Rectal colonization by multidrug-resistant Gram-negative bacteria and subsequent bacteraemia in haematological patients.

Objectives: This study assessed the prevalence of multidrug-resistant Gram-negative bacilli (MDR-GNB) colonization in rectal swabs from haematological patients with malignancies undergoing routine surveillance and explored the relationship between MDR-GNB colonization and subsequent development of bloodstream infections (BSIs).

Methods: Between January 2020 and September 2022, all patients admitted to our haematology ward underwent weekly MDR-GNB colonization screening via rectal swabs. A retrospective analysis was performed. MDR-GNB were defined per 2022 European Society of Clinical Microbiology and Infectious Diseases criteria: (a) third-generation cephalosporin-resistant Enterobacterales (3GCephRE), (b) carbapenem-resistant Enterobacterales (CRE), (c) Pseudomonas aeruginosa with difficult-to-treat resistance (DTR), and (d) carbapenem-resistant Acinetobacter baumannii.

Results: Among 3024 rectal swabs from 699 patients, 503 of 3024 (16.6%) tested positive for MDR-GNB in 192 of 699 patients (27.5%). The most prevalent organisms were Escherichia coli (248/503; 49.3%), Klebsiella pneumoniae complex (125/503; 24.9%), and P. aeruginosa (36/503; 7.2%). A total of 59 of 503 (11.7%) colonizations of CRE were identified. Overall, 27 of 192 (14.1%) patients were colonized at admission, primarily by 3GCephRE (27/29; 93.1%). Colonization with CRE and DTR P. aeruginosa was more frequently documented after several days of hospitalization. BSI occurred in 74 of 192 (38.5%) colonized and 61 of 507 (12.0%) non-colonized patients. MDR-GNB caused 57 of 166 BSIs episodes, 50 of 57 (87.7%) of which were in colonized patients. The unadjusted concordance rate between rectal swab isolates and blood cultures was observed in 43 of 90 BSIs (47.8%) occurring in colonized patients, with a positive predictive value (PPV) of 36.4% and a negative predictive value (NPV) of 99.9% for DTR P. aeruginosa; a PPV of 25.0% and an NPV of 99.9% for CRE; and a PPV of 14.6% and an NPV of 99.0% for 3GCephRE.

Discussion: Routine weekly surveillance for MDR-GNB in haematological patients enables early identification of colonization, often preceding MDR-GNB BSIs. Further studies using adjusted analyses are needed to establish its independent predictive value.