September 20, 2009 to September 26, 2009 (Week 38)

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 1,479 hospitalized cases including 292 (19.7%) cases admitted to ICU and 153 (10.3%) cases required ventilation as well as 78 deaths of Pandemic (H1N1) 2009 were reported to PHAC as of September 26, 2009. The proportion of females affected, the median age and the proportion of cases with underlying medical conditions increased with severity of illness (see Characteristics table). Aboriginals were over-represented amongst those who were hospitalized or admitted to ICU. They account for 3% of the national population; however, 18% of hospitalizations, 15% of cases admitted to ICU and 12% of deaths were in this group. Aboriginal communities have more pregnant women, young children, and underlying chronic disease than the general Canadian population, which may explain the disproportionate number of severe cases in this population. Pregnant women also had a higher burden of morbidity and mortality. Assuming 1% of the population is pregnant in a given year, approximately 5% of hospitalized cases and 5% of deaths occurred in this group. The median difference between symptom onset date/specimen collection and date of hospitalization increased with severity of illness; 3.0 days for all hospitalized cases compared to 4.0 and 5.0 for ICU-admitted cases and deaths, respectively.

The national hospitalization rate was 4.4 per 100,000 population with the highest rates in children aged less than 15 years of age (10.5 per 100,000). The national mortality rate was 0.23 per 100,000 population; those 45 years and older had the highest mortality rate (0.34 per 100,000). ICU admission rate and ventilation rate were also elevated in children under five years of age (1.6 and 1.1 per 100,000, respectively).

Amongst all laboratory-confirmed hospitalized cases, 261 (17.6%) were Aboriginal (157 First Nations, 80 Inuit, 19 Metis and 5 unknown ethnicity). Approximately 46% of the hospitalized cases among those of First Nations ethnicity were living on a reserve. Cases among all Inuit including those from Nunavut had higher hospitalization rates compared to the First Nations population (158.5 vs. 22.5 per 100,000) and higher mortality rates (4.0 vs 0.7 per 100,000) (caution : rate based on small fatality numbers reported). However, hospitalized cases from Nunavut and those that were Inuit were younger (median age 4.5 vs. 19.0), admitted to ICU less frequently (11.3% vs. 21.0%), required ventilation less frequently (3.8% vs. 19.1%) and had fewer underlying medical conditions (31.9% vs. 65.4%) compared to First Nations hospitalized cases.

Weekly and cumulative numbers of hospitalizations, ICU admissions and deaths among
Pandemic (H1N1) 2009 confirmed cases, Canada, to 26 September, 2009

Province/Territory	This week			Cumulative
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU-admitted cases	Deaths
BC	1	1	0	52	21	6
AB	0	0	0	129	30	8
SK	1	0	0	24	12	4
MB	0	0	0	221	43	7
ON	3	0	0	374	65	24
QC	4	0	0	580	104	27
NB	0	0	0	2	1	0
NS	0	0	0	17	8	1
PE	0	0	0	1	0	0
NL	0	0	0	3	1	0
YT	0	0	0	0	0	0
NT	3	1	0	10	1	0
NU	0	0	0	66	6	1
Canada	12	2	0	1479	292	78

 

Descriptive characteristics of laboratory-confirmed Canadian Pandemic (H1N1) 2009 hospitalized cases, cases admitted to ICU and deaths with core information available, reported to the Public Health Agency of Canada as of 26 September 2009

1 Proportion of cases with at least one underlying medical condition (excluding pregnancy) among those for whom the information was available. 2 Percent of pregnant women among women 15 to 44 years of age.
	Hospitalizated cases (n=1,479)	Cases admitted to ICU (n=292)	Deaths (n=78)
Females, %	51.3	56.8	59.0
Median age	23	37	50
Aboriginal status, %	17.6	15.4	11.5
Underlying medical conditions1, %	61.7 (605/981)	71.6 (156/218)	81.4 (48/59)
Pregnancy2, %	27.7 (77/278)	19.2 (15/78)	28.6 (4/14)

Overall Influenza Summary - Week 38 (September 20 to September 26, 2009)

The overall influenza activity increased for a second consecutive week, but still relatively low. The national ILI consultation rate remained similar to the previous week and was slightly above the expected range for this time of the year. The proportion of positive tests and the number of regions with localized or widespread activity were also higher than the previous week.

Two regions reported widespread activity in BC and six regions in BC, NB, NL & NT reported localized activity, while thirty-two regions reported sporadic activity in every provinces and territories and fourteen regions in MB, ON, QC, NB & NS reported no activity. Sixteen new influenza outbreaks were reported this week; fifteen were in schools (10 in BC, 3 in NB and 2 in NT) and one occured in a long-term care facility in BC.

Map of overall Influenza activity level
by provinces and territories, Week 38, 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 31 consultations per 1,000 patient visits (see ILI graph) which remained similar compared to the previous week but was slightly above the expected range for this time of the year. The sentinel response rate was 89.3%. Five provinces (ON, NS, NL, YK and NT) had provincial ILI consultation rates higher than the national level this week. People under 20 years of age had the highest consultations rates with 51.3 and 70.0 per 1,000 patient visits among children under 4 years of age and between 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 2007/08 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 restrospectively.

Paediatric Influenza Hospitalizations and deaths

In week 38, one laboratory-confirmed influenza-associated paediatric hospitalization was reported through the Immunization Monitoring Program Active (IMPACT) network. The hospitalization reported this week was due to Pandemic (H1N1) 2009. 366 hospitalizations had been reported since week 17 (April 26); 92.3% of these hospitalizations were due to Pandemic (H1N1) 2009. Since the beginning of the pandemic, four 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 3.8% which was slightly higher than the previous week (see Tests table). A total of 234 specimens tested positive for influenza this week (all A). This week, 99.1% of the positive influenza A subtyped specimens were Pandemic (H1N1) 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

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. * Not subtyped
Reporting provinces	Weekly						Cumulative
	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	156	0	0	91	65	0	310	0	0	163	147	0
AB	44	0	0	8	36	0	144	0	0	24	120	0
SK	5	0	0	5	0	0	18	0	0	17	1	0
MB	0	0	0	0	0	0	3	0	0	1	2	0
ON	16	0	0	9	7	0	58	1	0	16	41	0
QC	9	0	0	0	9	0	38	0	0	0	38	0
NB	0	0	0	0	0	0	5	0	1	2	2	0
NS	1	0	0	1	0	0	8	0	0	5	3	0
PE	2	1	0	1	0	0	3	1	0	2	0	0
NL	1	0	0	1	0	0	2	0	0	2	0	0
Canada	234	1	0	116	117	0	589	2	1	232	354	0

 

Sale of antivirals (AV) in Canada

In week 38, compared to other prescriptions filled in Canada, the sale of AV suggested continued increases in most Provinces/Territories. The most pronounced increases were in British Columbia and among children.

Reference: H1N1 Antiviral and OTC Surveillance Weekly Report. For more information including a copy of the report, please contact Frank Pollari 519-826-2184, Frank.Pollari@phac-aspc.gc.ca.

Canadian situation

Antigenic Characterization

Since September 1, 2009, NML has antigenically characterized one influenza virus that was received from Ontario: influenza A (H1N1). The Pandemic (H1N1) 2009 characterized was antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO as a potential candidate for Pandemic (H1N1) 2009 vaccine. WHO recommended composition of influenza virus vaccines for use in the 2010 southern hemisphere influenza season is as follow: an A/California/7/2009 (H1N1)-like virus, an A/Perth/16/2009 (H3N2)-like virus and a B/Brisbane/60/2008-like virus.

Antiviral Resistance

NML: The Pandemic (H1N1) 2009 virus had been tested for resistance to neuraminidase inhibitors (oseltamivir and zanamivir) by phenotypic assay and/or sequencing. The testing results showed that the virus was sensitive to oseltamivir and zanamivir.

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

International update

Global information

• WHO: As of September 25, 2009, WHO reported at least 3,917 deaths with Pandemic (H1N1) 2009. In the temperate regions of the southern hemisphere, influenza transmission largely returned to baseline or continued to decline. In the temperate regions of the northern hemisphere, influenza-like-illness (ILI) activity continued to increase in many areas. In Europe and Central and Western Asia, the United Kingdom were reporting regional increases in ILI activity in Northern Ireland and Scotland and the Netherlands, France, Ireland, and Israel were reporting rates above the seasonal baseline. Although most countries in the tropical regions of the Americas were still reporting regional to widespread geographic spread of influenza activity, there was no consistent pattern in the trend of respiratory diseases. Pandemic (H1N1) 2009 was the predominant influenza strain worldwide. <http://www.who.int/csr/don/2009_09_25/en/index.html>
• Antiviral resistance: To date, 28 resistant viruses had been detected and characterized worldwide. All of these viruses showed the same H275Y mutation that confers resistance to the antiviral oseltamivir, but not to the antiviral zanamivir. Twelve of these drug-resistant viruses were associated with the use of oseltamivir for post-exposure prophylaxis. Six were associated with the use of oseltamivir treatment in patients with severe immunosuppression. Four were isolated from samples from patients receiving oseltamivir treatment. However, cases of oseltamivir-resistant viruses continued to be sporadic and infrequent, with no evidence that oseltamivir-resistant Pandemic (H1N1) 2009 are circulating within communities or worldwide. <http://www.who.int/csr/disease/swineflu/notes/h1n1_antiviral_use_20090925/en/index.html>

Northern Hemisphere

• United States: During week 37 (September 13-19, 2009), influenza activity increased in the U.S. The proportion of outpatient visits for influenza-like illness (ILI) was above the national baseline. Twenty-six states reported geographically widespread influenza activity. The CDC reported 8,392 hospitalizations for Influenza and Pneumonia Syndrome, and 1,690 for laboratory-confirmed influenza (7,295 new hospitalizations and 1,427 lab-confirmed new cases since Sept.10, 2009). Deaths from Influenza and Pneumonia Syndrome were reported as 822, with 114 laboratory-confirmed influenza deaths (total of 740 new deaths since Sept. 10, 2009). Even if the numbers were high, the proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold. <http://www.cdc.gov/flu/weekly/>
• Mexico: As of October 1, 2009, the number of confirmed cases in Mexico reached higher levels in September than the Pandemic (H1N1) peak in April, with 574 new cases in just one day this month alone based on symptom onset date. Mexico reported 32,950 confirmed cases of Pandemic (H1N1) 2009, and 236 deaths. <http://portal.salud.gob.mx/>
• United Kingdom: As of September 24, 2009, pandemic influenza activity continued to increase across the UK, particularly in school-aged children. HPA modelling gave an estimate of 9000 (range 5000 – 20,000) new cases in England in week 38. The estimated number of new cases increased in all regions and age groups. The main influenza virus circulating in the UK continued to be the Pandemic (H1N1) 2009 strain, with few influenza H1 (non-pandemic), H3 and B viruses detected. The majority of pandemic influenza cases continued to be mild. The cumulative number of deaths reported due to pandemic (H1N1) 2009 in the UK was 82.
  <http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1242949541993?p=1242949541993>
• France: As of September 29, 2009, the circulation of Pandemic (H1N1) 2009 was still ongoing. In each provinces of France, the influenza activity continued to increase. From September 21 to September 29, 2009 the ILI consultations rate was still increasing (234 cases per 100,000 compared to threshold of 96 cases per 100,000). The proportion of positive tests remained low. <http://www.invs.sante.fr>

Southern Hemisphere

• Australia: As of September 30, 2009, Australia had 36,629 confirmed cases and 180 deaths. The number of new confirmed Pandemic (H1N1) 2009 cases and hospitalisations decreased nationally with a number of jurisdictions reporting no new notifications in the last week, indicating that the first wave of the pandemic has subsided. Due to the presence of underlying chronic disease, some of which is undiagnosed, and their higher level of social disadvantage, Indigenous Australians were 10 times more likely than non-Indigenous Australians to be hospitalized for Pandemic (H1N1) 2009. <http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/updates, and Content/ozflu2009.htm>
• New Zealand: As of September 23, 2009, the total number of confirmed cases in New Zealand was 3,163 and 18 deaths. The reported level of influenza has declined to levels similar to the level at this time in the past two years. The number of ILI consultations continued to decline and was only a little higher than at the same time in the last two years. <http://www.moh.govt.nz/moh.nsf/indexmh/influenza-a-h1n1-news-media>

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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