Background: Traditional methods of measuring the impact and cost of in
fluenza virus have focused on epidemic years and morbidity and mortali
ty due to pneumonia and influenza. Methods: Annualized age-sex-race ad
justed rates of hospitalization for pneumonia and influenza and other
diagnoses among elderly Medicare beneficiaries during the epidemic inf
luenza season of 1989 to 1990 and the nonepidemic season of 1990 to 19
91 were compared with an interim period in 1990 without influenza viru
s circulation. Results: The rates of hospitalization for pneumonia and
influenza, acute bronchitis, chronic respiratory disease, and congest
ive heart failure were significantly greater during each influenza per
iod compared with the interim period. The highest rates were found in
the epidemic season of 1989 to 1900. The amount reimbursed by Medicare
to hospitals for the treatment of excess hospitalizations during peri
ods of influenza activity was more than $1 billion in 1989 to 1990 and
almost $750 million in 1990 to 1991. Conclusions: Measures of the imp
act and cost of influenza in elderly Americans should include all of t
he diagnoses listed above and should recognize that the impact of infl
uenza virus is significant even in nonepidemic years. There are great
opportunities for cost savings if effective control programs are imple
mented.