May 24, 2009 to May 30, 2009 (Week 21)

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Overall influenza activity remains similar from previous week
During week 21, ILI consultation rates and the proportion of tests positive for influenza are still higher than expected for this time of the year. However, activity level and number of new outbreaks were similar to the previous week. Seven regions in BC, AB, ON & NB reported localized activity, 35 regions in BC, AB, SK, MB, ON, QC, NB, NS, NL, NT & NU sporadic activity, and 12 regions in NB, PEI, NS, NL, YK, NT & NU reported no activity (see map). This week, the ILI consultation rate increased to 24 consultations per 1,000 patient visits (see ILI graph) which is higher than expected for this time of year. The proportion of tests positive for influenza was 8.5%. This is less than what was reported in the previous week but still relatively high compared to weeks 14 to 19* (see table). The majority (66.5%) of influenza virus detections this season have been for influenza A. Three new influenza outbreaks were reported; one occurred in a LTC facility in BC, one in a school in NB and one in unspecified location in SK.
*There was a substantial increase in positive tests from week 20 not previously reported that was due to late reporting from provincial laboratories.

H1N1 Flu Virus
As of June 4, 2009 (15:00 EDT), a total of 1,795 laboratory-confirmed cases of the H1N1 Flu Virus were reported in all provinces and territories except Newfoundland. Among cases with information available (n=1,695), the median age was 17 years (range <1 to 80 years) and 57.8% were between 10-29 years. 5.9% cases were 0-4 years, 10.6% cases were 5-9 years of age, and 0.7% were ≥65 years old. Information on travel history was not available for 165 cases (9.2%) and of the remaining 1,630 cases only 182 (10.7%) reported a history of travel in the 7 days prior to symptom onset. Eighty-four cases have been hospitalized: British Columbia (3), Alberta (6), Saskatchewan (4), Manitoba (3), Ontario (24), Quebec (41), and Nunavut (3). The median age of hospitalized cases was 17 years (range 1 to 78 years). Thirteen (15.5%) hospitalized cases were admitted to the ICU. Age distribution was as follows: 1 case <1 year, 2 cases were 5-9 years, 4 cases were 10-19 years, 6 cases were 20-54 years. Information regarding underlying medical conditions was available for 40 (47.6%) hospitalized cases. Twelve (30.0%) had underlying medical conditions; lung disease (3 cases), chronic heart disease (2 cases) and other underlying medical conditions were reported in 7 cases. One hospitalized case was pregnant. Three deaths have been reported: a 39 year-old female in Alberta and 2 males aged 44 and 59 in Ontario.

Antigenic Characterization:

*No update from the NML for this week.

Since 1 September 2008, the NML has antigenically characterized 953 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), 167 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 June 4, 2009 the NML tested 254 specimens for influenza H1N1 Flu Virus and 153 were positive. Positive samples were from AB, SK, MB, ON, QC, NB, PEI and NS. *Provincial labs are also doing their own confirmation using RT-PCR.

Antiviral Resistance:

*No update from the NML for this week.

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; 252 (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.

Forty H1N1 Flu Virus isolates have been tested for resistance to amantadine, 56 for oseltamivir and 8 for zanamivir. The testing results showed all were resistant to amantadine but suspectible to oseltamivir and zanamivir.

Influenza-associated Paediatric Hospitalizations:
In week 21, ten laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. Three were type A (all in MB) and seven were H1N1 Flu Virus (1 BC, 3 ON and 3 QC). Since its emergence there have been 19 hospitalizations due to H1N1 Flu Virus. This season there has been 448 hospitalizations in total, this is within the normal range for this time of year (range 340- 474); 53.8% of hospitalizations were due to influenza A. The proportion of cases to date by age group are as follows: 13.5% were 0-5 month olds; 31% were 6-23 month olds; 23% were 2-4 year-olds; 16.5% were 5-9 year-olds; and 16% were 10-16 year-olds. The distribution of cases to date by province are as follows: 9% from BC, 9% from AB, 5% from SK, 5% from MB, 29% from ON, 40% from QC, 2.5% from NS & 0.5% from NL.

International:

CDC: During week 20 (May 17-23, 2009), influenza activity decreased in the U.S, however there are still higher levels of influenza-like illness than is normal for this time of year. 1,423 specimens tested positive for influenza A (77%) were positive for H1N1 Flu Virus. One-hundred and thirty-nine samples of H1N1 Flu Virus were tested for antiviral resistance. None were resistant to Oseltamivir or Zanamivir. Of 119 samples tested for resistance to Adamantanes 100% were resistant. One influenza -associated pediatric death was reported this week due to influenza A. The death reported this week occurred during week 5 (the week ending February 7, 2009). Bacterial co-infections were observed in 13 (42%) of children and Staphylococcus aureus was identified in eight (62%) of children tested.

• CDC

EISS: In week 22 (May 25-31, 2009), the regular influenza season can be considered to be over. Meanwhile, a 99% increase in recorded cases of H1N1 Flu Virus infections in the European region compared to the previous week has brought the total to 937 (as of 4 June). 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. For the geographical spread indicator, all countries but Italy (local activity) reported sporadic or no activity. All novel influenza A (H1N1) viruses tested were sensitive to oseltamivir and zanamivir but resistant to M2 inhibitors.

• EISS

Human Avian Influenza: During week 21, the WHO reported two new cases of 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 24, 2009 to May 30, 2009				Season to Date: August 24, 2008 to May 30, 2009
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	12	0	1	1	1212	128	26	154
PE	2	0	0	0	221	17	9	26
NS	53	4	1	5	2149	100	60	160
NB	120	0	0	0	2219	267	95	362
QC	1016	90	3	93	38577	2596	1411	4007
ON	1742	103	4	107	36436	1986	1346	3332
MB	211	46	2	48	3104	147	37	184
SK	333	75	2	77	6954	505	218	723
AB	790	34	3	37	35396	1035	460	1495
BC	200	11	1	12	6999	911	208	1119
Canada	4479	363	17	380	133267	7692	3870	11562

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 24, 2009 to May 30, 2009 (Week 21)
	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=1047]

{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