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Updated Sep 22, 2004
How many people in the United States are
hospitalized with influenza in a typical year?
A
study conducted by CDC and published in the Journal
of American Medical Association (JAMA) on September
15 has provided new information on the number of people
in the United States that are hospitalized from influenza-related
complications each year. The study is based on records
from 1979 to 2001 from about 500 hospitals across the
United States. The study concluded that, on average,
more than 200,000 people in the United States
are hospitalized each year for respiratory and heart
conditions illnesses associated with influenza virus
infections.
Updated Sep 22, 2004
Is the number of people in the United States being
hospitalized for flu complications each year increasing?
The
results of a study conducted by CDC and published in
the Journal
of American Medical Association (JAMA) on September
15 indicate an overall increasing trend in the number of
flu-related hospitalizations in the United States each year.
The study looked at hospital records from 1979 to 2001.
In 1979, there were 120,929 flu-related hospitalizations.
The number was lower in some years after that, but there
was an overall upward trend. During the 1990s, the average
number of people hospitalized was over 200,000 but individual
seasons ranged from a low of 157,911 in 1990-91 to a high
of 430,960 in 1997-98.
Updated Sep 22, 2004
What was the previous estimate of the number of
people in the United States hospitalized as a result
of influenza?
In a paper published in 2000, CDC
estimated that an average of 114,000 people were hospitalized
as a result of influenza-associated infections each year.
Updated Sep 22, 2004
What accounts for the increase in the number of
people in the United States hospitalized for influenza
each year?
The new estimates about the number
of influenza-associated hospitalizations in the United
States each year are higher for several reasons.
- The range of illnesses analyzed in the new study is
broader than in the previous study. The new study includes respiratory
and heart diseases associated with influenza infections. The
earlier CDC study published in 2000 only analyzed
pneumonia and influenza hospitalizations. When analyses
were restricted only to pneumonia and influenza hospitalizations,
however, there was still an increase in hospitalizations.
- Influenza A (H3N2) viruses predominated in several
recent influenza seasons, and these viruses generally
have been associated with higher numbers of serious
illnesses than influenza A (H1N1) or influenza B viruses.
The higher numbers of people hospitalized during H3N2
influenza seasons may have increased the average.
- The U.S. population is growing older and therefore,
more vulnerable to developing severe complications
from influenza.
- During the 1990s influenza viruses have either circulated
or been detected for longer periods of time.
Updated Sep 22, 2004
What else did the new study on influenza-associated
hospitalizations find?
- The study found that while the number of influenza-associated
hospitalizations is increasing, the rates of influenza
associated hospitalizations were stable after accounting
for the length of the influenza season.
- The study concluded that the rates of influenza-associated
hospitalization during an influenza season are highest
when influenza A (H3N2) viruses predominate compared
to years when influenza A (H1N1) or influenza B viruses
predominated.
- The study found that people 85 years and older have
the highest rates of influenza-associated hospitalization.
- The study found that children younger than 5 years
old had rates of hospitalization similar to people 50
to 64 years of age.
These findings support previously published data.
Updated Sep 22, 2004
What is the main lesson learned from this study?
Influenza
is associated with large numbers of hospitalizations. The
results of this study demonstrate the substantial health
impact of influenza and underscore the need to ensure vaccination
of people at increased risk of serious influenza complications,
especially people 65 years and older.
Updated Sep 22, 2004
Can you provide more information about the study
on influenza-associated hospitalizations?
The
study is entitled “Influenza-Associated
Hospitalizations in the United States 1979 Through the
2000-2001 Respiratory Seasons.” It appeared
in the Journal of American Medical Association’s
September 14, 2004 issue (volume 292, no. 11). The study
was co-authored by 7 CDC staff members.
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