Objective: review of the time series and panel studies on the short term effects of PM10 on the increases of the illness in childhood.
Design: meta-analysis of panel and time-series studies.
Methods: all studies cited in PubMed that were published between 1990 and 2003 were selected. The results of individual studies were combined to provide an overall estimate of the effect of PMl0 exposure on hospital admissions or emergency room visits for asthma, the frequency of asthmatic symptoms (wheezing and cough), the use of anti-asthma medications (in addition to regular therapy) and lung functioning (peak expiratory flow PEE 1/min) using fixed effects models. Random effects models were used (ORRE or betaRE, 95% CI) when heterogeneity (p <0.10) was present. The presence of publication bias was tested using Egger's test and the bias was corrected with the "trim and fill" method
Results: ten time series studies and 23 panel studies fit the search criteria. Exposure to PM10 was associated with an increase in hospitalizations for asthma (ORRE= 1.017, 95% CI 1.008;1.025), with episodes of wheezing (ORRE= 1.063, 95% CI 1.038;1.087) and coughing (ORRE= 1.026, 95% CI 1.013;1.039), in the use of medications for asthma (ORRE= 1.033, 95% CI 1.008;1.059) and to a decrease in lung function (PRE=-0.269, 95% CI -0.451;-0. 087). We observed heterogeneity and publication bias. The correction for publication bias mitigated the estimates of risk but the most important impact on the results was due to a single, multicenter european study (PEACE) that was very influential
Conclusion: exposure to PM10 was associated with an increase in hospitalizations for asthma and, in asthmatic children, with the frequency of asthmatic symptoms (wheezing and cough), the use of anti-asthma medications (in addition to regular therapy) and a decrease in lung functioning. Additional research is necessary to explain the causes of the heterogeneity in the estimates.