Background:Clinically diagnosed ventilator-associated pneumonia (VAP) is common in the long-term acute-care hospital (LTACH) setting and may contribute to adverse ventilator-associated events (VAEs). Pseudomonas aeruginosais a common causative organism of VAP. We evaluated the impact of respiratory P. aeruginosacolonization and bacterial community dominance, both diagnosed and undiagnosed, on subsequent P. aeruginosaVAP and VAE events during long-term acute care. Methods:We enrolled 83 patients on LTACH admission for ventilator weaning, performed longitudinal sampling of endotracheal aspirates followed by 16S rRNA gene sequencing (Illumina HiSeq), and bacterial community profiling (QIIME2). Statistical analysis was performed with R and Stan; mixed-effects models were fit to relate the abundance of respiratory Psaon admission to clinically diagnosed VAP and VAE events. Results:Of the 83 patients included, 12 were diagnosed with P. aeruginosapneumonia during the 14 days prior to LTACH admission (known P. aeruginosa), and 22 additional patients received anti–P. aeruginosaantibiotics within 48 hours of admission (suspected P. aeruginosa); 49 patients had no known or suspected P. aeruginosa(unknown P. aeruginosa). Among the known P. aeruginosagroup, all 12 patients had P. aeruginosadetectable by 16S sequencing, with elevated admission P. aeruginosaproportional abundance (median, 0.97; IQR, 0.33–1). Among the suspected P. aeruginosagroup, all 22 patients had P. aeruginosadetectable by 16S sequencing, with a wide range of admission P. aeruginosaproportional abundance (median, 0.0088; IQR, 0.00012–0.31). Of the 49 patients in the unknown group, 47 also had detectable respiratory Psa, and many had high P. aeruginosaproportional abundance at admission (median, 0.014; IQR, 0.00025–0.52). Incident P. aeruginosaVAP was observed within 30 days in 4 of the known P. aeruginosapatients (33.3%), 5 of the suspected P. aeruginosapatients (22.7%), and 8 of the unknown P. aeruginosapatients (16.3%). VAE was observed within 30 days in 1 of the known P. aeruginosapatients (8.3%), 2 of the suspected P. aeruginosapatients (9.1%), and 1 of the unknown P. aeruginosapatients (2%). Admission P. aeruginosaabundance was positively associated with VAP and VAE risk in all groups, but the association only achieved statistical significance in the unknown group (type S error <0.002 for 30-day VAP and <0.011 for 30-day VAE). Conclusions:We identified a high prevalence of unrecognized respiratory P. aeruginosacolonization among patients admitted to LTACH for weaning from mechanical ventilation. The admission P. aeruginosaproportional abundance was strongly associated with increased risk of incident P. aeruginosaVAP among these patients.Funding:NoneDisclosures:None