Methods: Endotracheal aspirates (ETA), nasal swabs, and clinical data were collected from 238 patients admitted to 3 ICUs at the Lahey Clinic (Burlington, MA) between June 2014 and June 2015 who were mechanically ventilated for >48 hours. S. aureus colonization was analyzed by semi-quantitative microbiological analysis of ETAs. Heavy colonization was defined as moderate/many (3+/4+) bacterial growth. VAP was assessed according to standard criteria. S. aureus active antibiotics were analyzed by chart review.
Results: 71 patients (29.8%) were nasally colonized with S. aureus, 50 of whom (70.4%) had tracheal colonization and 29 of those (40.8%) were heavily colonized. Among the 167 patients not colonized nasally, only 20 (12.0%) had tracheal colonization and 8 of these (4.8%) had heavy colonization. The positive and negative predictive values of nasal colonization for subsequent tracheal heavy colonization were 40.9% and 95.2%. Of the total population (n = 238), 37 patients (15.6%) had heavy tracheal colonization with 11 of them (29.7%) progressing to S. aureus VAP. MSSA strains were more prevalent among the isolates from VAP patients compared to MRSA strains (63.6% versus 36.4%), while heavily colonized patients had a more balanced MSSA-MRSA isolate profile (52.6% vs. 47.4%). Of note, 8 of the 11 VAP patients (72.7%) had S. aureus nasal colonization at enrollment.
Of the 37 patients with heavy tracheal S. aureus colonization, 28 (75.7%) received S. aureus active antibiotics during the 3 days preceding the start of heavy colonization. Additionally, S. aureus active antibiotics were administered in 10 out of 11 VAP patients (90.9%) in the 3 days preceding the VAP diagnosis.
Conclusion: Close to one-third of patients with heavy tracheal S. aureus colonization progressed to VAP. Microbiologically appropriate antibiotics did not prevent or impact heavy colonization in the vast majority of patients and did not halt progression to VAP. High progression rate to VAP reflects resilience of the pathogen to conventional therapy.
Arsanis Biosciences GmbH:
A. Waqas, None
J. Hudcova, Arsanis Biosciences GmbH: Investigator , Research support
J. Rashid, None
C. Scopa, None
M. Khan, None
M. Goggin, None
L. Stulik, Arsanis Biosciences GmbH: Employee and Shareholder , Salary
E. Nagy, Arsanis Biosciences GmbH: Employee , Salary
Arsanis, Inc.: Board Member and Shareholder , Salary
Austrian Research Promotion Agency FFG: Grant Investigator , Research grant
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