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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

2009 H1N1 Flu: International Situation Update

September 18, 2009, 11:00 AM ET

This report provides an update to the international situation as of September 18, 2009. As of September 13, 2009, the World Health Organization (WHO) regions have reported more than 296,471 laboratory-confirmed cases of 2009 H1N1 influenza virus (2009 H1N1) with at least 3,486 deaths, which is an increase of at least 18,864 cases and 281 deaths since September 6th. The laboratory-confirmed cases represent a substantial underestimation of total cases in the world, as many countries focus surveillance and laboratory testing only on people with severe illness. The 2009 H1N1 influenza virus continues to be the dominant influenza virus in circulation in the world. Since April 2009, 60.7% of influenza specimens reported to WHO were 2009 H1N1 viruses. In temperate regions of the Southern Hemisphere, disease due to 2009 H1N1 is largely declining. In tropical regions, there is still substantial disease due to 2009 H1N1. In temperate regions of the Northern Hemisphere, there is some increased disease activity due to 2009 H1N1, including in parts of the United States, Canada and Europe.

Selected Highlights

  • The 2009 H1N1 influenza virus is the predominant influenza virus in circulation worldwide.
  • The epidemiology of the disease caused by the 2009 H1N1 influenza virus in the Southern Hemisphere is very similar to that described in the United States this past spring.
  • There have been no significant changes detected in the 2009 H1N1 influenza virus isolated from persons in the Southern Hemisphere as compared to viruses isolated from persons in the Northern Hemisphere.
  • In August, a White House report was prepared by the Department of Health and Human Services (HHS) in coordination with the Office of the Director for National Intelligence (ODNI) and the Department of State (DoS) and describes the characteristics and impact of 2009 H1N1 influenza A virus in the Southern Hemisphere. The full report can be accessed by the link provided in the Reports and Publications section below.
  • Worldwide, more than 10,000 isolates of 2009 H1N1 influenza have been tested and found to be sensitive to oseltamivir, an antiviral medicine used to treat influenza disease. Only 21 2009 H1N1 isolates tested have been found to be resistant to oseltamivir –10 of these were detected in the United States.

International Resources for 2009 H1N1 Information

Health Organizations

World Health Organization (WHO) Regional Offices

Travel and 2009 H1N1 Flu

Human cases of 2009 H1N1 flu virus infection have been identified in the United States and several countries around the world. For information on 2009 H1N1 flu and travel, see the CDC H1N1 Flu and Travel website.

Reports and Publications

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