Low levels of influenza activity in Canada
Influenza activity in Canada continued to decline since the beginning of April and remained at low levels in week 20 (see map). During weeks 19 and 20, widespread influenza activity continued be reported in Toronto and localized activity continued to be reported in most of the influenza surveillance regions in Ontario, as from previous weeks. In week 20, 77 (7%) of the specimens tested for influenza viruses were positive (see table). Note that there were no lab reports received from Quebec this week. Of the 77 positive detections, 71 (92%) were influenza A and 6 (8%) were influenza B. The majority of the positive influenza detections were from Ontario (38%), Alberta (27%) and the Atlantic Provinces (23%). In the current season to date, a mix of influenza A (61%) and influenza B (39%) viruses have been detected in Canada. In week 20, the ILI consultation rate was calculated as 5 per 1000 patient visits (see ILI graph). During week 20, 3 new outbreaks were reported, all were LTCFs. To date this season, 160 LTCF outbreaks have been reported.

Antigenic Characterization:
Since the start of the 2005-2006 influenza season, the National Microbiology Laboratory (NML) has antigenically characterized 951 influenza viruses (see pie chart). Since March 2006, all of the influenza B viruses characterized have been B/Malaysia/2506/2004-like (B/Victoria/02/1987 lineage), which is the recommended influenza B component for next season's vaccine.

Vaccine Match:
To date, 100% of the influenza A strains characterized by the NML have matched those included in the 2005-2006 Canadian vaccine. However, 99% of the influenza B strains characterized belong to the B/Victoria/02/1987 lineage and are not covered by this year's vaccine.

Influenza-associated Pediatric Hospitalizations:
During week 20, 6 new laboratory-confirmed influenza-associated hospitalizations were reported through the IMPACT (Immunization Monitoring Program ACTive) network, the majority of which were from Quebec. Since the start of this influenza season, 373 cases have been reported to IMPACT from the 12 pediatric hospitals. Sixty-two percent of the hospitalizations to date were due to influenza A. There have been three influenza-associated pediatric deaths in Canada this season as reported through IMPACT.

International:
CDC: During week 19, influenza activity in the Unites States continued at low levels. Influenza activity peaked in early March and continued to decline since then. During week 19, the proportion of patient visits to sentinel providers for ILI (1.2%) was below baseline levels and the proportion of deaths due to pneumonia and influenza (6.6%) was below baseline levels. Since 1 October 2005, the CDC has antigenically characterized 819 influenza viruses: 503 A(H3N2) viruses (381 were A/California/07/2004-like viruses and 122 showed reduced titers with antisera produced against A/California/07/2004-like viruses); 88 A(H1) viruses (85 were similar antigenically to the hemagglutinin protein of the A/New Caledonia/20/1999-like viruses) and 3 showed reduced titers with antisera against A/New Caledonia/20/1999-like viruses); and 228 influenza B viruses (52 were B/Yamagata/16/1988-lineage viruses and 176 were B/Victoria/2/1987-lineage viruses). Seventy of the 122 A/H3N2 samples showing reduced titers with A/California/07/2004-like antisera are A/Wisconsin/67/2005-like viruses (the H3N2 component selected for the 2006-07 vaccine) and 175 (77%) of the influenza B viruses identified were B/Ohio/1/2005-like viruses (the influenza B component selected for the 2006-2007 vaccine).

• CDC

Human Avian Influenza:
The WHO reported 1 additional case of human infection with the H5N1 avian influenza virus. The case was a 32-year-old man from Indonesia who developed symptoms on 15 May and died on 22 May. The man is the seventh member of an extended family to become infected with the H5N1 virus and is the sixth to die. The case was from the same family cluster reported previously.

• WHO

Antiviral Resistance
The Public Health Agency of Canada recommends that health care providers in Canada not prescribe amantadine to treat and prevent influenza during the current flu season following testing showing viruses currently in circulation in Canada and the US are resistant to the drug.

Notice: This is the last FluWatch report of the influenza season. Influenza surveillance such as laboratory detections, sentinel physician reporting and provincial/territorial assignment of influenza activity levels will continue weekly, however, the Public Health Agency of Canada will only publish FluWatch reports every two weeks (on even numbered weeks).

Total number of influenza tests performed and number of positive tests by province/territory of testing laboratory, Canada, 2005-2006

Province of reporting laboratories Report Period: May 14, 2006 to May 20, 2006 Season to Date: August 28, 2005 - May 20, 2006 Total # Influenza Tests # of Positive Tests Total # Influenza Tests # of Positive Tests Influenza A Influenza B Total Influenza A Influenza B Total NL 27 3 0 3 966 39 34 73 PE 0 0 0 0 139 5 3 8 NS 29 1 2 3 1019 27 89 116 NB 45 12 3 15 1464 78 192 270 QC 0 0 0 0 17646 1434 242 1676 ON 386 27 1 28 23728 1231 1056 2287 MB 43 0 0 0 2094 63 27 90 SK 92 1 0 1 5588 364 283 647 AB 390 19 0 19 18068 728 607 1335 BC 89 8 0 8 5000 474 333 807 Canada 1101 71 6 77 75712 4443 2866 7309

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.html>

Number of influenza surveillance regions† reporting widespread or localized influenza activity, Canada, by report week, 2005-2006 (N=76)

† 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 14, 2006 to May 20, 2006 (Week 20)
	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 the 2005-2006 season. 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, 2005-2006

Percent positive influenza tests, compared to other respiratory viruses by reporting week, Canada, 2005-2006

Influenza strain characterization, Canada, cumulative, 2005-2006 influenza season by the Respiratory Viruses Section at the National Microbiology Laboratory
[N=951]

(Strain characterization, number identified, per cent of total number)

NACI recommends that the trivalent vaccine for the 2005-2006 season in Canada contain A/New Caledonia/20/99 (H1N1)-like, A/California/7/2004 (H3N2)-like, and B/Shanghai/361/2002-like virus antigens.

* The B/Shanghai/361/2002-like virus belongs to the B/Yamagata/16/88 lineage; the B/Hong Kong/330/01-like and B/Malaysia/2506/2004-like viruses belong to the B/Victoria/02/87 lineage and are not covered by this year's vaccine.

Influenza-like illness (ILI) reporting rates, Canada, by report week, 2005-2006 compared to 1996/97 through 2004/2005 seasons

Note: No data available for mean rate in previous years for weeks 21 to 39 (1996-1997 through 2002-2003 seasons).

Number of New Outbreaks in Long Term Care Facilities by Report Week, Canada, 2005-2006

Please note that the above graphs may change as late returns come in.

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Definitions for the 2005-2006 season