December 20, 2009 to January 2, 2010 (Weeks 51 and 52)

Posted 2010-01-08

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 8,507 hospitalized cases including 1,426 (16.8%) cases admitted to ICU and 416 (4.9%) deaths of Pandemic (H1N1) 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 7,745 (91.0%) hospitalizations, 1,374 (96.4%) ICU admissions and 390 (93.5%) deaths. Nine of the 13 provinces and territories continued to show activity of Pandemic (H1N1) 2009 during the last week. Similar numbers of hospitalized cases (76 vs. 79), ICU admissions (22 vs. 21) and deaths (16 vs. 11) were reported over the two-week period 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. 16.1% for ICU admissions and 5.2% vs. 4.8% 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, 8 times more likely to be admitted to ICU and more than 15 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 (34.6%, 37.8% and 47.8%, respectively). Immunosuppression (including cancer) (15.6%) and diabetes (14.2%) were also frequently reported among hospitalized cases, while ICU cases were also affected by diabetes (22.5%) and chronic heart disease (19.4%). Among fatal cases, immunosuppression (34.7%) and chronic heart disease (32.1%) were most commonly reported.

Since the beginning of the pandemic, 577 hospitalized cases (7.4%) were among people of Aboriginal origin (419 First Nations, 105 Inuit, 43 Metis and 10 with unknown Aboriginal subgroup), however, this represents an underestimate since Ontario and Nova Scotia do not report on Aboriginal status (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 (median age of 26 years old vs. 12 years old) and the proportion of cases with underlying medical conditions among Aboriginals was slightly higher (49.4% vs. 41.5%) compared to the first wave. Fewer pregnant women among Aboriginal women of reproductive age (17.7% vs. 34.3%) were reported in the second wave.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic (H1N1) 2009 confirmed cases, Canada, to January 2, 2010†

*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	Weeks 51 & 52 (Dec. 20, 2009-Jan. 2, 2010)*			From August 30, 2009 to January 2, 2010**			From April 12, 2009 to August 29, 2009**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1	10	3	2	994	130	48	53	21	6
AB	5	0	4	1135	207	62	129	29	7
SK	2	2	0	39	35	11	23	12	4
MB1	8	2	1	149	18	4	224	43	7
ON	33	11	3	1407	238	96	389	68	25
QC1	8	2	2	2483	360	81	572	104	27
NB	0	1	1	162	34	8	2	1	0
NS1,2	--	0	0	261	42	6	17	8	1
PE	0	0	0	49	9	0	1	0	0
NL1	9	1	2	271	50	18	3	1	0
YT	1	0	0	15	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	76	22	15	7016	1133	338	1491	293	78

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 January 2, 2010^†

	From April 12 to August 29, 2009			From Aug. 30, 2009 to Jan. 2, 2010			Cumulative: From April 12 to Jan. 2, 2010
	Hospitalized cases (n=1,491)	ICU-admitted (n=293)	Deaths (n=78)	Hospitalized cases (n=6,254)	ICU-admitted  (n=1,081)	Deaths (n=312)	Hospitalized cases (n=7,745)	ICU-admitted (n=1,374)	Deaths (n=390)
Females, %	51.2	57.0	61.5	49.5	49.2	47.6	49.8	50.9	50.3
Median age	23.0	37.0	51.0	29.0	47.0	54.0	28.0	45.0	53.0
Aboriginal status, %	20.2	16	11.5	4.4	5.9	6.7	7.4	8.1	7.7
Underlying medical conditions1, %	47.0 (650/1,382)	58.2 (160/275)	71.1 (54/76)	52.4 (1,539/2,935)	62.6 (524/837)	76.2 (199/261)	50.7 (2,189/4,317)	61.5 (684/1,112)	75.1 (253/337)
Pregnancy2, %	28.0 (77/275)	19.7 (15/76)	28.6 (4/14)	18.5 (175/947)	9.0 (15/167)	0.0	20.6 (252/1,222)	12.3 (30/243)	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 - Weeks 51 and 52 (December 20, 2009 to January 2, 2010)

During weeks 51 and 52, influenza activity in Canada remained low with all influenza surveillance regions reporting either sporadic or no activity except one region (AB) in week 51 reported localized activity.

In week 52, thirty-four regions in BC, AB, SK, MB, ON, QC, NB, NS, NL & NU reported sporadic activity, while nineteen regions reported no activity in BC, NB, PE, NS, NL, YT & NT. One region in NU did not report in week 52 while one province (ON) and one territory (NU) did not report in week 51. Only 1 influenza outbreak was reported during the two-week period in a hospital or residential institution in Alberta. 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.

Map of overall Influenza activity level by provinces and territories, Week 52, 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

During weeks 51 and 52, the national ILI consultations rate were 27 and 19 consultations per 1,000 patient visits (see ILI graph) respectively which were below or within the expected range for these weeks. During week 51, those between 5 and 19 years of age had the highest consultation rate (66 per 1,000 patient visits). During week 52, the ILI consultation rate for children under the age of 5 years increased to 56 per 1000 patients from 36 per 1,000 patient 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 weeks 51 and 52, 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. 1,328 hospitalizations have been reported since week 17 (April 26): 97.1% 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 16 years of age or under.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza was 1.6% as a whole over the two-week period 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 week except NB and NS. During weeks 51 and 52, a total of 79 specimens tested positive for influenza (78 A and 1 B) and 98.5% of the positive influenza A subtyped specimens were Pandemic (H1N1) 2009. Note that QC reported 44 positive specimen for A/H3N2 and 6 specimen for influenza B 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. 20, 2009 to Jan. 2, 2010)						Cumulative (Aug. 30, 2009 to Jan. 2, 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	11	0	0	11	0	0	6362	0	1	5796	565	0
AB	10	0	0	8	2	0	5854	2	5	5750	97	0
SK	4	0	0	4	0	0	2597	0	1	2297	299	0
MB	23	0	0	23	0	0	1907	0	0	1781	126	0
ON	15	0	0	7	8	0	7862	2	0	3527	4333	4
QC	10	0	1	9	0	1	10679	1	44	10634	0	6
NB	4	0	0	4	0	0	1854	1	1	1833	19	1
NS	1	0	0	1	0	0	782	0	0	751	31	0
PE	0	0	0	0	0	0	103	0	0	101	2	0
NL	0	0	0	0	0	0	951	0	0	951	0	0
Canada	78	0	1	67	10	1	38951	6	52	33421	5472	11

 

Sale of antivirals (AV) in Canada

During weeks 51 and 52, antiviral prescriptions monitoring results demonstrated a levelling-off in antiviral prescriptions among most provinces and territories. However, antiviral prescriptions appeared to be increasing moderately in Saskatchewan during the period from December 27, 2009 to January 2, 2010 (week 52).

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 595 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 595 Pandemic (H1N1) 2009 viruses characterized, 591 (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. Four 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 (758 samples) but resistant to amantadine (783 samples).

NML/Provinces: Ten cases of oseltamivir resistant Pandemic (H1N1) 2009 were reported to date in Canada: one in Alberta, one in Manitoba, five in Ontario, two in Quebec, and one in New Brunswick. Eight of the nine resistant cases were associated with oseltamivir treatment. One case (NB) appeared to be the result of infection with an antiviral-resistant strain of H1N1.

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 12,220 deaths. In the temperate regions of the northern hemisphere, transmission of Pandemic (H1N1) 2009 remained active and geographically widespread, however overall disease activity has recently peaked or has past its peak in much of the hemisphere. There continued to be increases in influenza activity in later affected areas of central and eastern Europe, Mongolia and southern Asia. In the temperate regions of the southern hemisphere, sporadic cases of pandemic influenza continued to be reported without evidence of sustained community transmission.
<http://www.who.int/csr/don/2009_12_23/en/index.html and http://www.who.int/csr/don/2009_12_30/en/index.html>

Antiviral resistance: To date, 168 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/laboratory30_12_2009/en/index.html>

Geographic update

Europe: For week 51/2009 (December 14-20, 2009), most countries experienced medium influenza intensity with only two reporting high levels (Bulgaria and Greece). In the majority of countries, activity was still widespread. Seventeen of the 20 countries reported decreasing trend in consultations. In particular, UK reported decreasing trends and low intensity except for Scotland, where the trend was stable and intensity medium. While the proportion of influenza-positive sentinel samples continued to decline, Pandemic (H1N1) 2009 still accounted for 99% of all subtyped viruses in sentinel patients and for 98% in severe acute respiratory infection (SARI) patients. One in five SARI cases had no known underlying medical condition. As of 31 December, the cumulative number of reported deaths since the beginning of the pandemic in EU/EFTA Member States has totalled 1,923.
<http://ecdc.europa.eu/en/activities/surveillance/EISN/Newsletter/091224_EISN_Weekly_Influenza_Surveillance_Overview.pdf and
http://ecdc.europa.eu/en/healthtopics/Documents/091231_Influenza_AH1N1_Situation_Report_0900hrs.pdf>

United States: During week 51 (December 20-26, 2009), influenza activity decreased slightly in the United States. Widespread activity was reported by four states; one state reported no influenza; and the remaining states reported regional, local, and sporadic influenza activity. ILI physician consultations increased slightly during this period and may reflect fewer people going to the doctor for routine health services during the holiday period. The proportion of deaths attributed to pneumonia and influenza increased over the previous week and was noted to be above the epidemic threshold. Four influenza-associated pediatric deaths were reported. Two of these deaths were associated with 2009 influenza A (H1N1) virus infection and two were associated with an influenza A virus for which the subtype was undetermined. All subtyped influenza A viruses reported to CDC were Pandemic (H1N1) 2009. <http://www.cdc.gov/flu/weekly and http://www.cdc.gov/h1n1flu/update.htm>

Asia: Influenza transmission has recently peaked in some places of central and west Asia (Israel, Iran, Iraq, Oman, and Afghanistan) although though these areas continued to have some active transmission and levels of respiratory disease activity have not yet returned to baseline levels. In east Asia, influenza transmission remained active but appeared to be declining overall. Influenza/ILI activity continued to decline in Japan, in northern and southern China, Chinese Taipei, and Hong Kong SAR (China). Slight increases in ILI were reported in Mongolia after weeks of declining activity following a large peak of activity over one month ago. In southern Asia, influenza activity continued to be intense, particularly in northern India, Nepal, and, Sri Lanka. Seasonal influenza A (H3N2) viruses are still being detected in very small numbers in China making up about 2.5% of the influenza A viruses detected there.
<http://www.who.int/csr/don/2009_12_30/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