In the period 1999-2002, a large study was conducted
to examine the link between fine particle air pollution and
hospital admissions for heart- and lung-related illnesses.
The study analyzed hospital admissions of all elderly
residents (>65 years) in 204 U.S. counties. Short-term
exposure to PM2.5 (from such sources as motor vehicle
exhaust and power plant emissions) significantly increased
the risk for cardiovascular and respiratory diseases.
Day-to-day variation in PM2.5 concentration was associated
with changes in number of hospital admissions for cardiorespiratory
outcomes, for at least 1-day exposure lag.
For respiratory outcomes, the largest effects occurred at lags 0-1 days for COPD (median day hospitalization rate per 100,000: 2.6) and at lag 2-day for respiratory tract infections (rate: 5.4). Participants aged 75 years or older experienced larger increases in admissions for heart problems and COPD. Importantly, this study showed that even small increases in PM2.5 (just based on natural day-to-day variations) resulted in increased hospital admissions (25)