Influenza

Influenza update - 8 October 2010

Introduction

The Global Influenza Programme is regularly monitoring influenza activity worldwide and publishing an update every two weeks.

The updates are based on all available epidemiological and virological data: influenza reports from WHO Regional Offices and Member States, data collected through FluNet and FluID. Data can vary in completeness and timeliness due to differences in available resources in Member States as well as influenza seasonality.

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 118

8 October 2010 - Summary:

Influenza activity is decreasing in most parts of the temperate Southern Hemisphere and the season does not yet appear to have definitively started in the temperate areas of the Northern Hemisphere. Influenza A(H3N2) is now the predominant influenza virus world wide after several weeks of increasing detections in much of the world, but many areas still have active transmission of H1N1 (2009) influenza. Most of the influenza A(H3N2) viruses detected are A/Perth/16/2009-like, which is the strain included in the seasonal vaccine for the Northern and Southern Hemispheres.

Southern hemisphere temperate countries

The winter influenza transmission season of the temperate countries of the southern hemisphere is now waning in most areas. The most common virus types associated with the influenza season of 2010 in the temperate southern hemisphere have varied greatly depending on the location. In Australia, influenza-like illness (ILI) activity, hospital, and intensive care unit admissions related to influenza in Australian sentinel hospitals have all decreased in the past week. The H1N1 (2009) influenza virus is still the most frequently detected virus in Australia, with a lower number of influenza type B and A(H3N2) viruses. Rates of ILI activity in New Zealand are below the baseline level for the second week with a low rate of influenza virus detection. The most common influenza virus found this season in New Zealand is H1N1 (2009) with very few other subtypes detected.

In the southern cone of South America, overall respiratory disease activity is decreasing, with a mixed picture of influenza viruses. In Chile the seasonal outbreak arrived at a later time than normal and respiratory disease activity is still high but decreasing, indicating that the peak activity has passed. Reported cases of severe acute respiratory infections (SARI) caused by influenza have decreased the last weeks, and emergency consultations for pneumonia have also declined. Although some regions of the country have experienced higher ILI activity this year than during last year's outbreak of H1N1 (2009), at a national level overall activity has been much lower. The most frequently detected virus in Chile this season has been A(H3N2) with co-circulation of smaller numbers of H1N1 (2009) and even fewer influenza type B viruses.

The influenza season in South Africa has peaked and is declining; influenza type B was the predominant virus of the season co-circulating with H1N1 (2009) and A(H3N2). The median age of influenza cases in South Africa was lower for those with H1N1 (2009) and influenza B infections than for those with influenza A(H3N2).

Tropical zone

Influenza activity in tropical areas of the world have been varied and discordant in time. While most tropical areas have seen recent peaks in transmission that are now decreasing in intensity, Southeast Asia is currently experiencing increasing levels of influenza activity. The viruses indentified in tropical areas have varied even between neighboring countries and co-circulation of multiple types has commonly been observed.

Influenza activity is decreasing in Central American. The influenza viruses detected have been a mixture of influenza A (H3N2), influenza H1N1 (2009), and influenza type B. Overall, influenza A(H3N2) is the most commonly detected but this is not uniformly true in every country. Among characterized influenza viruses in Costa Rica and Honduras in the last month, the large majority was A(H3N2), while Nicaragua has had predominantly influenza type B. Cuba had an outbreak of mainly H1N1 (2009) in April-May, but since August has detected much more influenza A(H3N2).

Mexico has detected an increase in ILI and acute respiratory disease (ARI) since August, particularly in the southern part of the country. This activity has coincided with an increased proportion of samples testing positive for influenza, but during September this proportion has again decreased. The majority of positive influenza samples have been influenza A(H3N2) viruses and a subset that was further characterized was all the A/Perth/16/2009-like strain, which is included in both the 2010-2011 Northern Hemisphere and the 2010 Southern Hemisphere influenza vaccine.

In south Asia, data from India indicates that the country-wide outbreak of H1N1 (2009) has peaked and a declining number of laboratory-confirmed cases has been reported the last weeks though activity is still quite high in some areas of the country. Bangladesh also has decreasing influenza activity, though with influenza A(H3N2) virus more commonly detected than H1N1 (2009).

Southeast Asia, in contrast, is experiencing increases in activity in some areas. Cambodia has reported increasing detections of influenza viruses for the last two weeks, with A(H3N2) the most frequent virus detected but with a high number of H1N1 (2009) detections and a few influenza B viruses. Neighbouring Thailand has reported on an increasing number of ILI cases and is experiencing local outbreaks of H1N1 (2009).

In Africa, Cameroon and Senegal continue to report a low number of circulating influenza B viruses, while the Eastern African countries Kenya, Tanzania and Madagascar have low circulation of predominantly A(H3N2).

Northern hemisphere temperate countries

In Asia, China is experiencing moderate circulation of influenza A(H3N2) virus with many fewer detections of influenza B. In Northern China, the proportion of outpatients with ILI in sentinel hospitals is increasing. In Hong Kong SAR, ILI activity in sentinel sites of general practitioners is decreasing but remains high and with a majority of influenza A(H3N2) viruses among the laboratory-confirmed cases.

In North America, both the United States and Canada are reporting low influenza activity with sporadic detections of A(H3N2) and influenza B in the US.

WHO Euro Region had low influenza activity last months; with Russia notably reporting increasing activity of ARI.

Qualitative indicators

The qualitative indicators monitor: the global geographic spread of influenza, trends in acute respiratory diseases, the intensity of respiratory disease activity, and the impact of the pandemic on health-care services.

The maps below display information on the qualitative indicators reported. Information is available for approximately 60 countries each week. Implementation of this monitoring system is ongoing and completeness of reporting is expected to increase over time.

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