title: Community-associated methicillin-resistant Staphylococcus aureus necrotizing pneumonia without evidence of antecedent viral upper respiratory infection.
abstract: BACKGROUND
  USA300 community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) strains causing necrotizing pneumonia have been reported in association with antecedent viral upper respiratory tract infections (URI).
  
  
  METHODS
  A case series of necrotizing pneumonia presenting as a primary or coprimary infection, secondary to CA-MRSA without evidence of antecedent viral URI, is presented. Cases were identified through the infectious diseases consultation service records. Clinical and radiographic data were collected by chart review and electronic records. MRSA strains were isolated from sputum, bronchoalveolar lavage, pleural fluid or blood cultures and confirmed using standard laboratory procedures. MRSA strains were characterized by susceptibility testing, pulsed-field gel electrophoresis, spa typing, agr typing and multilocus sequence typing. Testing for respiratory viruses was performed by appropriate serological testing of banked sera, or nucleic acid testing of nasopharyngeal or bronchoalveloar lavage specimens.
  
  
  RESULTS
  Ten patients who presented or copresented with CA necrotizing pneumonia secondary to CA-MRSA from April 2004 to October 2011 were identified. The median length of stay was 22.5 days. Mortality was 20.0%. Classical risk factors for CA-MRSA were identified in seven of 10 (70.0%) cases. Chest tube placement occurred in seven of 10 patients with empyema. None of the patients had historical evidence of antecedent URI. In eight of 10 patients, serological or nucleic acid testing testing revealed no evidence of acute viral coinfection. Eight strains were CMRSA-10 (USA300). The remaining two strains were a USA300 genetically related strain and a USA1100 strain.
  
  
  CONCLUSIONS
  Pneumonia secondary to CA-MRSA can occur in the absence of an antecedent URI. Infections due to CA-MRSA are associated with significant morbidity and mortality. Clinicians need to have an awareness of this clinical entity, particularly in patients who are in risk groups that predispose to exposure to this bacterium.
authors.affiliation: Departartments of Medicine, University of Calgary;
authors.forename: Cristina Moran
authors.initials: CM
authors.lastname: Toro
authors.affiliation: Departartments of Medicine, University of Calgary;
authors.forename: Jack
authors.initials: J
authors.lastname: Janvier
authors.affiliation: Departartments of Medicine, University of Calgary;
authors.forename: Kunyan
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Microbiology, Immunology and Infectious Diseases, University of Calgary; ; Provincial Laboratory of Alberta, Alberta Health Services;
authors.forename: Kevin
authors.initials: K
authors.lastname: Fonseca
authors.affiliation: Departartments of Medicine, University of Calgary; ; Pathology and Laboratory Medicine, University of Calgary; ; The Calvin, Phoebe and Joan Synder Institute for Chronic Diseases, Alberta Health Services - Calgary Zone and University of Calgary; ; Calgary Laboratory Services;
authors.forename: Dan
authors.initials: D
authors.lastname: Gregson
authors.affiliation: Departartments of Medicine, University of Calgary; ; Pathology and Laboratory Medicine, University of Calgary; ; The Calvin, Phoebe and Joan Synder Institute for Chronic Diseases, Alberta Health Services - Calgary Zone and University of Calgary; ; Calgary Laboratory Services;
authors.forename: Deirdre
authors.initials: D
authors.lastname: Church
authors.affiliation: Departartments of Medicine, University of Calgary; ; Pathology and Laboratory Medicine, University of Calgary; ; The Calvin, Phoebe and Joan Synder Institute for Chronic Diseases, Alberta Health Services - Calgary Zone and University of Calgary; ; Calgary Laboratory Services; ; Departments of Critical Care Medicine, University of Calgary; ; Community Health Sciences, University of Calgary;
authors.forename: Kevin
authors.initials: K
authors.lastname: Laupland
authors.affiliation: Departartments of Medicine, University of Calgary; ; Microbiology, Immunology and Infectious Diseases, University of Calgary; ; The Calvin, Phoebe and Joan Synder Institute for Chronic Diseases, Alberta Health Services - Calgary Zone and University of Calgary;
authors.forename: Harvey
authors.initials: H
authors.lastname: Rabin
authors.affiliation: Departments of Medicine, University of Western Ontario, London, Ontario ; Microbiology and Infectious Diseases, University of Western Ontario, London, Ontario.
authors.forename: Sameer
authors.initials: S
authors.lastname: Elsayed
authors.affiliation: Departartments of Medicine, University of Calgary;
authors.forename: John
authors.initials: J
authors.lastname: Conly
keywords: Community-associated methicillin-resistant; Necrosis; Pneumonia; Staphylococcus aureus; Viral infection