• C J Walsh, T Zaihra, A Benedetti, C Fugère, R Olivenstein, C Lemière, Q Hamid, and J G Martin.
• Department of Medicine, Institute of Medical Sciences, Keenan Centre for Biomedical Research, Li Ka Shing Knowledge institute, St. Michael's Hospital, University of Toronto, Toronto, ON, Canada.
• Clin. Exp. Allergy. 2016 Oct 1; 46 (10): 1291-302.

BackgroundAirway inflammatory phenotyping is increasingly applied to subjects with asthma. However, its relationship to clinical outcomes in difficult asthma is incompletely elucidated.ObjectiveThe goal of our study was to determine the relationship between exacerbation rates and phenotypes of difficult asthma based on the longitudinal measures of sputum eosinophils and neutrophils.MethodsSubjects in the longitudinal observational study from two tertiary care centres that completed 1 year of observation and provided at least three sputum samples were classified by inflammatory phenotypes using previously established thresholds. Kaplan-Meier curves and univariable and multivariable Cox proportional hazard models were used to determine the association between inflammatory phenotypes and exacerbation rate.ResultsDuring the study, 115 exacerbations occurred in 73 severe asthmatic subjects. Subjects with the persistently eosinophilic phenotype had a significantly shorter time to first exacerbation and greater risk of exacerbation over a 1-year period than those with the non-eosinophilic phenotype based on the univariable and multivariable Cox proportional hazard model (hazard ratio [HR], 3.24; 95% confidence interval [CI], 1.35-7.72; adjusted HR, 3.90; 95% CI, 1.34-11.36). No significant differences in time to first exacerbation or exacerbation risk over a 1-year period were observed among the neutrophilic phenotypes.ConclusionsThe persistent eosinophilic phenotype is associated with increased exacerbation risk compared with the non-eosinophilic phenotype in severe asthma. No differences in time to first exacerbation or exacerbation risk over a 1-year period were detected among neutrophilic phenotypes.© 2016 John Wiley & Sons Ltd.

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