Influenza activity in Canada increasing in the West; a few oseltamivir-resistant A(H1N1) strains detected in Canada and Europe
During week 04, overall influenza activity levels in Canada increased steadily from previous weeks. In week 04, more regions reported widespread (n=4 from BC and AB) and localized influenza activity (n=8 from BC, AB, SK, MB, ON, & NB) compared to previous weeks. Eighteen regions reported no activity and 25 reported sporadic activity (see map). Note: No data was received from PEI this week. In week 04, the number of specimens that tested positive for influenza was 9% (351/3,884). Of the influenza detections to date, 77% were influenza A and 23% were influenza B (see table). Although influenza A detections continue to predominate in most provinces, influenza B detections have increased steadily over recent weeks; particularly in AB where 56% of influenza detections in the province to date were for influenza B viruses. This week, the ILI consultation rate was 21 ILI consultations per 1,000 patient visits(see ILI graph), which is within the expected range for this week. The sentinel response rate was 66%. Thirty-two new outbreaks of influenza or ILI were reported this week as follows: 6 LTCFs, 1 hospital, 24 schools, and 1 other.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 243 influenza viruses for the 2007-2008 influenza season: 171 A(H1N1), 17 A(H3N2) and 55 B viruses. All influenza A(H1N1) viruses were antigenically similar to A/Solomon Islands/3/2006. Of the 17 influenza A(H3N2) viruses characterized, 5 were antigenically similar to A/Wisconsin/67/2005 and 12 were antigenically similar to A/Brisbane/10/2007. One of the 5 A/Wisconsin-like viruses had reduced titer to A/Wisconsin/67/2005 reference antiserum. Of the 55 influenza B isolates characterized, 3 were antigenically similar to B/Malaysia/2506/2004 and 52 were antigenically similar to B/Florida/4/2006 (belonging to the B/Yamagata lineage) (see pie chart).

Antiviral Resistance:
Since the start of the season, the NML has tested 188 influenza A isolates (163 H1N1 and 25 H3N2) for amantadine resistance and found that 23 (92%) of the 25 H3N2 isolates were resistant to amantadine and 4 (2.5%) of 163 H1N1 isolates was resistant (see recommendation from the 2006-2007 influenza season below).
NML also tested 184 influenza isolates (128 A/H1N1, 15 A/H3N2 & 41 B) for oseltamivir (Tamiflu) resistance and found that 8 (6.3%) of the 128 H1N1 isolates tested was resistant to oseltamivir.
The resistant isolates were from NF (1), ON (6) and BC (1). These oseltamivir resistant strains remain sensitive to the antiviral amantadine. PHAC is collaborating with provincial and territorial and international partners in monitoring, reporting and assessing the implications of the findings. While antivirals can be used to lessen the length and severity of influenza, vaccination remains the most effective method of preventing illness. This year's influenza vaccine protects against influenza A(H1N1) and therefore vaccination remains an effective measure in preventing illness.

Influenza-associated Paediatric Hospitalizations:
No new laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network this week.

International:

WHO: During weeks 2–3, the level of overall influenza activity in the world increased slightly. An increase in both influenza activity and the number of influenza viruses detected was observed in most countries of northern Europe and North America, where mostly influenza A (H1N1) virus circulated.

• WHO

CDC: During week 03, influenza activity continued to increase in the United States with more regions reporting widespread and regional activity. The proportion of specimens that tested positive for influenza virus increased to 11.1% this week. The majority of influenza detections to date were for influenza A viruses (85%). Since September 30, 2007, CDC antigenically characterized 197 influenza viruses: 101 influenza A(H1) (all A/Solomon Islands/3/2006), 53 influenza A(H3) (6 A/Wisconsin/67/2005-like and 46 A/Brisbane/10/2007-like, and 1 showed somewhat reduced titers with antisera produced against A/Wisconsin and A/Brisbane), and 43 influenza B viruses (3 belonging to the B/Victoria and 40 B/Yamagata lineage).

• CDC

EISS: In week 4, 18 countries are currently reporting a medium or high intensity of influenza activity. Although influenza A(H1) is the dominant virus strain circulating in Europe this season, influenza B still represents 19% of the total influenza virus detections since the start of the season. A significant proportion (14%) of the A(H1N1) viruses circulating in Europe were resistant to oseltamivir with resistant viruses found in 9 European countries.

• EISS

Human Avian Influenza: Since 26 January 2008, the WHO reported 4 additional cases (3 fatal) of H5N1 avian influenza infection from Indonesia.

• 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: January 20 to January 26, 2008				Season to Date: August 26, 2007 to January 26, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	39	2	0	2	226	15	0	15
PE	0	0	0	0	38	0	0	0
NS	26	1	1	2	256	2	2	4
NB	16	0	0	0	287	1	1	2
QC	858	48	7	55	8315	161	24	185
ON	1284	73	4	77	12351	657	24	681
MB	60	4	0	4	1484	6	1	7
SK	218	11	9	20	2502	56	33	89
AB	1209	61	82	143	14094	197	252	449
BC	174	45	3	48	1296	165	34	199
Canada	3884	245	106	351	40849	1260	371	1631

 

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, 20 January to 26 January, 2008 (Week 4)
	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=243]

{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