April 26, 2009 to May 2, 2009 (Week 17)

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Update on the Influenza A H1N1 virus (Human Swine Flu) Outbreak

Canada
As of May 7, 2009, 1500 EDT a total of 214 laboratory confirmed cases of influenza A H1N1 flu virus (Human Swine Flu) have been identified in nine provinces: PEI, NS, NB, PQ, ON, MB, SK, AB, BC. The first reported date of symptom was April 10, 2009 (n=176) and the most recent reported onset date is May 3, 2009. Almost all cases have been mild.

Fig 1. Number of Laboratory Confirmed Cases by Date of Symptom Onset (n=176)

As of May 7 2009, 77% of initial cases of influenza A H1N1 (Human Swine Flu) were in the 15-44 year old age group. Typically, half of seasonal laboratory-confirmed influenza cases are in the very young (under 5 years of age) and the older population (65 years and over). It is not surprising that the distribution of initial cases of influenza A H1N1is different from the seasonal influenza cases because the population who travels to Mexico in April tends to be young to middle aged adults. Three cases (1.4%) have been hospitalized and no deaths have been reported to date. Of 189 cases for which information is available 108 (57%) have a known history of travel in the previous seven days prior to symptom onset (travel history is unknown for 25 cases). The median age of those with a travel history is 24 years while the average age of non-travellers is 17 years; this difference is not of public health significance.

International
The WHO as of 06:00 GMT, May 8, 2009 has reported 2384 laboratory confirmed cases of Influenza A H1N1 world-wide. Mexico has reported 1112 laboratory-confirmed human cases of infection and 42 deaths. The United States has reported 896 confirmed cases and two deaths.

The following countries have reported laboratory confirmed cases with no deaths:

Austria (1), China, Hong Kong Special Administrative Region (1), Colombia (1), Costa Rica (1), Denmark (1), El Salvador (2), France (5), Germany (10), Guatemala (1), Ireland (1), Israel (6), Italy (5), Netherlands (2), New Zealand (5), Poland (1), Portugal (1), Republic of Korea (3), Spain (81), Sweden (1), Switzerland (1) and the United Kingdom (32).

The current WHO pandemic alert is at phase 5 which is characterized by human-to-human spread of the virus in at least two countries in one WHO region. Currently there are no travel advisory warnings or recommendations for border closures.

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April 26, 2009 to May 2, 2009 (Week 17)

Overall influenza activity declining but Consultation Rates and Lab Testing Increased
During week 17 there was a slight increase in the number of regions reporting localized or widespread influenza activity but the majority of regions still had either sporadic or no influenza activity. One region in MB reported widespread activity*, nine regions in BC, AB, ON & QC reported localized activity, 36 regions sporadic in BC, AB, SK, MB, ON, QC, NB, PE, NS, NL, NT & NU and 7 regions in NB, NS, & YK reported no activity, (see map). This week, the ILI consultation rate increased to 17 consultations per 1,000 patient visits (see ILI graph) which is significantly above the expected range for this time of year. This is likely due to concerns over the new Influenza A H1N1 virus (Human Swine flu) in which the general population will change their health seeking behaviours. The sentinel response rate was 56.8%. The overall number of samples submitted for testing this week increased three fold relative to the amount submitted in the previous week (8781 vs. 2918). This is also a result of increased screening for the Human Swine flu. Despite increased sample submissions, the proportion of tests that were positive for influenza decreased to 4.0%. This represents a 1.1% decrease relative to the previous week (see table). To date this season, 61.3% (5,862/9,559) of detections were for influenza A (see graph). Twelve new influenza outbreaks were reported, six were in LTCFs (2 in SK, 3 in MB and 1 in QC), five were in schools (1 in AB, 2 in SK and 2 in NS) and one occured in an unspecified location.

* There is not sufficient resolution on the map to see the area with widespread activity in Manitoba.

Antigenic Characterization:
Since 1 September 2008, the NML has antigenically characterized 906 influenza viruses: 226 influenza A/Brisbane/59/2007(H1N1)-like (from BC, AB, SK, MB, ON, QC, NB, NS & PEI), 154 influenza A/Brisbane/10/2007(H3N2)-like (from BC, AB, SK, MB, ON, QC, NB, PEI & NL),11 influenza B/Florida/4/2006-like (from AB, ON, QC & NB), 147 B/Brisbane/60/2008-like (from BC, SK, MB, ON, QC, NB, NL & NU) 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. Additionally, as of May 7, 2009 151 samples have been submitted to the NML for characterization for the H1N1 virus (Human Swine Flu) and 65 (43%) were found to be positive. Positive samples were from PEI, NS, QC, ON, MB, SK, and AB.

Antiviral Resistance:

Results from the NML:

Since the start of the season, the NML has tested 558 influenza A isolates (254 H1N1 and 304 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 930 influenza isolates (252 A/H1N1, 166 A/H3N2 & 511 type 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 875 influenza isolates (202 A/H1N1, 162 A/H3N2 & 511 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 17, three laboratory-confirmed influenza-associated paediatric hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network. The three cases were from BC (one type A) and AB (one type A & one Influenza A H1N1 (Human Swine Flu). To date, 417 hospitalizations have been reported of which 54.9% 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; 23.5% were 2-4 year-olds; 15.5% were 5-9 year-olds; and 16% were10-16 year-olds. The distribution of cases to date by province are as follows: 10% from BC, 9% from AB, 5% from SK, 4% from MB, 28% from ON, 40.5% from QC, 3% from NS & 0.5% from NL.

International:

WHO: During the weeks 15-16, influenza activity decreased and is below baseline levels in most countries.

• WHO

EISS: In week 18 (April 27- May 03, 2009), seasonal influenza activity in Europe continues to be low and declining in almost all countries and regions of Europe. For the intensity indicator, the national network levels of influenza-like illness (ILI) and/or acute respiratory infection (ARI) were low in all countries that reported this indicator but medium in two of seven regions (Siberian and Urals) of the Russian Federation. For the geographical spread indicator, the 32 countries reported sporadic or no activity and the Russian Federation reported local activity. Influenza A(H3N2) has been the dominant virus in Europe this season, accounting for an estimated 69% of total virus detections this season. 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 17, the WHO reported no new case of human H5N1 avian influenza infection.

• 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 26, 2009 to May 2, 2009				Season to Date: August 24, 2008 to May 2, 2009
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	106	5	5	10	988	109	24	133
PE	1	0	0	0	189	14	9	23
NS	394	11	0	11	1321	70	59	129
NB	94	9	3	12	1647	255	91	346
QC	1303	37	6	43	33823	2356	1390	3746
ON	865	31	5	36	29513	1152	1328	2480
MB	219	13	0	13	2333	63	33	96
SK	404	21	28	49	5519	247	197	444
AB	4543	53	35	88	26524	880	372	1252
BC	852	89	1	90	3730	716	194	910
Canada	8781	269	83	352	105587	5862	3697	9559

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 26, 2009 to May 2, 2009 (Week 17)
	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=906]

{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