1. University of Pennsylvania Perelman School of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, Philadelphia, Pennsylvania, USA
2. Johns Hopkins School of Medicine, Department of Pathology, Division of Microbiology, Baltimore, Maryland, USA
3. Johns Hopkins School of Medicine, Department of Medicine, Division of Pulmonary and Critical Care Medicine, Baltimore, Maryland, USA
4. Johns Hopkins Hospital, Microbiology Laboratory, Baltimore, Maryland, USA