May 10, 2009 to May 16, 2009 (Week 19)

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Overall influenza activity decreased slightly from previous week
During week 19 the reported activity level, consultations rates, number of new outbreaks and proportions of positive tests decreased. Ten regions in BC, AB, SK, ON & NF reported localized activity, 33 regions sporadic activity in BC, AB, SK, MB, ON, QC, NB, PE, NS, NL, YK, NWT & NU and 10 regions in MB, ON, NB, NS, NWT & NU reported no activity (see map). This week, the ILI consultation rate decreased to 15 consultations per 1,000 patient visits (see ILI graph) which is within the expected range for this time of year. The sentinel response rate was 52.4%. The proportion of tests that were positive for influenza was 4.1% which is similar to the two previous weeks (see table). The majority (62.9%) of influenza virus detections this season have been for influenza A. Seven new influenza outbreaks were reported this week; three were in LTCFs (BC, AB, SK), three were in schools (BC, AB, SK) and one occured in unspecified locations in AB.

H1N1 Flu Virus (Human Swine Flu)
As of May 20, 2009 (15:00 EDT), a total of 719 laboratory-confirmed cases of the H1N1 Flu Virus (Human Swine Flu) were reported from all but three jurisdictions in Canada (NL, NU, and NWT). Among cases with information available, (n=650), the median age was 21 years and 406 (62.5%) were between 10-29 years of age. Thirty-one (4.7%) cases were 0-4 years, 63 (9.7%) cases were 5-9 years of age, and 5 (0.8%) were >=65 years old. Typically influenza illness is observed in the very young (0-4 years) and older (>=65 years) age groups. Information on travel history was not available for 105 cases (16.2%) and of the remaining 545 cases, 161 (29.5%) reported a history of travel in the 7 days prior to symptom onset while 384 (70.5%) did not. Information on hospitalizations was available for 299 cases of which 17 cases (5.7%) had been hospitalized [BC (3; 18%), AB (4; 24%), MB (1; 6%), ON (7; 41%), and QC (2; 12%)]. The median age of hospitalized cases was 25 years compared to 17 years among non-hospitalized cases and 21 years among all reported cases. Globally there have been 11,168 cases of Influenza A (H1N1) and 86 deaths reported in 42 countries.

Antigenic Characterization:
Since 1 September 2008, the NML has antigenically characterized 950 influenza viruses: 239 influenza A/Brisbane/59/2007(H1N1)-like (from BC, AB, SK, MB, ON, QC, NB, NS & PEI), 163 influenza A/Brisbane/10/2007(H3N2)-like (from BC, AB, SK, MB, ON, QC, NB, PEI & NL), 11 influenza B/Florida/4/2006-like (from AB, ON, QC & NB), 164 B/Brisbane/60/2008-like (from BC, AB, SK, MB, ON, QC, NB, NL & NU) and 373 B/Malaysia/2506/2004-like (in all provinces except the Territories). A/Brisbane/59/2007(H1N1), A/Brisbane/10/2007(H3N2) and B/Florida/04/2006 are the influenza A and influenza B components recommended for the 2008-09 influenza vaccine. B/Malaysia/2506/2004 was the influenza B component for the 2007-2008 season vaccine (see pie chart). B/Brisbane/60/2008-like is the recommended influenza B component for the 2009-2010 season vaccine.

As of May 21, 2009 the NML has confirmed 94 specimens positive for Influenza H1N1 Flu Virus (Human Swine Flu). Positive samples were from AB, SK, MB, ON, QC, NB, PEI, NS. *Provincial labs have also been doing their own confirmation using RT-PCR.

Antiviral Resistance:

Results from the NML:

Since the start of the season, the NML has tested 562 influenza A isolates (257 H1N1 and 305 H3N2) for amantadine resistance. All of the H1N1 isolates were susceptible; all of the H3N2 isolates were resistant to amantadine (resistance = 100%). The resistant isolates were from BC, AB, SK, MB, ON, QC, NB, PEI, NL & NT. The NML has also tested 930 influenza isolates (253 A/H1N1, 166 A/H3N2 & 511 type B) for oseltamivir (Tamiflu) resistance. All of the A/H3N2 and B isolates were sensitive; however 99.6% of the A/H1N1 isolates were resistant to oseltamivir due to the H274Y mutation. The resistant isolates were from BC, AB, SK, MB, ON, QC, NB, NS, PEI & NL. All 875 influenza isolates (202 A/H1N1, 162 A/H3N2 & 511 B) tested for zanamivir resistance to date were sensitive to zanamivir. *Antigenic characterization of the novel H1N1 Flu Virus (Human Swine Flu) viruses isolated in Canada indicates that these viruses are antigenically and genetically unrelated to seasonal influenza A (H1N1) viruses, which suggests that there is no protection to be expected from vaccination with the current seasonal influenza vaccine. Thirty-five novel A/H1N1 have been tested for resistance to amantadine and 56 novel A/H1N1 for resistance to oseltamivir. The testing results showed that all were resistant to amantadine but sensitive to oseltamivir.

Influenza-associated Paediatric Hospitalizations:
In week 19, three laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network one from ON (type A), and two (1 in AB and 1 in QC) H1N1 Flu Virus (Human Swine Flu). Since its emergence a total of four hospitalizations have been associated with the H1N1 Flu Virus (Human Swine Flu). To date this season, 422 hospitalizations have been reported, this is similar to the number of hospitalizations seen at this same time during the past five years (range 334- 469); 54.7% of hospitalizations have been due to influenza A. The proportion of cases to date by age group are as follows: 14% were 0-5 month olds; 31% were 6-23 month olds; 23% were 2-4 year-olds; 16% were 5-9 year-olds; and 16% were10-16 year-olds. The distribution of cases to date by province are as follows: 10% from BC, 9% from AB, 4.5% from SK, 4.5% from MB, 28.5% from ON, 40% from QC, 3% from NS & 0.5% from NL.

International:

WHO: During the weeks 17-18, influenza seasonal activity continued to decrease in the northern hemisphere. More countries in the southern hemisphere reported sporadic activity due to H1, H3 or B than in previous weeks. Mexico reported regional activity due to the new influenza A (H1N1) virus and low level B activity.

• WHO

CDC: During week 18 (May 3-May 9, 2009), influenza activity remained at approximately the same level as last week in the United States, indicating that there are higher levels of influenza-like illness than is normal for this time of year. 1,452 specimens tested positive for influenza, of which 88.4% were influenza A and 11.6% were influenza B. The proportion of outpatient visits for influenza-like illness (ILI) was above the national baseline. Testing for antiviral resistance indicated that of the influenza virus A/H1N1 tested, 99.4% (860/865) were resistant to oseltamivir and 0.5% (4/876) resistant to amantadine. Of the influenza A/H3N2 viruses tested for resistance, 100% (145/145) were resistant to amantadine. All tested viruses remain sensitive to zanamivir. To date this season, 59 influenza-associated pediatric deaths have been reported to the CDC. Three deaths were reported this week in Arizona, California and Texas. Bacterial co-infections were confirmed in 13 (43.3%) of 30 tested children; Staphylococcus aureus was identified in 8 (61.5%) of 13 tested children.

• CDC

EISS: In week 20 (May 11-May 17, 2009), influenza activity remained at or below baseline levels in almost all of Europe. For the intensity indicator, the national network levels of influenza-like illness (ILI) and/or acute respiratory infection (ARI) were low in all countries that reported this indicator, with only one region (Urals) of the Russian Federation reporting medium intensity. For the geographical spread indicator, all countries reported sporadic or no activity. Influenza A(H3N2) has been the dominant virus in Europe this season, accounting for an estimated 67% of total virus detections this season. Of the 644 A(H3N2) isolates that were tested for adamantanes susceptibility, 644 (100%) were resistant. Of the 259 A(H1N1) virus isolates tested for resistance against neuraminidase inhibitors, 255 (98%) were resistant to oseltamivir, but all were sensitive to zanamivir.

• EISS

Human Avian Influenza: During week 19, the WHO reported one new case of human H5N1 avian influenza infection in Egypt.

• WHO

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Total number of influenza tests performed and number of positive tests by province/territory of testing laboratory, Canada, 2008-2009

Province of reporting laboratories	Report Period: May 10, 2009 to May 16, 2009				Season to Date: August 24, 2008 to May 16, 2009
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	55	5	0	5	1178	128	25	153
PE	16	0	0	0	215	17	9	26
NS	175	9	0	9	2021	94	59	153
NB	121	2	2	4	2053	267	94	361
QC	1076	51	2	53	36480	2449	1406	3855
ON	1224	35	3	38	31827	1246	1341	2587
MB	161	10	0	10	2704	87	35	122
SK	378	60	4	64	6290	324	207	531
AB	2660	38	27	65	33049	981	445	1426
BC	1587	52	8	60	6554	885	207	1092
Canada	7453	262	46	308	122371	6478	3828	10306

Specimens from NT, YT, and NU are sent to reference laboratories in other provinces.

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.

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)

Respiratory virus laboratory detections in Canada, by geographic regions, are available weekly on the following website:
<http://www.phac-aspc.gc.ca/bid-bmi/dsd-dsm/rvdi-divr/index-eng.php>

Number of influenza surveillance regions^† reporting widespread or localized influenza activity, Canada, by report week, 2008-2009 (N=54)

† sub-regions within the province or territory as defined by the provincial/territorial epidemiologist. Graph may change as late returns come in.

Influenza Activity Level by Provincial and Territorial Influenza Surveillance Regions, Canada, May 10, 2009 to May 16, 2009 (Week 19)
	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 outbreaks. Please refer to detailed definitions. For areas where no data is reported, late reports from these provinces and territories will appear on the FluWatch website. Select single maps by report week to get this updated information.
<http://dsol-smed.phac-aspc.gc.ca/dsol-smed/fluwatch/fluwatch.phtml?lang=e>

Click on the map to view provinces/territories and maps for other weeks.

Influenza tests reported and percentage of tests positive, Canada, by report week, 2008-2009

Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2008-2009

Influenza strain characterization, Canada, cumulative, 2008-2009 influenza season by the Respiratory Viruses Section at the National Microbiology Laboratory
[N=1044]

{Strain characterization, number identified, per cent of total number}

NACI recommends that the trivalent vaccine for the 2008-2009 season in Canada contain
A/Brisbane/59/2007 (H1N1)-like virus; an A/Brisbane/10/2007 (H3N2)-like virus; and a B/Florida/4/2006-like virus.

Influenza-like illness (ILI) consultation rates, Canada, by report week,
2008-2009 compared to 1996/97 through to 2007/08 seasons

Note: No data available for mean rate in previous years for weeks 19 to 39 (1996-1997 through 2002-2003 seasons).

Number of New Outbreaks in Long Term Care Facilities, Canada, by Report Week, 2008-2009

Please note that the above graphs may change as late returns come in.

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Definitions for the 2008-2009 season