1374. Utilizing Genomic Epidemiology to Explore SARS CoV-2 Transmission Patterns and Support Outbreak Investigations in Long Term Care Facilities, Washington State, April-October 2021

Abstract Background In Washington State, COVID-19 cases in long-term care facilities (LTCF) have accounted for less than 3% of all cases, yet 30% deaths. Understanding transmission patterns and outbreak epidemiology informs management. From April to October 2021, two large LTCFs experienced outbreaks. Whole genome sequencing phylogenetic analysis were leveraged explore complement epidemiology. Methods Epidemiologic data was exported from the Disease Reporting System. Sequences, retrieved GISAID, aligned Wuhan-1 reference using Nextalign version 1.11.0. Pairwise single nucleotide polymorphism (SNP) distance matrices calculated SNP-Dists 0.8.2. Phylogenetic trees each generated IQ-Tree multicore 2.2.0-beta COVID-edition GTR+F+G4 substitution model with 1000 bootstrap replicates. MicrobeTrace used visualize phylogeny, SNP heatmap, identify clusters among sequences. Results Weekly, LTCF A tested 162 residents 800 staff, B 60 144 staff. Of (n= 119), 23% (n =27) 77% = 92) compared 78% =28) 22% =7) staff total (n=36). A, 34% (n=40) had high-quality sequences available. Seven or more genetically related thirteen unrelated identified. Five involved resident linked by unit. Two remaining B, 40% (n=14) One cluster identified, floors. The differences between ranged 0 70, whereas 6. Conclusion outbreaks confirms disease patterns. Multiple independent introductions SARS-CoV-2 identified a introduction B. Genomic is valuable resource investigation Disclosures All Authors: No reported disclosures.