January 10 to January 16, 2010 (Week 2)

Posted 2010-01-22

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Pandemic (H1N1) 2009 virus Surveillance and Epidemiology

A total of 8,549 hospitalized cases including 1,434 (16.8%) cases admitted to ICU and 422 (4.9%) deaths of Pandemic (H1N1) 2009 were reported to PHAC since the beginning of the pandemic. Among the 1,088 ICU cases who had detailed information regarding ventilation status, 58% (n=634) required ventilation. Core data was available for 8,093 (94.7%) hospitalizations, 1,434 (100%) ICU admissions and 417 (98.8%) deaths. For the second week, only five of the 13 provinces and territories continued to report severe cases with Pandemic (H1N1) 2009. The number of hospitalized cases (29), ICU admissions (1) and deaths (4) were similar to those reported in the previous week. The peak periods of reported laboratory-confirmed hospitalizations and deaths occurred from weeks 22 to 24 (May 31, 2009 to June 20, 2009) for the first wave and from weeks 43 to 45 (October 25, 2009 to November 14, 2009) for the second wave.

The cumulative crude hospitalization, ICU admission and mortality rates showed that men and women have been equally affected since the beginning of the pandemic (data not presented). The median age for men and women were similar across severity of illness from April 12, 2009 to January 16, 2010 except for hospitalizations where for men, the median age was 21 years and for women, the median age was 33 years. The proportion of underlying medical conditions for men and women were similar across hospitalizations and ICU admissions: 50.6% and 51.9% for men and 60.1% and 63.3% for women, respectively. However, for deaths, the proportion of underlying medical conditions for men was higher than for women (80.5% vs. 71.4%). Among the young children (0-4 years), school-aged children (5-19 years), adults (20 to 64 years) and seniors (65 years and over), chronic pulmonary disease (including asthma) was the most commonly reported underlying medical condition (18.8%, 34.8%, 37.5% and 50.9%, respectively). The other underlying medical conditions associated with risk of admission to hospital were slightly different for seniors, adults and children. Immunosuppression (including cancer) (7.2%) was frequently reported among children (0-19 years) admitted to hospital, while adults were affected by diabetes (19.6%). Among hospitalized seniors, chronic heart disease (44.6%) was most commonly reported.

From April 12, 2009 to January 16, 2010, 601 reported hospitalized cases were among people of Aboriginal origin (430 First Nations, 109 Inuit, 48 Metis and 14 with unknown Aboriginal subgroup). Among 430 First Nations cases, 177 were from MB, 132 from AB, 53 from QC, 28 from BC, 21 from NT, 8 from YT, 7 from SK and 4 from NB. The 80 lab-confirmed hospitalized cases from Nunavut were assumed to be persons of Inuit ethnicity as the majority of the population in this territory is Inuit. Other Inuit cases were reported from QC (12), NT (10), AB (4), MB (1), NL (1) and YT (1). Métis cases were from AB (29), MB (16), BC (1), NL (1) and NT (1). Depending on the calculation method used (see footnote 1, Characteristics table), the proportion of hospitalized Aboriginal peoples among all hospitalized cases was between 7.4% and 9.3%, while the proportions of Aboriginal peoples admitted to ICU and that died were between 8.0%-10.7% and 7.2%-10.3%, respectively. The true proportion of affected Aboriginal peoples lies between these two estimates.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic (H1N1) 2009 confirmed cases, Canada, to January 16, 2010†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 These provinces reported aggregate counts this week. 2 Note change in total hospitalizations from last week's report: duplicates were removed. 3The new numbers reflect the situation since Jan. 4, 2010.  †Note that due to reporting delays, some PTs reported retrospectively on first wave cases.
Province/ Territory	Week 2 (January 10 to 16, 2010)*			From August 30, 2009 to January 16, 2010**			From April 12 to August 29, 2009**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1,2	--	0	1	981	132	50	51	20	6
AB	5	0	1	1144	208	64	129	29	7
SK	0	0	0	43	39	11	23	12	4
MB3	10	0	0	161	18	4	222	43	7
ON	11	1	2	1422	240	98	392	68	25
QC	0	0	0	2483	360	81	572	104	27
NB1	0	0	0	161	33	8	2	1	0
NS	0	0	0	272	42	6	17	8	1
PE	0	0	0	49	9	0	1	0	0
NL	0	0	0	274	51	18	3	1	0
YT	0	0	0	15	3	3	0	0	0
NT	0	0	0	46	7	1	6	0	0
NU†	3	0	0	6	0	0	74	6	1
Canada	29	1	4	7057	1142	344	1492	292	78

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 January 16, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to January 16, 2010			Cumulative: From April 12, 2009 to January 16, 2010
	Hospitalized cases (n=1492)	ICU-admitted (n=292)	Deaths (n=78)	Hospitalized cases (n=6601)	ICU-admitted  (n=1142)	Deaths (n=339)	Hospitalized cases (n=8093)	ICU-admitted (n=1434)	Deaths (n=417)
Females, %	51.3	57.2	62.8	49.7	49.6	46.9	50.0	51.1	49.9
Median age	23.0	37.0	51.0	30.0	47.0	54.0	28.0	46.0	53.0
Aboriginal status1, %	20.2-27.9	16.1-21.8	11.5-17.3	4.5-5.6	6.0-7.9	6.2-8.8	7.4-9.3	8.0-10.7	7.2-10.3
Underlying medical  conditions2, %	46.8 (647/1383)	58.0 (159/274)	71.1 (54/76)	53.2 (1726/3246)	62.8 (561/893)	77.2 (220/285)	51.3 (2373/4629)	61.7 (720/1167)	75.9 (274/361)
Pregnancy3, %	28.0 (77/275)	19.7 (15/76)	28.6 (4/14)	18.4 (186/1012)	8.5 (15/176)	0.0	20.4 (263/1287)	11.9 (30/252)	8.0 (4/50)
1 Aboriginal peoples represent 3.5% of the Canadian population; however, for this analysis, Aboriginal peoples account for 2.7% of the Canadian population since Aboriginal status was not reported by two provinces where 23% of the Aboriginal population lives (ON, NS). Two methods were used to calculate proportions: one proportion was calculated by including ON and NS cases in the denominator (which is an underestimate of the true proportion); while the other proportion was calculated by excluding ON and NS cases in the denominator (which is an overestimate). The true proportion of affected Aboriginal peoples lies between these two estimates. 2 Proportion of cases with at least one underlying medical condition (excluding pregnancy) among those for whom the information was available. 3 Percent of pregnant women among women 15 to 44 years of age. † All cases admitted to ICU are included in the hospitalization count; however, not all the death cases have been previously hospitalized.

Overall Influenza Summary - Week 2 (January 10 to January 16, 2010)

During week 2, all influenza indicators were still either back to baseline or considerably under the expected level for this time of the year. The national ILI consultation rate slightly increased compared to the previous week but was significantly below the expected range for this time of the year with 21 consultations per 1,000 patient visits. Only 0.6% of the specimens tested were positive for influenza compared to 16.6% for the respiratory syncytial virus.

In week 2, only one region (in ON) reported localized activity. Twenty-six regions in BC, AB, SK, MB, ON, QC, NB, NS & NU reported sporadic activity, while twenty-seven regions reported no activity in AB, SK, ON, QC, NB, PE, NS, NL, YT & NT. No influenza outbreaks were reported this week.

Map of overall Influenza activity level by provinces and territories, Week 2, 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

Note that this was the first year that all the provinces and territories were reporting on influenza outbreaks in schools (greater than 10% absenteeism on any day most likely due to ILI) which has increased considerably the total number of outbreaks reported compared to previous years.

ILI consultation rate

During week 2, the national ILI consultation rate was 21 consultations per 1,000 patient visits (see ILI graph) which slightly higher than last week but still significantly below the expected range for this time of the year. All provinces and territories had either similar or slightly higher ILI consultation rate compared to their respective ILI rates in the previous week except NS which had a lower rate this week. Those under 20 years of age still had the highest consultation rates, with 52 and 35 per 1,000 patient visits among children under 5 years of age and among those 5 to 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 2, no laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. 1,328 hospitalizations have been reported since week 17 (April 26): 97.1% of these hospitalizations were due to Pandemic (H1N1) 2009. Since the beginning of the pandemic, eleven paediatric deaths due to Pandemic (H1N1) 2009 were reported through the IMPACT network among children 16 years of age or under.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza was 0.6% during week 2 which remained low for a fourth consecutive week (see Tests table). All provinces had a lower proportion of positive tests for influenza compared to the previous week except QC which had similar proportions. During week 2, a total of 15 specimens tested positive for influenza (14 A and 1 B) and 100% of the positive influenza A subtyped specimens were Pandemic (H1N1) 2009. Note that QC reported 44 positive specimen for A/H3N2 and 7 specimen for influenza B while Ontario reported 5 specimen for influenza B since August 30, 2009.

The proportion of positive respiratory syncytial virus tests was 16.6% during week 2 which was still higher than the proportion observed for positive influenza tests over the past weeks.The proportion of positive parainfluenza and adenovirus tests were also slightly higher than the proportion of positive tests for influenza.

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
Reporting provinces	Weekly (January 10 to January 16, 2010)						Cumulative (August 30, 2009 to January 16, 2010)
	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	1	0	0	1	0	0	6369	0	1	5803	565	0
AB	2	0	0	2	0	0	5859	2	5	5754	98	0
SK	0	0	0	0	0	0	2598	0	1	2298	299	0
MB	0	0	0	0	0	0	1914	0	0	1787	127	0
ON	6	0	0	4	2	1	7884	2	0	3539	4343	5
QC	4	0	0	4	0	0	10688	1	44	10643	0	7
NB	1	0	0	1	0	0	1855	1	1	1834	19	1
NS	0	0	0	0	0	0	783	0	0	751	32	0
PE	0	0	0	0	0	0	97	0	0	96	1	0
NL	0	0	0	0	0	0	951	0	0	951	0	0
Canada	14	0	0	12	2	1	38998	6	52	33456	5484	13
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Sale of antivirals (AV) in Canada

During week 2, antiviral prescriptions monitoring results demonstrated a levelling-off in antiviral prescriptions among most provinces and territories. An analysis of antiviral data at the Health Region level demonstrates low antiviral prescription rates among all Health Regions for the week of January 10, 2010 to January 16, 2010. Only one Health Region (in SK) reported an antiviral rate greater than 2.5 antivirals/1000 other prescriptions.

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

Canadian situation

Antigenic Characterization

Since September 1, 2009, the National Microbiology Laboratory (NML) has antigenically characterized 732 Pandemic (H1N1) 2009 viruses and 10 seasonal influenza viruses (2 influenza A/H1N1, 7 H3N2, and 1 B virus) that were received from Canadian laboratories. Of the 732 Pandemic (H1N1) 2009 viruses characterized, 728 (99.5%) were antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO as the Pandemic (H1N1) 2009 vaccine. Four viruses (0.5%) tested showed reduced titer with antisera produced against A/California/7/09. Of the seven seasonal influenza A (H3N2) viruses characterized, one was related to A/Brisbane/10/07, which is the influenza A/H3N2 component recommended for the 2009-10 influenza vaccine and six viruses were antigenically related to A/Perth/16/09, which is the WHO recommended influenza A (H3N2) component for the 2010 Southern Hemisphere vaccine.

Antiviral Resistance

NML: Pandemic (H1N1) 2009 viruses tested so far have been sensitive to zanamivir (894 samples) but resistant to amantadine (968 samples).

NML/Provinces: Eleven cases of oseltamivir resistant Pandemic (H1N1) 2009 were reported to date in Canada: three in Alberta, one in Manitoba, four in Ontario, two in Quebec, and one in New Brunswick. Ten of the eleven resistant cases were associated with oseltamivir treatment. One case (NB) appeared to be the result of infection with an antiviral-resistant strain of H1N1.

International update

Global information

WHO: Worldwide more than 208 countries and overseas territories or communities reported laboratory confirmed cases of Pandemic (H1N1) 2009, including at least 13,554 deaths as of January 10, 2010. Currently, the most intense areas of Pandemic (H1N1) 2009 transmission were in parts of North Africa (Morocco, Algeria, and Egypt), South Asia (Nepal, India, Sri Lanka), and east and south eastern Europe (Romania, Ukraine, Turkey, Switzerland). In the temperate regions of the northern hemisphere, transmission of Pandemic (H1N1) 2009 continued to remain geographically widespread; however, overall activity continued to decline substantially, to remain low or has past its peak in much of the hemisphere since November. In temperate regions of the southern hemisphere, sporadic cases of Pandemic (H1N1) 2009 continued to be reported without evidence of sustained community transmission. This suggests that the level of population immunity in areas during a winter season that experienced intense, high-level transmission was high enough to prevent sustained transmission from recurring when the virus is less transmissible during the summer. For the week of December 27, 2009 to January 2, 2010, Pandemic (H1N1) 2009 accounted for 98.1% of all subtyped influenza A viruses detected in both northern and southern hemispheres. One of the exceptions was China where the Pandemic (H1N1) 2009 virus accounted for 90.2% of all specimens tested positive for influenza A viruses. Also in China, influenza B accounted for 12.6% among the specimens tested positive for influenza viruses. Sporadic detections of seasonal A(H1N1), A(H3N2) and influenza B viruses were reported from a few countries including some European countries. <http://www.who.int/csr/don/2010_01_15/en/index.html and
http://www.who.int/csr/disease/swineflu/laboratory15_01_2010/en/index.html>

Antiviral resistance:To date, 199 Pandemic (2009) H1N1 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y mutation. <http://www.who.int/csr/disease/swineflu/laboratory15_01_2010/en/index.html>

Geographic update

United States: During week 1 (January 3-9, 2010), influenza activity continued to decrease in the United States. Widespread influenza activity was not reported by any state, nine states reported regional influenza activity, and the remaining states reported either local or sporadic influenza activity with the exception of the U.S. Virgin Islands and two states which reported no activity. ILI physician consultations decreased this week over last week and overall hospitalization rates declined. The proportion of deaths attributed to pneumonia and influenza was below the epidemic threshold. Seven influenza-associated pediatric deaths were reported during week 1: six were associated with Pandemic (H1N1) 2009 infection and one was associated with influenza A virus for which the subtype was undetermined. All subtyped influenza A viruses reported to CDC were 2009 influenza A (H1N1) viruses. One human infection with a novel influenza A virus was reported by the Iowa Department of Public Health. The case, which had a September 2009 symptom onset date, did not require hospitalization and has fully recovered. The virus identified was a triple reassortant swine influenza H3N2 virus. Investigation in November 2009 revealed no clear exposure to swine and no evidence of sustained human-to-human transmission with this virus was found; however, the infected child lives in an area where swine farms are numerous. <http://www.cdc.gov/flu/weekly/ and http://www.cdc.gov/h1n1flu/update.htm>

Europe: For week 1/2010 (January 4-10, 2010), the majority of the 26 out of 29 reporting countries experienced low influenza activity while Bulgaria, Estonia, France, Greece, Malta, Romania and Scotland reported medium intensity and Poland reported high intensity. Regarding geographic spread, Greece and Slovenia reported widespread activity while Austria, France, Netherlands, Romania and Scotland reported regional activity, while the remaining countries reported local or sporadic activity. All countries reported either a decreasing trend or stable activity across influenza indicators except Austria, Bulgaria, Hungary, Italy, Latvia, Lithuania, Poland and Romania which reported an increasing trend. Since week 40/2009, influenza activity was above baseline levels and of the 26 countries reporting in week 1, Austria, Bulgaria, Hungary, Italy, Latvia, Lithuania, Poland and Romania observed increasing ILI/ARI rates after at least two weeks of decreasing activity. However, the increase in ILI/ARI activity was still at baseline levels and could reflect a minor fluctuation. The 2009/10 season has been characterized by influenza activity above baseline levels earlier than in recent seasons and higher peak incidences of ILI and/or ARI. Where information on the age of patients is collected, individuals younger than 15 years have been the most affected age group. As of January 19, 2010, the cumulative number of reported deaths since the beginning of the pandemic in EU/EFTA Member States has totalled 2,292.
<http://ecdc.europa.eu/en/healthtopics/Documents/100119_Influenza_AH1N1_Situation_Report_0900hrs.pdf and
http://ecdc.europa.eu/en/publications/Publications/100115_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: Northern and southern parts of south Asia continued to experience active influenza transmission. Specifically, Nepal reported increased ARI activity and geographically regional to widespread influenza activity during December and January. In India, overall activity may have peaked during mid to late December; however, transmission has been regionally variable with decreasing trends in the western states, overall low activity in the eastern and southern states and a recently increasing trend in the western states. Throughout December in Sri Lanka, geographically widespread transmission with increasing trend of respiratory diseases was reported, however activity may have recently plateaued. Influenza activity remained active but may have already peaked in west Asia. In east Asia, influenza activity remained widespread but continued to decline overall and has past its peak in some areas in November (Japan, northern and southern China, Mongolia). In Democratic People’s Republic of Korea, geographically regional influenza activity with increasing respiratory diseases trend was reported during early January 2010. Pandemic (H1N1) 2009 continued to be the predominant circulating virus in the region but seasonal H3N2 viruses continued to circulate in very small numbers in northern China. <http://www.who.int/csr/don/2010_01_15/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).

ILI definition for the 2009-2010 season
ILI in the general population: Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which could be due to influenza virus. In children under 5, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.

Definitions of ILI/Influenza outbreaks for the 2009-2010 season
Schools: greater than 10% absenteeism on any day most likely due to ILI.
Hospitals and residential institutions: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case. Institutional outbreaks should be reported within 24 hours of identification. Residential institutions include but not limited to long-term care facilities (LTCF), prisons.
Other: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case; i.e. workplace, closed communities.

Influenza Activity levels are defined as:
1 = No activity: i.e. no laboratory-confirmed influenza detections during the past four weeks, however, sporadically occurring ILI may be reported
2 = Sporadic: sporadically occurring ILI and lab confirmed influenza* with NO outbreaks detected within the influenza surveillance region†
3 = Localized: sporadically occurring ILI and lab confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in less than 50% of the influenza surveillance region(s)†
4 = Widespread: sporadically occurring ILI and lab confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in greater than or equal to 50% of the influenza surveillance region(s)†
* confirmation of influenza within the surveillance region at any time within the prior four weeks
† sub-regions within the province or territory as defined by the provincial/territorial epidemiologist

We would like to thank all the Fluwatch surveillance partners who are participating in this year's influenza surveillance program.
This report is available on the Public Health Agency website at the following address: http://www.phac-aspc.gc.ca/fluwatch/index.html. Ce rapport est disponible dans les deux langues officielles. Pour en recevoir un exemplaire dans l'autre langue chaque semaine, veuillez communiquer avec Estelle Arseneault, Division de l'immunisation et des infections respiratoires au (613) 952-8484

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Definitions for the 2009-2010 season