Influenza activity in Canada continues to decline; sporadic laboratory detections and a few outbreaks still occurring
During week 19, 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 ON, QC & NS)(see map). In week 19, the percentage of specimens that tested positive for influenza declined to 8.5% (219/2,575) for Canada (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 9 ILI consultations per 1,000 patient visits (see ILI graph), which is within the expected range for this week. The sentinel response rate was 49%. Three new outbreaks of influenza were reported this week; all were in LTCFs.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,256 influenza viruses for the 2007-2008 influenza season: 455 (36%) A(H1N1), 204 (16%) A(H3N2) and 597 (48%) 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 204 influenza A(H3N2) viruses characterized, 9 (4%) were antigenically similar to A/Wisconsin/67/2005 and 195 (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 597 influenza B isolates characterized, 15 (3%) were antigenically similar to B/Malaysia/2506/2004 and 582 (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 923 influenza A isolates (537 H1N1 and 386 H3N2) for amantadine resistance and found that 384 (99%) of the 386 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 1,279 influenza isolates (478 A/H1N1, 208 A/H3N2 & 593 B) for oseltamivir (Tamiflu) resistance and found that 125 (26%) of the 478 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 19, there were 5 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from BC, AB, ON & QC of which 3 (60%) were due to influenza B. Of the 469 hospitalizations reported so far this season, 63% (296/469) have been due to influenza A. The proportion of cases to date by age group are as follows: 21% were 0-5 month olds; 25% 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:

WHO: During weeks 18–19, the level of overall influenza activity in the world was low. Countries in the northern hemisphere reported sporadic or no activity. In the southern hemisphere, a few countries detected a slight increase in the level of influenza activity.

• WHO

CDC: During week 18, influenza activity continued to decrease in the United States with the majority of indicators having declined from the previous week. Since September 30, 2007, CDC antigenically characterized 794 influenza viruses: 381 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), 193 influenza A(H3) (47 A/Wisconsin/67/2005-like, 127 A/Brisbane/10/2007-like and 19 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 6.9% (101/1,474) of all influenza viruses tested (11.1% among H1N1 viruses tested). To date, CDC has received a total of 69 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: May 4, 2008 to May 10, 2008				Season to Date: August 26, 2007 to May 10, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	44	5	1	6	1313	78	133	211
PE	5	0	0	0	156	3	26	29
NS	34	5	4	9	1030	122	99	221
NB	41	1	8	9	1503	108	192	300
QC	682	19	38	57	29113	2205	1117	3322
ON	843	46	60	106	33738	2431	1710	4141
MB	51	0	3	3	2769	82	42	124
SK	97	1	4	5	5961	346	284	630
AB	728	13	4	17	29752	927	931	1858
BC	50	5	2	7	3560	586	475	1061
Canada	2575	95	124	219	108895	6888	5009	11897

 

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 4, 2008 to May 10, 2008 (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, 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=1,256]

{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