February 7 to February 13, 2010 (Week 6)

Posted 2010-02-19

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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 427 (5.0%) 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 (99.1%) 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 first wave and second wave retrospective cases; only 7 hospitalizations (BC, ON, QC & NS) and 1 death (BC) have occurred since the beginning of 2010. No hospitalizations and no ICU admissions were reported this week. The death reported this week in BC was a retrospective hospitalized case that died during the 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 25.5 per 100,000 population with the highest rates in children aged less than 5 years of age. The national crude mortality rate was 1.3 per 100,000 population; those 45 years and older had the highest mortality rate. The national crude ICU admission rate was 4.3 per 100,000 population. ICU admission rate was elevated in people 45 years and older as well as children under five years of age.

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 men and women were similar across severity of illness from April 12, 2009 to February 13, 2010 except for hospitalizations where the median age for men was 21 years versus 33 years for women.

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 10.7 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 13, 2010^†

*Based on reporting date. **Based on epidemiological date, hospitalization date, death date and reporting date. 1 Aggregate counts were reported this week. † Note that due to reporting delays, some PTs reported retrospectively on first and second wave cases.
Province/ Territory	Week 6 (February 7 to February 13, 2010)*			From August 30, 2009 to February 13, 2010**			From April 12 to August 29, 2009**
	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths	Hospitalized cases	ICU admissions	Deaths
BC1,†	0	0	1	1009	135	50	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	0	0	1	7127	1157	349	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 13, 2010^†

	From April 12 to August 29, 2009			From August 30, 2009 to February 13, 2010			Cumulative: From April 12, 2009 to February 13, 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 ince 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 6 (February 7 to February 13, 2010)

During week 6, all influenza indicators continued to decline compared to the previous week and were still considerably under the expected level for this time of the year. Only 0.24% of the specimens tested were positive for influenza A. Three out of four (75%) of the positive influenza A subtyped specimens were pandemic H1N1 2009 this week.

In week 6, nineteen regions in BC, AB, MB, ON, QC, NS & NU reported sporadic activity, while thirty-five regions reported no activity in BC, AB, SK, MB, ON, QC, NB, PE, NS, NL, YT & NT. The 5 influenza outbreaks reported this week were all in schools (NS).

Map of overall Influenza activity level by provinces and territories, Week 6, 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 6, the national ILI consultation rate was 11 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 similar ILI consultation rates compared to their respective ILI rates in the previous week. Those under 20 years of age still had the highest consultation rates, with 64 and 13 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 6, no laboratory-confirmed influenza-associated paediatric (under 17 years of age) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. 1325* hospitalizations have been reported since week 17 (April 26): 97.0% 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.

During week 6, no report was received from the Canadian Nosocomial Infection Surveillance Program (CNISP) on influenza-associated adult (16 years of age or older) hospitalizations and deaths. 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. For these pandemic H1N1 2009 cases, most were among women (51%), 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 6 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 6, 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 increased to 27.0% during week 6. 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 (February 7 to February 13, 2010)						Cumulative (August 30, 2009 to February 13, 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	0	1	0	5867	2	5	5759	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	4	1	0	2	1	0	7906	3	0	3552	4351	6
QC	0	0	0	0	0	0	10689	1	44	10644	0	8
NB	0	0	0	0	0	0	1856	1	1	1835	19	0
NS	1	0	0	1	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	39035	7	52	33480	5496	14
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 6, antiviral prescription monitoring demonstrated a levelling-off in antiviral prescriptions in 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 February 7 to February 13, 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 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 for 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 212 countries and overseas territories or communities reported laboratory confirmed cases of pandemic H1N1 2009, including at least 15,292 deaths as of February 7, 2010. In the temperate zone of the Northern hemisphere, overall pandemic influenza activity continued to decline in most countries. The most active areas of transmission continue to be in later peaking areas, particularly Northern Africa, South Asia, and East Asia. In Europe, although pandemic influenza virus continues to circulate widely, particularly across central, southern, and eastern Europe, the overall intensity of pandemic influenza activity has declined substantially from peaks of activity seen earlier during the winter transmission period. 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. 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 are circulating in parts of Africa, East and Southeast Asia and are being detected only sporadically in other continents.
<http://www.who.int/csr/don/2010_02_12/en/index.html> and
<http://www.who.int/csr/disease/swineflu/laboratory12_02_2010/en/index.html>

Antiviral resistance: To date, 245 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/laboratory12_02_2010/en/index.html>

Geographic update

United States: During week 5 (January 31-February 6, 2010), influenza activity remained at approximately the same levels as last week in the United States. 4.8% of the specimens tested this week were positive for influenza. While no states reported widespread influenza activity, 6 states reported regional influenza activity, Puerto Rico and 11 states reported local activity and the majority of the states reported sporadic influenza activity. The proportion of outpatient visits for influenza-like illness (ILI) was 2.1% which was below the national baseline of 2.3%. Three of 10 regions reported ILI above region-specific baseline levels. The proportion of deaths attributed to pneumonia and influenza decreased slightly over the previous week and remained below the epidemic threshold for this time of the year. Three influenza-associated pediatric deaths were reported during week 5: two 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/>

Europe: In Europe for week 5/2010 (February 1-7, 2010), the pandemic H1N1 2009 was well past its peak. In eight countries (Austria, Bulgaria, Czech Republic, Germany, Greece, Italy, Malta, Slovakia), local or regional transmission of the pandemic virus continues at low to medium intensity. Elsewhere intensity was low, but sporadic transmission of the pandemic virus was reported in the majority of countries. For the majority of countries that reported age-specific incidence of ILI, the most affected age group was 0–14. The number of reported SARI (severe acute respiratory illness) cases continued to decline. Of the 62 SARI cases reported this week, 30 (48%) were known to have required ICU admission and 16 (24%) needed ventilator support. Of the 39 SARI cases for whom underlying conditions were reported, 9 (23%) had no known underlying condition. Asthma and other chronic lung diseases alone or associated with other conditions were reported in 12 (31%) cases. Of the 910 specimens collected by sentinel physicians, 76 (8.4%) were positive for influenza virus, mainly the pandemic virus; this is consistent with a declining trend. Since their peak in week 01/2010, the total number of respiratory syncytial virus (RSV) detections in 11 countries has been decreasing. However in Austria, Denmark, Estonia, Germany, Latvia and Sweden, the number of RSV positive samples has increased for at least two consecutive weeks. In contrast to the pandemic virus there is currently no evidence of virus circulation due to other influenza A viruses this week, but there is some circulation of influenza B viruses.
<http://ecdc.europa.eu/en/publications/Publications/100212_EISN_Weekly_Influenza_Surveillance_Overview.pdf>

Asia: In South and Southeast Asia, pandemic influenza virus continues to circulate widely across the region, however, overall activity continues to decrease or remain low in most places. In India, influenza activity continued to decline in all regions of the country, however, the most active areas of transmission are currently in the western states. In Thailand, overall activity remains low, although focal areas of increased ILI activity were reported in central and northern Thailand. In East Asia, pandemic influenza transmission remains geographically widespread across the region, however, overall activity continued to decline. In China, pandemic and seasonal influenza viruses continue to co-circulate, however, over the last several weeks, seasonal influenza type B viruses have been predominant. In Japan, influenza activity continues to decrease towards seasonal baselines, including in Okinawa which is experiencing greater levels of influenza activity than other parts of the country. In Republic of Korea (S. Korea), levels of ILI have decreased substantially to near baseline levels. 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 are circulating in parts of East and Southeast Asia.
<http://www.who.int/csr/don/2010_02_12/en/index.html>

Real-time weekly and cumulative numbers of deaths due to pandemic H1N1 2009, by province/territory, Canada, as of February 18, 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