FluWatch report: February 3, 2019 to February 9, 2019 (week 06)
- Influenza activity in Canada continues to decline slowly. Influenza activity is past the peak in most regions in western Canada, but continues to circulate in eastern regions.
- At the national level, most indicators of influenza activity declined in week 06.
- Influenza A(H1N1)pdm09 continues to be the most common influenza virus circulating in Canada. There is currently very little influenza B circulation compared to previous seasons.
- The higher proportion of laboratory detections, hospitalizations and outbreaks among people in younger age-groups reflects the increased impact of A(H1N1)pdm09 on people under 65 years of age compared to the past two seasons.
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- Influenza/ILI Activity (geographic spread)
- Laboratory Confirmed Influenza Detections
- Syndromic/Influenza-like Illness Surveillance
- Participatory Syndromic Surveillance
- Influenza Outbreak Surveillance
- Severe Outcomes Influenza Surveillance
- Influenza Strain Characterizations
- Antiviral Resistance
- Provincial and International Influenza Reports
Influenza/Influenza-like Illness Activity (geographic spread)
During week 06, fewer regions reported high levels of activity compared to the previous week. The following influenza activity levels were reported (Figure 1):
- 16 regions reported localized activity: in Alta.(2), Ont.(6), Que.(3), N.S.(3) and N.B.(2).
- 34 regions reported sporadic activity: in B.C.(5), Alta.(3), Sask.(3), Man.(4), Que.(4), N.B.(5), N.S.(1), N.L.(3), P.E.I.(1), Nvt.(3), N.W.T(1), and Y.T.(1).
- Three regions: in Man.(1), N.L.(1), and N.W.T(1) reported no activity.
Laboratory Confirmed Influenza Detections
- The percentage of tests positive for influenza decreased slightly compared to the previous week at 18.1%.
- A total 1,684 laboratory detections of influenza were reported, of which 98% were influenza A.
To date this season, 29,374 laboratory-confirmed influenza detections have been reported:
- 99% have been influenza A.
- Among the 10,418 influenza A viruses subtyped, 91% 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 22,979 laboratory-confirmed influenza cases (Table 1):
- 85% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
- 61% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.
Figure 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-06
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 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-06
|Age groups (years)||Cumulative (August 26, 2018 to February 9, 2019)|
|Influenza A||B||Influenza A and B|
|A Total||A(H1) pdm09||A(H3)||A (UnS)Footnote 1||Total||#||%|
Syndromic/Influenza-like Illness Surveillance
Healthcare Professionals Sentinel Syndromic Surveillance
In week 06, 1.1% 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.
Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-19-06
Number of Sentinels Reporting in Week 06: 98
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18
Participatory Syndromic Surveillance
In week 06, 2,207 participants reported to FluWatchers, of which 57 (2.6%) reported symptoms of cough and fever (Figure 5).
Among the 57 participants who reported fever and cough:
- 11% consulted a healthcare professional;
- 82% reported days missed from work or school, resulting in a combined total of 114 missed days of work or school.
- 69% reported having been vaccinated for influenza this season.
Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-06
Number of Participants Reporting in Week 06: 2,207
Influenza Outbreak Surveillance
In week 06, 27 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (17), acute care facilities (5), and other settings (5). Six new ILI outbreaks in schools/daycares were also reported in week 06. The number of new outbreaks reported each week continues to decline from the peak in week 01.
To date this season, 357 laboratory-confirmed influenza outbreaks have been reported (Figure 6):
- 215 (60%) outbreaks were in LTCF, 23 were in schools, 48 in acute care facilities, and 71 were in other settings.
- Among the 332 outbreaks for which the influenza type was available 98% (327) were associated with influenza A.
- Among the 149 outbreaks for which the influenza A subtype was available, 71% (106) were associated with influenza A(H1N1)pdm09;
To date this season, 89 ILI outbreaks have been reported; 43 occurred in LTCF, 43 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 2019-06
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 1,933 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.
Hospitalizations (Table 2):
- 99.7% (1,927) 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 356 ICU admissions and 82 deaths have been reported.
- 44% (156) of reported ICU admissions were in adults aged 45-64 years.
- All the ICU admissions, and all but one of the deaths were associated with influenza A.
|Age Groups (years)||Cumulative (August 26, 2018 to February 9, 2019)|
|Influenza A||Influenza B||Rate per 100,000 population|
Pediatric Influenza Hospitalizations and Deaths
In week 06, 36 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, 845 pediatric hospitalizations have been reported (Figure 8):
- 69% of cases were in children under 5 years of age.
- 99% (836) of cases have been associated with influenza A.
- Among the 285 cases for which the influenza subtype was available, 273 (96%) were associated with A(H1N1)pdm09.
To date this season, 140 ICU admissions, and 10 deaths have been reported.
- 63% (86) of ICU admissions were in children under 5 years of age.
- All but one 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.
Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-06
The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
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 2019-06
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 2018-19 season.
To date this season, 481 hospitalizations, 50 ICU admissions and 17 deaths have been reported (Figure 9):
- 436 (91%) hospitalizations were associated with influenza A.
- A greater proportion of hospitalizations have been reported among adults ≥65 years of age (57.2%) compared to adults <65 years of age (42.8%).
- Hospitalizations among adults peaked in week 01 then declined, followed by a plateau in week 03-05, and increased slightly in week 06.
- Among hospitalized cases with available information (428), the most commonly reported comorbidity was endocrine disorders, which were reported in 87% of hospitalized cases. However, 83% of cases reported more than one type of comorbid condition.
Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-06
Influenza Strain Characterizations
Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,103 influenza viruses (87 A(H3N2), 992 A(H1N1) and 24 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):
45 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:
- Seven viruses belonged to genetic group 3C.2a.
- 37 viruses belonged to subclade 3C.2a1.
- 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.
Influenza A (H3N2):
- 33 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.
- Nine 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.
- 22 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. Seven viruses belonged to genetic group 3C.2a and seven to 3C.3a. Sequencing is pending for the remaining isolates.
- 966 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.
- 26 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015
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).
- Seven 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
- 17 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 – Amantadine:
325 influenza A (47 A(H3N2) and 278 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:
- All 325 influenza A viruses were resistant to amantadine.
Antiviral Resistance – Oseltamivir:
730 influenza viruses (61 A(H3N2), 647 A(H1N1) and 22 B) were tested for resistance to oseltamivir and it was found that:
- All 61 A(H3N2) viruses were sensitive to oseltamivir.
- Of the 647 A(H1N1) viruses tested, 646 were sensitive to oseltamivir and one virus was resistant to oseltamivir with a H275Y mutation.
- All 22 B viruses were sensitive to oseltamivir.
Antiviral Resistance – Zanamivir:
729 influenza viruses (61 A(H3N2), 646 H1N1 and 22 B) were tested for resistance to zanamivir and it was found that:
- All 729 influenza viruses were sensitive to zanamivir.
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