January 31 to February 6, 2010 (Week 5)

Posted 2010-02-12

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Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,615 hospitalized cases including 1,449 (16.8%) cases admitted to ICU and 426 (4.9%) deaths with pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 8,162 (94.7%) hospitalizations, 1,449 (100%) ICU admissions and 423 (99.3%) deaths. Among the cases for whom detailed information was available, only 6 hospitalizations and 1 death occurred in 2010. Only two of the 13 provinces and territories continued to report severe cases with pandemic H1N1 2009 this week. The number of hospitalized cases (21), ICU admissions (4) and deaths (1) were lower than 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 national hospitalization rate was 25.5 per 100,000 population with the highest rates in children aged less than 5 years of age (94.4 per 100,000). The national mortality rate was 1.3 per 100,000 population; those 45 years and older had the highest mortality rate (2.1 per 100,000). ICU admission rate was also elevated in people 45 years and older and children under five years of age (6.2 and 6.1 per 100,000, respectively).

Since the beginning of the pandemic, 24 paediatric deaths occurred in children aged 0 to 16 years. These deaths accounted for 5.6% of all cumulative deaths reported. The majority of these deaths occurred in children less than nine years of age (62.5%), were female (62.5%) and were admitted to ICU (58.3%). Four of these deaths were among Aboriginal children (16.7%). Underlying medical conditions were reported in 60% of these deaths for whom detailed information was available, most common being chronic pulmonary disease (including asthma) and chronic heart disease.

No deaths were reported during the second wave among pregnant women compared to four deaths in the first wave. Since the beginning of the pandemic, 262 pregnant women have been hospitalized with pandemic H1N1 2009 among 1,290 hospitalized women aged between 15 and 44 years of age.

From April 12, 2009 to February 6, 2010, 604 reported hospitalized cases were among people of Aboriginal origin. Since Aboriginal status was not reported by two provinces (which comprise 23% of the Aboriginal population), two methods were used to calculate proportions. Depending on the methods, the proportions of hospitalized people of Aboriginal origin among all hospitalized cases were between 7.4% and 10.0%, while the proportions of those admitted to ICU and died were between 7.9%-10.6% and 7.1%-10.4%, respectively. The true proportion of Aboriginal peoples affected lies between these two estimates.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic H1N1 2009 confirmed cases, Canada, to February 6, 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 drop in the total number of cases is due data clean up and case re-classification. † Note that due to reporting delays, some PTs reported retrospectively on first and second wave cases.
Province/ Territory	Week 5 (January 31 to February 6, 2010)*			From August 30, 2009 to February 6, 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	--	--	--	1009	135	49	49	19	6
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	17	4	1	1444	248	103	399	69	25
QC	0	0	0	2490	361	81	572	104	27
NB1,2	--	0	0	161	33	8	2	1	0
NS	4	0	0	276	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	0	0	0	6	0	0	74	6	1
Canada	21	4	1	7127	1157	348	1488	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 February 6, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to February 6, 2010			Cumulative: From April 12, 2009 to February 6, 2010
	Hospitalized cases (n=1488)	ICU-admitted (n=292)	Deaths (n=78)	Hospitalized cases (n=6674)	ICU-admitted  (n=1157)	Deaths (n=345)	Hospitalized cases (n=8162)	ICU-admitted (n=1449)	Deaths (n=423)
Females, %	51.3	57.2	62.8	49.7	49.7	46.7	50.0	51.2	49.6
Median age	23.0	37.0	51.0	30.0	47.0	54.0	29.0	46.0	53.0
Aboriginal status1, %	20.2-28.0	16.1-21.9	11.5-17.3	4.6-6.1	5.9-7.8	6.1-8.9	7.4-10.0	7.9-10.6	7.1-10.4
Underlying medical  conditions2, %	47.5 (652/1373)	60.2 (162/269)	73.3 (55/75)	54.8 (1763/3216)	63.8 (567/889)	76.8 (218/284)	52.6 (2415/4589)	63.0 (729/1158)	77.4 (273/359)
Pregnancy3, %	27.6 (75/272)	19.7 (15/76)	28.6 (4/14)	18.4 (187/1018)	8.4 (15/178)	0.0 (0/36)	20.3 (262/1,290)	11.8 (30/254)	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 5 (January 31 to February 6, 2010)

During week 5, all influenza indicators remained low for this time of the year. Only 0.4% of the specimens tested were positive for influenza A and the pandemic H1N1 2009 strain still accounted for 100% of the positive influenza A subtyped specimens this week.

In week 5, only one region (BC) reported localized activity. Twenty regions in BC, AB, MB, ON, QC, NB, NS & NU reported sporadic activity, while thirty-three regions reported no activity in BC, AB, SK, MB, ON, QC, NB, PE, NS, NL, YT & NT. The 8 influenza outbreaks reported this week were all in schools (1 in BC, 2 in NB and 5 in NS).

Map of overall Influenza activity level by provinces and territories, Week 5, 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 5, the national ILI consultation rate was 13 consultations per 1,000 patient visits (see ILI graph) which was similar to the 10 previous weeks and still significantly below the expected range for this time of the year. All provinces and territories had either similar or slightly lower ILI consultation rates compared to their respective ILI rates in the previous week except NL which had a slightly higher rate this week. Those under 20 years of age still had the highest consultation rates, with 57 and 21 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 and Adult Influenza Hospitalizations and Deaths

In week 5, no laboratory-confirmed influenza-associated paediatric (under 17 years of age) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. 1328* 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.

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

In week 5, no laboratory-confirmed influenza-associated adult (16 years of age or older) hospitalizations were reported through the Canadian Nosocomial Infection Surveillance Program (CNISP) from 12 of 50 reporting sites during this period. 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 5, 2010, of the 552 laboratory-confirmed influenza cases among hospitalized adults reported through 27 of CNISP sentinel sites, 70% were pandemic H1N1 2009 cases. For these pandemic H1N1 2009 cases, most were among women (51%), 1.4% presented with influenza-associated bacteremia, 26% were admitted to the ICU, and 5% died (90% of whom had at least one underlying medical condition).

Please note the total number of CNISP reporting sites fluctuates weekly.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza A was 0.4% during week 5 which remained at a very low level (see Tests table). All provinces had a similar or lower proportion of positive tests for influenza compared to the previous week. During week 5, a total of 10 specimens tested positive for influenza (all A) and 100% of the positive influenza A subtyped specimens were pandemic H1N1 2009. Note that QC reported 44 positive specimens for A/H3N2 and 8 specimens for influenza B, ON reported 6 specimens for influenza B and 1 positive specimen for influenza B in NB since August 30, 2009. The proportion of positive respiratory syncytial virus tests increased to 25.2% during week 5. Positive specimens were reported from all provinces except NB (data not shown). Also, the proportion of positive parainfluenza and adenovirus tests were 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 31 to February 6, 2010)						Cumulative (August 30, 2009 to February 6, 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	3	0	0	2	1	0	5866	2	5	5759	100	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	5	0	0	2	3	0	7902	2	0	3550	4350	6
QC	1	0	0	1	0	0	10689	1	44	10644	0	8
NB	0	0	0	0	0	0	1856	1	1	1835	19	1
NS	1	0	0	1	0	0	785	0	0	752	33	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	10	0	0	6	4	0	39029	6	52	33477	5494	15
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Sale of antivirals (AV) in Canada

Nationally, antiviral prescriptions appear to be at the levels seen prior to the second wave. During week 5, 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 demonstrated low antiviral prescription rates among the vast majority of Health Regions for the week of January 31, 2010 to February 6, 2010. Like last week, only one Health Region had an antiviral rate greater than 2.5 antivirals/1000 other prescriptions in NS.

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 790 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 790 pandemic H1N1 2009 viruses characterized, 786 (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 (981 samples) but resistant to amantadine (1051 samples).

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.

International update

Global information

WHO:Worldwide more than 209 countries and overseas territories or communities reported laboratory confirmed cases of pandemic H1N1 2009, including at least 15,174 deaths as of January 31, 2010. In the temperate zone of the northern hemisphere, overall pandemic influenza activity continued to decline or remained low in most regions since peaking during late October and November 2009. Several areas continued to have evidence of active but declining transmission, particularly in North Africa (Morocco, Egypt) and in limited areas of Eastern Europe (Albania, Bulgaria, the Czech Republic, Georgia, Greece, Luxembourg, Romania) and East Asia (Japan, South Korea, Mongolia, Hong Kong SAR, northern and southern China). In temperate regions of the southern hemisphere, sporadic cases of pandemic H1N1 2009 continued to be reported without evidence of sustained community transmission. Pandemic H1N1 2009 virus continued to be the predominant virus circulating worldwide. Besides 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, East and Southeast Asia and sporadic detections were reported in other continents.
<http://www.who.int/csr/don/2010_02_5/en/index.html> and
<http://www.who.int/csr/disease/swineflu/laboratory05_02_2010/en/index.html>

Antiviral resistance: To date, 225 pandemic H1N1 2009 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y mutation and all remain sensitive to zanamivir.
<http://www.who.int/csr/disease/swineflu/laboratory05_02_2010/en/index.html>

Geographic update

United States: During week 4 (January 24-30, 2010), influenza activity remained at much the same levels in the United States. While no states reported widespread influenza activity, the majority of states reported regional (6), local (10) or sporadic (31) activity. The U.S. Virgin Islands and three states reported no influenza activity. The proportion of outpatient visits for influenza-like illness (ILI) was 1.9% which was below the national baseline of 2.3% and region-specific baselines. Cumulative hospitalization rates leveled off in all age groups and very few laboratory-confirmed pandemic H1N1 2009 hospitalizations were reported during week 4. The proportion of deaths attributed to pneumonia and influenza decreased slightly over the previous week, but was still higher than expected for this time of year. Nine influenza-associated pediatric deaths were reported during week 4: eight deaths were associated with pandemic H1N1 2009 virus infection and one was associated with influenza A virus for which the subtype was undetermined. Of the subtyped influenza A viruses reported to CDC, 100% were pandemic H1N1 2009 viruses.
<http://www.cdc.gov/flu/weekly/> and <http://www.cdc.gov/h1n1flu/update.htm>

Europe: In Europe for week 4/2010 (January 25-31, 2010), the pandemic H1N1 2009 was well past its peak and medium intensity transmission was confined to five countries (Bulgaria, Greece, Malta, Romania, Slovakia) while remaining countries reported low intensity. Widespread activity was reported in Greece and local or regional activity was reported in Austria, Bulgaria, Czech Republic, France, Germany, Italy, Malta, Romania, Slovakia, Sweden and Scotland. Sporadic or no activity was reported in the remaining 14 countries and England, Northern Ireland and Wales. For the majority of countries that reported age-specific incidence of ILI, the most affected age group was 0–14 years except in Austria and Norway; the most affected age group was 15–64 years. The number of reported SARI cases continued to decline. During week 4, 64 cases of severe acute respiratory infection were reported. All of the 41 influenza viruses isolated from among these cases were subtyped as the pandemic H1N1 2009 virus. Of these 41 cases, 27% had no known underlying medical condition. Of the 816 specimens collected by sentinel physicians in week 4, 9% were found positive for influenza A virus. Since week 40/2009, 99.4% of all subtyped specimens were identified as the pandemic H1N1 2009 virus. There was no indication of any increase in the circulation of non-pandemic influenza viruses since the beginning of the New Year. In week 4, seven countries reported 74 additional deaths which brought the total number of deaths since the beginning of the season to 1528 deaths.
<http://ecdc.europa.eu/en/activities/surveillance/EISN/Newsletter/100205_EISN_
Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In south and southeast Asia, pandemic influenza activity remained active but geographically localized to regional with overall intensity reported as low to moderate in most places. In India, while activity continued to decline, the most active areas of transmission were in the western states. Overall ILI activity in Thailand remained low with some focal activity increases reported in several central and northern provinces. In east Asia, despite pandemic influenza transmission remaining active and geographically widespread; overall activity continued to decline (Japan, South Korea, Mongolia). In northern and southern China, ILI rates returned to seasonal levels; however, active transmission persisted. In China over the past few weeks, as the circulation of pandemic H1N1 2009 continued to decline an increase in the circulation of seasonal influenza type B viruses was noted (pandemic H1N1 2009 and seasonal type B viruses accounted for 34% and 66% of all influenza viruses detected, respectively). Active transmission of the pandemic H1N1 2009 virus also persisted in Hong Kong, although at much lower levels than an earlier peak of activity during September and October 2009. <http://www.who.int/csr/don/2010_02_5/en/index.html>

Real-time weekly and cumulative numbers of deaths due to pandemic H1N1 2009, by province/territory, Canada, as of February 11, 2010, 12h00 EDT

 

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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