1918 Influenza Pandemic: In Utero Exposure in the United States and Long-Term Impact on Hospitalizations.

OBJECTIVES: To explore associations between in utero exposure to the 1918 influenza pandemic and hospitalization rates in old age (≥ 70 years) in the United States.

METHODS: We identified individuals exposed (mild and deadly waves) and unexposed in utero to the 1918 influenza pandemic (a natural experiment) by using birth dates from the Asset and Health Dynamics Among the Oldest Old survey. We analyzed differences in hospitalization rates by exposure status with multivariate linear regression.

RESULTS: In utero exposure to the deadly wave of the 1918 influenza pandemic increased the number of hospital visits by 10.0 per 100 persons. For those exposed in utero to the deadliest wave of the influenza pandemic, high rates of functional limitations are shown to drive the higher rates of hospitalizations in old age.

CONCLUSIONS: In utero exposure to the influenza pandemic increased functional limitations and hospitalization rates in old age. Public Health Implications. To determine investments in influenza pandemic prevention programs that protect fetal health, policymakers should include long-term reductions in hospitalizations in their cost-benefit evaluations.