H1N1 Flu

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.

Questions & Answers

2009 H1N1 Flu In The News

November 4, 2009 1:00 PM ET

2009 H1N1 Hospitalizations in People with Asthma

What does CDC know about hospitalizations among people with asthma who get 2009 H1N1 flu?

People with asthma are at higher risk for serious complications from influenza (flu), including 2009 H1N1 flu. This can place people with asthma at higher risk of hospitalization when they have 2009 H1N1 flu. CDC monitors 2009-H1N1 related hospitalizations, including among people with asthma, through the Emerging Infections Program (EIP).

What is the Emerging Infections Program (EIP)?

The EIP Influenza Project conducts surveillance for laboratory-confirmed influenza (flu) related hospitalizations in children (persons younger than 18 years) and adults in 62 counties covering 13 metropolitan areas of 10 states (for more information see the overview of influenza surveillance in the United States). Cases are identified by reviewing hospital laboratory and admission databases and infection control logs for children and adults with a documented positive influenza test* conducted as a part of routine patient care. EIP estimated hospitalization rates are reported every week during the flu season.

*Tests used by EIP to confirm influenza infection include viral culture, direct/indirect fluorescent antibody assay (DFA/IFA), real-time reverse transcriptase polymerase chain reaction (rRT-PCR), or a commercial rapid antigen test.

What percentage of people hospitalized with 2009 H1N1 flu have asthma?

According to Emerging Infections Program (EIP) data collected from April 15 through October 27, 2009, 32% of people hospitalized with 2009 H1N1 had asthma. Among adults hospitalized with 2009 H1N1, 30% had asthma, whereas 35% of hospitalized children with 2009 H1N1 had asthma.

What percentage of people hospitalized with asthma and 2009 H1N1 are admitted to an Intensive Care Unit (ICU)?

According to Emerging Infections Program (EIP) data collected from April 15 - October 27, 2009, 21% of hospitalized adults with asthma and a 2009 H1N1 infection and 18% of hospitalized children with asthma and a 2009 H1N1 infection were admitted to an ICU. No significant differences in the number of ICU admissions were noted between 2009 H1N1 infected people hospitalized with or without asthma.