Influenza

Influenza update - 14 January 2011

Introduction

The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.

The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance Network), FluID and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.

Description: Displayed data reflect the most recent information reported to FluNet, WHO regional offices or on ministry of health websites in the last 2 weeks.

The percent of specimens tested positive for influenza includes all specimens tested positive for all influenza subtypes. The pie charts show the distribution of virus subtypes among all specimens that were tested positive for influenza.

The available country data were joined in larger geographical areas (Influenza transmission zones)with similar influenza transmission patterns in order to present an overview.

Influenza - Update 125

14 January 2011 - Summary:

North America is continuing to report increases in influenza activity primarily related to influenza A (H3N2) with lower numbers of influenza type B. In the United Kingdom, severe and fatal cases are increased compared to 2 weeks ago, associated predominantly with influenza A (H1N1) 2009 and less commonly with influenza type B. Currently, 25% of intensive care beds in the U.K. are occupied by influenza patients. Notably, the Chief Medical Officer has issued an alert to clinicians warning of increasing rates of bacterial infections often associated with influenza (S. pneumoniae, Group A streptococcus, and meningococcus), though the association with the current influenza circulation is still under investigation. Severe disease associated with H1N1 (2009) and to a lesser extent influenza type B is also being increasingly reported on the European continent and areas of the Middle East. Tropical areas of the world and the temperate countries of the Southern Hemisphere are currently reporting very little influenza circulation.

Countries in the temperate zone of the Northern Hemisphere

North America:

Rates of influenza-like illness (ILI) and hospital admissions due to influenza continue to increase in Canada. The rate of ILI reporting is similar to influenza seasons prior to 2009. About 25% of specimens tested in Canada are positive for influenza and influenza type A makes up about 98% of influenza detections. Of the influenza type A viruses characterized, 94% are H3N2 and the other 6%, H1N1 (2009). In the United States (U.S.), the proportion of outpatient visits due to ILI decreased slightly in the last week, perhaps due to the holiday season, but remains slightly above the epidemic threshold. Six U.S. states are reporting high ILI activity. Rates of death due to pneumonia and influenza from a sentinel surveillance system that includes data from 122 cities across the country are below the epidemic threshold. About 20% of clinical specimens tested in the last week of 2009 were positive for influenza. In contrast to the situation in Canada, approximately one-third (34.1%) of influenza detections in the U.S. are type B and two-thirds are type A. Of the influenza type A viruses that have been sub-typed, 86% are H3N2 and the other 14% are H1N1 (2009). As in previous weeks, all of the influenza A and 91% of the influenza type B viruses characterized antigenically are of the same lineages as contained in the current seasonal influenza vaccine.

Europe:

The United Kingdom (U.K.) continues to report high rates of ILI and influenza-related hospitalizations. Currently approximately 25% of intensive care beds are occupied by influenza cases and 112 influenza-related deaths have been reported. 95 of 100 fatal cases from which the virus has been sub-typed have been H1N1 (2009) related and the other 5, influenza type B. The majority of severe and fatal cases have been between the ages of 15 and 64 years; only 16% of fatal cases were over the age of 64 years. 78% of the fatal cases for which there are data had an underlying risk condition. Of note, the Chief Medical Officer of the U.K. has issued an alert to clinicians noting recent increases in some bacterial infections that are sometimes seen as co-infections with influenza, particularly S. pneumoniae, invasive Group A streptococcus, and meningococcal disease. The association of this increase with the current influenza transmission is unclear and is under investigation. Two percent (17/811) H1N1 (2009) viruses tested in the U.K. have been found to carry the H275Y mutation which confers resistance to the antiviral drug oseltamivir. Elsewhere in the European Region there have been increasing numbers of hospitalized cases and deaths associated with Influenza A(H1N1) and Influenza B virus infections in several countries. France, Portugal, the Netherlands, and Denmark have all reported deaths and cases admitted to intensive care. The percentage of intensive care beds occupied by influenza cases in Denmark has reached 4%, which is as high as it was during the peak of the 2009/2010 influenza season. The pattern seen in severe cases in continental Europe is similar to that seen in the U.K. primarily affecting adults between the ages of 15 and 64 years with 60 - 80% reporting a history of underlying risk factors. In areas where H1N1 (2009) and type B viruses are co-circulating in the community, H1N1 (2009) appears to be disproportionately detected in the severe cases. Overall, 45% of specimens tested from sentinel sites in Europe were positive for influenza virus, an increase from previous reports. 77% of influenza viruses were type A and 23%, influenza type B. Of the 307 influenza A viruses that were sub-typed, 85% were H1N1 (2009) 15% were H3N2.

North Africa and the Middle East:

Several countries of North Africa and the Middle East are also experiencing increases in influenza activity. Morocco, Algeria, and Tunisia have had modestly increased levels of influenza detections in the last 2 to 3 weeks. Influenza type B has been the predominant virus reported with lesser amounts of H1N1 (2009). Limited data suggests that H1N1 (2009) is circulating in Egypt where 122 H1N1 (2009) related deaths have been reported since October 2010. Iran and Pakistan have also had a steady increase in influenza detection in the same period of time with the majority of viruses being H1N1 (2009).

North Asia:

The temperate areas of Asia, including Mongolia, northern China, the Republic of Korea, and Japan have all reported slight increases in respiratory disease activity in recent weeks. In Mongolia and northern China, the increase in activity was associated with influenza A (H3N2), which appears to have peaked around the third week of December. However, in the Republic of Korea, very little H3N2 was detected; over 90% of influenza viruses reported there were H1N1 (2009). Japan had earlier detections of H3N2 coinciding with those of Mongolia and northern China but more recently, H1N1 (2009) has become the predominant virus detected there.

Countries in the tropical zone

Very little transmission of influenza viruses is currently being reported in tropical regions of the world. Previously reported circulation of H3N2 in Paraguay, though still elevated, continues to decline. Elsewhere in the topical areas of the Americas, levels of influenza detection are low. In Asia, the previously reported surge in severe H1N1 (2009) related cases in Sri Lanka is decreasing for the last four weeks. Other countries in the region and extending into South East Asia report only small numbers of influenza virus detections and no increases in respiratory disease activity. A mixture of viruses is being reported with influenza type B and (H1N1) 2009 being the most common types in most countries. No new information is available this week from sub-Saharan Africa. Madagascar, however, has been experiencing moderate levels of circulation of H3N2 and lesser amounts of influenza type B for several weeks.

Countries in the temperate zone of the Southern Hemisphere

The countries of the southern temperate regions of the world have had very little influenza transmission since the end of their winter season. Australia is the notable exception with persistence of small numbers of H3N2 and influenza type B viruses.

Virological surveillance

During weeks 49 to 52, influenza activity in the northern hemisphere increased, in particular in Europe, with A(H1N1) and B viruses predominating. In Asia and North Americas, influenza A(H3N2) and B viruses co-circulated.

FluNet reports

During this reporting period, National Influenza Centres (NICs) from 71 countries, areas or territories reported data to FluNet*. A total of 18,757 specimens were reported as positive for influenza viruses, 14,423 ( 76.9%) were typed as influenza A and 4,335 (23.1%) as influenza B. Of the sub-typed influenza A viruses reported, 53.2% were influenza H1N1(2009) and 46.7% were influenza A (H3N2).

Influenza virus detection by type/subtype in countries:

  • Influenza H1N1 (2009): Algeria, Australia, Austria, Belgium, Bulgaria, Cambodia, Cameroon, Canada, China, China Hong Kong SAR, Colombia, Croatia, Czech Republic, Denmark, Ecuador, Ethiopia, Finland, France, Georgia, Germany, Ghana, Hungary, Indonesia, Iran (Islamic Republic of), Italy, Japan, Kenya, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Malta, Mexico, Morocco, Netherlands, Norway, Oman, Pakistan, Poland, Portugal, Republic of Korea, Russian Federation, Senegal, Singapore, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom and United States of America.
  • Influenza A(H1N1)(old seasonal virus): Canada.
  • Influenza A(H3N2): Algeria, Argentina, Australia, Austria, Belgium, Bolivia, Cambodia, Canada, China, China Hong Kong SAR, Colombia, Cuba, Denmark, Ecuador, France, French Guiana, Germany, Ghana, Guadeloupe, Indonesia, Italy, Japan, Kenya, Lao People's Democratic Republic, Latvia, Madagascar, Martinique, Mexico, Mongolia, Morocco, Norway, Paraguay, Portugal, Republic of Korea, Russian Federation, Serbia, Singapore, Spain, Thailand, Tunisia, Turkey, United Kingdom and United States of America.
  • Influenza B: Algeria, Argentina, Australia, Austria, Belarus,Belgium, Bulgaria, Cambodia, Cameroon, Canada, Central African Republic, China, China Hong Kong SAR, Costa Rica, Cuba, Denmark, Dominican Republic, Finland, France, Germany,Georgia, Guadeloupe, Honduras, India, Indonesia, Iran (Islamic Republic of), Italy, Japan, Kenya, Kyrgyzstan, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Malta, Mexico, Morocco, Netherlands, Norway, Oman, Pakistan, Paraguay, Peru, Poland, Portugal, Russian Federation, Singapore, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom and United States of America.
  • No influenza activity reported: Albania, Armenia, Azerbaijan, Bangladesh, Bosnia and Herzegovina, El Salvador, Greece, Romania, Rwanda and Uruguay.

* Some NICs report to FluNet retrospectively leading to updates of previous summary data.

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