Influenza activity and laboratory detections in Canada continue to decline
During week 20, overall influenza activity in Canada continued to decline. Fewer regions reported localized activity this week (7 regions from BC, AB, MB & ON) compared to the previous weeks and the majority of the provinces and all of the territories reported only either sporadic activity or no activity in their regions (see map). In week 20, the percentage of specimens that tested positive for influenza declined to 4.8% (102/2,137) for Canada as a whole; and regionally ranged from 25% in NS to 0% in PEI (see table). To date this season, 58% of influenza detections in Canada were for influenza A viruses and 42% were for influenza B viruses. This week, the ILI consultation rate was 13 ILI consultations per 1,000 patient visits (see ILI graph), which is slightly above the expected range for this week. The sentinel response rate was 43%. Five new outbreaks of influenza were reported this week; four were in LTCFs and there was one other.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,281 influenza viruses for the 2007-2008 influenza season: 461 (36%) A(H1N1), 218 (17%) A(H3N2) and 602 (47%) B viruses. Of the 461 influenza A(H1N1) viruses characterized, 439 (95%) were antigenically similar to A/Solomon Islands/3/2006 and 22 (5%) were antigenically similar to A/Brisbane/59/2007. Of the 218 influenza A(H3N2) viruses characterized, 9 (4%) were antigenically similar to A/Wisconsin/67/2005 and 209 (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 602 influenza B isolates characterized, 16 (3%) were antigenically similar to B/Malaysia/2506/2004 and 586 (97%) 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 946 influenza A isolates (538 H1N1 and 408 H3N2) for amantadine resistance and found that 406 (99.5%) of the 408 H3N2 isolates were resistant to amantadine and 6 (1%) of 538 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 1,301 influenza isolates (481 A/H1N1, 221 A/H3N2 & 599 B) for oseltamivir (Tamiflu) resistance and found that 125 (26%) of the 481 H1N1 isolates tested were resistant to oseltamivir. The resistant isolates were from NL, NS, NB, QC, ON, MB, SK, AB and BC. Of the 125 resistant viruses, 121 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 20, there were 2 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from ON & QC; 1 was due to influenza A and the other due to influenza B. Of the 478 hospitalizations reported so far this season, 63% (301/478) have been due to influenza A. The proportion of cases to date by age group are as follows: 21% 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. Since the start of the season, 2 influenza-associated pediatric deaths have been reported to PHAC.

International:

CDC: During week 19, influenza activity continued to decrease in the United States. Since September 30, 2007, CDC antigenically characterized 881 influenza viruses: 381 (43%) influenza A(H1) (261 A/Solomon Islands/3/2006-like, 20 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 100 were A/Brisbane/59/2007-like), 280 (32%) influenza A(H3) (59 A/Wisconsin/67/2005-like, 182 A/Brisbane/10/2007-like and 39 showed somewhat reduced titers with antisera produced against A/Wisconsin and A/Brisbane), and 220 (25%) 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 6.7% (106/1,591) of all influenza viruses tested (10.9% among H1N1 viruses tested). To date, CDC has received a total of 71 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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Notice: This is the last weekly FluWatch report for the 2007-2008 influenza season and bi-weekly reporting will commence on June 6th 2008 (for weeks 21 and 22). However, influenza laboratory detections through the RVDSS and influenza activity level maps will be updated weekly on the website.
<http://www.phac-aspc.gc.ca/fluwatch/index-eng.php>

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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: May 11, 2008 to May 17, 2008				Season to Date: August 26, 2007 to May 17, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	61	5	0	5	1374	83	133	216
PE	0	NA	0	0	156	3	26	29
NS	16	1	3	4	1046	123	102	225
NB	27	0	1	1	1530	108	193	301
QC	621	17	12	29	29734	2222	1129	3351
ON	607	21	23	44	34345	2452	1733	4185
MB	49	3	0	3	2818	85	42	127
SK	127	3	2	5	6112	349	287	636
AB	584	4	4	8	30336	931	935	1866
BC	45	3	0	3	3605	589	475	1064
Canada	2137	57	45	102	111056	6945	5055	12000

 

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, May 11, 2008 to May 17, 2008 (Week 20)
	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=1,281]

{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