[Source: World Health Organization, full PDF document: (LINK). Extract, edited.]
Influenza Update N° 176 - 04 January 2013
- Reporting of influenza activity has been irregular in the past two weeks due to the holiday season in many countries. As a result, overall virus detections reported have dropped off although in most countries in the northern temperate regions, influenza activity appears to have continued rising.
- Many countries of North America, Europe, north Africa, eastern Mediterranean and temperate Asia have reported increasing influenza activity over the past weeks. North China has started its influenza season.
- In tropical Asia, influenza activity was similar to previous weeks, with persistent low-level circulation.
- Influenza activity in sub-Saharan Africa has declined in most countries, with the exception of the Democratic Republic of Congo and Ghana.
- In the Caribbean, central America and tropical south America, influenza activity decreased to low levels, except for Bolivia, where there is increasing circulation of influenza A(H3N2).
- Influenza activity in countries of the southern hemisphere is currently at inter-seasonal levels.
- Several unconfirmed media stories have reported a number of deaths related to infection with influenza A(H1N1)pdm09 in different parts of the world. As with other seasonal influenza viruses, it is expected that some deaths would occur with infection, in particular now when influenza season starts in Northern Hemisphere. These reports at times refer to this A(H1N1)pdm09 virus as “swine flu”, causing some confusion with other viruses that recently reported in the United States. A H1N1)pdm09 virus has been circulating in humans for more than 3 years and now is a seasonal human influenza virus.
- Note: Global epidemiology and surveillance updates are periodically collected from data reported by National authorities or organizations responsible for reporting this data. For further information on specific influenza virus activity in the world and scientific literature for practitioners and other professionals in the field, please visit the links provided at the end of this document.
Countries in the temperate zone of the northern hemisphere
Influenza activity in North America has increased sharply since the last report with Canada and the United States both reporting widespread transmission of influenza.
Influenza activity in Canada continued to rise with increases in all indicators in the last two weeks.
The influenza-like illness (ILI) consultation rate increased from 4% at the time of the previous report to 6.6%, with the highest rate observed in children <5 years old, followed by 5-19 year olds. The percentage of samples that tested positive for influenza also increased from 17.8% to 31.1%. In the last two weeks, 127 new influenza outbreaks were reported: 87 in long-term-care facilities, nine in hospitals, one in a school, and 30 in other facilities or communities. This represents a marked increase from the previous report of 22 outbreaks. 241 laboratory confirmed influenza associated hospitalizations were reported in five provinces; 97% (236/241) were influenza A, of which, half (117/236) were sub-typed. Of those with subtype information, 97.5% (114/117) were influenza A(H3N2) and 1.5% (3/117) were A(H1N1)pdm09. Just over half of these cases (51%, 123/241) were aged 65 years or older. Sixteen influenza associated deaths were reported in the last two weeks of 2012; all with influenza A.
Influenza A continued to predominate in Canada, with very few detections of influenza B. Of the respiratory specimens that were positive for influenza in the previous reporting week, 97.7% (4525/4632) were positive for influenza A, and 2.3% (107/4632) for influenza B. Of the influenza A viruses that were sub-typed, 97.4% (1164/1195) were A(H3N2) and 2.6% (31/1195) were A(H1N1)pdm09. Since the start of the season, the National Microbiology Laboratory has antigenically characterized 177 influenza viruses (136 A(H3N2), 17 A(H1N1)pdm09 , and 24 influenza B). The 136 influenza A(H3N2) viruses were antigenically similar to the vaccine virus A/Victoria/361/2011. The 17 A(H1N1)pdm09 viruses were antigenically similar to the vaccine virus A/California/07/09. Among the influenza B viruses, 20 were antigenically similar to the vaccine virus B/Wisconsin/01/2010 (Yamagata lineage) and four were similar to B/Brisbane/60/2008 (Victoria lineage; component of the previous 2011-2012 seasonal influenza vaccine). None of the viral samples tested were resistant to the neuraminidase inhibitors oseltamivir (n=128) or zanamivir (n=127).
In the United States of America (USA), influenza activity has also been increasing and the Centers for Disease Control and Prevention reports that this is the earliest season in nearly a decade. ILI consultation rates increased from 4.2% to 5.6% in the previous week, while the percent of clinical specimens testing positive for influenza increased from 29.6% to 31.6%. Earlier in the season, the most active areas of influenza activity in terms of geographic spread was in the eastern half of the country; this has now increased to include almost all states, with the exception of the Pacific coast.
Widespread influenza activity was reported by 41 states (compared to 31 previously). The proportion of deaths attributed to pneumonia and influenza has been under the epidemic threshold for most of the season. Two influenza-associated pediatric deaths were reported (compared to eight in the previous report); both were associated with influenza B viruses.
In the USA, the majority of influenza viruses detected were A(H3N2), however influenza B accounted for a larger proportion than in Canada. Of the 2961 influenza positive specimens in the last week of 2012, 79% were influenza A and 21% were influenza B. Of the influenza A viruses with sub-type information, 98% were A(H3N2). Since 1 October 2012, the CDC has antigenically characterized 413 influenza viruses. All 17 A(H1N1)pdm09 viruses tested were characterized as A/California/7/2009-like and 99.3% of the 279 A(H3N2) influenza viruses tested were A/Victoria/361/2011-like. Of the 115 influenza B viruses characterized 69% were B/Wisconsin/1/2010-like of the Yamagata lineage, the B virus component of this seasons trivalent influenza vaccine, and 31% were of the Victoria lineage. Since 1 October, none of the 526 A(H3N2), 39 A(H1N1)pdm09, or 226 B viruses have been resistan to neuraminidase inhibitors.
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