1. Division of Medical Microbiology and Genitourinary Medicine, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GA, UK
2. Laboratory of HealthCare Associated Infection, Health Protection Agency, 61 Colindale Avenue, London NW9 5HT, UK
3. Regional Adult Cystic Fibrosis Unit, Cardiothoracic Centre, Liverpool L14 3PE, UK