title: Aetiology of hospital-acquired pneumonia and trends in antimicrobial resistance.
abstract: OBJECTIVE
  Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) continue to present very significant diagnostic and management challenges. The development, introduction and use of a wider range of immunosuppressive therapies are leading to a broader spectrum of microorganisms causing HAP and VAP. The persistent clinical dilemma regarding their cause is that detection of a microorganism from a respiratory tract sample does not necessarily signify it is the causative agent of the pneumonia. The ever-increasing antibiotic resistance problem means that HAP and VAP are becoming progressively more difficult to treat. In this article, we review the cause, antimicrobial resistance, diagnosis and treatment of HAP and VAP and encapsulate recent developments and concepts in this rapidly moving field.
  
  
  RESULTS
  Although the microbial causes of HAP and VAP remain at present similar to those identified in previous studies, there are marked geographical differences. Resistance rates among Gram-negative bacteria are continually increasing, and for any species, multiresistance is the norm rather than the exception. The development and introduction of rapid point-of-care diagnostics may improve understanding of the cause of HAP and VAP and has immense potential to influence the treatment and clinical outcomes in HAP/VAP, with patients likely to receive much faster, microorganism-specific treatment with obvious downstream improvements to clinical outcome and antimicrobial stewardship.
  
  
  CONCLUSIONS
  We describe recent trends in aetiology of HAP and VAP and recent trends in antimicrobial resistance, including resistance mechanisms causing particular concern. The potential for novel molecular diagnostics to revolutionize the diagnosis and treatment of HAP/VAP is discussed.
authors.affiliation: aCentre for Clinical Microbiology, Division of Infection and Immunity, University College London bUniversity College London Hospitals NHS Foundation Trust, London, UK.
authors.forename: Virve I
authors.initials: VI
authors.lastname: Enne
authors.forename: Yoann
authors.initials: Y
authors.lastname: Personne
authors.forename: Ljuban
authors.initials: L
authors.lastname: Grgic
authors.forename: Vanya
authors.initials: V
authors.lastname: Gant
authors.forename: Alimuddin
authors.initials: A
authors.lastname: Zumla
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D003428:Cross Infection / Q000175:diagnosis* / Q000517:prevention & control; D004352:Drug Resistance, Microbial; D005260:Female; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000302:isolation & purification; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification; D006801:Humans; D017053:Infection Control / Q000379:methods / Q000592:standards; D008297:Male; D011014:Pneumonia / Q000175:diagnosis* / Q000209:etiology / Q000517:prevention & control; D053717:Pneumonia, Ventilator-Associated / Q000175:diagnosis / Q000382:microbiology; D015995:Prevalence; D012307:Risk Factors; D012122:Ventilators, Mechanical / Q000009:adverse effects / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents