2468. Is On-Demand Multilocus Sequence Typing of Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile Hospital Isolates Useful for Infection Control Practice?

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Abstract Background MRSA and C. diff are important causes of hospital-onset (HO) or healthcare-associated infections (HAI). Molecular sequencing of bacterial pathogens is often used retrospectively during outbreak investigations to determine phylogenetic linkage. We evaluated the utility of on-demand multilocus sequence typing (MLST) in characterizing hospital transmission events. Methods Using VA or NHSN criteria, inpatients with MRSA-HAI or HO-C. difficile infection (HO-CDI) were identified by infection preventionists (IPs) for MLST (by time and location) during active hospital surveillance starting October 2016 or September 2017 (for C. difficile and MRSA, respectively) through March 2019. Vitek 2 identified MRSA from blood or other sources, and stool samples positive for C. difficile by Cepheid Xpert® C. difficile or FilmArray® Gastrointestinal (GI) Panel were collected and C. diff isolated on CCFA plates. Sequence types (STs) were generated by Sanger sequencing and MLST using standard protocols (pubmlst.org). C. difficile genes included adk, atpA, dxr, glyA, recA, sodA, tpi. MRSA genes included arc, aro, glp, gmk, pta, tpi, yqil. Staphylococcal protein A gene (spa) type was determined by spa gene sequencing. Results MLST assay (C. diff 33, MRSA 26) intervals ranged from 1–4 weeks based on IP request. 109 C. diff isolates from 105 patients representing 44 STs (10 unique) were found. ST1 and ST2 (27, 20) were most common. 5 patients had 2–3 identical ST isolates over 21–180 days. Of 72 HO-CDI identified, 9 possible person-to-person transmissions events (33 cases) were ruled out; 3 events (9 cases) were ruled in; 14 events (21 cases) were not resolved due to missing samples or no growth. 100 MRSA isolates from 96 patients representing 26 STs (9 unique) were found. ST8/spa t008 (USA300) and ST5/spa t002 (USA100) (44, 29) were most common. 11 patients had 2–3 identical ST isolates over 2–367 days. Of 16 MRSA-HAI identified, 1 transmission event (4 cases) was ruled out, 1 event (2 cases) lacked one strain and was unresolvable. Conclusion Common MRSA and C. diff STs predominated among hospital isolates, yet significant heterogeneity was seen over a 2-year period and few true transmission events were documented. On-demand MLST-augmented IP surveillance was useful to rule-out hospital transmission. Disclosures All authors: No reported disclosures.

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