Pulmonary exacerbations are common events in patients with CF lung disease. Although we lack a consensus definition, they are generally defined as worsening of the daily respiratory and systemic symptoms, often with an acute drop in pulmonary function. For a myriad of reasons, described here, the current best definition of a pulmonary exacerbation is the physician's decision to treat for that indication. The problem with this definition is demonstrated by the variability among clinicians. Issues with other attempts at a definition are also reviewed here. Similarly, there are hurdles to establishing the severity of an exacerbation, as treatment decisions such as hospitalisation are influenced by factors other than worse illness. Exacerbations are associated with multiple adverse outcomes, including loss of lung function, high financial burden and even mortality. Understanding the causes of exacerbations and development of therapies to prevent them are of utmost importance.

Cite as: Flume PA, VanDevanter DR. Cystic fibrosis: definition, severity and impact of pulmonary exacerbations. In: Burgel PR, Contoli M, López-Campos JL, eds. Acute Exacerbations of Pulmonary Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2017; pp. 25–37 [https://doi.org/10.1183/2312508X.10015716].