546. Seasonal Changes in the Prevalence of Antibiotic-Susceptible Acinetobacter baumannii Results in Increased Multidrug Resistance Rates During Winter Months

BACKGROUND: Understanding the seasonal behavior of infections (“seasonality”) caused by Gram-negative pathogens, including Acinetobacter baumannii, is essential for the design of effective healthcare policies; however, the factors mediating seasonality remain elusive. METHODS: Over 2,000 A. baumannii cases identified in the BJC Health System between 2007 and 2017, were retrospectively analyzed according to isolation month, hospital acquisition, anatomical source, and antibiotic susceptibility profile. RESULTS: Compared with quarter 1 (Q1, December–February), A. baumannii case incidence was similar in Q2 (March–May) but significantly higher in Q3 (June–August) and Q4 (September–November). This seasonality was exhibited by antibiotic-susceptible but not antibiotic-resistant isolates. This was independent of tested antibiotic, anatomic source, or hospital vs. community acquisition. CONCLUSION: Seasonality is absent from antibiotic-resistant A. baumannii cases. Selective decrease of antibiotic-susceptible cases in Q1/Q2 results in 50–100% increase in resistance rates compared with Q3/Q4. A. baumannii seasonality is possibly linked to the increased use of antibiotics during winter. As resistance determinants tend to be genetically linked in A. baumannii, pressure from community antibiotics may have the inadvertent effect of selecting for multidrug resistance. This link must be further studied, as it may also explain seasonality in other, more antibiotic-susceptible Gram-negative pathogens. DISCLOSURES: All authors: No reported disclosures.