September 13, 2009 to September 19, 2009 (Week 37)

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 1,467 hospitalized cases including 292 (19.9%) cases admitted to ICU and 151 (10.3%) cases required ventilation as well as 78 deaths of Pandemic (H1N1) 2009 had been reported to PHAC as of September 19, 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. 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 national hospitalization rate was 4.4 per 100,00 population with the highest rates in children aged less than 15 years of age (10.4 per 100,000). In comparison, the national mortality rate was 0.23 per 100,000 population; those 45 and older had the highest mortality rate (0.33 per 100,000). ICU admission rate and ventilation rate were also elevated in the population under five years of age.

Amongst all laboratory-confirmed hospitalized cases, 258 (17.6%) were Aboriginal (ie. First Nations, Inuit or Metis). Among 155 First Nations cases, 94 were from MB, 41 from QC, 11 from AB, 4 from BC, 4 from NWT and one from SK. The 66 lab-confirmed hospitalized cases from Nunavut were assumed to be persons of Inuit ethnicity since the majority (85%) of the population in this territory is Inuit. Other Inuit cases were reported from QC (10), AB (2) and NWT (2). Metis (18) were from MB (13) and AB (5). Ethnicity was unknown for 5 hospitalized Aboriginals from SK. Approximately 46% of the First Nations hospitalized cases are living on a reserve. Cases from Nunavut and those who were Inuit had higher hospitalization rates compared to the First-Nations population (158.5 vs. 22.2 per 100,000) and higher mortality rates (4.0 vs 0.7 per 100,000). Because of small numbers reported, this should be interpreted with caution. 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. 20.6%), required ventilation less frequently (3.8% vs. 18.7%) and had fewer underlying medical conditions (31.9% vs. 64.7%) than those First Nations hospitalized cases.

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

Province/Territory	This week			Cumulative
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU-admitted cases	Deaths
BC	3	0	1	51	20	6
AB	0	0	0	129	30	8
SK	0	0	0	23	12	4
MB	1	1	0	221	43	7
ON	1	3	1	371	67	24
QC	2	0	0	576	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	1	0	0	7	0	0
NU	0	0	0	66	6	1
Canada	8	4	2	1467	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 19 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 aged between 15 and 44.
	Hospitalizated cases (n=1,467)	Cases admitted to ICU (n=292)	Deaths (n=78)
Females, %	51.2	56.5	60.5
Median age	23	37	50
Aboriginal status, %	17.6	15.1	11.8
Underlying medical conditions1, %	61.7 (604/979)	72.1 (158/219)	81.7 (49/60)
Pregnancy2, %	28.1 (77/274)	19.5 (15/77)	28.6 (4/14)

Overall Influenza Summary - Week 37 (September 13 to September 19, 2009)

The overall trend of influenza activity increased this week ; the national ILI consultation rate, the proportion of positive tests, the number of regions with localized activity and the number of influenza outbreak are higher compared to the previous week.

Two regions reported localized activity in BC, thirty-four regions reported sporadic activity in BC, AB, SK, MB, ON, QC, NB, NS, NL, YK, NT & NU and 15 regions in SK, MB, ON, QC, NB, NS, NL & PEI reported no activity. Three regions in SK, QC and NL did not report this week. Two new influenza outbreaks were reported in a school and in a long-term care facility in BC this week.

Map of overall Influenza activity level
by provinces and territories, Week 37, 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.

Number of New Outbreaks in Long Term Care Facilities, Canada, by Report Week, 2009-2010

ILI consultation rate

The national ILI consultation rate increased to 32 consultations per 1,000 patient visits (see ILI graph) this week which was increasing for a second consecutive week and was above the expected range for this time of the year. The sentinel response rate was 83.7%.

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.

Sale of antivirals (AV) and over-the-counter (OTC) cough medicines

In week 37, compared to other prescriptions filled in Canada, the sale of AV was high (rate between 2 and 5 per 100 prescriptions) for a second consecutive week in southern BC and NT. A map showing the AV sale in Canada will be added in the FluWatch report of week 38.

Paediatric Influenza Hospitalizations and deaths

In week 37, two laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. One of the two hospitalizations this week was due to Pandemic (H1N1) 2009 and the other to seasonal influenza A. 365 hospitalizations have been reported since week 17 (April 26); 92.3% of these hospitalizations have been 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 aged under 16 years of age.

Laboratory Surveillance Summary

This week, the proportion of tests that were positive for influenza was 3.5% which is slightly higher than the previous week (see Tests table). A total of 191 specimen tested positive for influenza this week (all A). This week, 98.3% 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	116	0	0	100	16	0	212	0	0	122	90	0
AB	38	0	0	4	34	0	100	0	0	16	84	0
SK	2	0	0	2	0	0	13	0	0	12	1	0
MB	0	0	0	0	0	0	3	0	0	1	2	0
ON	17	0	0	4	13	0	42	1	0	7	34	0
QC	6	0	0	0	6	0	29	0	0	0	29	0
NB	8	0	2	2	4	0	9	0	2	3	4	0
NS	4	0	0	2	2	0	7	0	0	4	3	0
PE	0	0	0	0	0	0	2	1	0	1	0	0
NL	0	0	0	0	0	0	1	0	0	1	0	0
Canada	191	0	2	114	75	0	418	2	2	167	247	0

Canadian situation

Antigenic Characterization

NML has antigenically characterized 336 Pandemic (H1N1) 2009 isolates by HI assay. The results revealed that these viruses are antigenically related to A/California/7/2009 (H1N1), which is the variant reference virus selected by WHO as a potential candidate for Pandemic (H1N1) 2009 vaccine. Antigenic characterization also indicates that these viruses are antigenically and genetically unrelated to seasonal influenza A (H1N1) viruses, which suggests that there is little or no protection to be expected from vaccination with seasonal influenza vaccine.

Antiviral Resistance

NML: All Pandemic (H1N1) 2009 viruses tested so far by NMLhave been sensitive to zanamivir (317 samples) but resistant to amantadine (416 samples). 573 pandemic influenza A (H1N1) viruses have been tested for resistance to oseltamivir by phenotypic assay and/or sequencing. The testing results showed that 572 were sensitive to oseltamivir. One isolate tested was resistant to oseltamivir with the H274Y mutation.

Two cases of oseltamivir resistant Pandemic (H1N1) 2009 were reported so far 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 18 September 2009, WHO reported at least 3,486 deaths with Pandemic (H1N1) 2009. In the temperate regions of the southern hemisphere, influenza activity continued to decrease or has returned to the seasonal baseline in most countries. In the tropical regions of the Americas and Asia, influenza transmission remained active. In the temperate regions of the northern hemisphere activity was variable. In Europe and Central Asia influenza activity remained low overall, except in France, while in Japan, the influenza activity increased above the seasonal epidemic threshold. Pandemic (H1N1) 2009 was the predominant influenza strain worldwide.
• Antiviral resistance: 26 isolated cases of oseltamivir-resistant virus have been reported worldwide from different countries all of which carry the same H275Y mutation that confers resistance to the antiviral oseltamivir but not to the antiviral zanamivir. Of these, 12 have been associated with post-exposure prophylaxis and five with long-term oseltamivir treatment in patients with immunosuppression.
  <http://www.who.int/csr/disease/swineflu/updates/en/index.html>

Northern Hemisphere

• United States: During week 36, the influenza activity increased in the US. The seasonal influenza A (H1) and A (H3) viruses co-circulated at low levels with Pandemic (H1N1) 2009. Ninety-nine percent of all subtyped influenza A viruses being reported to CDC this week were Pandemic (H1N1) 2009. From August 30-September 12, 2009 4,569 hospitalizations and 364 deaths associated with influenza virus infection, or based on syndromic surveillance for influenza and pneumonia, were reported to CDC.
  <http://www.cdc.gov/flu/weekly/>
• Mexico: As of September 22, 2009, Mexico reported 27,660 confirmed cases of Pandemic (H1N1) 2009, and 222 deaths. The majority (77.1%) of confirmed cases were in patients below 29 years of age. However, the largest proportion of all deaths was observed in the older age groups, with 71.4% of all fatal cases in patients 20 to 54 years old. No information found on current activity level.
  <http://portal.salud.gob.mx/>
• United Kingdom: As of September 17, 2009, several indicators suggested that pandemic influenza activity has started to increase in many areas of the UK, particularly in school-aged children. 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 through sentinel and non-sentinel surveillance. 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 78. <http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1242949541993?p=1242949541993>
• France: As of September 20, 2009, the overall activity level continued to increase. Since the beginning of the pandemic, 29 deaths due to Pandemic (H1N1) 2009 were reported. <http://www.invs.sante.fr/display/?doc=surveillance/grippe_dossier/index_h1n1.htm>

Southern Hemisphere

• Australia: As of September 22, 2009, Australia had 36,270 confirmed cases and 172 deaths. As of September 11, current national influenza continued to decrease. The overall hospitalisation rate was 16.1 per 100,000 population with the highest rates in children aged less than 5 years of age. Due to the presence of underlying chronic disease, some of which is undiagnosed, and their higher level of social disadvantage, Indigenous Australians were 8 times more likely than non-Indigenous Australians to be hospitalised for Pandemic (H1N1) 2009. About 5% of hospitalised cases have been reported as pregnant, reinforcing the fact that pregnancy, particularly in the second and third trimesters, was a risk factor for hospitalisation with 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 3,152 and 17 deaths. While numbers of swine flu cases in New Zealand appeared to be declining the virus was still circulating. The number of ILI consultations continued to decrease, although is still a little higher than at the same time in previous years. <http://www.moh.govt.nz/moh.nsf/indexmh/influenza-a-h1n1-news-media, and http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php>
• Argentina: As of September 12, Argentina reported 8,851 confirmed cases of Pandemic (H1N1), a total of 9,480 cases of severe acute respiratory infection requiring hospitalization, and 514 Pandemic (H1N1)-associated deaths. The peak period of Pandemic (H1N1) 2009 occurred between June 21 to 25 with a generalized transmission throughout the country. As of week 35, Pandemic (H1N1) 2009 and unsubtyped influenza A represented 92.9% of respiratory virus detections in patients >5 years old. In contrast, in children <5 years old, Pandemic (H1N1) 2009 and unsubtyped influenza A represented only 23.5% of detections, and RSV accounts for 70%. <http://www.msal.gov.ar/htm/site/default.asp>
• Chile: As of September 9, the number of laboratory-confirmed cases in Chile was 12,205 (rate 21.4/100,000 population). In week 35 ILI activity was mild. 1,561 confirmed cases have required hospitalization, representing a rate of 9.2 cases of acute infection per 100,000 population. The median age of severe cases was 33 years and 47% had underlying chronic disease. Of 132 deaths, the median age was 49 years and 64.3% had underlying illness. Since EW 30, RSV was the predominant respiratory virus. <http://www.minsal.cl/>
• South Africa: As of September 22, South Africa reported a total of 11,545 laboratory-confirmed cases and 59 deaths from Pandemic (H1N1) 2009. The incidence of confirmed cases was reported to be 23.41 / 100,000 population. <http://www.nicd.ac.za/>

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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