The Burden of Influenza-Associated Critical Illness Hospitalizations

A doctor applies ozygen to a patient in the emergency room.

Influenza is often unrecognized by physicians treating critically ill patients in the hospital.

The Issue:

Influenza is the most common vaccine-preventable disease in the United States. Many critically ill people hospitalized with an influenza virus infection do not know they have one. They are not tested in the hospital or test negative (due to insensitive tests) for the flu. Therefore, the burden of critical illness hospitalizations due to influenza is not known.

In this study, researchers determined the proportion of all critical illness hospitalizations that could be attributed to seasonal influenza.

Key Findings

  • Some 1.3 percent of all critical illness hospitalizations (defined as hospitalization with acute respiratory failure, severe sepsis, or in-hospital death) were attributable to influenza.

  • During flu season the percentage of critical illness hospitalizations attributable to influenza rises to 3.4 percent.

  • Extrapolating those incidence estimates, 28,000 adults are hospitalized for influenza-associated critical illness annually.


Critical care physicians should heighten their suspicion for influenza in their patients, particularly during flu season when it is circulating in their community. Medical staff should be vaccinated and infection control procedures reinforced.

About the Study:

Researchers used hospitalization data, and influenza surveillance data from the Centers for Disease Control and Prevention for adults in three states—Arizona, California, and Washington—from 2003 to 2009.