The impact of influenza epidemics on hospitalizations

J Infect Dis. 2000 Mar;181(3):831-7. doi: 10.1086/315320.


The traditional method for assessing the severity of influenza seasons is to estimate the associated increase (i.e., excess) in pneumonia and influenza (P&I) mortality. In this study, excess P&I hospitalizations were estimated from National Hospital Discharge Survey Data from 26 influenza seasons (1970-1995). The average seasonal rate of excess P&I hospitalization was 49 (range, 8-102) /100,000 persons, but average rates were twice as high during A(H3N2) influenza seasons as during A(H1N1)/B seasons. Persons aged <65 years had 57% of all influenza-related hospitalizations; however, the average seasonal risk for influenza-related P&I hospitalizations was much higher in the elderly than in persons aged <65 years. The 26 pairs of excess P&I hospitalization and mortality rates were linearly correlated. During the A(H3N2) influenza seasons after the 1968 pandemic, excess P&I hospitalizations declined among persons aged <65 years but not among the elderly. This suggests that influenza-related hospitalizations will increase disproportionately among younger persons in future pandemics.

MeSH terms

  • Adult
  • Age Factors
  • Aged
  • Hospitalization*
  • Humans
  • Influenza, Human / epidemiology*
  • Influenza, Human / mortality
  • Middle Aged
  • Pneumonia / epidemiology
  • Pneumonia / mortality
  • Seasons