Context Ozone has been associated with various adverse health effects, including
increased rates of hospital admissions and exacerbation of respiratory illnesses.
Although numerous time-series studies have estimated associations between
day-to-day variation in ozone levels and mortality counts, results have been
inconclusive.
Objective To investigate whether short-term (daily and weekly) exposure to ambient
ozone is associated with mortality in the United States.
Design and Setting Using analytical methods and databases developed for the National Morbidity,
Mortality, and Air Pollution Study, we estimated a national average relative
rate of mortality associated with short-term exposure to ambient ozone for
95 large US urban communities from 1987-2000. We used distributed-lag models
for estimating community-specific relative rates of mortality adjusted for
time-varying confounders (particulate matter, weather, seasonality, and long-term
trends) and hierarchical models for combining relative rates across communities
to estimate a national average relative rate, taking into account spatial
heterogeneity.
Main Outcome Measure Daily counts of total non–injury-related mortality and cardiovascular
and respiratory mortality in 95 large US communities during a 14-year period.
Results A 10-ppb increase in the previous week’s ozone was associated
with a 0.52% increase in daily mortality (95% posterior interval [PI], 0.27%-0.77%)
and a 0.64% increase in cardiovascular and respiratory mortality (95% PI,
0.31%-0.98%). Effect estimates for aggregate ozone during the previous week
were larger than for models considering only a single day’s exposure.
Results were robust to adjustment for particulate matter, weather, seasonality,
and long-term trends.
Conclusions These results indicate a statistically significant association between
short-term changes in ozone and mortality on average for 95 large US urban
communities, which include about 40% of the total US population. The findings
indicate that this widespread pollutant adversely affects public health.