Determinants of mortality among cystic fibrosis patients

Marie-Hélène Cazes, Institut National d'Études Démographiques (INED)
Gil Bellis, Institut National d'Études Démographiques (INED)
Arnaud Bringe, Institut National d'Études Démographiques (INED)
Elisabeth Morand, Institut National d'Études Démographiques (INED)

This paper examines the risk factors of mortality among cystic fibrosis patients in France. Cystic fibrosis is a lethal hereditary disease with autosomal recessive transmission that occurs in most countries, and especially in Europe, the United States and Canada. It is a childhood-onset disease that affects an estimated 1 in 3,500 newborns. The main factor associated with mortality is a loss of respiratory function due to recurrent lung infections by highly pathogenic bacteria. In France, where the estimated incidence of cystic fibrosis is 1 in 4,600 births, a national cystic fibrosis observatory (Observatoire National de la Mucoviscidose, ONM) was set up in 1992 to improve knowledge of the medical, genetic, epidemiological and sociodemographic characteristics of the disease. Data are collected via an annual medical questionnaire sent to specialized hospital services where cystic fibrosis patients are treated. Using data on 3,219 patients registered by the ONM in 1999, we conducted a longitudinal study from 1999 to 2005 (2,218 individuals followed throughout the period) to record the annual number of deaths (276 in all), along with the demographic (sex, age), genetic (mutations), clinical (respiratory function, anthropometry, microbiology), and therapeutic characteristics (antibiotic treatment courses) liable to affect mortality. In the first section, we establish the survival curves by age observed over the seven-year observation period. We then apply a Cox model to analyse the relative contributions of the various recorded factors to the occurrence of death. This approach enables us to analyse in detail the main predictive factors of cystic fibrosis mortality, and thereby to provide pointers for improving therapeutic management of the disease.