The influence of ambient coarse particulate matter on asthma hospitalization in children: case-crossover and time-series analyses.

Abstract

In this study, we used both case-crossover and time-series analyses to assess the associations between size-fractionated particulate matter and asthma hospitalization among children 6-12 years old living in Toronto between 1981 and 1993. Specifically, we used exposures averaged over periods varying from 1 to 7 days to assess the effects of particulate matter on asthma hospitalization. We calculated estimates of the relative risk of asthma hospitalization adjusted for daily weather conditions (maximum and minimum temperatures, and average relative humidity) for an incremental exposure corresponding to the interquartile range in particulate matter. Both bidirectional case-crossover and time-series analyses revealed that coarse particulate matter (PM10-2.5) averaged over 5-6 days was significantly associated with asthma hospitalization in both males and females. The magnitude of this effect appeared to increase with increasing number of days of exposure averaging for most models, with the relative risk estimates stabilizing at about 6 days. Using a bidirectional case-crossover analysis, the estimated relative risks were 1.14 [95% confidence interval (CI), 1.02, 1.28] for males and 1.18 (95% CI, 1.02, 1.36) for females, for an increment of 8.4 microg/m(3) in 6-day averages of PM10-2.5. The corresponding relative risk estimates were 1.10 and 1.18, respectively, when we used time-series analysis. The effect of PM10-2.5 remained positive after adjustment for the effects of the gaseous pollutants carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and ozone (O3). We did not find significant effects of fine particulate matter (PM2.5) or of thoracic particulate matter (PM10) on asthma hospitalizations using either of these two analytic approaches. For the most part, relative risk estimates from the unidirectional case-crossover analysis were more pronounced compared with both bidirectional case-crossover and time-series analyses.

Association between particulate matter and emergency room visits, hospital admissions and mortality in Spokane, Washington

“…This caution means that we do not need to discount selectively our marginally significant (P ¼ 0.058) estimate of a protective effect of CO on COPD at the 1-day lag. Moreover, the lags that we found to be significant were longer than we expected a priori Atkinson et al, 2001), although associations at the 3-day lag have been reported (Norris et al, 2000;Lin et al, 2002). Particulate matter is a diverse mix of solid and liquid, organic and inorganic particles, some of which may be causing a health effect.…”

Particulate matter and hospital admission due to arterial hypertension in a medium-sized Brazilian city

“…Conceição et al 16 showed that the difference between results obtained using linear and additive models of Poisson regression is nominal and another study found that the results obtained using time-series and case-crossover analysis are also largely similar 17 .…”

Coarse Particulate Matter and Hospitalization for Respiratory Infections in Children Younger Than 15 Years in Toronto: A Case-Crossover Analysis

“…4,7,16 A recent study observed that the estimated effect of multiple-day exposures to air pollution could be stabilized on 5 to 6 days. 17 In this study, we calculated 1-to 7-day exposure averages ending on the admission date as the exposures in the case period.Control periods of 2 weeks before and after the admission date were used in the bidirectional scheme to minimize autocorrelation between case and control exposures and to control for seasonal and long-term effects. 17,18 To be matched with the case period, exposures in the control period were expressed as 1-to 7-day averages for each pollutant ending on the date 2 weeks before and after the admission date.…”