Overall influenza activity declined slightly from previous week; influenza B detections continue to increase steadily
During week 15, overall influenza activity in Canada declined slightly from the previous week: 2 regions reported widespread influenza activity (in ON and QC) and localized influenza activity reported by 21 regions. Six regions reported no activity and 25 reported sporadic activity (see map). In week 15, the percentage of specimens that tested positive for influenza increased slightly to 18.2% (880/4,822) for Canada as a whole; and regionally ranged from 34% in NS to 5% in MB (see table). The proportion of influenza B virus detections continue to increase steadily whereas the proportion of influenza A virus detections have remained fairly stable over the last several weeks. This week, the ILI consultation rate was 28 ILI consultations per 1,000 patient visits see ILI graph), which is above the expected range for this week. The sentinel response rate was 58%. Twenty-eight new outbreaks of influenza or ILI were reported this week as follows: 16 LTCFs and 12 schools.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,078 influenza viruses for the 2007-2008 influenza season: 440 (41%) A(H1N1), 147 (14%) A(H3N2) and 491 (46%) B viruses. Of the 440 influenza A(H1N1) viruses characterized, 422 (96%) were antigenically similar to A/Solomon Islands/3/2006 and 18 (4%) were antigenically similar to A/Brisbane/59/2007. Of the 147 influenza A(H3N2) viruses characterized, 6 (4%) were antigenically similar to A/Wisconsin/67/2005 and 141 (96%) were antigenically similar to A/Brisbane/10/2007. One of the 6 A/Wisconsin-like viruses had reduced titer to A/Wisconsin/67/2005 reference antiserum. Of the 491 influenza B isolates characterized, 8 (2%) were antigenically similar to B/Malaysia/2506/2004 and 483 (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 806 influenza A isolates (515 H1N1 and 291 H3N2) for amantadine resistance and found that 289 (99%) of the 291 H3N2 isolates were resistant to amantadine and 5 (1%) of 515 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 1,069 influenza isolates (454 A/H1N1, 146 A/H3N2 & 469 B) for oseltamivir (Tamiflu) resistance and found that 107 (23.6%) of the 454 H1N1 isolates tested were resistant to oseltamivir. The resistant isolates were from NL, NS, NB, QC, ON, MB, AB and BC. Of the 107 resistant viruses, 105 were A/Solomon Islands/3/06/-like and 2 were A/Brisbane/59/07-like. These oseltamivir resistant strains remain sensitive to the antiviral amantadine.

Influenza-associated Paediatric Hospitalizations:
In week 15, there were 13 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from BC, AB, ON, QC and NS of which 10 (77%) were due to influenza A. Of the 398 hospitalizations reported so far this season, 63% (251/398) 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, 1 influenza-associated pediatric death has been reported to PHAC.

International:

CDC: During week 14, influenza activity and laboratory detections for influenza continued to decrease in the United States. Since September 30, 2007, CDC antigenically characterized 608 influenza viruses: 290 influenza A(H1) (200 A/Solomon Islands/3/2006-like, 20 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 70 were A/Brisbane/59/2007-like), 161 influenza A(H3) (35 A/Wisconsin/67/2005-like, 115 A/Brisbane/10/2007-like and 11 showed somewhat reduced titers with antisera produced against A/Wisconsin and A/Brisbane), and 157 influenza B viruses (8 belonging to the B/Victoria and 149 B/Yamagata lineage). Small numbers of influenza viruses resistant to oseltamivir have been detected in the United States, representing 7.3% (84/1,153) of all influenza viruses tested (10.2% among H1N1 viruses tested). To date, CDC has received a total of 65 reports of influenza-associated pediatric deaths that occurred this season.

• CDC

EISS: Influenza activity has returned to low levels in all countries across Europe. Influenza virus type B accounted for 82% of the total positive specimens collected in week 15/2008. However the majority of virus detections since the start of the season has been influenza A(H1N1) viruses. Influenza A(H1N1) viruses resistant to oseltamivir have been found in 19 countries in Europe with an overall prevalence of 24% (570/2409).

• EISS

Human Avian Influenza: Since 12 April 2008, the WHO reported 2 additional cases (1 fatal) of H5N1 avian influenza infection from Egypt.

• WHO

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 6 to April 12, 2008				Season to Date: August 26, 2007 to April 12, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	57	5	8	13	1064	63	122	185
PE	9	0	2	2	125	2	18	20
NS	99	18	16	34	818	85	70	155
NB	159	11	38	49	1105	100	156	256
QC	1519	101	121	222	24696	2008	778	2786
ON	1566	213	231	444	28275	1981	1092	3073
MB	94	2	3	5	2521	80	33	113
SK	252	14	6	20	5375	331	273	604
AB	933	37	20	57	26364	851	904	1755
BC	134	17	17	34	3269	533	446	979
Canada	4822	418	462	880	93612	6034	3892	9926

 

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 6 to April 12, 2008 (Week 15)
	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=1,078]

{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