The Impact of Influenza Epidemics on Hospitalizations

TLDR

Influenza season severity is traditionally measured by excess pneumonia and influenza mortality. The authors estimated excess P&I hospitalizations using National Hospital Discharge Survey data across 26 influenza seasons (1970‑1995). Across 26 seasons, excess P&I hospitalizations averaged 49 per 100,000 (range 8–102), were twice as high during A(H3N2) seasons, and were linearly correlated with excess mortality; while <65 years accounted for 57% of cases, the elderly had higher per‑capita risk, and post‑1968 pandemic data suggest future pandemics may disproportionately raise hospitalizations among younger adults.

Abstract

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.