CDC Reports U.S. H1N1 Flu Activity Falls to Normal Low Summer Level

H1N1 "swine flu" activity has fallen to a low level typically observed for seasonal influenza during the summer months in the U.S., according to the latest update from the Centers for Disease Control and Prevention (CDC). During the week of May 9-15, doctor visits for flu-like symptoms decreased, flu-related hospitalizations leveled off, and the number of deaths attributed to influenza or pneumonia remained stable. Globally, the most active areas of H1N1 flu transmission are in the tropical regions of the Caribbean, South America, and Southeast Asia.

The most recently distributed CDC weekly update reported that visits to doctors for influenza-like illness decreased from the previous week, and numbers were low in all 10 agency-defined U.S. regions. For the fifth consecutive week, no states reported widespread or regional influenza activity, and most reported either no activity or only sporadic activity.

The proportion of deaths attributed to influenza and pneumonia (7.1%), based on reports from 122 cities, "remained about the same as last week," and no flu-related deaths of children were reported.

The report noted that the majority of the influenza viruses identified continue to be 2009 H1N1 influenza A strains. "These viruses remain similar to the virus chosen for the 2009 H1N1 vaccine and remain susceptible to the antiviral drugs oseltamivir and zanamivir with rare exception," the CDC stated.

For more information, see the CDC's U.S. 2009 H1N1 Flu Situation Update at

Further details regarding the latest weekly statistics are available on the FluView web page at

Internationally, according to data from the World Health Organization (WHO) collected through May 16, the Caribbean, South America, and Southeast Asia are currently the most active areas of 2009 H1N1 A influenza transmission. In addition, influenza B viruses are also being reported in parts of Southeast Asia and account for the majority of flu viruses in East Asia.

Influenza activity is relatively low in most temperate (non-tropical) parts of the northern and southern hemispheres, except for a recent localized outbreak of flu-like illness in Chile. Both H1N1 and seasonal influenza B viruses are being detected in Europe, while H1N1 transmission in sub-Saharan Africa "appears to have dropped markedly."

For more global information, see the CDC's 2009 H1N1 Flu International Situation Update at



Centers for Disease Control and Prevention. 2009 H1N1 Flu: Situation Update. May 21, 2010.