FluWatch report: November 25, 2018 to December 1, 2018 (Week 48)
- Influenza activity continued to increase in week 48.
- 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 48. In particular, the number of pediatric hospitalizations is significantly higher than in recent years.
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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 48, influenza activity levels continued to increase (Figure 1):
- Nine regions reported localized activity: in Alta.(2), Sask.(1), Man.(1), Ont.(2), Que.(1), N.B.(1) and N.S.(1).
- Sporadic activity was reported by 29 regions in Alta.(3), Sask.(2), Man.(4), Ont.(5), Que.(5), N.B.(3), N.S.(1), N.L.(2), N.W.T(2), Nvt.(1) and Yt.(1).
- No activity was reported by 10 regions.
Laboratory Confirmed Influenza Detections
In week 48, the following results were reported from sentinel laboratories across Canada (Figure 2):
- The percentage of tests positive for influenza continued to increase to 18.1% 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 48, 1,301 laboratory detections of influenza were reported, of which 99% were influenza A.
To date this season 4,485 laboratory-confirmed influenza detections have been reported (Figure 3):
- 99% have been influenza A.
- Among the 2,384 influenza A viruses subtyped, 93% have been A(H1N1)pdm09.
To date this season, detailed information on age and type/subtype has been received for 4,409 laboratory-confirmed influenza cases (Table 1):
- 70% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 45 years of age.
- 70% 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 2018-48
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 2018-48
|Age groups (years)||Cumulative (August 26, 2018 to December 1, 2018)|
|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 48, 2.3% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is slightly above expected levels.
Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2018-48
Number of Sentinels Reporting in Week 48: 86
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 48, 2,226 participants reported to FluWatchers, of which 53 (2.3%) reported symptoms of cough and fever (Figure 5).
Among the 53 participants who reported fever and cough:
- 21% consulted a healthcare professional;
- 64% reported days missed from work or school, resulting in a combined total of 89 missed days of work or school.
Figure 5 – Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2018-48
Number of Participants Reporting in Week 48: 2,226
Influenza Outbreak Surveillance
In week 48, seven new laboratory-confirmed influenza outbreaks were reported in long-term care (4), acute care facilities (2) and other settings (1).
To date this season, 44 laboratory-confirmed influenza outbreaks have been reported (Figure 6):
- 23 outbreaks were in LTCF, nine were in schools, six in acute care facilities, and six were in other settings.
- All of the 36 outbreaks for which the influenza type was available were associated with influenza A.
- Among the 27 outbreaks for which the influenza A subtype was available:
- 21 were associated with influenza A(H1N1)pdm09;
- 6 were associated with A(H3N2),
Three new ILI outbreaks were reported in week 48.
To date this season, 31 ILI outbreaks have been reported; 25 occurred in LTCF, three 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 2018-48
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, more than 588 influenza-assocaited hospitalizations have been reported by participating provinces and territoriesFootnote 1.
Hospitalizations (Table 2):
- 99% (588) 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 65 ICU admissions and 9 deaths have been reported.
|Age Groups||Cumulative (August 26, 2018 to December 1, 2018)|
|Influenza A||Influenza B||Rate per 100,000 population|
Pediatric Influenza Hospitalizations and Deaths
In week 48, 44 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 (approximately 4 weeks earlier than in recent seasons) (Figure 7).
To date this season, 189 pediatric hospitalizations have been reported (Figure 8):
- All but three cases have been associated with influenza A.
- Among the 132 cases for which the influenza subtype was available, 130 (98.5%) were associated with A(H1N1)pdm09.
To date this season, 28 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 2018-48
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 2018-48
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, 23 hospitalizations have been reported:
- 20 (87%) were associated with influenza A and 3 with influenza B.
- 11 of the 23 cases (48%) were adults 65 years of age and older.
Influenza Strain Characterizations
Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 142 influenza viruses (20 A(H3N2), 112 A(H1N1) and 10 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A (H3N2):
19 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:
- Two viruses belonged to genetic group 3C.2a.
- 17 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.
- 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.
- 112 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 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).
- Ten 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:
130 influenza A (20 A(H3N2) and 110 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:
- All 130 influenza A viruses were resistant to amantadine.
Antiviral Resistance – Oseltamivir:
138 influenza viruses (18 A(H3N2), 110 A(H1N1) and 10 B) were tested for resistance to oseltamivir and it was found that:
- All 138 influenza viruses were sensitive to oseltamivir
Antiviral Resistance – Zanamivir:
138 influenza viruses (18 A(H3N2), 110 H1N1 and 10 B) were tested for resistance to zanamivir and it was found that:
- All 138 influenza viruses were sensitive to zanamivir.
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