FluWatch report: January 27, 2019 to February 2, 2019 (week 05)
- Influenza activity in Canada is declining but influenza continues to circulate with eastern regions continuing to report higher levels of influenza activity compared to western regions.
- At the national level, the influenza season appears to be past the peak of activity, with most indicators showing stable or downward trends in week 05. Influenza A(H1N1)pdm09 continues to be the most common influenza virus circulating in Canada.
- A report on influenza vaccine coverage in Canada for 2017-18 shows that coverage was low among adults (38%) and highest among seniors (71%). These results are similar to recent seasons.
- The effectiveness of the influenza vaccine for the 2018-19 season is estimated to be 72% against the predominant circulating strain this season, with significant protection observed in all age groups.
On this page
- Influenza/ILI Activity (geographic spread)
- Laboratory Confirmed Influenza Detections
- Syndromic/Influenza-like Illness Surveillance
- Participatory Syndromic Surveillance
- Influenza Outbreak Surveillance
- Severe Outcomes Influenza Surveillance
- Antiviral Resistance
- Provincial and International Influenza Reports
Influenza/Influenza-like Illness Activity (geographic spread)
During week 05, fewer regions reported high levels of activity compared to the previous week. The following influenza activity levels were reported (Figure 1):
- 17 regions reported localized activity: in Alta.(1), Ont.(6), Que.(3), N.L.(1), N.S.(3) and N.B.(3).
- 34 regions reported sporadic activity: in B.C.(5), Alta.(4), Sask.(3), Man.(5), Ont.(1), Que.(3), N.B.(4), N.S.(1), N.L.(3), P.E.I.(1), Nvt.(3) and Y.T.(1).
- Two regions in N.W.T reported no activity.
Laboratory-Confirmed Influenza Detections
- The percentage of tests positive for influenza was similar to the previous week at 19.7%.
- A total 2,002 laboratory detections of influenza were reported, of which 98% were influenza A.
To date this season, 27,645 laboratory-confirmed influenza detections have been reported:
- 99% have been influenza A.
- Among the 10,014 influenza A viruses subtyped, 92% 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 21,728 laboratory-confirmed influenza cases (Table 1):
- 86% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
- 62% 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 2019-05
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 2019-05
|Age groups (years)||Cumulative (August 26, 2018 to February 2, 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 05, 1.5% 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 2019-05
Number of Sentinels Reporting in Week 05: 106
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 05, 2,196 participants reported to FluWatchers, of which 66 (3.0%) reported symptoms of cough and fever (Figure 5).
Among the 66 participants who reported fever and cough:
- 27% consulted a healthcare professional;
- 83% reported days missed from work or school, resulting in a combined total of 190 missed days of work or school.
- 68% reported having been vaccinated for influenza this season.
Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-05
Number of Participants Reporting in Week 05: 2,196
Influenza Outbreak Surveillance
In week 05, 24 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (16), acute care facilities (3), and other settings (5). Ten new ILI outbreaks in long-term care facilities (1) and schools/daycares (9) were also reported in week 05.
To date this season, 322 laboratory-confirmed influenza outbreaks have been reported (Figure 6):
- 193 (60%) outbreaks were in LTCF, 23 were in schools, 42 in acute care facilities, and 64 were in other settings.
- Among the 301 outbreaks for which the influenza type was available 98% (296) were associated with influenza A.
- Among the 140 outbreaks for which the influenza A subtype was available:
- 74% (104) were associated with influenza A(H1N1)pdm09;
- 26% (36) were associated with A(H3N2),
To date this season, 82 ILI outbreaks have been reported; 42 occurred in LTCF, 37 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 2019-05
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 1,833 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.
Hospitalizations (Table 2):
- 99.7% (1,828) 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 336 ICU admissions and 77 deaths have been reported.
- 43% (145) of reported ICU admissions were in adults aged 45-64 years.
- All but one of the reported deaths were associated with influenza A.
|Age Groups (years)||Cumulative (August 26, 2018 to February 2, 2019)|
|Influenza A||Influenza B||Rate per 100,000 population|
Pediatric Influenza Hospitalizations and Deaths
In week 05, 56 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, 802 pediatric hospitalizations have been reported (Figure 8):
- 69.5% of cases were in children under 5 years of age.
- 99% (795) of cases have been associated with influenza A.
- Among the 279 cases for which the influenza subtype was available, 270 (97%) were associated with A(H1N1)pdm09.
To date this season, 135 ICU admissions, and 10 deaths have been reported.
- 63% (85) 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 2019-05
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 2019-05
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, 430 hospitalizations, 47 ICU admissions and 16 deaths have been reported (Figure 9):
- 388 (90%) hospitalizations were associated with influenza A.
- A similar proportion of hospitalizations are reported among adults <65 years of age (43.3%) and adults ≥65 years of age (56.7%).
- Similar to other indicators this season, hospitalizations among adults peaked in week 01, but has been stable over the past three weeks.
- Among hospitalized cases with available information (367), the most commonly reported comorbidity was endocrine disorders, which were reported in 88% of hospitalized cases. However, 84% 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 2019-05
Influenza Strain Characterizations
Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 972 influenza viruses (69 A(H3N2), 882 A(H1N1) and 21 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):
42 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.
- 34 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):
- 23 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.
- Four 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.
- 17 influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Three viruses belonged to genetic group 3C.2a and five to 3C.3a. Sequencing is pending for the remaining isolates.
- 861 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.
- 21 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).
- Four 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:
322 influenza A (46 A(H3N2) and 276 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:
- All 322 influenza A viruses were resistant to amantadine.
Antiviral Resistance – Oseltamivir:
664 influenza viruses (53 A(H3N2), 593 A(H1N1) and 18 B) were tested for resistance to oseltamivir and it was found that:
- All 53 A(H3N2) viruses were sensitive to oseltamivir.
- Of the 593 A(H1N1) viruses tested, 592 were sensitive to oseltamivir and one virus was resistant to oseltamivir with a H275Y mutation.
- All 18 B viruses were sensitive to oseltamivir.
Antiviral Resistance – Zanamivir:
664 influenza viruses (53 A(H3N2), 593 H1N1 and 18 B) were tested for resistance to zanamivir and it was found that:
- All 664 influenza viruses were sensitive to zanamivir.
Report a problem or mistake on this page
- Date modified: