Seasonal analysis of emergency department presentations in Western Australia, 2009/10–2014/15

Understanding the dynamic effects of seasonal variations of emergency department (ED) presentations is necessary to enhance health service planning and delivery, avoid overcrowding and meet the demand of the population. Time series analysis of seasonal trend decomposition using Loess (STL) was used to decompose and isolate the seasonal component of the ED presentations in Western Australia (WA) hospitals. Between 2009/10 and 2014/15, there were 5,652,556 ED presentations that show distinctive seasonal pattern. The overall seasonal variation was 7.0% (95% CI: 6.0–8.4%) and peaked in winter, with the highest in August. However, stratification analysis revealed that patients aged 15–64 years and those with triage 4 and 5 peaked in summer. The stratification for the most frequent conditions presented to metropolitan EDs and triaged as categories 1, 2 or 3 (most urgent conditions) shown that acute upper respiratory infection, pneumonia, viral infection, status asthmaticus and breathing abnormalities peaked in winter, whereas cellulitis, urinary tract infection, threatened abortion, intestinal infection, gastroenteritis and colitis, nausea and vomiting, and open wound of finger peaked in summer. The findings may be important in developing strategies and policies to manage ED demand in peak periods to avoid overcrowding and improve service delivery.