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The effect of ambient ozone and hydrocarbons on childhood wheezy episodes

Aim: To explore the hypothesis that speciated hydrocarbons accumulate at low levels of ozone (O3) and are more directly associated with acute childhood wheezy episodes than O3 itself or sulphur dioxide (SO2), nitrogen dioxide (NO2), small participates (PM10)1. Method, setting and subjects: Prospective observational study over a one year period (1/12/95 to 30/11/96) measuring the daily attendance rate at The Lewisham Children's A & E dept. Daily mean concentrations of air pollutants measured at the Bexley and Eltham Dept of Environment automatic monitoring sites within 10 miles of the hospital (air quality information available at: www.aeat.co.uk/netcen/aqarchive/auto.html). Daily mean weather variables from the London Weather Centre. Results: Compared to the 21631 non respiratory attendances and after adjustment for season, temperature and wind speed, the 1461 acute wheezers were more likely to attend 2 days after high hydrocarbon levels. For O3 there was a same day U-shape effect between incidence and O3 with a significant inverse relation at low concentrations. The effects of both hydrocarbons and O3 were strongest in children under the age of 2 years (n=572). For example, in this group the incidence increased by 8% (95% CI: 3 to 10%) per standard deviation (sd =2.8μg/M3) increase in benzene concentration. For O3 the incidence increased by 141% (95% CI: 54 to 267%) at -1 sd = 18.8μg/M3 below the mean annual daily O3 concentration of 32.7μg/M3 and by 47% (95%CI: -4% to 126%) at +1 sd above the mean. The effects of NO2, SO2 and PM10 were not significant. Conclusion: The inverse relationship between O3 and wheezy episodes confirms an earlier observation2 in W London and supports the hypothesis that primary hydrocarbon pollutants play a more important causative role in triggering childhood wheezy episodes than the secondary pollutant O31.