August 2, 2009 to August 8, 2009 (Week 31)

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

National abbreviated line list data was available for 6,966 cases, 1,341 (19.3%) hospitalized cases including 240 (17.9%) patients admitted to ICU and 65 deaths. The proportion of females affected, the median age and the proportion of cases with underlying medical conditions are still increasing with severity of illness. There is a higher proportion of Aboriginals as well as a higher proportion of pregnant women among hospitalized cases, ICU-admitted cases and deaths compared to overall cases reported (see Characteristics table).

The age distribution was available for 1,298 hospitalized cases and 65 deaths from the abbreviated line-list. The highest hospitalization rate is among the cases below 1 year of age (27.5 per 100,000) followed by the cases between 1 and 4 years of age (11.2 per 100,000). In comparison, the highest mortality rate is among the cases over 65 years of age (0.39 per 100,000), followed by the cases below 1 year of age (0.27 per 100,000) and cases between 45 and 64 years old (0.26 per 100,000).

Among the pregnant women with Pandemic (H1N1) 2009, there is a higher proportion of Aboriginals (29.5% vs. 11.1%), and a higher proportion of hospitalization (85.3% vs. 19.3%) than the proportion of these factors observed overall.

Pandemic (H1N1) 2009 Nunavut and Inuit cases have a higher hospitalization rate (116.6 vs. 18.1 per 100,000) than First Nations cases. However, Nunavut and Inuit hospitalized cases have lower median age (2 vs. 19 years old), a lower proportion of ICU-admitted cases (5.1% vs. 23.1%) and underlying medical conditions (12.5% vs. 56.7%) than First Nations hospitalized cases.

Weekly and cumulative numbers of hospitalizations and deaths among
Pandemic (H1N1) 2009 confirmed cases, Canada, to 8^st August, 2009

Province/Territory	This week (August 2-8, 2009) hospitalized cases	This week (August 2-8, 2009) deaths	Cumulative hospitalized cases	Cumulative deaths cases
BC	9	2	36	4
AB	6	2	122	7
SK	0	0	22	4
MB	0	0	201	7
ON	18	2	332	21
QC	5	0	584	21
NB	1	0	2	0
NS	5	0	15	1
PE	0	0	1	0
NL	0	0	2	0
YT	0	0	0	0
NT	1	0	1	0
NU	6	0	48	1
Canada	51	6	1366	66

Note that 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 8^st August 2009

	Overall cases reported (n=6,966)	Hospitalizated cases (n=1,341)	Cases admitted to ICU (n=240)	Deaths (n=65)
Females, %	51.8	51.3	58.8	63.1
Median age	18	23	40	51
Aboriginal status, %	11.1	15.6	15.0	12.3
Underlying medical conditions1, %	35.4 (585/1,577)	54.3 (485/894)	65.6 (122/186)	81.3 (39/48)
Pregnancy2, %	3.6 (61/1,676)	21.8 (52/238)	15.6 (10/64)	18.2 (2/11)
1 Among those for whom information was provided. Pregnancy is no longer considered as an underlying medical condition which may explain the lower percentage this week. 2 Among women between 15 and 44 years old.

Overall Influenza Summary - Week 31 (August 2 to August 8, 2009)

The overall influenza activity remains similar to the previous week; the reported activity level (4 regions reported localized activity) and the national ILI consultation rate (15 consultations per 1,000 visits) are comparable to last week. While the proportion of influenza positive tests decreased this week, the overall number of influenza outbreaks increased.

Four regions in AB, ON & QC reported localized activity, 45 regions reported sporadic activity in BC, AB, SK, MB, ON, QC, NB, NS, PEI, YT, NT & NU and 1 region in NB reported no activity (No report received from NL). Four new influenza outbreaks were reported this week; three in long-term care facilities (AB, ON & QC) and one in an unspecified location (AB).

Map of overall Influenza activity level
by provinces and territories, Week 31 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 15 consultations per 1,000 patient visits (see ILI graph) which is decreasing for the second consecutive week. The sentinel response rate was 78%.

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 31, 2 laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. One of the two hospitalizations this week is due to Pandemic (H1N1) 2009. 321 hospitalizations have been reported since week 17 (April 26 to May 2, 2009); 99.4% of these hospitalizations have been due to Pandemic (H1N1) 2009. There were six deaths reported so far this season including four deaths due to Pandemic (H1N1) 2009.

Laboratory Surveillance Summary

This week, the proportion of tests that were positive for influenza was 5.5% which is lower than the previous week (see Tests table). A total of 282 specimen tested positive for influenza this week (all type A). 98.5% of the positive influenza A subtyped specimens were due to Pandemic (H1N1) 2009 this week.The majority (83.0%) 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	44	0	0	36	8	0	1613	9	9	541	1054	210
AB	61	0	0	16	45	0	2969	0	8	644	2317	467
SK	2	0	0	2	0	0	1408	31	79	862	436	219
MB	12	0	0	10	2	0	1073	7	35	769	262	37
ON	39	0	0	13	26	0	6751	146	157	3015	3433	1355
QC	21	0	0	0	21	0	3873	0	0	0	3873	1417
NB	7	0	0	7	0	0	488	3	3	115	367	95
NS	27	1	0	26	0	0	602	24	23	461	94	60
PE	2	1	0	1	0	0	36	9	0	13	14	9
NL	17	0	0	17	0	0	228	11	4	90	123	26
Canada	232	2	0	128	102	0	19041	240	318	6510	11973	3895

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 245 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 (421 samples) and zanamivir (235 samples) but resistant to amantadine (340 samples).
However, Canada reported its first case of oseltamivir resistant Pandemic (H1N1) 2009 on July 21, 2009.

International update:

Global information

WHO: As of 6 August 2009, 1,462 deaths with Pandemic (H1N1) 2009 have been reported in over 170 countries worldwide. Pandemic (H1N1) 2009 has been the predominant influenza virus in nearly all of the temperate regions of the Southern Hemisphere, except in South Africa which experienced an early influenza season of predominantly seasonal A(H3N2). As the influenza season in South Africa reached its peak in early to mid June and began to decline, Pandemic (H1N1) 2009 appeared and has now become the dominant subtype there. Australia and countries in the southern part of South America are now starting to report decreases in the numbers of people seeking care and being admitted to hospital. Tropical regions of the world, which typically experience year round transmission of influenza viruses, are now seeing increases in cases. In general, the impact and severity of the season in these areas appears slightly worse than a normal influenza season, with increased hospitalization requiring respiratory critical care.

Southern Hemisphere

• Australia: As of August 12, 2009, Australia has 28,307 confirmed cases and 100 deaths. There are currently 441 people in hospital across Australia with Pandemic (H1N1) 2009, and 113 (26%) of these are in intensive care units. As of July 24th, around 80% of confirmed influenza A cases are Pandemic (H1N1) 2009, and of seasonal influenza A, A/H3N2 was the predominant subtype. Indigenous Australians are approximately 5 times more likely than non-Indigenous Australians to be hospitalized for Pandemic (H1N1) 2009, representing 10.4% of all hospitalizations. Most cases had underlying medical conditions, including cancer, diabetes mellitus and morbid obesity. With a 20% clinical attack rate and no intervention; it has been projected that by the end of winter 1 in 5 Australians (4.3 million) could become infected with the pandemic virus, leading to 40 to 80,000 hospitalizations, and 6,000 deaths.
• New Zealand: As of August 12, 2009, the total number of confirmed cases in New Zealand is 3,000, including 14 deaths where Pandemic (H1N1) 2009 was a primary cause. The number of people reporting to GPs and hospitals with influenza-like illnesses continues to fall. There has been a continuing decline in consultations for ILI but the rate is still higher than in previous years. The highest notification and hospitalization rates were seen in the <1 year old age group.
• Argentina: Summary of epi weeks 20 to 30 (as of August 5th): In the previous 3 weeks, a downward trend in the number of cases is observed in 18 of 24 provinces. From epi week 21, there was a significant increase in circulation of Pandemic (H1N1) 2009 influenza and unsubtyped influenza, up to the peak in week 25, coinciding with the peak in severe acute respiratory infections. In the past 2 weeks, influenza A detections have been declining, and the greater proportion of viral circulation has been from RSV. However, the predominant viral pathogens vary by age group. There were 6,384 cases of severe acute respiratory infection requiring hospitalization. Of the 337 Pandemic (H1N1) 2009-associated deaths reported, the most affected age group is those 50-59 years of age, and 47% of cases had a history of chronic illness or other risk factor for disease. For both sexes, the most common risk factors are obesity (18%), heart disease (8%), and COPD (7%).
• Chile: There has been a decline in the incidence of Pandemic (H1N1) 2009 influenza and a decrease in ILI cases. Of confirmed cases of Pandemic (H1N1) 2009, 1,126 have presented with severe acute respiratory infection. 45% of these cases had underlying chronic disease. The rate of severe infection has been declining since its peak in week 27 (127.8 per 100,000) to 10.1 per 100,000 in week 30. Prior to epi week 20, RSV, parainfluenza and adenovirus were predominant. From week 20 to 29, Pandemic (H1N1) 2009 increased to 64% of circulating respiratory viruses (week 27). In the past two weeks, the proportion of Pandemic (H1N1) 2009 has declined from 34 to 20% of all respiratory virus detections, and there has been a increase in RSV and parainfluenza detections.
• South Africa: As of August 11, South Africa reported 1,910 laboratory-confirmed cases and 3 deaths from Pandemic (H1N1) 2009. For epi week 31, there has been an increase in the proportion of Pandemic (H1N1) 2009 influenza detected compared to other influenza types and subtypes, with the predominant detections being A(H3N2) (71%), followed by Pandemic (H1N1) 2009 (22%).
  • NICD <http://www.nicd.ac.za/>

Northern Hemisphere

• United States: As of August 6, 2009, the CDC reports 6,506 hospitalized cases, and 436 deaths due to Pandemic (H1N1) 2009. During week 30 (ending August 1, 2009) influenza activity decreased in the United States; however, there were still higher levels of ILI than normal.
• Mexico: As of August 11, 2009, Mexico reports 18,390 confirmed cases of Pandemic (H1N1) 2009, and 162 deaths. The largest proportion of deaths was observed in the older age groups, with 71.6% of all fatal cases in patients 20 to 54 years old. Of underlying conditions observed, the four most common were metabolic disorders, smoking, cardiovascular disease and respiratory disease. In fatal cases, the three most common symptoms reported were fever (84.0%), cough (82.1%) and shortness of breath (75.3%).
• United Kingdom: As of August 6, Pandemic influenza activity appears to be decreasing across most of the UK. In epi week 31, GP consultation rates decreased in England, though remained above baseline thresholds. This is coincident with the introduction of National Pandemic Flu Service (NPFS) and the start of the school summer holidays. HPA modeling gives an estimate of 30,000 (range 15,000 – 85, 000) new cases in England in week 31 compared to an estimated 110,000 cases in the previous week. The main influenza virus circulating in the UK continues to be the Pandemic (H1N1) 2009 strain. Deaths reported due to Pandemic (H1N1) 2009 in the UK are now 40. There was a decrease in the number of new patients hospitalized with suspected pandemic influenza in week 31, to 1,299. The highest hospitalization rates have consistently been in the under 5-year age group.
• Thailand: As of August 9, the WHO Southeast Asia Region reports 10,043 confirmed cases, and 81 deaths from Pandemic (H1N1) 2009 in Thailand. There is an increasing trend in respiratory disease compared to last week; ILI activity is increasing over the past 2 weeks; and more deaths have been observed this season than in the past 2 years. The impact on health services is described as moderate.

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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