Influenza activity in Canada continues to decline; few regions still reporting localized influenza activity
During weeks 21 and 22, overall influenza activity in Canada continued to decline with the majority of the provinces and all of the territories reporting only either sporadic activity or no activity in their regions. However, a few regions still reported localized influenza activity in those weeks (see map). The percentage of specimens that tested positive for influenza declined to 2.73% (99/3,633) for Canada as a whole over the two-week period (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 4 ILI consultations per 1,000 patient visits (see ILI graph), which is well below the expected range for this week. The sentinel response rate was low at 35%. One new LTCF outbreak of influenza was reported this week.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,334 influenza viruses for the 2007-2008 influenza season: 463 (35%) A(H1N1), 231 (17%) A(H3N2) and 640 (48%) B viruses. Of the 463 influenza A(H1N1) viruses characterized, 441 (95%) were antigenically similar to A/Solomon Islands/3/2006 and 22 (5%) were antigenically similar to A/Brisbane/59/2007. Of the 231 influenza A(H3N2) viruses characterized, 12 (5%) were antigenically similar to A/Wisconsin/67/2005 and 219 (95%) were antigenically similar to A/Brisbane/10/2007. One of the 12 A/Wisconsin-like viruses had reduced titer to A/Wisconsin/67/2005 reference antiserum. Of the 640 influenza B isolates characterized, 17 (3%) were antigenically similar to B/Malaysia/2506/2004 and 623 (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 979 influenza A isolates (545 H1N1 and 434 H3N2) for amantadine resistance and found that 432 (99.5%) of the 434 H3N2 isolates were resistant to amantadine and 6 (1%) of 545 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 1,348 influenza isolates (486 A/H1N1, 231 A/H3N2 & 631 B) for oseltamivir (Tamiflu) resistance and found that 127 (26%) of the 486 H1N1 isolates tested were resistant to oseltamivir. Resistant isolates were detected in all 10 provinces. Of the 127 resistant viruses, 123 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 weeks 21 & 22, there were 2 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network: one from BC (influenza A) and the other from QC (influenza B). Of the 474 hospitalizations reported so far this season, 63% (298/474) 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:

WHO: During weeks 20–21, 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, influenza activity remained low or moderate.

• WHO

CDC: During week 20, influenza activity continued to decrease in the United States. Since September 30, 2007, CDC antigenically characterized 947 influenza viruses: 395 (42%) influenza A(H1) (267 A/Solomon Islands/3/2006-like, 20 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 108 were A/Brisbane/59/2007-like), 280 (30%) 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 272 (29%) influenza B viruses (8 belonging to the B/Victoria and 264 B/Yamagata lineage). To date, CDC has received a total of 72 reports of influenza-associated pediatric deaths that occurred this season.

• CDC

EISS: Low levels of influenza activity were reported in Europe. Influenza A (mostly of the H1N1 subtype) predominated in the first half of the season while influenza B was dominant toward the end of the season. There have been no reports of unusual influenza activity in Europe at a community level since week 16/2008.

• EISS

Human Avian Influenza: Since 24 May 2008, the WHO retrospectively reported the first case of H5N1 avian influenza infection in Bangladesh. The case is a 16-month-old male from Komalapur, Dhaka who developed symptoms on 27 January 2008 and subsequently recovered.

• 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: May 18, 2008 to May 31, 2008				Season to Date: August 26, 2007 to May 31, 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	1	0	1	1413	84	133	217
PE	8	0	0	0	164	3	26	29
NS	28	0	2	2	1074	123	104	227
NB	19	0	0	0	1549	108	193	301
QC	902	7	17	24	30636	2229	1146	3375
ON	1251	20	27	47	35900	2482	1793	4275
MB	106	0	0	0	2924	82	45	127
SK	163	0	1	1	6251	359	302	661
AB	1053	16	6	22	31389	947	941	1888
BC	64	0	2	2	3669	589	477	1066
Canada	3633	44	55	99	114969	7006	5160	12166

 

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 25, 2008 to May 31, 2008 (Week 22)
	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=1,334]

{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