February 14 to February 20, 2010 (Week 7)

Posted 2010-02-26

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Pandemic H1N1 2009 virus Surveillance and Epidemiology

A total of 8,637 hospitalized cases including 1,449 (16.8%) cases admitted to ICU and 428 (5.0%) deaths with pandemic H1N1 2009 were reported to PHAC since the beginning of the pandemic. The core information did not change over the past 2 weeks with 8,162 (94.5%) hospitalizations, 1,449 (100%) ICU admissions and 423 (98.8%) deaths. Among the 1,097 ICU cases who had detailed information regarding ventilation status, 58.5% (n=642) required ventilation since the beginning of the pandemic. Most of the reported cases were retrospective cases from 2009. To date, only 8 hospitalizations (BC, ON, QC & NS) and 1 death (BC) have occurred since the beginning of 2010. The one death and 22 hospitalized cases reported this week in BC were retrospective cases that occurred during the first and second wave. 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 25.6 per 100,000 population with the highest rates in children less than 5 years of age (100.5 per 100,000). The national crude mortality rate was 1.3 per 100,000 population with those 45 years and older had the highest mortality rate (2.1 per 100,000). The national crude ICU admission rate was 4.3 per 100,000 population. The ICU admission rate was elevated in children under five years of age as well as adults 45 years and older.

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 (21 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 5.9 times higher, an ICU admission rate 10.7 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 (36.6%, 40.6% and 51.3%, respectively). Diabetes (15.2%) and immunosuppression (including cancer) (15.1%) were also frequently reported among hospitalized cases, while ICU cases were also affected by diabetes (23.5%) and chronic heart disease (21.2%) and the fatal cases had chronic heart disease (35.5%) and immunosuppression (34.7%).

Weekly and cumulative numbers of hospitalized cases, ICU admissions and deaths among Pandemic H1N1 2009 confirmed cases, Canada, to February 20, 2010^†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 Aggregate counts were reported this week. 2 This change from the previous count reflects more detailled accounting of case records with the regional health authorities rather than a true increase in recent case reports. † Note that due to reporting delays, some PTs reported retrospectively on first and second wave cases.
Province/ Territory	Week 7 (February 14 to February 20, 2010)*			From August 30, 2009 to February 20, 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	22	0	1	1031	135	51	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	0	0	0	1444	248	103	399	69	25
QC	0	0	0	2490	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
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	22	0	1	7149	1157	350	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 20, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to February 20, 2010			Cumulative: From April 12, 2009 to February 20, 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, %	20.0-27.7	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)	58.4 (1884/3226)	72.9 (655/899)	84.2 (240/285)	55.1 (2536/4599)	69.9 (817/1168)	81.9 (295/360)
Pregnancy3, %	27.6 (75/272)	19.7 (15/76)	28.6 (4/14)	18.5 (188/1018)	8.4 (15/178)	0.0 (0/36)	20.4 (263/1290)	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 7 (February 14 to February 20, 2010)

During week 7, 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. While only 0.24% (6/2505) of the specimens tested were positive for influenza A this week, respiratory syncytial virus increased to 28.0% of positive respiratory specimens tested during week 7.

In week 7, twenty regions in AB, MB, ON, QC, 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. One region in BC did not report activity this week. The 4 influenza outbreaks reported this week were all in schools (all in NS).

Map of overall Influenza activity level by provinces and territories, Week 7, 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 7, the national ILI consultation rate was 15 consultations per 1,000 patient visits (see ILI graph) which was similar to previous weeks and is still below the expected range for this time of year. All provinces and territories had similar or lower ILI consultation rates compared to their respective ILI rates in the previous weeks except PE, NS and NL which had a slightly higher rate this week. Those under 20 years of age still had the highest consultation rates: 40 per 1,000 among children under 5 years of age and 27 per 1,000 among those 5 to 19 years of age.

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 7, one laboratory-confirmed influenza-associated paediatric (under 17 years of age) hospitalization was reported through the Immunization Monitoring Program Active (IMPACT) network. The case was reported as pandemic H1N1 2009. 1327* hospitalizations have been reported since week 17 (April 26): 96.9% of these hospitalizations 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. The total number of paediatric deaths has changed from 11 to 10 since an investigation confirmed that the case was not pandemic H1N1 2009 positive. 70% of those deaths reported at least one underlying medical condition.

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

During weeks 6 and 7, 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 15 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, 70% were pandemic H1N1 2009 cases, 28% were unsubtyped influenza A and the remaining 2% were either influenza A/H1N1, influenza A/H3N2 or influenza B. For these pandemic H1N1 2009 cases, 1.4% presented with influenza-associated bacteremia, 27% 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 0.24% during week 7 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 except Quebec which had a higher proportion this week. During week 7, a total of 6 specimens tested positive for influenza (all A) and 3/4 (75%) 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 and ON reported 6 specimens for influenza B since August 30, 2009. The proportion of specimens positive for respiratory syncytial virus (RSV) increased to 28.0% during week 7. Positive specimens for RSV were reported from all provinces except NB (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

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 14 to February 20, 2010)						Cumulative (August 30, 2009 to February 20, 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	1	0	0	1	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	1	1	0	0	0	0	7907	4	0	3552	4351	6
QC	4	0	0	2	2	0	10693	1	44	10646	2	8
NB	0	0	0	0	0	0	1856	1	1	1835	19	0
NS	0	0	0	0	0	0	786	0	0	753	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	6	1	0	3	2	0	39041	8	52	33483	5498	14
Specimens from NT, YT, and NU are sent to reference laboratories in other provinces

Sale of antivirals (AV) in Canada

During week 7, 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 14 to February 20, 2010. None of the Health Regions 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 13 seasonal influenza viruses (3 influenza A/H1N1, 9 H3N2, and 1 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 nine seasonal influenza A (H3N2) viruses characterized, one was 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.

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 (1031 samples) but resistant to amantadine (1115 samples).

International update

Global information

WHO: As of February 14, 2010, over 212 countries and overseas territories or communities worldwide reported cases of pandemic H1N1 2009 (at least 15,921 deaths). During weeks 1-4, pandemic H1N1 2009 viruses persisted in some countries around the world although the majority of Northern Hemisphere countries reported decreasing activity. Activity in the Southern Hemisphere was variable but mainly sporadic. The pandemic virus continued to be the predominant circulating influenza virus in all countries where influenza was reported with the exception of China where influenza B was the predominant virus.
<http://www.who.int/csr/don/2010_02_19/en/index.html> and
<http://www.who.int/csr/disease/influenza/update/en/index.html>

On February 23, 2010, the Director General of the WHO sought the Emergency Committee's views on the determination of the pandemic status. After reviewing the evidence (i.e. new community level transmission activity in West Africa, winter months of the Southern Hemisphere has not yet started), and holding extensive discussion, it was determined that there had been no change in the pandemic phase. The situation will be monitored closely and the Committee will convene again to discuss the global pandemic status in the next several weeks.
<http://www.who.int/csr/disease/swineflu/7th_meeting_ihr/en/index.html>

Antiviral resistance: To date, 248 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/update_oseltamivir_resistant20100210.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 6, influenza activity remained at approximately the same levels as last week in the United States with the majority of states reporting sporadic influenza activity (6 states reported regional and 11 states and Puerto Rico reporting localized). Of the 3,656 specimens tested for influenza in week 6, 129 (3.5%) were positive for influenza (125 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 increased slightly but remained below the epidemic threshold. The proportion of outpatient visits for ILI (2.1%) remained below baseline levels. Two influenza-associated pediatric deaths were reported this week and both were associated with pandemic H1N1 2009 virus infection.
<http://www.cdc.gov/flu/weekly/>

Europe: The 2009 influenza A(H1N1) pandemic is well past its winter peak in Europe, with the majority of the countries reporting only sporadic transmission of the pandemic virus. In seven countries (the majority of which are in Eastern Europe), local or regional transmission of the pandemic virus continued at low to medium intensity. In addition to the pandemic H1N1 2009 virus, there was currently no evidence of wide circulation of other influenza A viruses. A few influenza B viruses have been detected. Respiratory syncytial virus detections continued to decline since peaking in week 1. Additionally, the number of severe acute respiratory infection cases by week of onset (29 reported in week 6) has been declining since the peak in week 46.
<http://ecdc.europa.eu/en/publications/Publications/100219_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In Southeast Asia, several countries (Thailand, Myanmar and Indonesia) reported an increasing trend of respiratory diseases activity but overall intensity remained low. In South Asia, influenza activity persisted in the northern and western states of India, however, overall influenza activity continued to decline or remained low in other countries. In East and West Asia, transmission of pandemic influenza virus persisted but was either steadily declining or the overall intensity of current activity remained low, with the exception of North Korea where an increasing trend of respiratory diseases activity was reported.
<http://www.who.int/csr/don/2010_02_19/en/index.html>

Africa: Several countries in West Africa reported increases in the number of cases but there is as yet insufficient evidence to conclude that widespread community transmission is occurring. In North Africa, pandemic influenza transmission persists but activity has declined substantially over the past month. In Sub-Saharan Africa, sporadic pandemic influenza virus transmission was reported.
<http://www.who.int/csr/don/2010_02_19/en/index.html>

Southern Hemisphere

Australia: As at 12 February 2010, there have been 37,713 confirmed cases of pandemic (H1N1) 2009 and 191 deaths reported in Australia. National influenza activity remains low and is 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 21, 2010, there have been 3,300 cases of pandemic H1N1 2009 reported in New Zealand with 20 deaths. ILI consultation rates have remained below baseline levels since the beginning of the year. <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, as of February 25, 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