National Prevalence of Multidrug-Resistant Acinetobacter baumannii (MDR AB) infections in the Ambulatory and Acute Care Settings, Including Carbapenem-Resistant Acinetobacter Infections, in the United States in 2015

Background: In 2013 the CDC classified MDR AB infections as a serious threat. The purpose of this study was to estimate the national prevalence of MDR AB events in the acute care and ambulatory settings based on a large database from Becton Dickinson & Company.

Methods: Susceptibility data from non-duplicate isolates was collected from 346 hospitals nationwide and identified as MDR per NHSN definitions. Organisms were classified into ambulatory, admission, and hospital-onset periods based on collection time. All data were consolidated into CMS National Hospital Data Provider IDs. The raking method was applied per CMS national hospital distribution by location, teaching status, urban/rural status, and bed size to project the national prevalence estimates.

Results: Of 5,582 isolates tested, 2,124 were MDR AB. The national projected MDR AB events were 18,109 (see Table). The MDR AB rates were highest in the hospital onset period, followed by admission and ambulatory. Eighty percent of MDR AB isolates were also carbapenem resistant. National Projections for MDR AB for each region were: ambulatory (26.5, 21.5, 26.6, & 8.7%), admission (51.2, 45.7, 31.8 & 43.1%) and hospital-onset (63.4, 64.2, 47.4 & 45.7%) for the Midwest, Northeast (NE), South & West regions, respectively.

	Observed Events (346 hospitals)			National Projection
Period Tested	Isolates tested	Confirmed MDR AB	% MDR AB	Isolates tested	MDR AB Events	% MDR AB
Ambulatory	2,461	614	24.9	20,416	4,865	23.8
Admission	1,168	484	41.4	9,769	4,179	42.8
Hospital-onset	1,953	1,026	52.5	16,113	9,065	56.2
Total	5,582	2,124	38.1	46,318	18,109	39.1
Regions
Midwest	1,438	648	45.1	15,597	7,044	45.2
NE	940	406	43.2	8,553	3,710	43.4
South	2,664	882	33.1	17,314	5,956	34.4
West	540	188	34.8	4,854	1,399	28.8
Total	5,582	2,124	38.1	46,318	18,109	39.1

Conclusion: These data estimate that national hospital onset MDR AB rates in 2015 were higher than previously reported estimates. The highest rates of MDR AB events occur in the hospital-onset period, however 27% of MDR AB events occur in the ambulatory period. The highest rates of MDR AB events were in the hospital-onset period in the Midwest and NE regions.