P36 Evaluating the effect of a 5-year history of asthma exacerbations on the risk of future asthma exacerbations using electronic health records

Background Asthma exacerbations can lead to a reduction in quality of life. Many studies have explored risk factors for asthma exacerbations and have shown previous exacerbations to be a risk factor. However, few have explored how a history of exacerbations over a 5 year period can influence risk of future exacerbations or the impact of multiple exacerbations. Methods This study adopted a nested case control design using primary care data (Clinical Practice Research Datalink) linked to secondary care data from 2007–2015. Patients included had current asthma and were aged 18–54 years. Cases were patients who had an exacerbation in the period 2014–15. Controls were patients who did not exacerbate on the same day as the case. Cases were matched 3:1 based on age, gender and GP practice. Conditional logistic regression was used to measure the association between past exacerbations and future exacerbations. Adjusted odds ratios (AOR) were obtained by adjusting for disease severity, BMI, smoking status, social deprivation and related comorbidities. Results There were 4734 cases and 11 752 controls. A previous exacerbation in the last year had a stronger association with a future exacerbation than a history of a previous exacerbation in the years prior to that (previous exacerbation year 1: AOR: 5.59, 95% CI: 5.06 to 6.17; year 2: AOR: 3.14, 95% CI: 2.86 to 3.43; year 3: AOR: 2.43, 95% CI: 2.22 to 2.66; year 4: AOR 2.42, 95% CI: 2.20 to 2.66; year 5: AOR: 2.20, 95% CI 2.00 to 2.41) (figure 1). Patients who experienced ≥2 exacerbations in the previous year had higher odds (AOR: 7.77, 95% CI: 6.52 to 9.25) of a future exacerbation than patients who had only one (AOR: 4.58, 95% CI 4.03 to 5.21). Conclusion Previous exacerbations were found to be significant risk factors for future asthma exacerbations. The risk from previous exacerbations decreased after 1 year but remained significant for previous exacerbations that occurred up to 5 years before. Patients experiencing ≥2 exacerbations in a year were at greater risk of a future exacerbation than patients experiencing one, however, this affect also dissipated for patients with more historical exacerbations.