title: Accuracy of tracheal aspirate gram stain in predicting Staphylococcus aureus infection in ventilator-associated pneumonia.
abstract: BACKGROUND
  The Gram stain can be used to direct initial empiric antimicrobial therapy when complete culture is not available. This rapid test could prevent the initiation of inappropriate therapy and adverse outcomes. However, several studies have attempted to determine the value of the Gram stain in the diagnosis and therapy of bacterial infection in different populations of patients with ventilator-associated pneumonia (VAP) with conflicting results. The objective of this study is to evaluate the accuracy of the Gram stain in predicting the existence of Staphylococcus aureus infections from cultures of patients suspected of having VAP.
  
  
  METHODS
  This prospective single-center open cohort study enrolled 399 patients from December 2005 to December 2010. Patients suspected of having VAP by ATS IDSA criteria were included. Respiratory secretion samples were collected by tracheal aspirate (TA) for standard bacterioscopic analysis by Gram stain and culture.
  
  
  RESULTS
  Respiratory secretion samples collected by tracheal aspirates of 392 patients were analyzed by Gram stain and culture. When Gram-positive cocci were arranged in clusters, the sensitivity was 68.4%, specificity 97.8%, positive predictive value 88.1% and negative predictive value 92.8% for predicting the presence of Staphylococcus aureus in culture (p < 0.001).
  
  
  CONCLUSIONS
  A tracheal aspirate Gram stain can be used to rule out the presence of Staphylococcus aureus in patients with a clinical diagnosis of VAP with a 92.8% Negative Predictive Value. Therefore, 7.2% of patients with Staphylococcus aureus would not be protected by an empiric treatment that limits antimicrobial coverage to Staphylococcus aureus only when Gram positive cocci in clusters are identified.
authors: Hospital de Clinicas de Porto Alegre, Rua Ramiro Barcelos 2350, 90035-003 Porto Alegre, Brazil ; Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2400 - 4o Andar, 90035-003 Porto Alegre, Brazil.
authors: Renato
authors: R
authors: Seligman
authors: Hospital de Clinicas de Porto Alegre, Rua Ramiro Barcelos 2350, 90035-003 Porto Alegre, Brazil ; Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2400 - 4o Andar, 90035-003 Porto Alegre, Brazil.
authors: Beatriz Graeff Santos
authors: BG
authors: Seligman
authors: Hospital de Clinicas de Porto Alegre, Rua Ramiro Barcelos 2350, 90035-003 Porto Alegre, Brazil.
authors: Loriane
authors: L
authors: Konkewicz
authors: Hospital de Clinicas de Porto Alegre, Rua Ramiro Barcelos 2350, 90035-003 Porto Alegre, Brazil.
authors: Rodrigo Pires
authors: RP
authors: Dos Santos
mesh_terms: D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology*; D005840:Gentian Violet; D006801:Humans; D010619:Phenazines; D053717:Pneumonia, Ventilator-Associated / Q000175:diagnosis* / Q000382:microbiology*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000175:diagnosis*; D014132:Trachea / Q000382:microbiology*
chemical_list: C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet
keywords: Gram stain; Staphylococcus aureus; Tracheal aspirate; Ventilator-associated pneumonia