February 21 to February 27, 2010 (Week 8)

Posted 2010-03-05

PDF Version

Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,669 hospitalized cases including 1,472 (17.0%) cases admitted to ICU and 429 (4.9%) deaths with pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 8,221 (94.8%) hospitalizations, 1,472 (100%) ICU admissions and 424 (98.8%) deaths. Most of the reported cases in week 8 were retrospective cases from 2009. To date, only 10 hospitalizations (BC, ON & NS) and two deaths (ON) have occurred since the beginning of 2010. 32 hospitalized cases (QC & NL), 23 ICU admissions (BC, ON & NL) and one death (ON) with pandemic H1N1 2009 were reported this week. However, the majority were retrospective cases that occurred during either the first or second wave. Only the one hospitalized case in QC and the death in ON occurred during week 8. 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.

To date, the national crude hospitalization rate was 25.7 per 100,000 population with the highest rates in children less than 5 years of age (100.4 per 100,000). The national crude mortality rate was 1.3 per 100,000 population with those 45 years and older having the highest mortality rate (2.1 per 100,000). The national crude ICU admission rate was 4.4 per 100,000 population. The ICU admission rate was elevated in adults 45 to 64 years (6.4 per 100,000) as well as children under five years of age (6.2 per 100,000).

The cumulative crude hospitalization, ICU admission and mortality rates showed that men and women have been equally affected since the beginning of the pandemic. The median age for hospitalizations among men (22 years) was lower than the median age for women (33 years); however, the median age was similar for men and women for severe outcomes (ICU admissions and deaths).

Comparing rates of hospitalization, ICU admissions and deaths between those with underlying medical conditions and those without since the beginning of the pandemic, those with underlying medical conditions had a hospitalization rate 5.8 times higher, an ICU admission rate 10.9 times higher and a mortality rate 25.5 times higher than those without underlying medical conditions. Among the hospitalized cases, ICU admissions and deaths, chronic pulmonary disease (including asthma) was the most commonly reported underlying medical condition (36.7%, 40.4% and 51.3%, respectively). Diabetes (15.2%) and immunosuppression (including cancer) (15.2%) were also frequently reported among hospitalized cases, while ICU cases were also affected by diabetes (23.4%) and chronic heart disease (21.6%) and among the fatal cases, chronic heart disease (35.5%) and immunosuppression (34.7%) were reported.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic H1N1 2009 confirmed cases, Canada, April 12, to February 27, 2010^†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 Aggregate counts were reported this week. 2 The increase from last week is due to more detailed accounting of retrospective case records from the regional health authorities rather than an increase in new case reports. † Note that due to reporting delays, some provinces and territories reported retrospectively on first and second wave cases.
Province/ Territory	Week 8 (February 21 to February 27, 2010)*			From August 30, 2009 to February 27, 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	13	0	1031	148	52	49	19	5
AB	0	0	0	1147	210	64	129	29	7
SK	0	0	0	44	40	11	23	12	4
MB	0	0	0	166	18	4	213	43	7
ON	0	2	1	1444	250	104	399	69	25
QC	1	0	0	2491	361	81	572	104	27
NB1	0	0	0	161	33	8	2	1	0
NS	0	0	0	276	42	6	17	8	1
PE	0	0	0	49	9	0	1	0	0
NL2	31	8	0	305	59	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	0	0	0	6	0	0	74	6	1
Canada	32	23	1	7181	1180	352	1488	292	77

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 February 27, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to February 27, 2010			Cumulative: From April 12, 2009 to February 27, 2010
	Hospitalized cases (n=1488)	ICU-admitted (n=292)	Deaths (n=77)	Hospitalized cases (n=6733)	ICU-admitted  (n=1180)	Deaths (n=347)	Hospitalized cases (n=8221)	ICU-admitted (n=1472)	Deaths (n=424)
Females, %	51.3	57.2	62.3	49.7	49.4	47.0	50.0	51.0	49.8
Median age	23.0	37.0	51.0	30.0	47.0	54.0	29.0	46.0	53.5
Aboriginal status1, %	20.0-27.7	16.1-21.9	11.7-17.6	4.5-6.1	5.8-7.7	6.1-8.9	7.3-9.9	7.8-10.4	7.1-10.4
Underlying medical conditions2, %	47.5 (652/1373)	60.2 (162/269)	73.3 (55/75)	58.6 (1920/3275)	73.1 (669/915)	84.2 (240/285)	55.3 (2572/4648)	70.2 (831/1184)	81.9 (295/360)
Pregnancy3, %	27.6 (75/272)	19.7 (15/76)	28.6 (4/14)	18.2 (187/1027)	8.3 (15/180)	0.0 (0/36)	20.2 (262/1299)	11.7 (30/256)	8.0 (4/50)
1 Since Aboriginal status is not reported by two provinces (which comprise 23% of the Aboriginal population) 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). 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 fatal cases have been hospitalized before dying.

Overall Influenza Summary - Week 8 (February 21 to February 27, 2010)

During week 8, overall influenza activity remained at approximately the same level as last week and all influenza indicators were still considerably below expected levels for this time of the year. Of the 2,646 specimens tested for influenza in week 8, 7 (0.26%) were positive of which 6 (86%) were for influenza A and one (14%) was positive for influenza B. Of the 5 influenza A viruses that were subtyped, all were pandemic H1N1 2009. Respiratory syncytial virus detections were still high but the proportion of positive detections declined for the first time since the beginning of 2010 to 24.0% in week 8.

In week 8, 14 regions in AB, ON, QC & NS reported sporadic activity, while 39 regions reported no activity. One region in BC is not reporting until further notice. No influenza outbreaks were reported this week.

Map of overall Influenza activity level by provinces and territories, Week 8, 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 8, the national ILI consultation rate was 10 consultations per 1,000 patient visits (see ILI graph) which was still considerably below the expected range for this time of year (range from 25 to 44 consultations per 1,000 patient visits). All provinces and territories had similar or lower ILI consultation rates compared to their respective ILI rates in the previous weeks except NB which had a slightly higher rate this week. Those under 20 years of age still had the highest consultation rates with 18 ILI consultations per 1,000 patients visits.

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 and Adult Influenza Hospitalizations and Deaths

In week 8, one laboratory-confirmed influenza-associated paediatric (under 17 years of age) hospitalization was reported through the Immunization Monitoring Program Active (IMPACT) network. The hospitalization was due to influenza A (unsubtyped). A total of 1328* hospitalizations have been reported since week 17 (April 26, 2009), of which 96.8% were due to pandemic H1N1 2009. Since the beginning of the pandemic, ten paediatric deaths due to pandemic H1N1 2009 were reported through the IMPACT network among children 16 years of age or under. Seven (70%) of those deaths reported had at least one underlying medical condition.

*Delays in the reporting of data may cause data to change restrospectively.

During week 8, no new laboratory-confirmed influenza-associated adult (16 years of age and older) hospitalizations were reported through the Canadian Nosocomial Infection Surveillance Program (CNISP) from 14 of 50 reporting sites. Since week 47 (November 22, 2009), 55 hospitalizations and 8 deaths have been reported through CNISP among adults 16 years of age or older. All of these hospitalizations and deaths were due to pandemic H1N1 2009. From June 1, 2009 to February 19, 2010, of the 552 laboratory-confirmed influenza cases among hospitalized adults reported through 27 of CNISP sentinel sites, 385 (70%) were pandemic H1N1 2009 cases, 152 (28%) were unsubtyped influenza A and the remaining 11 (2%) were either influenza A/H1N1, influenza A/H3N2 or influenza B. For these pandemic H1N1 2009 cases, 1.3% (5/365) presented with influenza-associated bacteremia, 27% (100/376) were admitted to the ICU, and 5% (20/385) died (90% of whom had at least one underlying medical condition).

Please note the total number of CNISP reporting sites fluctuates weekly and most of the reporting sites started in late fall 2009.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza during week 8 (0.26%, 7/2,646) remained at a very low level for this time of year (see Tests table). Of the positive tests, 6 (86%) were for influenza A and one (14%) was positive for influenza B. Of the 5 influenza A viruses that were subtyped, all were pandemic H1N1 2009. All provinces had a similar or lower proportion of positive tests for influenza compared to the previous weeks. Note that since August 30, 2009, influenza A/H3N2 detections were highest in QC (84.6% or 44/52) and influenza B detections were highest in QC (60% or 9/15) and ON (40% or 6/15). Respiratory syncytial virus detections were still high but the proportion of positive detections declined for the first time since the beginning of 2010 to 24.0% in week 8. Positive specimens for RSV were reported from all provinces except NB and NL (data not shown). The proportion of positive parainfluenza and adenovirus tests remained under the 3% positivity rate.

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, Canada, 2009-2010

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 (February 21 to February 27, 2010)						Cumulative (August 30, 2009 to February 27, 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	0	0	0	0	0	0	6370	0	1	5804	565	0
AB	0	0	0	0	0	0	5868	2	5	5760	101	0
SK	0	0	0	0	0	0	2598	0	1	2298	299	0
MB	0	0	0	0	0	0	1915	0	0	1788	127	0
ON	3	0	0	3	0	0	7912	4	0	3556	4352	6
QC	2	0	0	2	0	1	10695	1	44	10648	2	9
NB	0	0	0	0	0	0	1856	1	1	1835	19	0
NS	1	0	0	0	1	0	787	0	0	753	34	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	6	0	0	5	1	1	39049	8	52	33489	5500	15
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Sale of antivirals (AV) in Canada

During week 8, antiviral prescription monitoring continued to demonstrate a levelling-off in antiviral prescriptions with little change compared to last week among all provinces and territories. An analysis of antiviral data at the Health Region level demonstrated low antiviral prescription rates among all Health Regions for the week of February 21 to February 27, 2010. Only one Health Region in AB 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 835 pandemic H1N1 2009 viruses and 16 seasonal influenza viruses (3 influenza A/H1N1, 10 H3N2, and 3 B virus) that were received from Canadian laboratories. Of the 835 pandemic H1N1 2009 viruses characterized, 831 (99.5%) were antigenically related to A/California/7/2009, which is the pandemic reference virus selected by WHO for the pandemic H1N1 2009 vaccine. Four viruses (0.5%) tested showed reduced titer with antisera produced against A/California/7/09. Of the ten seasonal influenza A (H3N2) viruses characterized, two were related to A/Brisbane/10/07, which was the influenza A/H3N2 component recommended for the 2009-10 influenza vaccine and eight viruses were antigenically related to A/Perth/16/09, which is the WHO recommended influenza A (H3N2) component for the 2010 -2011 Northern Hemishpere vaccine. Three seasonal influenza A/H1N1 viruses characterized were related to A/Brisbane/59/07, which was the influenza A/H1N1 component recommended for the 2009-10 influenza vaccine.Of the three influenza B virus characterized, two were antigenically related to B/Brisbane/60/08, which was the recommended influenza B component for the 2009-10 influenza vaccine. One B virus was related to the previous vaccine virus B/Florida/4/2006 (Yamagata lineage).

Antiviral Resistance

NML/Provinces: Thirteen cases of oseltamivir resistant pandemic H1N1 2009 were reported to date in Canada: one in British Columbia, four in Alberta, one in Manitoba, four in Ontario, two in Quebec, and one in New Brunswick. The 13 resistant cases were associated with oseltamivir treatment/prophylaxis

NML: All pandemic H1N1 2009 viruses tested so far have been sensitive to zanamivir (1042 samples) but resistant to amantadine (1121 samples).

International update

Global information

WHO: As of February 26, 2010, over 213 countries and overseas territories or communities worldwide reported cases of pandemic H1N1 2009 (at least 16,226 deaths). In the temperate zone of the northern hemisphere, pandemic influenza virus continued to be detected across many countries, however, overall influenza activity continued to wane in most places. The most active areas of transmission were currently in parts of South and Southeast Asia and in limited areas of Eastern and Southeastern Europe. Pandemic influenza (H1N1) 2009 virus continued to be the predominant influenza virus circulating worldwide. In addition to the increasing proportion of seasonal influenza type B viruses recently detected in China, low levels of seasonal H3N2 and type B viruses were circulating in parts of Africa and Asia. Respiratory disease activity was increasing in many areas of the world due to increasing transmission of influenza type B and respiratory syncytial virus. Seasonal influenza H3N2 continued to be detected in areas of Asia and east Africa.
<http://www.who.int/csr/don/2010_02_26/en/index.html>

Antiviral resistance: To date, 253 pandemic H1N1 2009 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y mutation and all remained sensitive to zanamivir.
< http://www.who.int/csr/disease/swineflu/Oseltamivirresistant2010_02_26.pdf>

2010-2011 influenza season vaccine: The WHO recommends that the following viruses be used for influenza vaccines in the 2010-2011 influenza season (northern hemisphere): an A/California/7/2009 (H1N1)-like virus; an A/Perth/16/2009 (H3N2)-like virus; and a B/Brisbane/60/2008-like virus.
<http://www.who.int/csr/disease/influenza/recommendations2010_11north/en/index.html>

Geographic update

United States: During week 7, influenza activity remained at approximately the same levels as last week in the United States with the majority of states reporting sporadic influenza activity (3 states reported regional and 8 states and Puerto Rico reporting localized). Of the 4,209 specimens tested for influenza in week 7, 185 (4.4%) were positive for influenza (181 were influenza A and 4 were influenza B). All of the influenza A viruses subtyped were pandemic H1N1 2009 viruses. The proportion of deaths attributed to pneumonia and influenza (7.4%) and the proportion of outpatient visits for ILI (1.8%) declined from the previous week and both remain below baseline levels. Three influenza-associated pediatric deaths were reported this week: one was associated with pandemic H1N1 2009 virus infection and the other two were associated with influenza A (subtype undetermined).
<http://www.cdc.gov/flu/weekly/index.htm>

Europe: The 2009 influenza A(H1N1) pandemic is well past its winter peak in Europe, with the majority of the countries reporting only sporadic activity or no geographic spread of the pandemic virus. Although circulation of 2009 pandemic A(H1N1) influenza virus has diminished, there was still no evidence of wide circulation of other influenza A viruses apart from few influenza A(H3N2) and B viruses.
< http://ecdc.europa.eu/en/activities/surveillance/EISN/Newsletter/100226_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In Southeast Asia, pandemic influenza virus continued to circulate in some areas, however, the overall intensity of respiratory diseases activity remained low and unchanged, except in a few countries (Brunei Darussalam, Myanmar and Thailand). Pandemic influenza and seasonal influenza type B viruses continued to co-circulate in East Asia. In China, the proportion of positive seasonal influenza type B viruses increased during the last week. Overall influenza activity continued to decline in Japan, South Korea, Hong Kong SAR (China) and in Chinese Taipei. In South Asia, overall influenza activity remained low, however, pandemic influenza virus transmission persisted in the western part of India. In West Asia, an increasing trend of respiratory diseases was reported in Afghanistan, however, it is unknown if the recent increase is associated with circulation of influenza virus.
<http://www.who.int/csr/don/2010_02_26/en/index.html>

Africa: In North Africa, pandemic influenza virus continued to circulate at low levels as rates of illness in most countries in the region continued to decline or return to baseline. In Sub-Saharan Africa, pandemic influenza virus transmission continued to be sporadic in most areas of the continent. Several countries in West Africa continued to report slight increases in the numbers of confirmed cases of pandemic influenza indicating that community transmission is likely beginning in the area; however, data were very limited.
<http://www.who.int/csr/don/2010_02_26/en/index.html>

Central & South America and the Caribbean: In the the Americas, pandemic influenza virus continued to circulate at low levels but overall pandemic influenza activity continued to decline or remain low in most places. In Central America and Caribbean, pandemic influenza virus transmission persisted but overall activity remained low or unchanged in most places.
< http://www.who.int/csr/don/2010_02_26/en/index.html>

Australia: As of 19 February 2010, there have been 37,713 confirmed cases of pandemic (H1N1) 2009 reported in Australia. National influenza activity remained low and was at levels experienced at the same time in previous years.
< http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/ozflucurrent.htm>

New Zealand: As of February 28, 2010, there have been 3,300 cases of pandemic H1N1 2009 reported in New Zealand with 20 deaths. The ILI consultation rate for week 8 was 14.3 per 100,000 which was below baseline.
< http://www.surv.esr.cri.nz/PDF_surveillance/Virology/FluWeekRpt/2010/FluWeekRpt201007.pdf>

Real-time weekly and cumulative numbers of deaths due to pandemic H1N1 2009, by province/territory, Canada, from February 25 to March 4, 2010, 12h00 EDT

 

---

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

Single Maps | Dual Maps | Animated Maps | FluWatch Reports

Definitions for the 2009-2010 season