The Seasonality and Enivronmental Triggers of Medical Contacts made by School-age Asthmatics and Non-asthmatics

Introduction: Asthma is a common chronic condition that affects up to 1.1 million children in the UK. Exacerbations of asthma follow a pronounced seasonal pattern and are associated with environmental triggers. A number of studies have investigated the associations. However, few studies have undertaken an asthmatic-non-asthmatic design and with even fewer set within the UK.
Aims: To investigate medical contacts made by school age asthmatics and non-asthmatics across different health care settings and geographies with respect to the seasonality of the medical contacts and the association between the medical contacts and outdoor environmental exposures
Study design: A retrospective time-series and spatial investigation.
Data: for the outcome, clinical data were obtained from three geographies decreasing in size (England and Wales, the Trent Region and Sheffield) for school-age asthmatics and non-asthmatics. Daily counts of medical contact made by asthmatics and non-asthmatics were obtained for the period 1999 to 2004. The difference between daily counts of asthmatics and non-asthmatics was calculated to create the second outcome, daily excess. For Sheffield, medical contacts made for asthmatic and non-asthmatic reasons were also aggregated by Middle Super Output Area level (MSOA) for the spatial analysis. For the exposures of interest, daily measures of outdoor pollution, weather and pollen exposures were obtained for the city of Sheffield.
Method of Analysis: Graphical assessment was undertaken to examine seasonal patterns of daily counts/excess. Accounting for covariates, the effect of pollutant, weather and pollen exposures were investigated using autoregressive analyses. Exposures lagged by seven days were investigated. A separate spatial analysis was undertaken on Sheffield. Comparative Hospital Ratios (CHRs) were calculated and correlated with area defined pollutant measures at MSOA level.
Results: Seasonal patterns were more apparent in England and Wales. Seasonal patterns were also observed with the daily excess. Peaks and troughs correlated well with the school calendar – troughs during Easter and summer holidays and peaks after the return to school. With a greater total number of events observed there were a higher number of significant environmental exposures associated with daily counts from England and Wales compared to the Trent Region or Sheffield. Evidence of lagged effects was inconsistent. Results suggest the associations to be greater in non-asthmatics. In Sheffield, results from the spatial investigation revealed three significant hotspots of CHRs for asthmatic contacts only. Significant associations were found between CHRs for asthmatics and air quality measures of NO2 (a positive correlation) and O3 (a negative correlation). Significant negative associations were also found between CHRs for asthmatic contacts and the proportion of domestically and commercially sourced emissions.
Conclusion: The seasonal effect in asthmatics is over and above the average (non-asthmatics) school population. Little difference was observed in environmental associations between asthmatics and non-asthmatics. Further research is required to investigate the associations between asthma and environmental triggers at small area levels in the UK.