Stochastic modelling of the onset of bronchiolitis obliterans syndrome following lung transplantation: An analysis of risk factors

Obliterative bronchiolitis is the main limitation to long-term survival after lung transplantation: it leads to reduced lung function and eventual death. Bronchiolitis obliterans syndrome (or BOS) which is related to lung function decline can be observed in lung transplant patients, and serves as a marker for obliterative bronchiolitis. Risk factors for developing BOS are the incidences of rejection, infection, and cytomegalovirus in the early postoperative period. Phase-type distributions provide a quite general framework for modelling the times of onset of BOS in lung transplant patients, and allow the above risk factors to be incorporated as covariates. What emerges from an analysis of data from over 300 lung transplant operations using such modelling is a pattern of risk where the hazard rates are not proportional.