August 16, 2009 to August 22, 2009 (Week 33)

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

National line list data was available for 7,107 cases including 1,441 (20.3%) hospitalized cases, 278 (19.3%) patients admitted to ICU and 70 deaths. 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, 17% of hospitalizations and 14% of cases admitted to ICU were in this group. 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 6% of deaths have occurred in this group.

Those under 1 year of age have the higher hospitalization rate (22.3 per 100,000) followed by the cases between 1 and 4 years of age (10.4 per 100,000) and between 5 and 14 years (7.6 per 100,000). In comparison, the highest mortality rate is occuring in those over 65 years of age (0.42 per 100,000), followed by the cases below 1 year of age (0.28 per 100,000) and between 45 and 64 years (0.27 per 100,000).

Amongst all laboratory- confirmed cases, 898 (12.6%) were Aboriginal (ie. First Nations, Inuit or Metis). Among 269 First Nations cases, 186 were from Manitoba, 41 from Quebec, 16 from British Columbia, 11 from Alberta, three from Saskatchewan and three from Northwest territories. The 559 lab-confirmed cases from Nunavut were assumed to be persons of Inuit ethnicity although 85% of the population in this territory is Inuit. Other inuit cases were reported from Quebec (9), Northwest Territories (3), Alberta (2), and Manitoba (1). Those cases that were Metis (51) were from Manitoba (41), Alberta (4), Northwest Territories (3), Saskatchewan (1), and British Columbia (1). Ethnicity is unknown for 13 Aboriginals (6 from NU, 5 from SK and 2 from NWT). Cases from Nunavut and those who were Inuit had higher hospitalization rates than the First-Nations population (140.6 vs. 20.6 per 100,000) and higher mortality rates (4.0 vs 0.6 per 100,000). However, hospitalized cases from Nunavut and those that were Inuit were younger (median age 4.5 vs. 20.0), admitted to ICU less frequently (11.3% vs. 20.8%) and had fewer underlying medical conditions (2.6% vs. 62.8%) than those First Nations hospitalized cases.

Weekly and cumulative numbers of hospitalizations and deaths among
Pandemic (H1N1) 2009 confirmed cases, Canada, to 22 August, 2009

Province/Territory1	This week (August 16-22, 2009) hospitalized cases	This week (August 16-22, 2009) deaths	Cumulative hospitalized cases	Cumulative deaths cases
BC	3	0	42	4
AB	3	0	126	7
SK	0	0	23	4
MB	0	0	217	7
ON	7	1	353	22
QC	1	0	591	25
NB	0	0	2	0
NS	0	0	17	1
PE	0	0	1	0
NL	0	0	3	0
YT	0	0	0	0
NT	0	0	4	0
NU	6	0	62	1
Canada	21	1	1441	71

¹ Hospitalizations and deaths are reported within the province of residence or the province where the case has been identified if province of residence is not available.

Descriptive characteristics of laboratory-confirmed Canadian Pandemic (H1N1) 2009 cases, hospitalized cases, cases admitted to ICU and deaths with core information available, reported to the Public Health Agency of Canada as of 22 August 2009

	Overall cases reported (n=7,107)	Hospitalizated cases (n=1,441)	Cases admitted to ICU (n=278)	Deaths (n=71)
Females, %	51.9	51.4	56.7	60
Median age	18	25	40	51
Aboriginal status, %	12.5	16.5	14.5	11.4
Underlying medical conditions1, %	39.2 (728/1,859)	57.2 (569/995)	68.2 (148/217)	76.9 (40/52)
Pregnancy2, %	5.0 (87/1,724)	27.9 (76/272)	18.1 (13/72)	30.8 (4/13)
1 Percent of persons with at least one underlying medical condition among those for whom the information was provided excluding pregnancy. 2 Percent of pregnant women among women aged between 15 and 44 years old

Overall Influenza Summary - Week 33 (August 16 to August 22, 2009)

The overall influenza activity slightly decreased this week relative to the previous week; the national ILI consultation rate is 12 consultations per 1,000 visits as opposed to 15 consultations last week and the proportion of influenza positive tests decreased to 3.4% from 4.2%. The number of regions reporting localized activity and the overall number of influenza outbreaks remain stable compared to last week.

Two regions in ON & NL reported localized activity, 49 regions reported sporadic activity in BC, AB, SK, MB, ON, QC, NB, NS, PEI, NL, YT, NT & NU and 3 regions in MB & NB reported no activity. Only one new influenza outbreak was reported this week in a hospital in NL.

Map of overall Influenza activity level
by provinces and territories, Week 33 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, 2008-2009 (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, 2008-2009

ILI consultation rate

This week, the ILI consultation rate was 12 consultations per 1,000 patient visits (see ILI graph) decreased slightly compared to the two previous weeks. The sentinel response rate was 69.4%.

Influenza-like illness (ILI) consultation rates, Canada, by report week,
2008-2009 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).
* Data arriving late may cause variations from results seen in previous weeks.

Paediatric Influenza Hospitalizations and deaths

In week 33, no laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. 323 hospitalizations have been reported since week 17 (April 26); 99.1% of these hospitalizations have been due to Pandemic (H1N1) 2009. To date, 734 hospitalizations and six deaths have been reported this season. Four of the deaths were due to Pandemic (H1N1) 2009.

Laboratory Surveillance Summary

This week, the proportion of tests that were positive for influenza was 3.4% which is lower than the previous weeks (see Tests table). A total of 149 specimen tested positive for influenza this week (all type A). This week, 96.2% of the positive influenza A subtyped specimens were Pandemic (H1N1) 2009. The majority (83.3%) of influenza virus detections this season have been for influenza A.

Influenza tests reported and percentage of tests positive, Canada,
by report week, 2008-2009

Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2008-2009

Weekly & Cummulative numbers of positive influenza specimens , by Provincial Laboratories

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	37	0	0	14	23	0	1710	11	9	585	1105	210
AB	44	0	0	4	40	0	3066	0	8	660	2398	467
SK	8	0	0	8	0	0	1423	31	79	876	437	219
MB	2	0	0	1	1	0	1078	7	35	771	265	37
ON	32	0	1	12	19	0	6828	146	158	3039	3485	1355
QC	12	0	0	0	12	0	3901	0	0	0	3901	1418
NB	4	0	0	4	0	0	495	3	3	122	367	95
NS	6	0	1	3	2	0	620	24	24	472	100	60
PE	0	0	0	0	0	0	35	6	0	15	14	9
NL	4	0	0	4	0	0	236	11	4	98	123	26
Canada	149	0	2	50	97	0	19392	239	320	6638	12195	3896

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

Canadian situation

Antigenic Characterization

NML has antigenically characterized 296 Pandemic (H1N1) 2009 isolates by HI assay. The results reveal 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 have been sensitive to oseltamivir (511 samples) and zanamivir (267 samples) but resistant to amantadine (359 samples). However, Canada reported one case of oseltamivir resistant Pandemic (H1N1) 2009 on July 21, 2009 in the province of Quebec.

International update:

Global information

• WHO: As of August 13, 2009, WHO reports 1,799 deaths with Pandemic (H1N1) 2009. Rates of influenza illness continue to decline in the temperate regions of the southern hemisphere, except in South Africa where Pandemic (H1N1) appeared slightly later than the other countries. Active transmission is still seen in some later affected areas of Australia, Chile and Argentina even as national rates decrease. Areas of tropical Asia are reporting increasing rates of illness as they enter their monsoon season.
• Antiviral resistance: WHO has also been notified of 12 cases of oseltamivir-resistant virus, following post-exposure prophylaxis (9), treatment of uncomplicated infection (1), or in immunocompromised patients (2). These isolated cases have arisen in different parts of the world (Japan 4, USA 2, Hong Kong SAR China 2, and 1 in Denmark, Canada, Singapore and China), and there are no epidemiological links between them. There is also no evidence of onward transmission.

Southern Hemisphere

• Australia: As of August 26, 2009, Australia has 34,180 confirmed cases and 138 deaths. There are currently 435 people in hospital across Australia with Pandemic (H1N1) 2009, and 21% of these are in ICU. As of August 14, national influenza activity appears to be steady. Most jurisdictions have reported that Pandemic (H1N1) 2009 activity has peaked or has plateaued. ILI presentations to Emergency Departments and absenteeism rates have decreased. Pandemic (H1N1) 2009 appears to be replacing the seasonal A(H1N1) strain. The highest hospitalisation rate occurred in young children <5 years of age.
• New Zealand: As of August 26, 2009, the total number of confirmed cases in New Zealand is 3,114 and 16 deaths. At its peak, the weekly ILI consultation rates were nearly three times higher than the winter peak experienced in the last two years. The number of ILI consultations has decreased over recent weeks. Healthline calls continue to be about 20% above normal levels, but have decreased since peaks in mid-June and early July. School are reporting usual levels of absenteeism for this time of year.
• Argentina: As of August 15, Argentina reports 7,173 confirmed cases of Pandemic (H1N1) 2009, a total of 6,346 cases of severe acute respiratory infection requiring hospitalization, and 439 Pandemic (H1N1)-associated deaths. In week 32, Pandemic (H1N1) 2009 influenza represented 92.4% of all respiratory viruses circulating in patients over 5 years old. In children under 5 years, RSV is responsible for 70.4% of cases, and Pandemic (H1N1) 2009 only for 23.47%.
  
• Chile: As of August 15, the number of laboratory-confirmed cases in Chile is 12,175, with the highest rate among those 5-14 years old. Of confirmed cases, 1,325 have presented with severe acute respiratory infection, representing a hospitalization rate of 7.8 cases per 100,000 population. Since epi week 28 the proportion of Pandemic (H1N1) 2009 relative to other respiratory viruses has declined to reach 11% of respiratory virus detections in week 32. Very few (<1%) of influenza detections are seasonal strains. In persons over 5 years old, Pandemic (H1N1) 2009 predominates. The proportion of RSV detections has increased considerably in those under 14 years old, and parainfluenza in those over 65 years old.
• South Africa: As of August 24, South Africa reported a total of 5,118 laboratory-confirmed cases and 15 deaths from Pandemic (H1N1) 2009. Pandemic (H1N1) influenza currently represents the vast majority of influenza virus detections.
  • NICD <http://www.nicd.ac.za/>

Northern Hemisphere

• United States: As of August 20, 2009, the CDC reports 7,983 hospitalized cases, and 522 deaths due to Pandemic (H1N1) 2009. During epi week 31, influenza activity remained stable in the United States; however, there were still higher levels of ILI than is normal for this time of year. Four oseltamivir-resistant Pandemic (H1N1) viruses have been identified. In addition, 3 seasonal influenza A(H1N1) viruses collected between February 8 and May 11, 2009, were found to be resistant to both oseltamivir and the adamantanes. No changes to the influenza antiviral treatment or prophylaxis recommendations will be made on the basis of these observations, and monitoring is ongoing.
• Mexico: As of August 25, 2009, Mexico reports 20,860 confirmed cases of Pandemic (H1N1) 2009, and 179 deaths. The majority (65.2%) of confirmed cases were in patients 5 to 29 years of age. However, the largest proportion of all deaths was observed in the older age groups, with 72.1% of all fatal cases in patients 20 to 54 years old.
• United Kingdom: As of August 27, 2009, Pandemic influenza activity continues to decrease across all regions of the UK and in all age groups, though remains at levels higher than expected for this time of year. There has been a general decrease in the number of assessments, and antiviral collections, from the National Pandemic Flu Service (NPFS) over the past week. HPA modelling gives an estimate of 5000 (range 3000 – 12, 000) new cases in England in week 34 compared to an estimated 11,000 (range 6000 – 25, 000) cases in the previous week. The cumulative number of deaths reported due to Pandemic (H1N1) 2009 in the UK is 65. A total of 413 new patients were hospitalised with suspected Pandemic (H1N1) 2009 in week 34. The highest hospitalisation rates have consistently been in the under 5-year age group.

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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 2008-2009 season