January 24 to January 30, 2010 (Week 4)

Posted 2010-02-05

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Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,596 hospitalized cases including 1,446 (16.8%) cases admitted to ICU and 426 (5.0%) deaths of pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 8,142 (94.7%) hospitalizations, 1,446 (100%) ICU admissions and 422 (99.1%) deaths. Among the 422 deaths for whom detailed information was available, only 1 occurred in 2010. Only five of the 13 provinces and territories continued to report severe cases with pandemic H1N1 2009. The number of hospitalized cases (31), ICU admissions (0) and deaths (1) were lower than those reported in the previous week. Almost all new reported cases were retrospective cases and occurred in 2009. 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 second wave was substantially larger than the first wave as illustrated by larger absolute numbers across all levels of severity. There were 5.5 times more hospitalized cases reported in the second wave as compared to the first wave (8,142 vs. 1,488); 5.0 more ICU cases (1,446 vs. 292); and 5.4 times more deaths (422 vs. 78). The proportion of severe cases (ICU admissions and deaths) among all hospitalized cases to date was still slightly lower in the second wave than in the first wave (19.6% vs. 16.2% for ICU admissions and 5.2% vs. 4.9% for fatal cases). All provinces and territories showed higher levels of transmission during the second wave with the exception of Manitoba and Nunavut which reported higher hospitalization rates in the first wave than in the second wave (1.3 and 12.4 times greater, respectively) (data not presented).

No deaths were reported during the second wave among pregnant women compared to four deaths in the first wave. The death of a pregnant woman reported in week 3 was incorrect and case counts in week 4 have been corrected to reflect this update. Since the beginning of the pandemic, 263 pregnant women have been hospitalized with pandemic H1N1 2009 among 1,289 hospitalized women aged between 15 and 44 years of age. From April 12, 2009 to January 30, 2010, 604 reported hospitalized cases were among people of Aboriginal origin (432 First Nations, 109 Inuit, 48 Metis and 15 with unknown Aboriginal subgroup). 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 8.0%-10.6% and 7.1%-10.4%, respectively. The true proportionof Aboriginal peoples affected lies between those two estimates.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic H1N1 2009 confirmed cases, Canada, to January 30, 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 The increase from last week is due to more detailed accounting of case reports from the second wave. 3 The drop in the total number of cases is due to health units conducting 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 4 (January 24 to 30, 2010)*			From August 30, 2009 to January 30, 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	27	0	0	1010	136	50	49	19	6
AB	1	0	0	1147	210	64	129	29	7
SK	0	0	0	44	40	11	23	12	4
MB	2	0	0	166	18	4	213	43	7
ON3	--	--	1	1427	244	102	399	69	25
QC	1	0	0	2490	361	81	572	104	27
NB1	0	0	0	162	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	0	0	0	6	0	0	74	6	1
Canada	31	0	1	7108	1154	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 January 30, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to January 30, 2010			Cumulative: From April 12, 2009 to January 30, 2010
	Hospitalized cases (n=1488)	ICU-admitted (n=292)	Deaths (n=78)	Hospitalized cases (n=6654)	ICU-admitted  (n=1155)	Deaths (n=344)	Hospitalized cases (n=8142)	ICU-admitted (n=1446)	Deaths (n=422)
Females, %	51.3	57.2	62.8	49.7	49.7	46.8	50.0	51.2	49.8
Median age	23.0	37.0	51.0	30.0	47.0	54.0	29.0	46.0	53.0
Aboriginal status1, %	20.0-27.8	16.1-21.9	11.5-17.3	4.6-6.2	5.9-7.8	6.1-8.9	7.4-10.0	8.0-10.6	7.1-10.4
Underlying medical  conditions2, %	47.5 (652/1373)	60.2 (162/269)	73.3 (55/75)	54.6 (1753/3212)	63.8 (567/889)	78.4 (222/283)	52.5 (2405/4585)	63.0 (729/1158)	77.4 (277/358)
Pregnancy3, %	27.6 (75/272)	19.7 (15/76)	28.6 (4/14)	18.5 (188/1017)	8.5 (15/177)	0.0 (0/36)	20.4 (263/1289)	11.9 (30/253)	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. Please note that results may differ slightly compared to the previous weeks due to updates in the national database. 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 4 (January 24 to January 30, 2010)

During week 4, all influenza indicators remained stable and continued to be either at baseline levels or considerably under the expected levels for this time of the year. While influenza activity was very low, the respiratory syncitial virus transmission continued to increase.

In week 4, only two regions (BC & NS) reported localized activity. Twenty-two regions in BC, AB, MB, ON, QC, NB, NS & NU reported sporadic activity, while thirty regions reported no activity in AB, SK, MB, ON, QC, NB, PE, NS, NL, YT & NT. 12 influenza outbreaks were reported this week; 11 in schools (2 in BC, 2 in NB and 7 in NS) while one occurred in a long-term care facility in NS.

Map of overall Influenza activity level by provinces and territories, Week 4, 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 4, the national ILI consultation rate was 16 consultations per 1,000 patient visits (see ILI graph) which was similar to the 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 SK which had a slightly higher rate this week. Those under 20 years of age still had the highest consultation rates, with 37 and 26 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 4, one laboratory-confirmed influenza-associated paediatric hospitalization was reported through the Immunization Monitoring Program Active (IMPACT) network. The case was reported as unsubtyped influenza A. 1318* hospitalizations have been reported since week 17 (April 26): 97.3% 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.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza A was 0.6% during week 4 which remained at a very low level for a sixth consecutive week (see Tests table). All provinces had a similar or lower proportion of positive tests for influenza compared to the previous week except NS which had a higher proportion. During week 4, a total of 14 specimens tested positive for influenza (13 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 8 specimen for influenza B while ON reported 6 specimen for influenza B since August 30, 2009. The proportion of positive respiratory syncytial virus tests increased to 24.1% during week 4. Positive specimens were reported from all provinces except NB (data not shown).

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 24 to January 30, 2010)						Cumulative (August 30, 2009 to January 30, 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	6370	0	1	5804	565	0
AB	3	0	0	2	1	0	5863	2	5	5757	99	0
SK	0	0	0	0	0	0	2598	0	1	2298	299	0
MB	1	0	0	1	0	0	1915	0	0	1788	127	0
ON	7	0	0	3	4	0	7897	2	0	3548	4347	6
QC	0	0	0	0	0	1	10688	1	44	10643	0	8
NB	0	0	0	0	0	0	1856	1	1	1835	19	1
NS	1	0	0	0	1	0	784	0	0	751	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	13	0	0	7	6	1	39019	6	52	33471	5490	15
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Sale of antivirals (AV) in Canada

During week 4, 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 all Health Regions for the week of January 24, 2010 to January 30, 2010. Only one Health Region reported 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 785 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 785 pandemic H1N1 2009 viruses characterized, 781 (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 (927 samples) but resistant to amantadine (996 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 14,711 deaths as of January 24, 2010. Most temperate regions in the northern hemisphere passed a fall and wintertime peak of influenza activity between last October and late November 2009. However, pandemic H1N1 2009 virus transmission continued in several later affected areas in North Africa (Morocco, Algeria, Libya, Egypt), limited areas of eastern and south eastern Europe (Austria, Albania, Bulgaria, Slovakia, Russian Federation), and in parts of south and east Asia (northern and western India, Nepal, Sri Lanka, Bangladesh). 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. For the week of January 10 to 16, 2010 from FluNet reporting, pandemic H1N1 2009 accounted for 95% of all subtyped influenza A viruses detected in both northern and southern hemispheres. China reported outbreaks due to influenza B (48.8% of all influenza positive specimens). Sporadic detections of seasonal A(H1N1), A(H3N2) and influenza B viruses were reported from a few countries such as Iran, Japan, the Russian Federation and Tunisia. <http://www.who.int/csr/don/2010_01_29/en/index.html> and
<http://www.who.int/csr/disease/swineflu/laboratory29_01_2010/en/index.html>

Antiviral resistance: To date, 220 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/laboratory29_01_2010/en/index.html>

Geographic update

United States: During week 3 (January 17-23, 2010), influenza activity remained at much the same levels in the United States. No states reported widespread influenza activity, five states reported regional influenza activity, Puerto Rico and nine states reported local influenza activity, the District of Columbia, Guam, and 33 states reported sporadic influenza activity, and the U.S. Virgin Islands and three states reported no influenza activity. The proportion of outpatient visits for influenza-like illness (ILI) was 1.7% which was below the national baseline of 2.3% with only two of the 10 regions reporting ILI equal to their region-specific baseline. Cumulative hospitalization rates leveled off in all age groups and very few laboratory-confirmed pandemic H1N1 2009 hospitalizations were reported during the week 3. The proportion of deaths attributed to pneumonia and influenza was above the epidemic threshold. This increase was thought to result from an increase in reports of pneumonia-associated deaths in older people which are not necessarily related to flu illness. Five influenza-associated pediatric deaths were reported during week 3: four deaths were associated with pandemic H1N1 2009 infection and one was associated with an 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: For week 3/2010 (January 18-24, 2010), of the 26 countries reporting, five reported medium activity (Bulgaria, Malta, Poland, Romania, Slovakia) while all other remaining countries reported low activity. Of the five countries that reported intensity above baseline levels, an increasing trend was reported in Poland and Slovakia, a stable trend reported in Bulgaria and Romania, and a decreasing trend in Malta. Widespread activity was reported in two countries (Greece, Wales), and local or regional activity was reported in 11 countries (Austria, Bulgaria, Czech Republic, Estonia, France, Germany, Malta, Romania, Slovakia, Sweden, Scotland). Sporadic or no activity was reported in the remaining countries. The number of severe acute respiratory infection cases continued to decline during this period. Fifty-two percent of new cases were admitted to intensive care units and 37% required ventilation. Since week 40/2009, 99% of sub-typed specimens were identified as the pandemic H1N1 2009. Among tested specimens, 2.7% were resistant to oseltamivir. In week 3, nine countries reported 91 additional deaths which brought the total number of deaths since the beginning of the season to 1429 deaths.
<http://ecdc.europa.eu/en/healthtopics/Documents/100201_Influenza_A(H1N1)_Weekly_Executive_Update.pdf> and
<http://ecdc.europa.eu/en/publications/Publications/100129_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In west Asia, pandemic influenza activity continued to be geographically regional to widespread, however activity levels continued to decline or remained low since December 2009. In south Asia, pandemic influenza activity remained active but geographically variable. Northern India, Nepal, and Sri Lanka experienced recent peaks in late December 2009 and early January 2010. Activity remained stable but elevated in western India with declines experienced in northern India and overall low activity in southern and eastern India. Regional spread with low intensity was reported in Bangladesh. Overall activity in east Asia continued to decline although transmission remained active in some areas (North Korea, South Korea, Japan). In northern and southern China, pandemic H1N1 2009 isolations declined substantially since peaking early to mid November 2009; however, detections of influenza type B viruses have increased in recent weeks. In southeast Asia, transmission of pandemic H1N1 2009 persisted however, current activity levels were low or have declined substantially (Vietnam, Thailand). <http://www.who.int/csr/don/2010_01_29/en/index.html>

Weekly and cumulative numbers of deaths among due to pandemic H1N1 2009, by province/territory, Canada, as of February 4, 2010, 11h00 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