Influenza

Influenza update - 24 September 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.

24 September 2010 (week 36) influenza surveilliance map, small version

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 117

24 September 2010 - Influenza virus circulation remains most active in areas of the temperate Southern Hemisphere and in parts of Asia, particularly South and Southeast Asia.

As of early to mid-September 2010, Chile continued to report an increasing national trend of ILI activity associated with increased co-circulation of seasonal and H1N1 (2009) influenza viruses. The current influenza season in Chile has been notable for its unusually late arrival and locally intense epidemics in several regions which have observed levels of ILI matching or slightly surpassing levels seen during the 2009 winter pandemic wave. Since the beginning of the current epidemic period, which began during early August 2010, the proportion of emergency department consultations for influenza has increased markedly among children <15 years of age followed by persons 15-64 years of age; during the same period, the proportion of emergency department consultations for pneumonia increased most among persons >65 years of age. In neighboring Argentina, limited data suggest that low levels of predominantly influenza type B viruses circulated between June and late August 2010.

In New Zealand, the national consultation rate for ILI fell below the seasonal baseline during the third week of September 2010 after peaking approximately one month earlier. Compared to the 2009 winter pandemic wave, the influenza season to date in New Zealand has been characterized by a late winter arrival, lower overall levels of ILI nationally but significant regional variability including locally intense outbreaks in some areas, and continued predominance of circulating H1N1 (2009) viruses relative to seasonal influenza viruses. In Australia, a steady increase in the national rate of ILI consultations was observed between late August and mid-September 2010, but overall levels remain well below those seen during the past three winter influenza seasons; geographically widespread activity has been recently reported in Victoria, South Australia, and Western Australia. Influenza H1N1 (2009) and seasonal type B viruses continue to co-circulate in Australia.

In Asia, significant influenza virus circulation continues to be reported in India and Thailand and to a lesser extent in China. In India, there is widespread persistence of active influenza virus circulation. As of mid-September 2010, at least 17 states and territories reported new cases, with the highest numbers reported in the Delhi, Maharashtra, and Karnataka; in all but a few states, overall influenza activity appears to be stable or declining suggesting that the national epidemic has passed its peak. Influenza H1N1 (2009) virus continues to be the predominant circulating influenza virus in India. In southern China and in Hong Kong (SAR China) and to a lesser extent in northern China, there has been an increasing reemergence of circulating seasonal influenza H3N2 viruses since July 2010. In Hong Kong (SAR China) but not in mainland China, increased detections of seasonal influenza H3N2 viruses over this period have been associated with a steady increase in the levels of consultations for ILI at sentinel sites. In Thailand, there has been active circulation of influenza H1N1 (2009) viruses and to a lesser extent seasonal influenza type B and H3N2 viruses since mid-July 2010, coinciding with a period of usual transmission of influenza viruses.

In South Africa, peak wintertime influenza activity has passed but there continues to be active co-circulation of seasonal influenza (type B and H3N2) viruses and also, more recently, influenza H1N1 (2009) viruses. Influenza virus detections among ILI and SARI patients at sentinel sites have declined since mid-August 2010.

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.