Carbapenem-resistant Acinetobacter baumannii (CRAB) carriage in post-acute care hospitals (PACH) reflects both importation of colonized patients and within-PACH transmission. We studied within-PACH transmission by examining the sameness of CRAB clusters, as identified by Fourier-transform infrared (FTIR) spectroscopy.

We conducted a point-prevalence survey in 55 wards in 18 Israeli PACH in 2021. Patients (n = 1,733) were screened for CRAB, and 461 isolates from 357 patients underwent FTIR typing (IR Biotyper, Bruker). We assigned each patient isolate to its cluster and paired each patient-cluster combination with every other patient-cluster combination. We examined the relationship between physical proximity of pairs (n = 75,047) and FTIR cluster sameness using generalized estimating equation logistic regression. To estimate within-ward transmission, we compared proportions of cluster sameness within wards versus between institutions.

The 461 CRAB isolates formed 23 FTIR clusters. Compared to being in different institutions, being in the same ward was associated with significantly higher odds of sharing the same cluster (odds ratio: 3.6, p < 0.001). Odds ratios were highest for patients in the same room (6.2) or adjacent rooms (6.1) (p < 0.001 for both). Based on same-cluster pairs we estimated that 70% of prevalent CRAB cases resulted from within-ward transmission.

CRAB strain similarity was strongly associated with spatial proximity within PACH wards, indicating that within-ward transmission is an important contributor to CRAB carriage prevalence. Similar risk in same and adjacent rooms suggests transmission via shared staff or equipment. Ward-level infection control interventions are warranted to interrupt spread.