Influenza detections declined slightly this week
During week 13, overall influenza activity in Canada remained fairly similar to the previous week and moderate overall. Widespread influenza activity was reported by 4 regions (in BC, AB, ON and QC) and localized influenza activity by 17 regions (in BC, AB, SK, ON, QC, NB & NS). Three regions reported no activity and 30 reported sporadic activity (see map). In week 13, the percentage of specimens that tested positive for influenza declined slightly to 16% (759/4,708) for Canada as a whole; and regionally ranged from 50% in PEI to 4% in MB (see table). This week, the ILI consultation rate remained stable at 22 ILI consultations per 1,000 patient visits (see ILI graph), which is within the expected range for this week. The sentinel response rate was 52%. Twenty seven new outbreaks of influenza or ILI were reported this week as follows: 19 LTCFs, 3 hospitals, 1 school and 4 others.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 952 influenza viruses for the 2007-2008 influenza season: 425 (45%) A(H1N1), 111 (12%) A(H3N2) and 416 (44%) B viruses. Of the 425 influenza A(H1N1) viruses characterized, 407 (96%) were antigenically similar to A/Solomon Islands/3/2006 and 18 (4%) were antigenically similar to A/Brisbane/59/2007. Of the 111 influenza A(H3N2) viruses characterized, 5 (5%) were antigenically similar to A/Wisconsin/67/2005 and 106 (95%) 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 416 influenza B isolates characterized, 7 (2%) were antigenically similar to B/Malaysia/2506/2004 and 409 (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 672 influenza A isolates (473 H1N1 and 199 H3N2) for amantadine resistance and found that 197 (99%) of the 199 H3N2 isolates were resistant to amantadine and 5 (1%) of 473 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 852 influenza isolates (418 A/H1N1, 101 A/H3N2 & 333 B) for oseltamivir (Tamiflu) resistance and found that 81 (19.4%) of the 418 H1N1 isolates tested were resistant to oseltamivir. The resistant isolates were from NL, NS, NB, QC, ON, MB, AB and BC. These oseltamivir resistant strains remain sensitive to the antiviral amantadine.

Influenza-associated Paediatric Hospitalizations:
In week 13, there were 27 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from AB, ON, QC and NL of which 14 (52%) were due to influenza A. Of the 355 hospitalizations reported so far this season, 63% (224/355) have been due to influenza A. The proportion of cases to date by age group are as follows: 21% were 0-5 month olds; 27% were 6-23 month olds; 23% were 2-4 year-olds; 19% 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 12, influenza activity continued to decrease in the United States. Since September 30, 2007, CDC antigenically characterized 540 influenza viruses: 256 influenza A(H1) (175 A/Solomon Islands/3/2006-like, 19 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 62 were A/Brisbane/59/2007-like), 127 influenza A(H3) (21 A/Wisconsin/67/2005-like, 97 A/Brisbane/10/2007-like and 9 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 6.8% (71/1,045) of all influenza viruses tested (9.5% among H1N1 viruses tested). To date, CDC has received a total of 53 reports of influenza-associated pediatric deaths that occurred this season.

• CDC

 

EISS: All countries in Europe are reporting stable or declining levels of clinical influenza activity. Influenza virus detections are declining for Europe as a whole with 14 countries that reported zero virus detections in sentinel respiratory specimens collected in week 13/2008. Whilst influenza activity was predominantly caused by the influenza A(H1N1) virus during most of the season, in recent weeks (since week 09/2008) influenza B has been dominant in Europe. Influenza A(H1N1) viruses resistant to oseltamivir have been found in 19 countries in Europe with an overall prevalence of 23% (507/2216).

• EISS

Human Avian Influenza: Since 22 March 2008, the WHO reported 5 additional cases of H5N1 avian influenza infection. Three cases were reported from Indonesia of which 2 were fatal. The other 2 cases were retrospectively confirmed from an investigation that started in December 2007 in Pakistan.

• 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: March 23 to March 29, 2008				Season to Date: August 26, 2007 to March 29, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	38	2	6	8	913	51	110	161
PE	6	0	3	3	105	1	8	9
NS	81	12	11	23	624	46	46	92
NB	91	6	27	33	838	84	87	171
QC	1576	153	102	255	21613	1770	544	2314
ON	1420	143	131	274	25052	1585	626	2211
MB	78	2	1	3	2331	73	28	101
SK	252	17	29	46	4942	307	258	565
AB	1009	42	27	69	24415	781	863	1644
BC	157	16	29	45	3010	496	406	902
Canada	4708	393	366	759	83843	5194	2976	8170

 

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, March 23 to March 29, 2008 (Week 13)
	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=952]

{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