Influenza activity in Canada continues to decline
During week 18, overall influenza activity in Canada continued to decline. The majority of the provinces and all of the territories reported only either sporadic activity or no activity in their regions. Nine regions reported localized activity (from MB, NB, NS & ON) and only 2 regions (from ON & QC) reported widespread influenza activity (see map). In week 18, the percentage of specimens that tested positive for influenza declined to 10.5% (373/3,564) for Canada (see table). To date this season, 58.2% of influenza detections in Canada were for influenza A viruses and 41.8% were for influenza B viruses. This week, the ILI consultation rate declined to 10 ILI consultations per 1,000 patient visits (see ILI graph), which is slightly below the expected range for this week. The sentinel response rate was 57%. Seven new outbreaks of influenza or ILI were reported this week as follows: 4 LTCFs, 1 hospital, 1 school and 1 in another institution.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,236 influenza viruses for the 2007-2008 influenza season: 455 (37%) A(H1N1), 201 (16%) A(H3N2) and 580 (47%) B viruses. Of the 455 influenza A(H1N1) viruses characterized, 433 (95%) were antigenically similar to A/Solomon Islands/3/2006 and 22 (5%) were antigenically similar to A/Brisbane/59/2007. Of the 201 influenza A(H3N2) viruses characterized, 9 (4%) were antigenically similar to A/Wisconsin/67/2005 and 192 (96%) were antigenically similar to A/Brisbane/10/2007. One of the 9 A/Wisconsin-like viruses had reduced titer to A/Wisconsin/67/2005 reference antiserum. Of the 580 influenza B isolates characterized, 14 (2%) were antigenically similar to B/Malaysia/2506/2004 and 566 (98%) were antigenically similar to B/Florida/4/2006 (belonging to the B/Yamagata lineage)(see pie chart).

***The WHO recommends that the vaccines to be used in the 2008-2009 season (northern hemisphere) contain the following: an A/Brisbane/59/2007 (H1N1)-like virus; an A/Brisbane/10/2007 (H3N2)-like virus; and a B/Florida/4/2006-like virus.

• WHO

Antiviral Resistance:
Since the start of the season, the NML has tested 915 influenza A isolates (537 H1N1 and 378 H3N2) for amantadine resistance and found that 376 (99%) of the 378 H3N2 isolates were resistant to amantadine and 6 (1%) of 537 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 1,257 influenza isolates (476 A/H1N1, 207 A/H3N2 & 574 B) for oseltamivir (Tamiflu) resistance and found that 123 (26%) of the 476 H1N1 isolates tested were resistant to oseltamivir. The resistant isolates were from NL, NS, NB, QC, ON, MB, SK, AB and BC. Of the 123 resistant viruses, 119 were A/Solomon Islands/3/06/-like and 4 were A/Brisbane/59/07-like. These oseltamivir resistant strains remain sensitive to the antiviral amantadine.

Influenza-associated Paediatric Hospitalizations:
In week 18, there were 7 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from BC, ON, QC, and NS of which 4 (57%) were due to influenza B. Of the 445 hospitalizations reported so far this season, 64% (283/445) have been due to influenza A. The proportion of cases to date by age group are as follows: 22% were 0-5 month olds; 26% were 6-23 month olds; 23% were 2-4 year-olds; 20% were 5-9 year-olds; and 10% were 10-16 year-olds. An influenza-associated pediatric death due to influenza B was retrospectively reported from Alberta and occurred in week 9. Since the start of the season, 2 influenza-associated pediatric deaths have been reported to PHAC.

International:

WHO: During weeks 16–17, the level of overall influenza activity in the world decreased. Countries in the northern hemisphere reported reduced activity.

• WHO

CDC: During week 17, influenza activity continued to decrease in the United States. Since September 30, 2007, CDC antigenically characterized 730 influenza viruses: 330 influenza A(H1) (220 A/Solomon Islands/3/2006-like, 20 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 90 were A/Brisbane/59/2007-like), 180 influenza A(H3) (39 A/Wisconsin/67/2005-like, 123 A/Brisbane/10/2007-like and 18 showed somewhat reduced titers with antisera produced against A/Wisconsin and A/Brisbane), and 220 influenza B viruses (8 belonging to the B/Victoria and 212 B/Yamagata lineage). Small numbers of influenza viruses resistant to oseltamivir have been detected in the United States, representing 7.0% (95/1,361) of all influenza viruses tested (10.8% among H1N1 viruses tested). To date, CDC has received a total of 68 reports of influenza-associated pediatric deaths that occurred this season.

• CDC

Recommendation for the Use of Amantadine for Treatment and Prevention of Influenza
The Public Health Agency of Canada does not recommend the use of amantadine for treatment or prevention of influenza for the 2006-2007 season. This recommendation will be revisited if new information becomes available.

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Total number of influenza tests performed and number of positive tests by province/territory of testing laboratory, Canada, 2007-2008

Province of reporting laboratories	Report Period: April 27, 2008 to May 3, 2008				Season to Date: August 26, 2007 to May 3, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	100	2	3	5	1269	73	132	205
PE	7	1	2	3	151	3	26	29
NS	51	11	6	17	996	117	95	212
NB	189	1	11	12	1462	107	184	291
QC	1071	41	61	102	28431	2186	1079	3265
ON	987	70	112	182	32692	2376	1633	4009
MB	65	0	2	2	2718	82	39	121
SK	155	2	1	3	5840	345	279	624
AB	864	15	5	20	29024	914	927	1841
BC	75	18	9	27	3510	581	473	1054
Canada	3564	161	212	373	106093	6784	4867	11651

 

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, 2007-2008 (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, April 27, 2008 to May 3, 2008 (Week 18)
	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, 2007-2008

Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2007-2008

Influenza strain characterization, Canada, cumulative, 2007-2008 influenza season by the Respiratory Viruses Section at the National Microbiology Laboratory
[N=1,236]

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

NACI recommends that the trivalent vaccine for the 2007-2008 season in Canada contain A/Solomon Islands/3/2006 (H1N1)-like virus; an A/Wisconsin/67/2005 (H3N2)-like virus; and a B/Malaysia/2506/2004-like virus.

Influenza-like illness (ILI) consultation rates, Canada, by report week, 2007-2008 compared to 1996/97 through to 2006/07 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, 2007-2008

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

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Definitions for the 2007-2008 season