April 19, 2009 to April 25, 2009 (Week 16)

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Special Report - Novel Influenza Virus Detected

In light of the rapidly evolving situation regarding the spread of the novel influenza A (H1N1) infection in Canada and across the world, this edition of FluWatch includes a special section dedicated to this important public health event. It covers the information about the influenza A (H1N1) situation and also the routinely reported seasonal influenza that occured between April 19, 2009 to April 25, 2009. As the influenza A (H1N1) situation progresses, it will eventually be integrated into the different sections of the routine FluWatch report.

Novel Influenza: H1N1 Flu Virus (Human Swine Flu)

Background:
On April 20, 2009 PHAC alerted the provincial and territorial (PT) health authorities, public health laboratories, the nosocomial infection surveillance and several other relevant agencies and groups about two international public health events. The first was in regards to clusters of Severe Respiratory Infections (SRI) in young adults in Mexico. The second was about the detection of a novel human swine influenza A (H1N1) virus in two un-linked children presenting with influenza-like-illness (ILI) in different counties in California of which neither had any previous contact with pigs. PHAC requested that the PTs enhance or re-activate their hospital-based SRI surveillance systems and also that they send any untypeable influenza A to the NML for further testing.

On April 26, Canada reported its first six cases of H1NI Flu Virus (Human Swine Flu) in the country. Four were from students in a boarding school in Nova Scotia and two were amongst unrelated adults returning from a trip in Mexico from British Columbia.

CANADA
As of April 30, 2009, 1300 EDT, a total of 31 laboratory-confirmed cases of H1NI Flu Virus (Human Swine Flu) have been identified in four provinces; NS, BC, ON, and AB.

Figure 1 Number of laboratory-confirmed cases of H1NI Flu Virus (Human Swine Flu in Canada (n=31)

Province	Number of Cases
NS	8
ON	8
AB	6
BC	9
Total	31

 

To date all Canadian cases have presented with mild influenza-like-illness symptoms and are recovering well and there have been no reports of hospitalization or death. The majority of cases have either a travel history to Mexico or have been in contact with someone who has travelled to Mexico. However, it is possible that community spread is also occurring.

INTERNATIONAL
As of 18h00 GMT, April 29, 2009, 257 confirmed cases of H1NI Flu Virus (Human Swine Flu infection in 11 countries were officially reported to the World Health Organization. In the U.S. there were 109 cases in 11 states, five reports of hospitalization (four of which had pre-existing medical conditions) and one death. As in Canada, the majority of cases have resulted in mild illness. As time goes by, there is evidence of community-based transmission among some cases in the U.S. and Mexico.

Table 2: Number of Confirmed Cases Reported by the World Health Organization (n=257)

Countries	Confirmed Cases (deaths)1
Austria	1 (0)
Canada *	19 (0)*
Germany	3 (0)
Israel	2 (0)
Mexico	97 (7)
New Zealand	3 (0)
Netherlands	1 (0)
Spain	13 (0)
Switzerland	1 (0)
United Kingdom	8 (0)
United States	109 (1)
Total	257 (8)

¹ Number of deaths is included in the number of cases

^* Canadian confirmed case count as per WHO website at 18:00 GMT, 29 April 2009. Source: http://www.who.int/csr/don/2009_04_29/en/index.html (accessed on 30 April, 2009: 12:00 EDT),

The WHO's Pandemic Alert Level is currently at Five, which is characterized by human-to-human spread of the virus in at least two countries in one WHO region. “While most countries are not affected at this stage, the declaration of level 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.” http://www.who.int/csr/disease/avian_influenza/phase/en/index.html

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April 19, 2009 to April 25, 2009 (Week 16)

Overall influenza activity in Canada continues to decline; mostly sporadic activity reported
During week 16, seven regions in AB, ON & NL reported localized activity, 42 regions sporadic in BC, AB, SK, MB, ON, QC, NB, PE, NS, NL, YK, NT & NU and 5 regions in NS, NB, MB & NT reported no activity (see map). The proportion of tests that were positive for influenza decreased by 5.1% (149/2,918) from the previous week (see table). To date this season, 60.7% (5,588/9,200) of detections are influenza A (see graph). This week, the ILI consultation rate fell to 7 ILI consultations per 1,000 patient visits (see ILI graph) which is below the expected range for this time of year. The sentinel response rate was 60.3%. In week 16, 3 new influenza outbreaks were reported, all in LTCFs (2 in ON, 1 in NS).

Antigenic Characterization: *No update from the NML since week 14.
Since 1 September 2008, the NML has antigenically characterized 828 influenza viruses: 202 influenza A/Brisbane/59/2007(H1N1)-like (from BC, AB, SK, MB, ON, QC, NB, NS & PEI), 142 influenza A/Brisbane/10/2007(H3N2)-like (from BC, AB, SK, MB, ON, QC, NB, PEI & NL), 9 influenza B/Florida/4/2006-like (from AB, ON, QC & NB), 107 B/Brisbane/60/2008-like (from BC, SK, MB, ON, QC, NB & NL) and 368 B/Malaysia/2506/2004-like (in all provinces except the Territories). A/Brisbane/59/2007(H1N1), A/Brisbane/10/2007(H3N2) and B/Florida/04/2006 are the influenza A and influenza B components recommended for the 2008-09 influenza vaccine. B/Malaysia/2506/2004 was the influenza B component for the 2007-2008 season vaccine (see pie chart). B/Brisbane/60/2008-like is the recommended influenza B component for the 2009-2010 season vaccine.

Antiviral Resistance:

Results from the NML: *No update from th NML since week 14.

Since the start of the season, the NML has tested 527 influenza A isolates (242 H1N1 and 285 H3N2) for amantadine resistance. All of the H1N1 isolates were susceptible; however all of the H3N2 isolates were resistant to amantadine (resistance = 100%). The resistant isolates were from BC, AB, SK, MB, ON, QC, NB, PEI, NL & NT. The NML has also tested 839 influenza isolates (225 A/H1N1, 154 A/H3N2 & 460 B) for oseltamivir (Tamiflu) resistance. All of the A/H3N2 and B isolates were sensitive; however all of the A/H1N1 isolates were resistant to oseltamivir due to the H274Y mutation (resistance = 100%). The resistant isolates were from BC, AB, SK, MB, ON, QC, NB, NS, PEI & NL. All 794 influenza isolates (176 A/H1N1, 152 A/H3N2 & 466 B) tested for zanamivir resistance to date were sensitive to zanamivir.

Oseltamivir resistance findings from Provincial laboratories:

To date this season, 163 influenza isolates in BC have been sub-typed as A/H1 and were assessed genotypically for oseltamivir resistance using an SNP assay. One hundred and forty-eight isolates tested positive for the H274Y mutation (resistance = 100% or 148/148), with the other 15 specimens still pending confirmatory testing.

Influenza-associated Paediatric Hospitalizations:
In week 16, 7 laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. The seven cases were from Ontario (One type A) and Quebec (Two type A & four type B). To date, 410 hospitalizations have been reported of which 55% have been due to influenza A. The proportion of cases to date by age group are as follows: 14% were 0-5 month olds; 31% were 6-23 month olds; 24% were 2-4 year-olds; 16% were 5-9 year-olds; and 15% were10-16 year-olds. The distribution of cases to date by province are as follows: 10% from BC, 9% from AB, 4% from SK, 4% from MB, 28.5% from ON, 41% from QC, 3% from NS & 0.5% from NL.

International:

WHO: During the weeks 13-14, the level of influenza activity globally continued to decrease.

• WHO

CDC: During week 15 (April 19- April 25, 2009), influenza activity decreased in the United States; 151 (6.2%) specimens tested positive for influenza, of which 49% were influenza A and 51% were influenza B. Testing for antiviral resistance indicated that of the influenza virus A/H1N1 tested, 99.4% (765/770) were resistant to oseltamivir and 0.4% (3/767) resistant to amantadine. Of the influenza A/H3N2 viruses tested for resistance, 100% (116/116) were resistant to amantadine. All tested viruses remain sensitive to zanamivir. To date this season, 55 influenza-associated pediatric deaths have been reported to the CDC. Two deaths were reported this week (April 19 - April 25, 2009) in New York and Ohio. Bacterial co-infections were confirmed in 12 (41.4%) of 29 tested children; Staphylococcus aureus was identified in 8 (67%) of 12 tested children.

• CDC

EISS: In week 17 (April 20- April 26, 2009), seasonal influenza activity continued to be low and declining in almost all countries and regions of Europe, but human infections with new influenza virus were reported. Only the Russian Federation reported a medium intensity of clinical activity. Influenza A(H3N2) has been the dominant virus in Europe, accounting for an estimated 69% of total virus detections this season. Of influenza B viruses that have been antigenically and/or genetically characterized the majority were B/Victoria lineage. With the exception of these B/Victoria lineage viruses, most of the viruses characterized are similar to the three components - A(H1N1), A(H3N2) and B/Yamagata lineage - included in the 2008/2009 Northern Hemisphere influenza vaccine. Of the 644 A(H3N2) isolates that were tested for adamantanes susceptibility, 644 (100%) were resistant. Of the 259 A(H1N1) virus isolates tested for resistance against neuraminidase inhibitors, 255 (98%) were resistant to oseltamivir, but all were sensitive to zanamivir.

• EISS

Human Avian Influenza: During week 16, the WHO reported three new cases of human H5N1 avian influenza infection in Egypt.

• WHO

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Total number of influenza tests performed and number of positive tests by province/territory of testing laboratory, Canada, 2008-2009

Province of reporting laboratories	Report Period: April 19, 2009 to April 25, 2009				Season to Date: August 24, 2008 to April 25, 2009
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	24	1	0	1	882	104	19	123
PE	2	0	0	0	188	14	9	23
NS	NA	NA	NA	0	891	56	57	113
NB	76	2	2	4	1553	246	88	334
QC	928	36	20	56	32520	2319	1384	3703
ON	809	41	5	46	28578	1119	1323	2442
MB	85	7	0	7	2114	50	33	83
SK	170	7	2	9	5115	226	169	395
AB	749	10	6	16	21981	827	337	1164
BC	75	7	3	10	2878	627	193	820
Canada	2918	111	38	149	96700	5588	3612	9200

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, 2008-2009 (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 19, 2009 to April 25, 2009 (Week 16)
	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, 2008-2009

Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2008-2009

Influenza strain characterization, Canada, cumulative, 2008-2009 influenza season by the Respiratory Viruses Section at the National Microbiology Laboratory
[N=828]

{Strain characterization, number identified, per cent of total number}

NACI recommends that the trivalent vaccine for the 2008-2009 season in Canada contain
A/Brisbane/59/2007 (H1N1)-like virus; an A/Brisbane/10/2007 (H3N2)-like virus; and a B/Florida/4/2006-like virus.

Influenza-like illness (ILI) consultation rates, Canada, by report week,
2008-2009 compared to 1996/97 through to 2007/08 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, 2008-2009

 

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

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Definitions for the 2008-2009 season