November 15, 2009 to November 21, 2009 (Week 46)

Posted 2009-11-27

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 6,992 hospitalized cases including 1,110 cases admitted to ICU and 501 cases requiring ventilation as well as 280 deaths of Pandemic (H1N1) 2009 were reported to PHAC since the beginning of the Pandemic. Core data was available for 6,328 (90.5%) hospitalizations, 1,067 (96.1%) ICU admissions and 269 (96.1%) deaths. The number of deaths decreased slightly this week (61 vs. 84) as well as the number of ICU admissions (243 vs. 261) and number of hospitalizations (1,554 vs. 1,674). However, the number of hospitalizations reported this week was again higher than the overall number of hospitalizations for the first wave. Since August 30, 2009, all the provinces and territories except SK, MB and NU have had cumulative crude hospitalization rates that surpass the respective cumulative hospitalization rates in the period before August 29, 2009.

The proportion of severe cases (ICU admissions and deaths) among all hospitalized cases was lower in the second wave than in the first wave. Slightly more men were hospitalized, admitted to ICU and died than women during the period from August 30 to November 21, 2009 compared to the first wave. All age groups had higher hospitalization, ICU and mortality rates in the second wave than in the first wave. In particular, people over 45 years of age and children between 1 and 5 years of age had hospitalization rates in the second wave that were nearly five times higher than their respective hospitalization rates in the first wave. Mortality rates among the people over 45 years of age and among children under 1 year of age were three times higher in the second wave as compared to their respective mortality rates in the first wave. The under 20 year olds continued to have the highest hospitalization rates while those 45 years of age and older had the highest mortality rates per 100,000 population. Children under 1 year of age had the highest ICU admission rate (data not shown). Comparing the cumulative rates of hospitalization, ICU admissions and deaths between those with underlying medical conditions and those without during the period up to November 21, 2009, those with underlying medical conditions were almost 5 times more likely to be hospitalized, 7 times more likely to be admitted to ICU and 8.5 times more likely to die compared to those without underlying medical conditions. Please note that with the increased number of cases reported in the last few weeks, important changes in the trends and characteristics of the populations affected may be seen.

Weekly and cumulative numbers of hospitalizations, ICU admissions and deaths among
Pandemic (H1N1) 2009 confirmed cases, Canada, to November 21, 2009

*Based on reporting date. ** Based on epidemiological date, hospitalization date and reporting date. 1 These provinces reported aggregate counts this week. 2 Since no report was received from NS last week, this week's update reflects the situation since week 44. † Note that due to reporting delays, some PTs are reporting retrospectively on first wave's cases.
Province/Territory	This week (Nov. 15-21, 2009)*			From August 30, 2009 to November 21, 2009**			From April 18, 2009 to August 29, 2009**†
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1	103	15	5	807	103	29	51	19	5
AB	210	35	8	974	190	43	129	29	7
SK	6	5	3	19	16	7	23	12	4
MB1	9	4	1	34	5	2	225	43	7
ON	256	38	18	946	124	54	379	67	25
QC	665	96	18	2056	280	49	572	104	27
NB1	47	9	4	126	17	6	5	1	0
NS2	139	18	2	204	29	3	18	9	1
PE1	10	1	0	46	7	0	1	0	0
NL1	96	21	0	235	39	7	3	1	0
YT	3	1	1	14	3	2	0	0	0
NT	2	0	1	44	6	1	6	0	0
NU	8	0	0	2	0	0	73	6	1
Canada	1554	243	61	5507	819	203	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 November 21, 2009^†

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. This may have affected the observed proportion this week. For these two provinces, missing information has been included in the denominator. 2 Percent of pregnant women among women 15 to 44 years of age. † Note that due to reporting delays, some PTs are reporting retrospectively on first wave's cases.
	From August 30, 2009 to November 21, 2009			From April 18, 2009 to August 29, 2009
	Hospitalized cases (n=4,843)	Cases admitted to ICU (n=776)	Deaths (n=129)	Hospitalized cases (n=1,485)	Cases admitted to ICU (n=291)	Deaths (n=77)
Females, %	49.0	47.6	47.9	51.4	57.4	62.3
Median age	27.0	47.0	54.0	23.0	37.0	51.0
Aboriginal status, %	4.0	6.4	6.8	18.3	15.1	11.7
Underlying medical conditions1 , %	51.6 (1 136/2 202)	60.2 (360/598)	67.4 (91/135)	46.6 (642/1 379)	56.6 (156/274)	65.3 (49/75)
Pregnancy2 , %	16.2 (119/736)	9.8 (12/123)	0.0	28.5 (79/277)	20.8 (16/77)	28.6 (4/14)

 

Overall Influenza Summary - Week 46 (November 15 to November 21, 2009)

Nationally, the activity level reported this week decreased compared to the previous week. All influenza indicators declined during week 46.

Ten regions reported widespread activity in BC, SK, ON, QC & NL and twenty-four regions in BC, MB, ON, QC, NB, PE, NS & NL reported localized activity, while nineteen regions reported sporadic activity in BC, AB, MB, ON, QC, NB, NS, YK, NT & NU and one region in NU reported no activity. The 330 influenza outbreaks reported this week were all in schools except 14 in hospitals and residential institutions (BC, AB, QC, NS & NL) and 1 in an unspecified location (AB). The schools outbreaks were in QC (217), SK (32), NS (22), BC (18), NB (10), AB (7), MB (6), NL (2) and PE (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 has considerably increased the total number of outbreaks reported compared to previous years.

Map of overall Influenza activity level by provinces and territories, Week 46, 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 57 consultations per 1,000 patient visits (see ILI graph) which was significantly lower than the previous weeks. All provinces and territories had lower ILI consultations rates compared to previous weeks except QC and PE. Those under 20 years of age still had the highest consultation rates, with 96 and 107 per 1,000 patient visits among children under 5 years of age and among those 5 and 19 years of age, respectively.

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 46, 99 laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. Of these, 22 were reported as Pandemic (H1N1) 2009 and 77 were reported as unsubtyped influenza A. 1,250 hospitalizations had been reported since week 17 (April 26): 88.0% of these hospitalizations were officially due to Pandemic (H1N1) 2009. Since the beginning of the pandemic, six deaths due to Pandemic (H1N1) 2009 had been reported through the IMPACT network among children under 16 years of age.

Laboratory Surveillance Summary

This week, the proportion of tests that were positive for influenza was 34.3% which is lower than the three previous weeks (see Tests table). All provinces and territories had a lower proportion of positive tests for influenza compared to the previous weeks except MB and PE. This week, a total of 4,189 specimens tested positive for influenza (all A except 1 B) and 99.9% of the positive influenza A subtyped specimens were Pandemic (H1N1) 2009. Note that QC reported this week 2 positive specimens for A/H3N2 and 1 B.

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 Note that an error occurred in the numbers PHAC reported for AB last week. Corrected numbers are presented.
Reporting provinces	Weekly (Nov. 15-21, 2009)						Cumulative (Aug. 30-Nov. 21, 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	345	0	0	345	0	0	6108	0	1	5545	562	0
AB	209	0	0	203	6	0	5473	0	0	1416	4057	0
SK	403	0	0	369	34	0	2297	0	1	2029	267	0
MB	757	0	0	696	61	0	1331	0	0	1243	88	0
ON	543	0	0	189	354	0	7293	1	0	3162	4130	4
QC	1477	0	2	1475	0	1	9444	1	39	9404	0	4
NB	261	0	0	257	4	0	1687	1	1	1666	19	1
NS	119	0	0	116	3	0	737	0	0	715	22	0
PE	11	0	0	11	0	0	97	0	0	95	2	0
NL	64	0	0	64	0	0	925	0	0	925	0	0
Canada	4189	0	2	3725	462	1	35392	3	42	26200	9147	9

 

Sale of antivirals (AV) in Canada

During week 46, antiviral prescriptions monitoring results demonstrated decreases in antiviral prescription sales among the provinces and territories.

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

Canadian situation

Antigenic Characterization

Since September 1, 2009, NML has antigenically characterized 310 Pandemic (H1N1) 2009 viruses and four seasonal influenza viruses (two influenza A/H1N1, one influenza A/H3N2 and one B virus) that were received from Canadian laboratories. Of the 310 Pandemic influenza A (H1N1) viruses characterized, 309 (99.7%) were antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO as Pandemic (H1N1) 2009 vaccine. One virus (0.3%) tested showed reduced titer with antisera produced against A/California/7/09. Sequence analysis of the HA showed that the virus with reduced titer did not have the mutation at amino acid position 222 as reported by Norway. CDC also reported that of the 348 pandemic H1N1 viruses tested, one virus showed reduced titer with antisera produced against A/California/7/09.

Antiviral Resistance

NML: Pandemic (H1N1) 2009 viruses tested so far have been sensitive to zanamivir (220 samples) but resistant to amantadine (231 samples). Of the 258 Pandemic (H1N1) 2009 viruses tested, 255 were sensitive to oseltamivir and three viruses were resistant to oseltamivir with the H275Y mutation. The three resistant cases, 2 from Ontario and 1 from Quebec, were associated with oseltamivir treatment.

Provinces: Three cases of oseltamivir resistant Pandemic (H1N1) 2009 were reported to date in Canada from the province of Quebec on July 21, 2009, from Alberta on September 15, 2009 and from Ontario on October 13, 2009.

International update

Global information

WHO: The early arriving winter influenza season continues to intensify across parts of North America and much of Europe. Pandemic (H1N1) 2009 continued to be the dominant influenza virus in circulation across the globe. From April 19 to November 7, 2009, 68.8% of specimens submitted to WHO FluNet were Pandemic (H1N1) 2009, 2.9% were seasonal A(H1), 8.5% were A(H3), 17.9% were A (not sub typed) and 2.1% were influenza B.

Virus mutation: Three Pandemic (H1N1) isolates were detected in Norway which carry the D222G mutation which may play a role in receptor binding of the virus. The same mutation has been observed in Brazil, China, Japan, Mexico, Ukraine, US, and Finland. The virus was isolated from the first 2 fatal cases in Norway, and a case of severe illness. However, it has been detected in both mild and severe cases in other countries. The clinical or public health significance of this mutation is not yet clear.

Antiviral resistance: To date, 57 resistant pandemic H1N1 influenza viruses have been detected and characterized worldwide. All of these viruses show the same H275Y mutation that confers resistance to the antiviral oseltamivir. In a review of 32 cases of oseltamivir-resistant Pandemic (H1N1) reported globally, the ECDC notes that 16 were associated with antiviral treatment, 13 with prophylaxis, and 3 had no history of oseltamivir exposure. Two factors are associated with isolation of oseltamivir-resistant influenza : immunosuppression and prophylactic use of oseltamivir. <http://www.who.int/csr/disease/swineflu/updates/en/index.html and http://www.ecdc.europa.eu/en/activities/sciadvice/Lists/ECDC%20Reviews/ECDC_DispForm.aspx?List=512ff74f-77d4-4ad8-b6d6-bf0f23083f30&ID=683&MasterPage=1&PDF=true>

Northern Hemisphere

United States: Influenza transmission remained active and geographically widespread, although disease activity appears to have recently peaked in most areas except in the north-eastern United States. ILI consultations decreased in all 10 surveillance regions, despite remaining above national and regional baseline levels. Forty-three states reported widespread influenza activity this week (3 less than last week). Since August 30, 2009, CDC has received 138 reports of influenza-associated paediatric deaths that occurred during the current influenza season, including 21 deaths this week. The proportion of deaths attributed to pneumonia and influenza (P&I) was above the epidemic threshold for the seventh consecutive week.<http://www.cdc.gov/flu/weekly/ and http://www.cdc.gov/h1n1flu/update.htm>

ECDC: Transmission appears to have peaked in some countries of Western Europe including Iceland, Ireland, the UK (Northern Ireland), and Belgium. Although influenza activity in Ukraine remained high, the incidence of acute respiratory infection (ARI) was lower than that reported last week. The weekly number of deaths due to Pandemic (H1N1) in Europe has nearly doubled every 2 weeks over the past 6 weeks and reached 169 last week, with a cumulative total of 670. Influenza activity was high in 18 European countries, especially in children up to the age of 15. Greater than 20% of all sentinel respiratory specimens tested positive for influenza in at least 20 countries, with ≥ 50% of samples testing positive for influenza in 15 countries. In Europe, the number of influenza detections has risen sharply each week, from 18% of sentinel specimens testing positive in week 40/2009 to 45% positive in week 46/2009. Over 99% of subtyped influenza A viruses in Europe this week were Pandemic (H1N1) 2009. <http://www.ecdc.europa.eu/en/activities/surveillance/EISN/Pages/EISN_Bulletin.aspx and http://www.euroflu.org/index.php>

Ireland: Influenza activity remained at higher levels than recorded in previous seasons, but continued to decrease in week 46. The GP consultation rate for ILI decreased to 134.4 per 100,000 population; the number of laboratory-confirmed cases decreased sharply; and the number of hospitalized cases decreased by almost 50%. The proportion of sentinel specimens testing positive for Pandemic (H1N1) 2009 increased from 39.4% in week 45 to 47.6% in week 46. Children and young adults remained the most affected groups; 80.6% of cases are less than 35 years of age. As of 18 November, there have been 16 deaths among confirmed cases of Pandemic (H1N1) 2009. <http://www.hpsc.ie/hpsc/A-Z/EmergencyPlanning/AvianPandemicInfluenza/SwineInfluenza/Surveillance%20Reports/>

United Kingdom: Weekly influenza/ILI consultation rate was stable or decreased, though remained above the winter baseline thresholds. HPA modelling gave an estimate of 53,000 (range 26,000 – 114,000) new cases in England in week 46. There were a total of 1,483 new patients hospitalized in England with suspected Pandemic (H1N1) 2009 in the week from November 5 to 11 (increased from 1,355 in the previous week). Hospitalization rates have increased in the under 5-year age group, but have decreased in most other age groups recently.
<http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1242949541993?p=1242949541993>

Asia: In East Asia, influenza transmission remained active. Intense influenza activity continued to be observed in Mongolia with a severe impact on the healthcare system. In Japan, influenza activity remained elevated but stable nationally, and may be decreasing slightly in populated urban areas. In Hong Kong SAR, rates of ILI have returned to baseline. <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).

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Definitions for the 2009-2010 season