Letter: Respiratory filters in clinical practice.
D000391:Air Microbiology; D003428:Cross Infection / Q000517:prevention & control; D004209:Disposable Equipment; D004739:England; D005374:Filtration / Q000295:instrumentation*; D006801:Humans; D013242:Sterilization / Q000295:instrumentation*; D012122:Ventilators, Mechanical / Q000592:standards*