February 28 to March 6, 2010 (Week 9)

Posted 2010-03-12

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Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,669 hospitalized cases including 1,472 (17.0%) cases admitted to ICU and 429 (4.9%) deaths with pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 8,221 (94.8%) hospitalizations, 1,472 (100%) ICU admissions and 424 (98.8%) deaths. No new hospitalized cases were reported during week 9. To date, only 10 hospitalizations (BC, ON & NS) and two deaths (ON) have occurred since the beginning of 2010.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic H1N1 2009 confirmed cases, Canada, April 12, 2009 to March 6, 2010^†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 Aggregate counts were reported this week. † Note that due to reporting delays, some provinces and territories reported retrospectively on first and second wave cases.
Province/ Territory	Week 9 (February 28 to March 6, 2010)*			From April 12, 2009 to March 6, 2010**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1	0	0	0	1080	167	57
AB	0	0	0	1276	239	71
SK	0	0	0	67	52	15
MB	0	0	0	379	61	11
ON	0	0	0	1843	319	129
QC	0	0	0	3063	465	108
NB1	0	0	0	163	34	8
NS	0	0	0	293	50	7
PE	0	0	0	50	9	0
NL	0	0	0	308	60	18
YT	0	0	0	15	3	3
NT	0	0	0	52	7	1
NU	0	0	0	80	6	1
Canada	0	0	0	8669	1472	429

To date, the national cumulative crude hospitalization rate was 25.7 per 100,000 population with the highest rates in children less than 5 years of age (100.4 per 100,000). The cumulative crude mortality rate was 1.3 per 100,000 population with those 45 years and older having the highest mortality rate (2.1 per 100,000). The national crude ICU admission rate was 4.4 per 100,000 population. The ICU admission rate was elevated in adults 45 to 64 years (6.4 per 100,000) as well as children under five years of age (6.2 per 100,000).

Descriptive characteristics of laboratory-confirmed Canadian pandemic H1N1 2009 hospitalized cases, ICU-admitted cases and deaths with core information available, reported to PHAC as of March 6, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to March 6, 2010			Cumulative: From April 12, 2009 to March 6, 2010
	Hospitalized cases (n=1488)	ICU-admitted (n=292)	Deaths (n=78)	Hospitalized cases (n=6733)	ICU-admitted  (n=1180)	Deaths (n=347)	Hospitalized cases (n=8221)	ICU-admitted (n=1472)	Deaths (n=424)
Females, %	51.3	57.2	62.3	49.7	49.4	47.0	50.0	51.0	49.8
Median age	23.0	37.0	51.0	30.0	47.0	54.0	29.0	46.0	53.5
Aboriginal status1, %	20.0-27.7	16.1-21.9	11.7-17.6	4.5-6.1	5.8-7.7	6.1-8.9	7.3-9.9	7.8-10.4	7.1-10.4
Underlying medical conditions2, %	47.5 (652/1373)	60.2 (162/269)	73.3 (55/75)	58.6 (1920/3275)	73.1 (669/915)	84.2 (240/285)	55.3 (2572/4648)	70.2 (831/1184)	81.9 (295/360)
Pregnancy3, %	27.6 (75/272)	19.7 (15/76)	28.6 (4/14)	18.2 (187/1027)	8.3 (15/180)	0.0 (0/36)	20.2 (262/1299)	11.7 (30/256)	8.0 (4/50)
1 Since Aboriginal status is not reported by two provinces (which comprise 23% of the Aboriginal population) two methods were used to calculate proportions: one proportion was calculated by including ON and NS cases in the denominator (which is an underestimate of the true proportion); while the other proportion was calculated by excluding ON and NS cases in the denominator (which is an overestimate). 2 Proportion of cases with at least one underlying medical condition (excluding pregnancy) among those for whom the information was available. 3 Percent of pregnant women among women 15 to 44 years of age. † All cases admitted to ICU are included in the hospitalization count; however, not all the fatal cases have been hospitalized before dying.

Overall Influenza Summary - Week 9 (February 29 to March 6, 2010)

During week 9, the overall influenza activity remained low for at least 11 consecutive weeks and all influenza indicators were still considerably below expected levels for this time of the year. For the first time since the beginning of the pandemic, the proportion of positive tests for influenza B (0.08%) was higher than the proportion for influenza A (0,04%).

In week 9, only one region (BC) reported localized activity. 10 regions in ON, QC & NS reported sporadic activity, while 41 regions reported no activity. One region in AB did not report this week, and one region in BC is not reporting until further notice. One influenza outbreak was reported this week in a school (BC).

Map of overall Influenza activity level by provinces and territories, Week 9, Canada
	No Data No Activity Sporadic Activity Localized Activity Widespread Activity
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.

Number of influenza surveillance regions^† reporting widespread or localized influenza activity,
Canada, by report week, 2009-2010 (N=54)

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

Overall Number of Influenza Outbreaks, Canada, by Report Week, 2009-2010

Note that this was the first year that all the provinces and territories were reporting on influenza outbreaks in schools (greater than 10% absenteeism on any day most likely due to ILI) which has increased considerably the total number of outbreaks reported compared to previous years.

ILI consultation rate

During week 9, the national ILI consultation rate was 17.4 consultations per 1,000 patient visits (see ILI graph) which was still considerably below the expected range for this time of year (range from 31.8 to 53.0 consultations per 1,000 patient visits). All reporting provinces and territories had similar or lower ILI consultation rates compared to their respective ILI rates in the previous weeks except NB which had a slightly higher rate again this week. Those under 20 years of age still had the highest consultation rates: 29.7 per 1,000 among children under 5 years of age and 32.3 per 1,000 among those 5 to 19 years of age.

Influenza-like illness (ILI) consultation rates, Canada, by report week,
2009-2010 compared to 1996/97 through to 2008/09 seasons

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.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza during week 9 (0.12%, 3/2,574) remained at a very low level for this time of year (see Tests table). Of the three positive specimens, one (33%) was positive for influenza A (pandemic H1N1 2009) and two (67%) were positive for influenza B. All provinces had a similar or lower proportion of positive tests for influenza compared to the previous weeks. Note that since August 30, 2009, influenza A/H3N2 detections were highest in QC (85% or 44/52) and influenza B detections were highest in QC (53% or 9/17) and ON (47% or 8/17). Respiratory syncytial virus detections were still high with a proportion of positive tests of 24.0% in week 9. Positive specimens for RSV were reported from all provinces except NB (data not shown). The proportion of positive parainfluenza and adenovirus tests remained under the 3% positivity rate.

Influenza tests reported and percentage of tests positive, Canada,
by report week, 2009-2010

Percent positive influenza tests, compared to other respiratory viruses, Canada,
by reporting week, 2009-2010

Weekly & Cumulative numbers of positive influenza specimens, by Provincial Laboratories, Canada, 2009-2010

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. * Not subtyped
Reporting provinces	Weekly (February 28 to March 6, 2010)						Cumulative (August 30, 2009 to March 6, 2010)
	Influenza A					B	Influenza A					B
	A Total	A(H1)	A(H3)	Pand H1N1	A (NS)*	Total	A Total	A(H1)	A(H3)	Pand H1N1	A (NS)*	Total
BC	1	0	0	1	0	0	6371	0	1	5805	565	0
AB	0	0	0	0	0	0	5868	2	5	5760	101	0
SK	0	0	0	0	0	0	2598	0	1	2298	299	0
MB	0	0	0	0	0	0	1915	0	0	1788	127	0
ON	0	0	0	0	0	2	7800	4	0	3556	4240	8
QC	0	0	0	0	0	0	10698	4	44	10648	2	9
NB	0	0	0	0	0	0	1856	1	1	1835	19	0
NS	0	0	0	0	0	0	787	0	0	753	34	0
PE	0	0	0	0	0	0	97	0	0	96	1	0
NL	0	0	0	0	0	0	951	0	0	951	0	0
Canada	1	0	0	1	0	2	38941	11	52	33490	5388	17
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Canadian situation

Paediatric and Adult Influenza Hospitalizations and Deaths

In week 9, no laboratory-confirmed influenza-associated paediatric (16 years of age and under) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. A total of 1328* hospitalizations have been reported since week 17 (April 26, 2009), of which 96.8% were due to pandemic H1N1 2009. Of the 936 peadiatric hospitalizations reported since August 30, 2009, 13 (1.4%) cases presented with influenza-associated bacteremia. Since the beginning of the pandemic, ten paediatric deaths due to pandemic H1N1 2009 were reported through the IMPACT network among children 16 years of age or under. Seven (70%) of those deaths reported had at least one underlying medical condition.

*Delays in the reporting of data may cause data to change restrospectively.

During week 9, no new laboratory-confirmed influenza-associated adult (16 years of age and older) hospitalizations were reported through the Canadian Nosocomial Infection Surveillance Program (CNISP) from 15 of 50 reporting sites. Since week 47 (November 22, 2009), 55 hospitalizations and 8 deaths have been reported through CNISP among adults 16 years of age and older. All of these hospitalizations and deaths were due to pandemic H1N1 2009. From June 1, 2009 to March 5, 2010, of the 552 laboratory-confirmed influenza cases among hospitalized adults reported through 27 of CNISP sentinel sites, 385 (70%) were pandemic H1N1 2009 cases, 156 (28%) were unsubtyped influenza A and the remaining 11 (2%) were either seasonal influenza A/H1N1, influenza A/H3N2 or influenza B. Among the pandemic H1N1 2009 cases, 1.3% (5/365) presented with influenza-associated bacteremia, 26% (100/385) were admitted to the ICU, and 5% (20/385) died (90% of whom had at least one underlying medical condition). The median lenght of stay for those pandemic H1N1 2009 cases was 6 days.

Please note the total number of CNISP reporting sites fluctuates weekly and most of the reporting sites started surveillance in late fall 2009.

Sale of antivirals (AV)

During week 9, antiviral prescription sales continued to demonstrate a levelling-off in antiviral prescriptions among provinces and territories. Some evidence suggested mild short-term increases in British Columbia and Newfoundland. An analysis of antiviral sales data at the Health Region level demonstrated low antiviral prescription sales rates among all Health Regions for the week of February 28 to March 6, 2010. No Health Region reported an antiviral sales rate greater than 2.5 antivirals/1000 other prescriptions.

Antigenic Characterization

Since September 1, 2009, the National Microbiology Laboratory (NML) has antigenically characterized 836 pandemic H1N1 2009 viruses and 16 seasonal influenza viruses (3 seasonal influenza A/H1N1, 10 H3N2, and 3 B virus) that were received from provincial laboratories. Of the 836 pandemic H1N1 2009 viruses characterized, 832 (99.5%) were antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO for the pandemic H1N1 2009 vaccine. Four viruses (0.5%) tested showed reduced titer with antisera produced against A/California/7/09. Of the ten seasonal influenza A (H3N2) viruses characterized, two were related to A/Brisbane/10/07, which was the influenza A/H3N2 component recommended for the 2009-10 influenza vaccine and eight viruses were antigenically related to A/Perth/16/09, which is the WHO recommended influenza A (H3N2) component for the 2010 -2011 Northern Hemishpere vaccine. Three seasonal influenza A/H1N1 viruses characterized were related to A/Brisbane/59/07, which was the influenza A/H1N1 component recommended for the 2009-10 influenza vaccine. Of the three influenza B viruses characterized, two were antigenically related to B/Brisbane/60/08, which was the recommended influenza B component for the 2009-10 influenza vaccine. One B virus was related to the previous vaccine virus B/Florida/4/2006 (Yamagata lineage).

Antiviral Resistance

NML/Provinces: Thirteen cases of oseltamivir resistant pandemic H1N1 2009 were reported to date in Canada: one in British Columbia, four in Alberta, one in Manitoba, four in Ontario, two in Quebec, and one in New Brunswick. The 13 resistant cases were associated with oseltamivir treatment/prophylaxis.

NML: All pandemic H1N1 2009 viruses tested so far have been sensitive to zanamivir (1043 samples) but resistant to amantadine (1121 samples).

International update

Global information

WHO: As of February 28, 2010, over 213 countries and overseas territories or communities worldwide reported cases of pandemic H1N1 2009 (at least 16,455 deaths). In the temperate zone of the northern hemisphere, virus transmission persisted in some areas of Europe and Asia but influenza activity was declining and at low levels in most areas. The most active areas of transmission were currently observed in parts of Southeast Asia and East and South-eastern Europe. Recently, influenza type B was increasingly reported in Asia.
<http://www.who.int/csr/don/2010_03_05/en/index.html>

Antiviral resistance: For this reporting week (25 February - 3 March 2010), 11 new sporadic cases of oseltamivir resistant pandemic H1N1 2009 viruses have been reported. To date, 264 pandemic H1N1 2009 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y substitution and are assumed to remain sensitive to zanamivir.
< http://www.who.int/csr/disease/swineflu/oseltamivirresistant20100305.pdf>

2010-2011 influenza season vaccine: The WHO recommends that the following viruses be used for influenza vaccines in the 2010-2011 influenza season (northern hemisphere): an A/California/7/2009 (H1N1)-like virus; an A/Perth/16/2009 (H3N2)-like virus; and a B/Brisbane/60/2008-like virus.
<http://www.who.int/csr/disease/influenza/recommendations2010_11north/en/index.html>

Geographic update

United States:During week 8, influenza activity remained at approximately the same levels as last week in the United States with the majority of states reporting sporadic influenza activity (4 states reported regional and 8 states and Puerto Rico reporting localized). Of the 4,128 specimens tested for influenza in week 8, 263 (6.4%) were positive for influenza (262 were influenza A and 1 was influenza B). All of the influenza A viruses subtyped were pandemic H1N1 2009 viruses except for one influenza A/H3N2 virus. The proportion of deaths attributed to pneumonia and influenza (7.9%) and the proportion of outpatient visits for ILI (1.7%) remained similar compared to previous week and both remained below baseline levels. One influenza B-associated pediatric death was reported this week; however the death occurred during the 2008-09 influenza season.
<http://www.cdc.gov/flu/weekly/index.htm>

Europe: The pandemic H1N1 2009 is well past its winter peak in Europe, with the majority of the countries reporting sporadic activity or no geographic spread of the pandemic virus. Austria, Greece and Italy reported regional activity and Malta and Slovakia reported localized activity. Of the 449 specimens collected by sentinel physicians, 26 (5.8%) were positive for influenza virus of which most were pandemic A(H1N1). Only Sweden reported influenza B virus as dominant. The number of severe acute respiratory infection cases by week of onset (23 reported in week 8) has been declining since the peak in week 46.
< http://ecdc.europa.eu/en/activities/surveillance/EISN/Newsletter/100226_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: Pandemic influenza virus continued to circulate at low levels in South and Southeast Asian countries. However, the overall intensity of activity nationally was still low in both countries. Of note, seasonal influenza B virus activity had been increasing in the area and was now the predominant influenza virus in Mongolia, China, and parts of South East Asia. Japan had also reported clusters of influenza B related cases. In West Asia, respiratory tract infections in the north western area of Pakistan and Afghanistan were reportedly increasing. Whether this increased activity was due to circulation of influenza was not known.
<http://www.who.int/csr/don/2010_03_05/en/index.html>

Africa: While In North Africa influenza activity was low, in Sub-Saharan Africa, several West African countries were increasingly reporting pandemic influenza cases, though surveillance data from the area is quite limited. Data from the rest of Africa suggested that influenza activity in most countries was low and transmission continued to be sporadic. Some detections of seasonal influenza H1N1, H3N2, and influenza type B were still being reported.
<http://www.who.int/csr/don/2010_03_05/en/index.html>

Latin America : In the northern temperate zones of the Americas, pandemic H1N1 2009 continued to circulate at very low levels yielding an overall low and declining pattern of pandemic influenza activity. However, in Mexico and Peru, there was a slight increase in respiratory disease activity, though the overall intensity remained low and it was unclear how much was related to pandemic influenza.
<http://www.who.int/csr/don/2010_03_05/en/index.html>

Australia: Since the beginning of 2010, there have been 44 cases of pandemic (H1N1) 2009 and 186 positive influenza A cases (not subtyped). National influenza activity remains low. However, some indicators are at levels slightly above those experienced at the same time in previous years.
< http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/ozflucurrent.htm>

New Zealand: The ILI consultation rate for week 8 was 18.0 per 100,000 which was below baseline.
< http://www.surv.esr.cri.nz/PDF_surveillance/Virology/FluWeekRpt/2010/FluWeekRpt201009.pdf>

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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; national pandemic H1N1 2009 surveillance; and WHO and other international reports of influenza activity.
The map shows influenza activity in the “influenza surveillance regions” † within each jurisdiction, as determined by the provincial/territorial epidemiologists.

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 2009-2010 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 could be due to influenza virus. 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 2009-2010 season
Schools: greater than 10% absenteeism on any day most likely due to ILI.
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), prisons.
Other: 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 are defined as:
1 = No activity: i.e. no laboratory-confirmed influenza detections during the past four weeks, however, sporadically occurring ILI may be reported
2 = Sporadic: sporadically occurring ILI and lab confirmed influenza* with NO outbreaks detected within the influenza surveillance region†
3 = Localized: sporadically occurring ILI and lab confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in less than 50% of the influenza surveillance region(s)†
4 = Widespread: sporadically occurring ILI and lab confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in greater than or equal to 50% of the influenza surveillance region(s)†
* confirmation of influenza within the surveillance region at any time within the prior four weeks
† sub-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.
This report is available on the Public Health Agency website at the following address: http://www.phac-aspc.gc.ca/fluwatch/index.html. Ce rapport est disponible dans les deux langues officielles. Pour en recevoir un exemplaire dans l'autre langue chaque semaine, veuillez communiquer avec Estelle Arseneault, Division de l'immunisation et des infections respiratoires au (613) 952-8484

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Definitions for the 2009-2010 season