FluWatch report: January 20, 2019 to January 26, 2019 (week 04)
- Influenza continues to circulate across Canada with eastern regions reporting 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 04.
- Influenza A is the most common influenza virus circulating in Canada, and the majority of these viruses are A(H1N1)pdm09.
- Based on a recently published Canadian influenza vaccine effectiveness study, mid-season vaccine effectiveness estimates indicate that this year’s flu shot is approximately 72% effective against the predominant circulating strain. Significant protection was observed in all age groups, especially young children who have been disproportionately affected by influenza this season.
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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
- Antiviral Resistance
- Provincial and International Influenza Reports
Influenza/Influenza-like Illness Activity (geographic spread)
During week 04, the following influenza activity levels were reported (Figure 1):
- 2 regions reported widespread activity: in Que.(1) and P.E.I.(1).
- 19 regions reported localized activity: in Alta.(1), Ont.(6), Que.(3), N.L.(1) N.S.(4) and N.B.(4).
- 31 regions reported sporadic activity: in B.C.(5), Alta.(4), Sask.(3), Man.(5), Que.(3), N.B.(3), N.L.(3), Nvt.(3), N.W.T.(1) and Y.T.(1).
- One region reported no activity: in N.W.T.(1).
Laboratory Confirmed Influenza Detections
In week 04, the following results were reported from sentinel laboratories across Canada (Figure 2):
- The percentage of tests positive for influenza was similar to the previous week at 20.7%.
- A total 2,270 laboratory detections of influenza were reported, of which 98% were influenza A.
To date this season, 25,764 laboratory-confirmed influenza detections have been reported:
- 99% have been influenza A.
- Among the 9,479 influenza A viruses subtyped, 93% have been A(H1N1)pdm09.
- Provincial and territorial differences in influenza type/subtype distribution are observed (Figure 3).
To date this season, detailed information on age and type/subtype has been received for 20,254 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 2019-04
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 2019-04
|Age groups (years)||Cumulative (August 26, 2018 to January 26, 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 04, 1.8% 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 2018-19-04
Number of Sentinels Reporting in Week 04: 93
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 04, 2,207 participants reported to FluWatchers, of which 64 (2.9%) reported symptoms of cough and fever (Figure 5).
Among the 64 participants who reported fever and cough:
- 25% consulted a healthcare professional;
- 75% reported days missed from work or school, resulting in a combined total of 147 missed days of work or school.
Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-04
Number of Participants Reporting in Week 04: 2,207
Influenza Outbreak Surveillance
In week 04, 27 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (12), acute care facilities (6), schools/daycares (1) and other settings (8). Fourteen new ILI outbreaks in long-term care facilities (3) and schools/daycares (11) were also reported in week 04.
To date this season, 296 laboratory-confirmed influenza outbreaks have been reported (Figure 6):
- 175 outbreaks were in LTCF, 23 were in schools, 39 in acute care facilities, and 59 were in other settings.
- Among the 278 outbreaks for which the influenza type was available 99% (274) were associated with influenza A.
- Among the 131 outbreaks for which the influenza A subtype was available:
- 76% (99) were associated with influenza A(H1N1)pdm09;
- 24% (32) were associated with A(H3N2),
To date this season, 72 ILI outbreaks have been reported; 41 occurred in LTCF, 28 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 2019-04
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 1,761 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.
Hospitalizations (Table 2):
- 99.7% (1,755) 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 319 ICU admissions and 75 deaths have been reported.
- 43% (137) 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 January 26, 2019)|
|Influenza A||Influenza B||Rate per 100,000 population|
Pediatric Influenza Hospitalizations and Deaths
In week 04, 65 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, 747 pediatric hospitalizations have been reported (Figure 8):
- 70% of cases were in children under 5 years of age.
- 99% (740) of cases have been associated with influenza A.
- Among the 266 cases for which the influenza subtype was available, 259 (97%) were associated with A(H1N1)pdm09.
To date this season, 126 ICU admissions, and 10 deaths have been reported.
- 63% (80) of ICU admissions were in children under 5 years of age.
- 99% (125) of 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 2019-04
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 2019-04
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, 373 hospitalizations have been reported (Figure 9):
- 336 (90%) were associated with influenza A.
- A similar proportion of hospitalizations are reported among adults <65 years of age (45.5%) and adults ≥65 years of age (55.5%).
- The most commonly reported comorbidity among hospitalized cases was endocrine disorders, which were reported in 70% of hospitalized cases.
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 2019-04
Influenza Strain Characterizations
Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 785 influenza viruses (66 A(H3N2), 701 A(H1N1) and 18 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):
- 20 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.
- 16 influenza A (H3N2) viruses characterized belonged to genetic group 3C.2a1. Two viruses belonged to genetic group 3C.2a and five to 3C.3a. Sequencing is pending for the remaining isolate.
- 686 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.
- 15 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).
- Three 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
- 15 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:
311 influenza A (44 A(H3N2) and 267 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:
- All 311 influenza A viruses were resistant to amantadine.
Antiviral Resistance – Oseltamivir:
601 influenza viruses (52 A(H3N2), 533 A(H1N1) and 16 B) were tested for resistance to oseltamivir and it was found that:
- All 601 influenza viruses were sensitive to oseltamivir
Antiviral Resistance – Zanamivir:
601 influenza viruses (52 A(H3N2), 533 H1N1 and 16 B) were tested for resistance to zanamivir and it was found that:
- All 601 influenza viruses were sensitive to zanamivir.
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