December 13 to December 19, 2009 (Week 50)

Posted 2009-12-31

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 8,436 hospitalized cases including 1,404 (16.6%) cases admitted to ICU and 401 (4.8%) deaths of Pandemic (H1N1) 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 7,564 (89.7%) hospitalizations, 1,344 (95.7%) ICU admissions and 379 (94.5%) deaths. 7 of the 13 provinces and territories continued to show activity of Pandemic (H1N1) 2009 during the last week. Although activity is present, a continued decline was experienced by all PTs, indicated by the decreasing number of reported hospitalized cases (79 vs. 159), ICU admissions (21 vs. 40) and deaths (11 vs. 21) reported this week compared to the previous week. The number of hospitalizations due to Pandemic (H1N1) 2009 in the second wave was 4.7 times higher than the number reported during the first wave. The peak periods of reported laboratory-confirmed hospitalizations and deaths occurred from weeks 22 to 24 (May 31, 2009 to June 20, 2009) for the first wave and from weeks 43 to 45 (October 25, 2009 to November 14, 2009) for the second wave.

The proportion of severe cases (ICU admissions and deaths) among all hospitalized cases to date was still slightly lower in the second wave than in the first wave; however, this difference is continuing to narrow (19.6% vs. 16.0% for ICU admissions and 5.2% vs. 4.7% for fatal cases). Comparing the rates of hospitalization, ICU admissions and deaths between those with underlying medical conditions and those without since the beginning of the pandemic, those with underlying medical conditions were almost 5 times more likely to be hospitalized, 7 times more likely to be admitted to ICU and more than 14 times more likely to die compared to those without underlying medical conditions. Among the hospitalized cases, ICU admissions and deaths, chronic pulmonary disease (including asthma) was the most commonly reported underlying medical condition (33.9%, 37.1% and 47.0%, respectively). Immunosuppression (including cancer) (15.1%) and diabetes (14.0%) were also frequently reported among hospitalized cases, while ICU cases were also affected by diabetes (22.0%) and chronic heart disease (19.4%). Among fatal cases, chronic heart disease (32.2%) and immunosuppression (30.3%) were most commonly reported.

Since the beginning of the pandemic, 536 hospitalized cases (7.1%) were among people of Aboriginal origin (382 First Nations, 105 Inuit, 39 Metis and 10 with unknown Aboriginal subgroup), however, this represents an underestimate since Ontario and Nova Scotia do not report on Aboriginal ethnicity (Aboriginal populations in these two provinces account for 23% of the total Canadian Aboriginal population). To date in the second wave, the proportion of people of Aboriginal origin continued to be lower among all levels of severity of illness (hospitalizations, ICU admission and deaths) compared to the first wave. aboriginal peoples hospitalized during the second wave have been older (25 vs. 12 years old) and the proportion of cases with underlying medical conditions among Aboriginals was slightly higher (51.3% vs. 41.5%) compared to the first wave. Fewer pregnant women among Aboriginal women of reproductive age (19.4% vs. 34.3%) were reported inthe second wave.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic (H1N1) 2009 confirmed cases, Canada, to December 19, 2009†

*Based on reporting date. ** Based on epidemiological date, hospitalization date and reporting date. 1 These provinces reported aggregate counts this week. 2 Note change in total hospitalizations from last week's report: duplicates were removed. † Note that due to reporting delays, some PTs reported retrospectively on first wave cases.
Province/Territory	This week (Dec. 13-Dec. 19, 2009)*			From August 30, 2009 to December 19, 2009**			From April 12, 2009 to August 29, 2009**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1	5	3	1	986	129	47	51	19	5
AB	9	2	1	1130	207	58	129	29	7
SK	3	3	1	37	33	11	23	12	4
MB1	9	0	0	141	16	3	224	43	7
ON	38	6	5	1378	227	93	385	68	25
QC	14	5	3	2475	358	79	572	104	27
NB1,2	--	1	0	162	33	7	2	1	0
NS1	1	1	0	266	42	6	17	8	1
PE	0	0	0	49	9	0	1	0	0
NL1	0	0	0	262	49	16	3	1	0
YT	0	0	0	14	3	3	0	0	0
NT	0	0	0	46	7	1	6	0	0
NU	0	0	0	5	0	0	72	6	1
Canada	79	21	11	6951	1113	324	1485	291	77

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 December 19, 2009^†

	From April 12 to August 29, 2009			From Aug. 30, 2009 to Dec. 19, 2009			Cumulative: From April 12 to Dec. 19, 2009
	Hospitalized cases (n=1.485)	ICU-admitted (n=291)	Deaths (n=77)	Hospitalized cases (n=6,079)	ICU-admitted  (n=1,053)	Deaths (n=302)	Hospitalized cases (n=7.564)	ICU-admitted (n=1,344)	Deaths (n=379)
Females, %	51.4	57.4	62.3	49.4	49.7	48.7	49.8	51.3	51.5
Median age	23.0	37.0	51.0	29.0	47.0	53.0	28.0	45.0	53.0
Aboriginal status, %	20.3	16.2	11.7	3.9	5.9	6.6	7.1	8.1	7.7
Underlying medical conditions1, %	47.0 (647/1,376)	57.5 (157/273)	68.0 (51/75)	52.5 (1,468/2,794)	62.1 (510/821)	73.8 (136/202)	50.7 (2,115/4,170)	61.0 (667/1,094)	72.5 (240/331)
Pregnancy2, %	28.0 (77/275)	19.7 (15/76)	28.6 (4/14)	19.1 (173/907)	9.2 (15/163)	0.0	21.2 (250/1,182)	12.6 (30/239)	8.5 (4/47)
1 Proportion of cases with at least one underlying medical condition (excluding pregnancy) among those for whom the information was available. Missing/unknown information has been removed from all calculations except for data reported on underlying condition from MB and ON, where it was not possible to delineate missing information from absence of underlying condition. For these two provinces, missing information has been included in the denominator. Note that Ontario retrospectively provided information to PHAC on underlying medical conditions of fatal cases. This increased the proportion of underlying medical conditions among deaths. 2 Percent of pregnant women among women 15 to 44 years of age. †Note that due to reporting delays, some PTs reported retrospectively on first wave cases.

Overall Influenza Summary - Week 50 (December 13 to December 19, 2009)

At the national level, the overall influenza activity continued to decrease this week. All FluWatch influenza indicators declined for at least the fifth consecutive week. The ILI consultation rate remained well below the expected ranged for this time of the year.

On week 50, only one region in NL reported localized activity and none have reported widespread activity. The 3 influenza outbreaks reported this week were all in schools and occurred in QC (2) and NB (1). Note that this is the first year that all the provinces and territories are reporting on influenza outbreaks in schools (greater than 10% absenteeism on any day most likely due to ILI) which is increasing considerably the total number of outbreaks reported compared to previous years.

Map of overall Influenza activity level by provinces and territories, Week 50, 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

ILI consultation rate

This week, the national ILI consultation rate was 20 consultations per 1,000 patient visits (see ILI graph) which was slightly higher compared to last week but remained well below the expected range for this time of the year. Those under between 5 and 19 years of age still had the highest consultation rates (36 per 1,000 patient visits), while the ILI consultation rate for children under the age of 5 years decreased substantially to 15 per 1000 patients from 57 per 1000 visits during the previous week.

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.

Paediatric Influenza Hospitalizations and Deaths

In week 50, 2 laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. Both of these cases were due to Pandemic (H1N1) 2009. 1,325 hospitalizations had been reported since week 17 (April 26): 97.0% of these hospitalizations were due to Pandemic (H1N1) 2009. Since the beginning of the pandemic, eleven paediatric deaths due to Pandemic (H1N1) 2009 were reported through the IMPACT network among children equal to or less than 16 years of age.

Laboratory Surveillance Summary

This week, the proportion of tests that were positive for influenza was 3.9% which represents a significant decrease compared to the previous weeks (see Tests table). All provinces and territories had a lower proportion of positive tests for influenza compared to the previous weeks except PE. This week, a total of 121 specimens tested positive for influenza (all A) and 99.1% of the positive influenza A subtyped specimens were Pandemic (H1N1) 2009. Note that QC reported 43 positive specimen for A/H3N2 since August 30, 2009.

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

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 (Dec. 13-Dec. 19, 2009)						Cumulative (Aug. 30 to Dec. 19, 2009)
	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	13	0	0	13	0	0	6351	0	1	5785	565	0
AB	14	0	0	13	1	0	5444	2	5	5345	92	0
SK	3	0	0	3	0	0	2593	0	1	2293	299	0
MB	29	0	0	28	1	0	1884	0	0	1758	126	0
ON	24	0	0	17	7	0	7845	2	0	3518	4325	4
QC	35	0	1	34	0	0	10669	1	43	10625	0	5
NB	2	0	0	2	0	0	1850	1	1	1829	19	1
NS	0	0	0	0	0	0	781	0	0	750	31	0
PE	1	0	0	1	0	0	103	0	0	101	2	0
NL	0	0	0	0	0	0	951	0	0	951	0	0
Canada	121	0	1	111	9	0	38471	6	51	32955	5459	10

 

Sale of antivirals (AV) in Canada

During week 50, antiviral prescriptions monitoring results demonstrated a levelling off antiviral prescriptions among all provinces and territories.

Reference: H1N1 Antiviral and OTC Surveillance Weekly Report. CFEZID, PHAC.

Canadian situation

Antigenic Characterization

Since September 1, 2009, the National Microbiology Laboratory (NML) has antigenically characterized 554 Pandemic (H1N1) 2009 viruses and 8 seasonal influenza viruses (2 influenza A/H1N1, 5 H3N2, and 1 B virus) that were received from Canadian laboratories. Of the 554 Pandemic (H1N1) 2009 viruses characterized, 550 (99.3%) were antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO as the Pandemic (H1N1) 2009 vaccine. 4 viruses (0.7%) tested showed reduced titer with antisera produced against A/California/7/09. Of the five seasonal influenza A (H3N2) viruses characterized, one was related to A/Brisbane/10/07, which is the influenza A/H3N2 component recommended for the 2009-10 influenza vaccine and four viruses were antigenically related to A/Perth/16/09, which is the WHO recommended influenza A (H3N2) component for the 2010 Southern Hemisphere vaccine.

Antiviral Resistance

NML: Pandemic (H1N1) 2009 viruses tested so far have been sensitive to zanamivir (619 samples) but resistant to amantadine (665 samples).

Provinces: Nine cases of oseltamivir resistant Pandemic (H1N1) 2009 were reported to date in Canada: one in Alberta, one in Manitoba, four in Ontario, two in Quebec, and one in New Brunswick.

International update

Global information

WHO: Worldwide more than 208 countries and overseas territories or communities have reported laboratory confirmed cases of Pandemic (H1N1) 2009, including at least 10,582 deaths. In the temperate zone of the northern hemisphere, Pandemic (H1N1) 2009 activity remains active but geographically widespread. In particular, activity has peaked or has passed its peak in North America and in most parts of Europe; however activity continued to increase in parts of central and south-eastern Europe, as well as in central and south Asia. Influenza transmission remained active in much of western and central Asia and activity declines were noted in east Asia and Japan. There was evidence of Pandemic (H1N1) 2009 circulation in most regions of Africa. <http://www.who.int/csr/don/2009_12_18a/en/index.html>

Antiviral resistance: To date, 136 Pandemic (2009) H1N1 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y mutation.
<http://www.who.int/csr/disease/swineflu/laboratory18_12_2009/en/index.html>

Geographic update

Europe: For week 51/2009 (14-20 December, 2009), seventeen countries reported decreasing rates of influenza-like illness or acute respiratory infection; two countries reported stable rates (Scotland and Cyprus), while one country (Bulgaria) reported increasing rates. Most countries experienced medium influenza intensity with two reporting high levels (Bulgaria and Greece), and five countries reported low levels (Belgium, Cyprus, Germany, Netherlands and UK. Activity remained widespread in six countries, while the remaining countries reported sporadic or local activity . 2009 pandemic influenza A(H1N1) virus still accounted for 99% of all subtyped viruses in sentinel patients and for 98% in severe acute respiratory infection (SARI) patients. As of 21 December, the cumulative number of reported deaths since the beginning of the pandemic in EU/EFTA Member States has totalled 1652.
<http://ecdc.europa.eu/en/healthtopics/Documents/091221_Influenza_A(H1N1)_Weekly_Executive_Update.pdf>
<http://ecdc.europa.eu/en/activities/surveillance/EISN/
Newsletter/091218_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

United States: Overall influenza activity continued to decline for the 6th consecutive week. Widespread activity was reported by seven states; Guam and one state reported no activity, while the remaining states reported regional, local or sporadic activity. Proportional mortality due to pneumonia and influenza continued to decrease to levels below the epidemiologic threshold; lab-confirmed hospitalizations/deaths continued to decline. 99% of all subtyped influenza A viruses being reported to CDC were 2009 Pandemic (H1N1) 2009.
<http://www.cdc.gov/flu/weekly/ and http://www.cdc.gov/h1n1flu/update.htm>

Asia: In Western and Central Asia, influenza transmission remained active. In East Asia, influenza transmission remained active but appeared to be declining overall. Influenza activity has recently peaked and begun to decline in Japan. ILI activity continued to decline but remained elevated in northern and southern China, Chinese Taipei and in Mongolia. In southern Asia, influenza activity continued to increase in the northern parts of India, Nepal, Sri Lanka, and the Maldives. ILI/ARI activity continued to increase in Kazakhstan and Kyrgyzstan, and has peaked in some countries including in Afghanistan, Oman, and Israel. Influenza virus continued to circulate in Iran, Iraq, Jordan, Egypt and in much of the surrounding region but may have recently peaked in some parts.
<http://www.who.int/csr/disease/swineflu/updates/en/index.html>

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FluWatch reports include data and information from five main sources:laboratory reports of positive influenza tests in Canada; sentinel physician reporting of influenza-like illness (ILI); provincial/territorial assessment of influenza activity based on various indicators, including laboratory surveillance, ILI reporting, school and work site absenteeism, and outbreaks; influenza-associated pediatric hospitalizations; 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