.9%
5	3.0%
6	2.6%
7	2.7%
8	2.5%
9	2.7%
10	3.1%
11	2.6%

Influenza Outbreak Surveillance

In week 11, 29 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (16), acute care facilities (2) and other settings (11). Two new ILI outbreaks (one in a school and one in a LTCF) were also reported in week 11.

To date this season, 586 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

• 346 (59%) outbreaks were in LTCF, 29 were in schools, 86 in acute care facilities, and 125 were in other settings.
• Among the 523 outbreaks for which the influenza type was available, 98% (512) were associated with influenza A.
• Among the 221 outbreaks for which the influenza A subtype was available, 55% (121) were associated with influenza A(H1N1)pdm09;

To date this season, 121 ILI outbreaks have been reported; 65 occurred in LTCF, 52 in schools, and four in acute care facilities.

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	0	0	0	0
39	0	0	0	0	0
40	0	2	0	1	0
41	0	0	0	0	0
42	0	1	1	0	0
43	0	3	1	0	0
44	0	1	1	2	0
45	0	2	1	3	0
46	2	5	1	3	0
47	2	4	0	1	0
48	2	6	1	5	0
49	1	2	3	1	0
50	3	8	5	4	0
51	3	12	4	2	0
52	4	24	5	0	0
1	5	40	11	0	0
2	8	38	7	0	0
3	3	27	10	0	0
4	6	18	10	1	0
5	5	22	7	0	0
6	9	20	7	0	0
7	6	18	5	0	0
8	4	26	12	4	0
9	9	22	13	2	0
10	12	23	8	0	0
11	2	16	11	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,474 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 99.0% (2,449) were associated with influenza A
• The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

• To date this season 446 ICU admissions and 109 deaths have been reported.
  • 42% (189) of reported ICU admissions were in adults aged 45-64 years.
  • All but four ICU admissions were associated with influenza A.
  • All but one of the deaths were associated with influenza A.

Table 2 - Cumulative number of hospitalizations by age-group and influenza type, reported by participating provinces and territories^{Footnote 1}, Canada, weeks 2018-35 to 2019-11

Age Groups (years)	Cumulative (August 26, 2018 to March 16, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	343	9	73.95
5-19	204	8	15.28
20-44	311	1	10.97
45-64	670	2	30.88
65+	921	5	76.11
Total	2449	25
%	99.0%	1.0%
Table 2 - Note 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 - Note 1

Pediatric Influenza Hospitalizations and Deaths

In week 11, 37 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7).

To date this season, 1,046 pediatric hospitalizations have been reported (Figure 8):

• 67% of cases were in children under 5 years of age.
• 97% (1,017) of cases have been associated with influenza A.
• Among the 316 cases for which the influenza subtype was available, 286 (91%) were associated with A(H1N1)pdm09.

To date this season, 188 ICU admissions, and 10 deaths have been reported.

• 61% (114) of ICU admissions were in children under 5 years of age.
• All but two of the ICU admissions have been associated with influenza A.
• 80% (8) of deaths occurred in children 2 to 4 years of age.
• All deaths have been associated with influenza A.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Figure 7 - Text equivalent

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	5	1	0	4
43	11	1	0	3
44	15	3	1	6
45	37	3	2	4
46	41	5	1	13
47	36	4	0	9
48	43	9	2	23
49	43	15	3	28
50	51	23	4	47
51	85	32	4	72
52	89	47	7	92
1	93	40	5	75
2	60	35	4	62
3	70	38	4	67
4	60	35	7	47
5	51	40	11	59
6	48	38	15	79
7	44	40	17	120
8	44	47	25	139
9	36	50	13	153
10	45	48	17	135
11	37	41	18	118

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	111
6-23 mo	268
2-4 yr	325
5-9 yr	235
10-16 yr	107

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, 729 hospitalizations, 88 ICU admissions and 32 deaths have been reported (Figure 9):

• 676 (93%) hospitalizations were associated with influenza A.
• A greater proportion of hospitalizations have been reported among  adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
• 86% of hospitalized cases reported more than one type of comorbid condition.  
• The most commonly reported comorbidity was endocrine disorders, which were reported in 82% of hospitalized cases.

Figure 9 - Text equivalent

Age Group	Total
20-34 yr	65
35-49 yr	71
50-64 yr	160
65-79 yr	213
80+ yr	220

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,622 influenza viruses (212 A(H3N2), 1,375 A(H1N1) and 35 B) that were received from Canadian laboratories. 

Genetic Characterization of Influenza A(H3N2):

102 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:

• 17 viruses belonged to genetic group 3C.2a.
• 82 viruses belonged to subclade 3C.2a1.
• Two viruses belonged to 3C.3a.
• One isolate could not be sequenced.

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):

• 74 influenza A(H3N2) viruses were 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.
• 27 viruses showed reduced titer with ferret antisera 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.
• 53 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 16 viruses belonged to genetic group 3C.2a and 21 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,336 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.
• 39 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

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).

• Nine influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
• Seven viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
• 19 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:

376 influenza A (59 A(H3N2) and 313 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 376 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

992 influenza viruses (101 A(H3N2), 857 A(H1N1) and 34 B) were tested for resistance to oseltamivir and it was found that:

• All 101 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 857 A(H1N1) viruses tested, 854 were sensitive to oseltamivir and three viruses were resistant to oseltamivir with a H275Y mutation.
• All 34 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

989 influenza viruses (93 A(H3N2), 835 H1N1 and 32 B) were tested for resistance to zanamivir and it was found that:

• All 989 influenza viruses were sensitive to zanamivir.