Influenza update - 25 February 2011
Update number 128
Influenza activity is increasing in parts of North America coincident with increasing numbers of detections of influenza A(H1N1)2009 and influenza type B, though the dominant virus in North America is still currently influenza A(H3N2). Rates of pneumonia and influenza mortality in the United States of America (USA) have remained above the epidemic threshold for the past two to three weeks. Transmission of influenza appears to have peaked in much of Western Europe, though case counts of severe and fatal cases continue to accumulate. The appearance of severe cases in Europe is similar to the 2009-2010 season; the highest number have been in the age group from 15-64 years, 60-70% have a pre-existing medical condition associated with increased risk of severe influenza, and most have not been vaccinated. Transmission in tropical zones of the world is sporadic (the Americas) or low (tropical Asia). Countries in the southern temperate zone have little influenza activity; however Australia continues to have transmission of influenza A at low-levels. The majority of the viruses characterized from North America and Europe are closely related to the vaccine viruses for the current seasonal vaccines, though small numbers of influenza type B of the Yamagata lineage are reported in both regions.
North America: Influenza activity continues to be elevated and has intensified somewhat since the last report across North America. In Canada, influenza activity continues to increase in some areas including Quebec and the Atlantic provinces. Consultation rate for Influenza-Like Illness (ILI) are elevated and have increased to 35.7 consultations per 1000 patient visits nationally, which is within the expected range when compared to previous influenza seasons. Approximately 20% of specimens tested in Canada are positive for influenza virus. Influenza type A accounts for around 90% of all influenza detections, decreasing slightly compared to previous weeks as the proportion of influenza type B viruses rises. Influenza A(H1N1)2009 viruses are increasingly being detected in Canada, though H3N2 viruses still make up approximately 88% of all influenza A specimens subtyped. In contrast to observations in Europe where H1N1 (2009) virus has been the predominant virus circulating and severe cases are primarily occurring in younger age groups, 65% of fatal cases in Canada have occurred in age group >65 years. Influenza activity in the USA remains elevated with widespread activity reported by 36 states. Twenty states are reporting high ILI activity, and nationally the proportion of outpatient visits for ILI is 4.5%, which is above the national baseline of 2.5% and increased from 4.0% reported two weeks ago. Influenza virus was detected in approximately 35% of specimens tested in the USA. Sixty-seven percent of influenza viruses detected were influenza A viruses, decreased from 72% two weeks ago as the proportion of influenza B viruses detected in the USA continues to rise. Of influenza viruses A further characterized, 81% were influenza A(H3N2) and 19% were influenza A(H1N1)2009 and nearly all were cross reactive antigenically with influenza A strains found in the current trivalent seasonal influenza vaccine. Of the type B viruses characterized, 94% were influenza B (Victoria), the B lineage included in the current vaccine, and 6% were influenza B of the Yamagata lineage. Deaths reported as due to pneumonia or influenza in a USA surveillance system encompassing data from 122 cities were reported at 8.9% of all deaths, which is increased over previous reports and above the epidemic threshold.
Europe: Influenza activity remains high in most of Europe, though activity appears to have peaked in many western and northern European countries as evidenced by decreasing rates of ILI and the proportion of respiratory specimens testing positive for influenza virus. Of the 41 countries reporting on consultation rates for ILI and Acute Respiratory Infection (ARI), 8 (Albania, Belarus, the Czech Republic, Iceland, Kazakhstan, the Republic of Moldova, Serbia and Slovakia) reported increases while 6 (Ireland, Israel, Malta, Norway, Spain and the United Kingdom) reported decreases. Two countries (Georgia and Luxembourg) and the Siberian region of the Russian Federation reported very high intensity of influenza activity. Fifteen countries in the European Region reported moderate to severe impact on the health care system. Many countries of the region are reporting severe and fatal cases of influenza, though numbers of severe and fatal cases are not being formally tracked this season. In the United Kingdom, the number of fatal influenza-related cases has increased over the last two weeks from 395 to 494, a number slightly in excess of the reported fatal cases last year. In general, severe cases from Europe continue to occur in a pattern similar to that seen last season. Most are in the age group from 15-64 years, 60-70% have a pre-existing medical condition associated with increased risk of severe influenza, and most have not been vaccinated. Notably, although both influenza A(H1N1)2009 and influenza type B are circulating in most countries, H1N1 (20009) virus continues to be over-represented in severe cases. The percentage of influenza B virus detections is ten times higher in the outpatient sentinel samples than it is for the for the severe influenza cases admitted to hospital. Overall, 44% of specimens collected tested positive for influenza. Of these, 44% were influenza A(H1N1)2009, 3% were influenza A(H3N2), and 48% were influenza type B.
North Africa and the Middle East: In North Africa and the Middle East, influenza activity has been declining for several weeks and the overall number of specimens testing positive for influenza continues to decrease. Most countries have a mixture of influenza B and influenza A(H1N1)2009.
Northern Asia: In the temperate regions of Asia, ILI activity has been variable, though generally has either recently peaked or is decreasing. In northern China, during 17-23 January, there was a slight decrease in ILI activity; with levels continuing to remain below that observed during the previous three seasons. During 17-23 January, 28% of 548 specimens tested were positive for influenza: 99% were influenza A and 1% influenza B. Of the 149 influenza A detections: 70% were H1N1 (2009) and 24% H3N2. In Japan, ILI activity continued to decline during 7-13 February. Of the 382 influenza viruses detected during 1 to 22 February, 57% were H1N1 (2009), 30% H3N2, and 13% were influenza type B. In the Republic of Korea, ILI activity is now stable following a declining trend, and H1N1 (2009) is co-circulating with H3N2. In Mongolia, ILI activity increased during 7-13 February, showing fluctuating activity for the past few weeks. In most countries of northern Asia, there has been a recent shift from H3N2, which was previously predominant, to H1N1 (2009) which has become predominant in recent weeks.
Influenza transmission is generally low throughout the tropical zone though the most active area is in parts of eastern Africa and tropical areas of Asia. Countries of Central America and the Caribbean islands have reported only sporadic influenza virus detections in recent weeks. In sub-Saharan Africa, available data indicate little activity in most countries. However, Madagascar is reporting continuing active influenza transmission with a high proportion (53%) of specimens testing positive for influenza viruses with nearly equal numbers of influenza A(H3N2) and influenza type B. Kenya has recently reported decreasing numbers of influenza viruses detected, most of which are H1N1 (2009). Low level transmission is reported in several parts of tropical Asia. In southern China, ILI activity has been fluctuating but overall has remained low; however, 46% of 969 specimens tested were positive for influenza: 95% were influenza A and 5% were influenza B. Of the 425 influenza A detections: 88% were H1N1 (2009) and 6% were H3N2. Hong Kong Special Administrative Region reports sustained ILI activity with a predominance of H1N1 (2009) co-circulating with low levels of H3N2 and influenza type B. In Singapore, there has been fluctuating acute respiratory infection (ARI) activity with recent levels above the epidemic threshold; 2% of polyclinic ARI cases are exhibiting ILI, and majority of the ILI cases were H1N1 (2009), co-circulating with low levels of H3N2 and influenza type B. In the Pacific Islands, increased numbers of ILI cases were reported from the Federated States of Micronesia, Kiribati, and Tuvalu. Sustained activity was reported from the Marshall Islands and French Polynesia. A decrease in weekly ILI activity was reported from Fiji. Low ILI activity was reported from American Samoa, Cook Islands, Guam, and Palau. In Nauru, 6 of 15 specimens submitted to a WHO Collaborating Center laboratory in January 2011 were positive for influenza A(H3N2).
The countries in the southern temperate regions of the world continue to have very little influenza transmission since the end of their winter season. Australia, however, continues to report out-of-season, low level detection of influenza A(H3N2) with lower numbers of influenza A(H1N1)2009.
During weeks 5 to 6, regional and widespread outbreaks of laboratory confirmed influenza A(H1N1)2009, A(H3N2) and B viruses continued to be reported in many parts of Asia, Europe and the north Americas. The predominant virus subtype circulating in the various regions differed. Influenza A(H1N1)2009 viruses predominated in China, while both influenza A(H1N1)2009 and B viruses co-circulated at high levels in many European countries. In the United States, influenza A(H1N1)2009, A(H3N2) and B viruses co-circulated, while in Canada, the predominant viruses were still A(H3N2). Currently, the vast majority of antigenically characterized viruses from the 2010-2011 influenza season are similar to the viruses WHO recommended for the 2010-2011 northern hemisphere influenza vaccines.
During weeks 5 to 6 (30 January 2011 to 12 February 2011), National Influenza Centres (NICs) from 67 countries, areas or territories reported data to FluNet*. A total of 26 600 specimens were reported as positive for influenza viruses, 20 073 (75.5%) were typed as influenza A and 6527 (24.5%) as influenza B. Of the sub-typed influenza A viruses reported, 84.3% were (H1N1) 2009 and 15.7% were influenza A(H3N2).
Influenza virus detection by type/subtype in countries, areas or territories:
- Influenza A(H1N1)2009: Afghanistan, Albania, Algeria, Australia, Austria, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Cambodia, China, Colombia, Costa Rica, Croatia, Cuba, Czech Republic, Denmark, Estonia, Finland, France, France - French Guiana, France - Guadeloupe, France - Martinique, Georgia, Germany, Ghana, Greece, Hungary, India, Iran (Islamic Republic of), Italy, Japan, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Malta, Mexico, Mongolia, Netherlands, Norway, Paraguay, Poland, Portugal, Republic of Korea, Romania, Russian Federation, Serbia, Singapore, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland, United States of America and Uruguay.
- Influenza A(H1N1) (old seasonal virus): no report.
- Influenza A(H3N2): Albania, Algeria, Australia, Austria, Brazil, China, Colombia, Cuba, France, France - French Guiana, France - Martinique, Germany, Greece, Iceland, India, Italy, Jamaica, Japan, Kyrgyzstan, Latvia, Madagascar, Mexico, Netherlands, Norway, Paraguay, Republic of Korea, Russian Federation, Serbia, Singapore, Spain, Sweden, Switzerland, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland, United States of America and Uruguay.
- Influenza A(H5): Cambodia.
- Influenza B: Albania, Algeria, Armenia, Australia, Austria, Belarus, Belgium, Brazil, Bulgaria, Cambodia, China, Cuba, Czech Republic, Denmark, Estonia, Finland, France, France - French Guiana, France - Guadeloupe, Georgia, Germany, Ghana, Greece, Honduras, Hungary, Iceland, India, Indonesia, Iran (Islamic Republic of), Italy, Jamaica, Japan, Kyrgyzstan, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Mexico, Netherlands, Norway, Poland, Portugal, Romania, Russian Federation, Serbia, Singapore, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland and the United States of America.
- No influenza activity reported: Austria, Azerbaijan, Central African Republic, Dominican Republic, Ethiopia, France - New Caledonia, Mauritius, Panama and Senegal.
* Some NICs report to FluNet retrospectively leading to updates of previous summary data.
* Some NICs report to FluNet retrospectively leading to updates of previous summary data.
Source of data
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) 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.
FluNet data as of 22 February 2011, 11:00 UTC