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February 19 to February 25, 2012 (Week 08)

Posted 2012-03-02

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Overall Influenza Summary

  • Influenza activity in Canada in week 08 has slightly increased compare to the previous week; activity remains low in the Territories and in a few other regions across the country
  • One region reported widespread influenza activity, 10 regions reported localized influenza activity and 22 regions reported sporadic influenza activity
  • Twenty outbreaks of influenza were reported this week (8 in LTCFs, 5 in schools 4 in community and 3 others).
  • In week 08, 537 laboratory detections of influenza were reported (22.0% - A(H3); 9.1% - A(H1N1)pdm09; 28.5% - unsubtyped and 40.4% influenza B)
  • The percent positive for influenza B detections decreased slightly compared to the previous week, the provinces with the highest proportion of influenza B detections compared to A include: ON and the Atlantic Provinces
  • Fifty-two influenza-associated hospitalizations were reported this week, with an increase in the number of paediatric cases reported and a decrease in the number of adult cases reported (33 paediatric and 19 adult)
  • The national ILI consultation rate slightly decreased this week compared to the previous week and remains within expected levels for this time of year

Influenza Activity (geographic spread) and Outbreaks

In week 08, 1 region reported widespread influenza activity (NL), 10 surveillance regions (within BC, SK, ON, NS & NL) reported localized activity and 22 regions (within BC, AB, SK, ON, QC, NB, PEI & NL) reported sporadic influenza activity (see Figure 1). Twenty outbreaks of influenza were reported this week: 8 in long-term care facilities ( 1 in BC, 6 in ON, &1 in NL), 5 in schools (3 in ON, 1 in NB, & 1 in NS) 4 in the community (NL) and 3 others (1 in SK & 2 in ON) (Figure 3).

Figure 1. Map of overall Influenza activity level by province and territory,
Canada, Week 8

Figure 1


Note: Influenza activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates (see graphs and tables) and reported outbreaks. Please refer to detailed definitions on the last page. For areas where no data is reported, late reports from these provinces and territories will appear on the FluWatch website.

Text equivalent for figure 1Map of overall Influenza activity level by province and territory, Canada

Figure 2. Number of influenza surveillance regions reporting widespread or
localized influenza activity, Canada, by report week, 2011-2012 (N=56)

Figure 2

† sub-regions within the province or territory as defined by the provincial/territorial epidemiologist. Graph may change as late returns come in.

Text equivalent for figure 2Number of influenza surveillance regions reporting widespread or localized influenza activity, Canada, by report week, 2011-2012 (N=56)

Figure 3. Overall Number of Influenza Outbreaks, Canada, by Report Week, 2011-2012

Figure 3

Text equivalent for figure 3Overall Number of Influenza Outbreaks, Canada, by Report Week, 2011-2012

Influenza and Other Respiratory Virus Detections

The proportion of positive influenza tests continued to increase and was 13.8% (537/3,886) for week 08 (Figure 4 & Figure5). Of the 537 positive influenza detections this week, 59.6% (320/537) were positive for influenza A and 40.4% (217/537) were positive for influenza B. To date this season, the provinces with the highest proportion of influenza B detections compared to influenza A detections include: ON & the Atlantic provinces.

Cumulative to date of influenza virus detections by type/subtype is as follows: 67.7% influenza A (55.7% - A(H3); 14.4% - A(H1N1)pdm09; 29.9% - unsubtyped) and 32.6% influenza B (Table 1).

Detailed information on age and type/subtype were received on 2,023 cases to date this season (Table 2).The proportions of cases by age group are as follows: 21.7% were < 5 years; 15.9% were between 5-19 years; 24.9% were between 20-44 years; 14.7% were between 45-64 years of age; 22.8% were ≥ 65 years ; and 0.1% with age unknown.

In week 08, the proportion of tests positive for RSV slightly increased to 17.8% (and has fluctuated between 17-19% since week 01) and remains the most prevalent among the other respiratory viruses being detected. The highest percent positives for RSV this week were reported in ON, the Prairie Provinces and the Atlantic Region. The percentage positive for parainfluenza (1.5%), human metapneumovirus (hMPV) (5.6%) and rhinovirus (5.7%)  decreased compared to the previous week, while the proportion of positive tests for the other respiratory viruses increased slightly from the previous week (adenovirus-2.1%; coronavirus-6.3%) (Figure 5). For more details, see the weekly Respiratory Virus Detections in Canada report.

Table 1: Weekly & Cumulative numbers of positive influenza specimens
by Provincial Laboratories, Canada, 2011-2012
Reporting provinces Weekly
(February 19 to February 25, 2012)
Cumulative
(August 28, 2011 to February 25, 2012)
Influenza A B Influenza A B
A Total A(H1) A(H3) Pand H1N1 A
( Un S)*
Total A Total A(H1) A(H3) Pand H1N1 A
(Un S) *
Total
* Unsubtyped: The specimen was typed as influenza A, but no test for subtyping was performed. Specimens from NT, YT, and NU are sent to reference laboratories in other provinces.
Note: Cumulative data includes updates to previous weeks; due to reporting delays, the sum of weekly report totals do not add up to cumulative totals.
BC 40 0 28 1 11 4 336 0 304 17 15 31
AB 60 0 38 10 12 5 346 0 297 25 24 30
SK 28 0 22 0 6 0 212 0 169 10 33 1
MB 0 0 0 0 0 0 9 0 4 0 5 2
ON 58 0 21 29 8 99 265 0 81 144 40 366
QC
127 0 4 8 115 98 386 0 11 29 346 261
NB
3 0 2 1 0 0 5 0 3 1 1 4
NS
1 0 0 0 1 0 1 0 0 0 1 1
PE
1 0 1 0 0 0 1 0 1 0 0 3
NL
2 0 2 0 0 11 5 0 3 0 2 57
Canada 320 0 118 49 153 217 1566 0 873 226 467 756

Table 2. Weekly & Cumulative numbers of positive influenza specimens by age groups
reported through case-based laboratory reporting, Canada, 2011-2012
Table 2 note*
Age groups Weekly
(February 19 to February 25, 2012)
Cumulative
(August 28, 2011 to February 25, 2012)
Influenza A B Influenza A B
A Total Pandemic H1N1 A/H3N2 A unsubtyped Total A Total Pandemic H1N1 A/H3N2 A unsubtyped Total
* Please note that this table reflects the number of specimens for which demographic information was reported. These represent a subset of all positive influenza cases reported. Delays in the reporting of data may cause data to change retrospectively.
< 5 49 6 12 31 21 284 55 141 88 154
5-19 22 1 7 14 44 167 11 119 37 154
20-44 61 6 15 40 20 393 40 211 142 110
45-64 39 4 8 27 16 240 34 118 88 58
65+ 41 6 13 22 21 358 25 267 66 103
Unknown 0 0 0 0 0 2 1 1 0 0
Total 212 23 55 134 122 1444 166 857 421 579

Figure 4. Influenza tests reported and percentage of tests positive, Canada,
by report week, 2011-2012

Figure 4.

Text equivalent for figure 4Influenza tests reported and percentage of tests positive, Canada, by report week, 2011-2012

Figure 5. Percent positive influenza tests, compared to other respiratory viruses,
Canada, by reporting week, 2011-2012

Figure 5

Text equivalent for figure 5Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2011-2012

Influenza strain characterizations

Since the start of the season, the National Microbiology Laboratory (NML) has antigenically characterized 443 influenza viruses (107 A/H3N2, 84 A/H1N1 and 252 B). All 107 A/H3N2 viruses (from BC, AB, SK, ON & QC) are antigenically related to A/Perth/16/2009. All 84 A/H1N1 viruses (from BC, AB, SK, ON, QC &NB) are antigenically related to A/California/07/2009. Of the 252 influenza B viruses characterized, 136 (54%) (from BC, AB, SK, ON, QC, NB & NL) are antigenically related to the vaccine strain B/Brisbane/60/2008 (Victoria lineage). The remaining 116 (46%) influenza B viruses (from BC, AB, ON, QC & NB) are antigenically related to the reference virus B/Wisconsin/01/2010-like, which belongs to the Yamagata lineage. (Figure 6)

Figure 6. Influenza strain characterizations, Canada, 2011-2012, N = 443

Figure 6

Note: The recommended components for the 2011-2012 Northern Hemisphere influenza vaccine include: A/Perth/16/2009 (H3N2), A/California/7/2009 (H1N1) and B/Brisbane/60/2008.

Text equivalent for figure 6Influenza strain characterizations, Canada, 2011-2012

Antiviral resistance

Since the beginning of the season, NML has tested 381 influenza viruses for resistance to oseltamivir (by phenotypic assay and/or sequencing) and 309 influenza viruses for resistance to zanamivir (by phenotypic assay) and it was found that all viruses tested were susceptible to oseltamivir and zanamivir. A total of 236 influenza A viruses (144 H3N2 and 92 H1N1) were tested for amantadine resistance; all but one influenza A(H3N2) virus tested were resistant. (Table 3)

Table 3. Antiviral resistance by influenza virus type and subtype, Canada, 2011-2012
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
* NA - not applicable
A (H3N2) 103 0 98 0 144 143 (99.2%)
A (H1N1) 79 0 61 0 67 92 (100%)
B 199 0 150 0 NA * NA *
TOTAL 381 0 309 0 188 235 (99.6%)

Influenza-like Illness (ILI) Consultation Rate

The national ILI consultation rate slightly decreased to 31.3 ILI consultations per 1,000 patient visits in week 08 but still remains within the expected levels for this time of year (Figure 7). The highest consultation rates this week were observed in children under 5 (108.3/1,000 visits) which increased compared to the previous week and in those 5 to 19 years old (49.6/1,000 visits).

Figure 7. Influenza-like illness (ILI) consultation rates, Canada, by report week, 2011-2012 compared to 1996/97 through to 2010/11 seasons (with pandemic data suppressed)

Figure 7

Note: No data available for mean rate in previous years for weeks 19 to 39 (1996-1997 through 2002-2003 seasons). Delays in the reporting of data may cause data to change retrospectively.

Text equivalent for figure 7Influenza-like illness (ILI) consultation rates, Canada, by report week, 2011-2012 compared to 1996/97 through to 2010/11 seasons (with pandemic data suppressed)

Severe Illness Surveillance

Paediatric Influenza Hospitalizations and Deaths
In week 08, 33 new laboratory-confirmed influenza-associated paediatric (16 years of age and under) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. Ten hospitalizations were due to influenza A (unsubtyped) (in BC, AB, ON & QC); two were due to A(H1N1) (in QC); three were due to A(H3N2) and 18 were due to influenza B (in AB, ON & QC).

To date this season, 120 influenza-associated paediatric hospitalizations have been reported through IMPACT (from BC, AB, SK, MB, ON, QC, & NL); 67 (55.8%) were due to influenza A and 53 (44.2%) were due to influenza B. The proportion of cases by age group is as follows: 15.8% among infants <6 months of age; 19.1% among children 6-23 months of age; 32.5% were between 2-4 years; 18.3% were between 5-9 years; and 14.2% were between 10-16 years.

Note: The number of hospitalizations reported through IMPACT represents a subset of all influenza-associate paediatric hospitalizations in Canada; therefore, the number of hospitalizations included in this report may differ from those reported by other Provincial and Territorial Health Authorities.

Adult Influenza Hospitalizations and Deaths
In week 08, 19 new laboratory-confirmed influenza-associated adult hospitalizations were reported: 17 in ON, 1 in AB and 1 in NL. In addition, two influenza-associated deaths were reported in ON; both were ≥65 years old one had A(H1N1) and the other had an influenza B infection.

To date this season, 158 influenza-associated adult hospitalizations have been reported from five provinces (AB, SK, MB, ON & NL). The proportion of cases by age group is as follows: 23.4% were in those 17-44 years of age; 26.9% were in those 45-64 years of age and 50.0% were in those ≥ 65 years. In addition, 7 adult influenza-associated deaths have been reported to date this season (6 in ON & 1 in MB); all were ≥ 65 years old.

Note: The reason for hospitalization or cause of death does not have to be attributable to influenza in order to be reported. Influenza-associated adult hospitalizations are not reported to PHAC by the following Provinces: BC,& QC. Only hospitalizations that require intensive medical care are reported by SK. ICU admissions are not reported in ON.

International influenza update

WHO: No new updates have been reported by the WHO since February 17, 2012.
World Health Organization influenza updateExternal link

PAHO: In week 7, in North America influenza activity increased but remains within the expected level for this time of year. Influenza A(H1N1)pdm09 was predominant in Mexico and has increased in the United States. Influenza A (H3N2) was predominant in the United States. In Mexico, from week 1, 2012 through February 24, 2012 the Ministry of Health reported 5,544 cases of influenza (90.9%- influenza A(H1N1)pdm09) and 180 influenza-associated deaths (92.2%- influenza A(H1N1)pdm09).
Pan American Health Organization influenza situation reportExternal link

United States: In week 7, the CDC reported that 14.4% (614/4,269) of influenza tests were positive. Since October 1, 2011, the CDC characterized 397 influenza viruses: 58 A/H1N1, 291 A/H3N2 and 48 B. Fifty-six (96.6%) of the A/H1N1 viruses were characterized as A/California/7/2009(H1N1)-like and 2 (3.4%) showed reduced titers with antiserum produced against A/California/7/2009(H1N1)-like. Of the 291 influenza A/H3N2 viruses that were characterized, 257 (95.2%) were A/Perth/16/2009-like and 14 (4.8%) showed reduced titers with antiserum produced against A/Perth/16/2009(H3N2)-like. Of the 48 influenza B viruses that were characterized, 22 (45.8%) were B/Brisbane/60/2008-like (B/Victoria lineage) and 26 (54.2%) belonged to the B/Yamagata lineage. The proportion of outpatient visits for ILI was 1.9%, which is below the national baseline. Widespread influenza activity was reported in 2 states (California & Colorado), 13 states reported regional influenza activity, 20 states reported localized influenza activity, while the rest reported either sporadic or no activity.
Centers for Disease Control and Prevention seasonal influenza reportExternal link

Europe: In week 8, influenza activity continues to increase in some countries. It has peaked and is decreasing in others in the WHO European Region. Consultation rates for ILI and acute respiratory infection (ARI) are increasing in 27 out of 42 countries; and similar to previous weeks, consultation rates in most countries continue to be well below the observed in the 2010/2011 season. Fourty- six percent of sentinel ILI/ARI samples tested positive for influenza of which 90% were for influenza A and 10% for influenza B. Circulation of influenza A(H3N2)virus is still prevalent, with some A(H1N1)pdm09 and influenza B detections reported. Since week 40, 275 influenza viruses have been characterized antigenically: 4 were A/California/7/2009(H1N1)-like; 241 were A/Perth/16/2009(H1N1)-like; 4 were B/Florida/4/2006-like (B/Yamagata/16/88 lineage), 8 were B/Bangladesh/3333/2007-like (B/Yamagata/16/88 lineage) and 8 were B/Brisbane/60/2008-like (B/Victoria/2/87 lineage).
EuroFlu weekly electronic bulletinExternal link

Human Avian Influenza Updates

The WHO reported three new cases of human A/H5N1 avian influenza infection. Two cases were from Egypt- a 32 year-old male from Egypt who developed symptoms on February 16, 2012, was hospitalized on February 21 and died on February 28. The second case was 37 year-old female. She developed symptoms on February 18, was hospitalized on February 23 and died on February 26. Both cases received oseltamivir treatment. The third case was a 12 year-old male from Indonesia. He developed symptoms on February 11, was hospitalized on February 20 and died on February 21.
WHO Avian influenza situation updatesExternal link



Definitions for the 2011-2012 season

FluWatch reports include data and information from the following sources: laboratory reports of positive influenza tests in Canada (National Microbiology Laboratory), sentinel physician reporting of influenza-like illness (ILI), provincial/territorial assessment of influenza activity based on various indicators, including laboratory surveillance, ILI reporting, and outbreaks, influenza-associated paediatric and adult hospitalizations, antiviral sales in Canada, and WHO and other international reports of influenza activity.

Abbreviations: Newfoundland/Labrador (NL), Prince Edward Island (PE), New Brunswick (NB), Nova Scotia (NS), Quebec (QC), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB), British Columbia (BC), Yukon (YT), Northwest Territories (NT), Nunavut (NU).

ILI definition for the 2011-2012 season

ILI in the general population:
Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which is likely due to influenza. In children under 5, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.
Definitions of ILI/Influenza outbreaks for the 2011-2012 season:

Schools:
Greater than 10% absenteeism (or absenteeism that is higher (e.g. >5-10%) than expected level as determined by school or public health authority) which is likely due to ILI. Note: it is recommended that ILI school outbreaks be laboratory confirmed at the beginning of influenza season as it may be the first indication of community transmission in an area.
Hospitals and residential institutions: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case. Institutional outbreaks should be reported within 24 hours of identification. Residential institutions include but not limited to long-term care facilities (LTCF) and prisons.
Other settings: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case; i.e. workplace, closed communities.
Influenza Activity Levels Definition for the 2011-2012 season. Influenza Activity levels are defined as:

1 = No activity: no laboratory-confirmed influenza detections in the reporting week, however, sporadically occurring ILI may be reported

2 = Sporadic: sporadically occurring ILI and lab confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region†

3 = Localized:

(1) evidence of increased ILI* and
(2) lab confirmed influenza detection(s) together with
(3) outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance region†

4 = Widespread:

(1) evidence of increased ILI* and
(2) lab confirmed influenza detection(s) together with
(3) outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance region†

Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.
* More than just sporadic as determined by the provincial/territorial epidemiologist.
† Influenza surveillance regions within the province or territory as defined by the provincial/territorial epidemiologist.

We would like to thank all the Fluwatch surveillance partners who are participating in this year's influenza surveillance program.

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