Ten-year retrospective analysis ofAcinetobacter baumanniiclinical isolates reveals a proportionately large, non-nosocomial, multidrug-resistant endemic reservoir

Background Acinetobacter baumannii ( Ab ) is a global health threat notorious for causing hospital-acquired (HA) infections, though many Ab infections are community-acquired (CA). Investigations describing contemporaneous, clinically-relevant CA and HA Ab populations, are lacking. Methods We conducted a retrospective ecological analysis of 2042 Ab clinical isolates identified from 2007 to 2017 in the BJC HealthCare System (BJC), a multi-hospital system located in and around the greater metropolitan area in St. Louis, Missouri. We described basic clinical characteristics and antibiotic susceptibility rates of CA and HA Ab isolates in comparative and longitudinal analyses. Results 62.1% of all Ab isolates were CA, i.e., isolated in ambulatory settings or <48 hours following hospital admission. Though HA isolates initially predominated in the largest BJC hospital, implementation of infection control efforts resulted in a disproportionate reduction in annual HA isolate occurrence. This revealed a stable, baseline occurrence of CA isolates. In all other hospitals, the annual proportion of isolates that were CA averaged 78.7% (95%CI=74.5-83.0). 42.9% and 30.4% of total CA isolates were from skin and soft tissue/musculoskeletal (SST/MSK) and urinary sources, respectively, while HA isolates were primarily respiratory (55.6%). Rates of carbapenem resistance, a surrogate for multidrug resistant (MDR) phenotypes, were higher among respiratory and HA cases (∼60%) compared to contemporaneous non-respiratory CA counterparts (∼40%). Conclusions MDR Ab reservoirs associated with SST/MSK and urinary niches persist outside of hospital environments in a large U.S. healthcare system, even after the implementation of effective hospital infection control measures. Summary We compared hospital-acquired and community-acquired Acinetobacter baumannii in a large U.S. healthcare system through a ten-year retrospective ecological analysis. Community-acquired isolates composed over 60% of total A. baumannii isolates, were primarily from non-respiratory sources and exhibited carbapenem resistance rates of 35-40%.