Date Published: July 18, 2017
Publisher: Public Library of Science
Author(s): Julie E. Goodman, Christine T. Loftus, Xiaobin Liu, Ke Zu, Alexander Larcombe.
Epidemiology studies have shown that ambient concentrations of ozone and fine particulate matter (PM2.5) are associated with increased emergency department (ED) visits and hospital admissions (HAs) for asthma.
Evaluate the impact of outdoor pollen, respiratory infections, and socioeconomic status (SES) on the associations between ambient ozone and PM2.5 and asthma HAs in New York City.
Daily ozone, PM2.5, meteorological factors, pollen, and hospitalization records during 1999 to 2009 were obtained for New York City residents. Daily counts of HAs for asthma and respiratory infections were calculated for all-age and specific age groups, and for high- and low-SES communities. Generalized additive models were used to examine ambient concentrations of ozone and PM2.5 and asthma HAs, potential confounding effects of outdoor pollen and HAs for respiratory infections, and potential effect modification by neighborhood SES.
Both ozone and PM2.5 were statistically significantly associated with increased asthma HAs in children aged 6–18 years (per 10 ppb increase in ozone: RR = 1.0203, 95% CI: 1.0028–1.0382; per 10 μg/m3 increase in PM2.5: RR = 1.0218, 95% CI: 1.0007–1.0434), but not with total asthma HAs, or asthma HAs in other age groups. These associations were stronger for children living in the high-SES areas. Adjustment for respiratory infection HAs at various lags did not result in changes greater than 10% in the risk estimates for either ozone or PM2.5. In contrast, adjustment for outdoor pollen generally attenuated the estimated RRs for both ozone and PM2.5.
Ambient ozone and PM2.5 are associated with asthma HAs in school-age children, and these associations are not modified by SES. HAs for respiratory infections do not appear to be a confounder for observed ozone- and PM2.5-asthma HAs associations, but pollen may be a weak confounder.
A number of epidemiology studies have reported positive associations between asthma exacerbation and ambient concentrations of ozone and fine particulate matter (PM2.5), measured as emergency department (ED) visits or hospital admissions (HAs) for asthma (e.g., [1–6]), and that children may be particularly susceptible to the effects of air pollution (e.g., see [7–10]). Many of these studies may have been vulnerable to confounding by time-varying factors such as temperature, outdoor pollen, and the start of the school year. Various methods have been developed to mitigate the effect of such confounding on effect estimates, but residual confounding remains an important source of uncertainty. Because the magnitude of associations between short-term air pollution and health effects are small, any residual confounding–even if small–could have had a substantial impact on the interpretation of study findings [11–13].
Daily counts of HAs for asthma and respiratory infections, daily ambient ozone, PM2.5, pollen concentrations, and daily temperatures in New York City are presented in Table 1 and S1 Table. There were a total of 295,497 (average daily count of 73.5) asthma HAs in New York City from 1999 to 2009, which included 113,144 (38.3%) patients who lived in high SES communities (mean daily counts = 28.2) and 179,743 (60.8%) who lived in low SES communities (mean daily counts = 44.7). Daily counts of respiratory infection HAs ranged from 0 to 534, with an average of 156.4. Daily pollen concentrations ranged from 0 to 16,425.2 grains/m3, with a mean of 234.6 grains/m3. Average daily concentrations of ozone and PM2.5 were 30.7 ppb and 13.8 μg/m3, respectively. Both ozone and PM2.5 were significantly correlated with temperatures and total weed pollens (S2 Table).
We conducted a time series analysis of ambient ozone and PM2.5 and daily counts of asthma HAs in New York City, and observed small elevations in the risk of asthma HAs among school-age children following elevated concentrations of pollutants. HAs for respiratory infections do not appear to be a confounder for observed air pollutant-asthma HAs associations, but pollen may be a weak confounder. SES did not appear to modify the observed associations between asthma HAs and air pollutants.