April 4 to April 10, 2010 (Week 14)

Posted 2010-04-16

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Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,678 hospitalized cases including 1,473 (17.0%) cases admitted to ICU and 428 (4.9%) deaths with pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. Core data was available for 8,227 (94.8%) hospitalizations, 1,473 (100%) ICU admissions and 423 (98.8%) deaths. Among the 1,117 ICU cases from whom we had detailed information regarding ventilation status, 58.5% (n=654) required ventilation since the beginning of the pandemic. No new H1N1-related hospitalizations and deaths have been reported this week. To date, only 14 hospitalizations (BC, ON, QC & NS) and two deaths (ON) have occurred since the beginning of 2010.

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among pandemic H1N1 2009 confirmed cases, Canada, April 12, 2009 to April 10, 2010^†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 Aggregate counts were reported by these two provinces. † Note that due to reporting delays, some provinces and territories reported retrospectively on first and second wave cases.
Province/ Territory	Week 14 (From April 4 to April 10, 2010)*			Total (From April 12, 2009 to April 10, 2010)**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1	0	0	0	1084	168	57
AB	0	0	0	1276	239	71
SK	0	0	0	67	52	15
MB	0	0	0	379	61	11
ON	0	0	0	1843	319	128
QC	0	0	0	3063	465	108
NB1	0	0	0	163	34	8
NS	0	0	0	293	50	7
PE	0	0	0	50	9	0
NL	0	0	0	308	60	18
YT	0	0	0	15	3	3
NT	0	0	0	52	7	1
NU1	0	0	0	85	6	1
Canada	0	0	0	8678	1473	428

To date, the national cumulative 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 cumulative 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 highest 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).

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 April 10, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to April 10, 2010			From April 12, 2009 to April 10, 2010
	Hospitalized cases (n=1490)	ICU-admitted (n=292)	Deaths (n=77)	Hospitalized cases (n=6737)	ICU-admitted  (n=1181)	Deaths (n=346)	Hospitalized cases (n=8227)	ICU-admitted (n=1473)	Deaths (n=423)
Females, %	51.4	57.2	62.3	49.7	49.4	46.8	50.0	51.0	49.6
Median age	23.0	37.0	51.0	30.0	47.0	54.0	29.0	46.0	53.0
Aboriginal status1, %	20.1-27.8	16.1-21.9	11.7-17.6	4.6-6.1	5.8-7.6	6.1-8.9	7.4-10.0	7.8-10.4	7.1-10.4
Underlying medical conditions2, %	47.5 (653/1374)	60.2 (162/269)	73.3 (55/75)	59.7 (1969/3299)	74.4 (683/924)	85.5 (247/289)	56.1 (2622/4673)	71.2 (849/1193)	83.0 (302/364)
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. 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 14 (April 4 to April 10, 2010)

Overall influenza activity has remained low for at least 16 consecutive weeks. All influenza indicators were still below expected levels for this time of the year. The proportion of tests that were positive for influenza during week 14 (0.36%, 6/1,671) remained at a very low level for this time of year.

In week 14, one region (in NS) reported localized activity, ten regions (in BC, AB, ON & QC) reported sporadic activity, and 35 regions reported no activity. Eight regions (in BC, SK and NL) did not report this week. One influenza outbreak was reported in a long-term care facility in NS this week.

Map of overall Influenza activity level by provinces and territories, Week 14, 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 14, the national ILI consultation rate was 9.1 consultations per 1,000 patient visits (see ILI graph) which was similar to the previous weeks and still remained below the expected range for this time of year (range from 17.4 to 25.3 consultations per 1,000 patient visits). All reporting provinces and territories had similar or lower ILI consultation rates compared to their respective ILI rates in the previous weeks except for YT and NT. Those in the 5 to 19 age group had the highest consultation rates (21.7 per 1,000) followed by those 65 years and over (11.3 per 1,000).

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.

Laboratory Surveillance Summary

The proportion of tests that were positive for influenza during week 14 (0.36%, 6/1,671) was similar to the previous week and still remained at a low level for this time of year (see Tests table).Of the six positive specimens, three (50%) were positive for pandemic H1N1 2009, two (33%) were unsubtyped influenza A and 1 (17%) was influenza B. BC, AB, ON and NS were the only provinces to report positive specimens. Note that since August 30, 2009, influenza A/H3N2 detections were highest in QC (85% or 44/52) and influenza B detections were highest in QC (41% or 9/22) and ON (55% or 12/22). Respiratory syncytial virus detections peaked during week 7 (28.3%) continued to decline progressively to 13.0% this week. The proportion of positive parainfluenza (2.6%) and adenovirus (1.7%) tests remained low during week 14.

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 (April 4 to April 10, 2010)						Cumulative (August 30, 2009 to April 10, 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	1	6382	0	1	5816	565	1
AB	2	0	0	2	0	0	5871	2	5	5763	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	1	0	0	0	1	0	7812	4	0	3561	4247	12
QC	0	0	0	0	0	0	10700	4	44	10650	2	9
NB	0	0	0	0	0	0	1856	1	1	1835	19	0
NS	1	0	0	0	1	0	788	0	0	753	35	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	5	0	0	3	2	1	38970	11	52	33511	5396	22
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Canadian situation

Paediatric and Adult Influenza Hospitalizations and Deaths

In week 14, no laboratory-confirmed influenza-associated paediatric (18 years of age and under) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. A total of 1327* hospitalizations have been reported since week 17 (April 26, 2009), of which 97.0% were due to pandemic H1N1 2009. Of the 985 paediatric hospitalizations reported since week 17, 43 (4.4%) cases developed bacterial infection (namely bacteremia and pneumonia). Since the beginning of the pandemic, ten paediatric deaths due to pandemic H1N1 2009 were reported through the IMPACT network among children 18 years of age or under. Seven (70%) of those deaths reported had at least one underlying medical condition. The median delay in hospitalization of the pandemic H1N1 2009 cases (time to hospital admission since symptom onset) was 3.0 days, while for fatal cases the delay was slightly higher with 4 days.

Please note that since the beginning of the 2009-2010 season IMPACT monitored paediatric hospitalizations among children up to 18 years of age instead of 16 years and under as seen during previous seasons. *Delays in the reporting of data may cause data to change restrospectively.

During week 14, 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 8 reporting sites. From June 1, 2009 to March 5, 2010, 552 laboratory-confirmed influenza cases among hospitalized adults were reported through 27 of CNISP sentinel sites. Among them, 385 (70%) were pandemic H1N1 2009 cases, 156 (28%) were unsubtyped influenza A and the remaining 11 (2%) were either seasonal influenza A/H1N1, influenza A/H3N2 or influenza B. Among the pandemic H1N1 2009 cases, 26% (100/385) were admitted to the ICU and 5% (20/385) died (90% of whom had at least one underlying medical condition). Only 1.3% (5/365) of the pandemic cases developed a bacterial infection. The median delay in hospitalization of the pandemic H1N1 2009 cases (time to hospital admission since symptom onset) was 2.5 days while the median length of stay was 6 days.

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

Sale of antivirals (AV)

During week 14, provincial and territorial antiviral prescription sales continued to demonstrate little change in antiviral prescriptions among provinces and territories. An analysis of antiviral sales data at the Health Region level demonstrated low antiviral prescription sales rates among all Health Regions for the week of April 4 to April 10, 2010. No Health Region reported an antiviral sales rate greater than 2.5 antivirals/1000 other prescriptions.

Antigenic Characterization

Since September 1, 2009, the National Microbiology Laboratory (NML) has antigenically characterized 848 pandemic H1N1 2009 viruses and 17 seasonal influenza viruses (3 seasonal A/H1N1, 10 A/H3N2, and 4 B) that were received from provincial laboratories. Of the 848 pandemic H1N1 2009 viruses characterized, 844 (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 (2009-10 vaccine) and eight viruses were antigenically related to A/Perth/16/09 (2010 -2011 Northern Hemisphere vaccine). Three seasonal influenza A/H1N1 viruses characterized were related to A/Brisbane/59/07 (2009-10 vaccine). Of the four influenza B viruses characterized, two were antigenically related to B/Brisbane/60/08 (2009-10 vaccine). One B virus was related to the previous vaccine virus B/Florida/4/2006 (Yamagata lineage) and one B virus was related to the 2007-2008 vaccine virus B/Malaysia/2506/2004 (Victoria lineage).

Antiviral Resistance

NML/Provinces: Since April 2009, 13 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. All 13 resistant cases were associated with oseltamivir treatment or prophylaxis.

NML: All pandemic H1N1 2009 viruses tested so far have been sensitive to zanamivir (1055 samples) but resistant to amantadine (1129 samples).

International update

Global information

WHO: As of April 4, 2010, over 213 countries and overseas territories or communities worldwide reported cases of pandemic H1N1 2009 (at least 17,700 deaths). The most active areas of pandemic H1N1 2009 transmission continued to be in parts of Southeast Asia, West Africa, and in the tropical zone of the Americas. Seasonal influenza B viruses continued to actively circulate in East Asia, but are also being detected at low levels across other parts of Asia and Europe.
< http://www.who.int/csr/don/2010_04_09/en/index.html>

Antiviral resistance: As of April 7, 2010, 278 pandemic H1N1 2009 isolates worldwide have been found to be resistant to oseltamivir, all with the same H275Y substitution and are assumed to remain sensitive to zanamivir.
<http://www.who.int/csr/disease/swineflu/oseltamivirresistant20100409.pdf>

2010-2011 influenza season vaccine: The WHO recommended 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 13, influenza activity decreased slightly in the United States with the majority of states reporting sporadic influenza activity. However, regional influenza activity was reported by three states (Alabama, Georgia, and South Carolina) and localized activity was reported by Puerto Rico and three states (Hawaii, Mississippi and Virginia). Of the 2,871 specimens tested for influenza in week 13, 105 (3.7%) were positive for influenza (98.1% were for influenza A). All influenza A viruses subtyped were pandemic H1N1 2009. The proportion of deaths attributed to pneumonia and influenza (7.2%) was below the epidemic threshold and the proportion of outpatient visits for ILI (1.1%) remained below national baseline levels.
< http://www.cdc.gov/flu/weekly/index.htm>

Europe: For the fifth consecutive week, all reporting countries experienced low intensity influenza activity. Of the 49 positive influenza specimens collected this week, 55% were influenza B. All of the sub-typed influenza A viruses were pandemic H1N1 2009.
< http://ecdc.europa.eu/en/publications/Publications/100409_SUR_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In Southeast Asia, the most active transmission of pandemic influenza virus continued to be in Thailand, however, overall disease activity has declined substantially. Low levels of seasonal influenza A/H3N2 and type B viruses have also been detected in Thailand in recent weeks. In Indonesia, recent low level circulation of seasonal influenza A/H3N2 viruses appeared to be subsiding. In South Asia, limited data suggested an increasing number of cases have been detected in Bangladesh since late February 2010. In East Asia, pandemic influenza virus continued to circulate at very low levels as overall rates of respiratory diseases remained low across much of the region. Influenza B viruses continued to circulate in China, Mongolia, Republic of Korea, Hong Kong SAR and Chinese Taipei.
<http://www.who.int/csr/don/2010_04_09/en/index.html>

Africa: In Sub-Saharan Africa, limited data suggested that active circulation of pandemic influenza virus continued across parts of West and West-Central Africa, and to a lesser extent in limited areas of East Africa. In Cameroon, although the majority of influenza detections were for pandemic viruses, seasonal influenza type B viruses were also detected. Pandemic influenza virus continued to be the predominant influenza virus circulating in West and East Africa, however, small numbers of seasonal influenza A/H3N2 viruses have also been identified.
< http://www.who.int/csr/don/2010_04_09/en/index.htmll>

Latin America & the Caribbean: In the temperate countries of the southern hemisphere, overall influenza activity remained low, with mostly sporadic detections of pandemic and seasonal influenza viruses. Of note, Chile has reported new detections of the pandemic virus, including small numbers of severe cases in at least three regions over the past two weeks. The significance of this early limited circulation of pandemic virus in advance of the usual winter influenza season is not yet known.
<http://www.who.int/csr/don/2010_04_09/en/index.html>

Australia & New Zealand: In Australia, pandemic influenza activity remained low and sporadic cases of pandemic influenza continued to be reported without evidence of sustained community transmission. There was one new laboratory confirmed pandemic H1N1 2009 case diagnosed during week 14, however, there were 8 cases of influenza A not sub-typed and 2 cases of influenza B identified. In New Zealand, one influenza A virus was identified in week 14 and ILI rates remained below baseline levels.
<http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/ozflu2010.htm
/$File/ozflu-no13-2010.pdf > and
<http://www.surv.esr.cri.nz/PDF_surveillance/Virology/FluWeekRpt/2010/FluWeekRpt201014.pdf >

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