• Chloe I Bloom, Thomas Palmer, Johanna Feary, Jennifer K Quint, and Paul Cullinan.
• National Heart and Lung Institute, Imperial College London, London, United Kingdom.
• Am. J. Respir. Crit. Care Med. 2019 Feb 15; 199 (4): 446-453.

RationaleAsthma is heterogeneous and knowledge on exacerbation patterns is lacking. Previous studies have had a relatively short follow-up or focused on severe disease.ObjectivesTo describe exacerbation patterns over a prolonged follow-up in a population that includes patients of all disease severity.MethodsWe used electronic health care records to identify patients with asthma aged 18-55 years and their exacerbations from 2007 to 2015. A cohort with greater than or equal to 7 years of data was used to describe exacerbation patterns by asthma severity defined by medication use. Effect estimates for risk factors were calculated for sporadic (single year of exacerbations) and recurrent (>1 yr) exacerbation patterns, using logistic regression. In a nested case-control design, the association between a history of exacerbations, spanning 5 years, and a future exacerbation was examined.Measurements And Main ResultsA total of 51,462 patients were eligible for the 7-year cohort; 64% had no exacerbations. Of those who exacerbated, 51% did so only once; exacerbation frequency increased with disease severity. Only 370 patients (0.7%) were characterized by a frequent-exacerbator phenotype (yearly exacerbations), of whom 58% had mild/moderate asthma. Exacerbation risk factors were not uniquely associated with a particular exacerbation pattern. A past exacerbation increased the risk of a future exacerbation more than all other factors, although this effect dissipated over 5 years.ConclusionsDuring 7 years of follow-up, exacerbations occur in around one-third of patients. Of those who exacerbate, half do not do so again; the timing of future exacerbations is largely unpredictable. Just 2% exhibit a frequent-exacerbator phenotype. Past exacerbation patterns are the most informative risk factor for predicting future exacerbations.

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