An increase in the number of P. fluorescens isolates in blood cultures was noted in June 2022, leading to a retrospective clinical chart review of patients with a positive culture. Demographic and clinical data and data regarding microbiologic culture results were retrieved for each patient. This information included name, diagnosis, chemotherapy regimen, invasive procedures, date of positive blood culture, isolated microorganism, and antibiogram; it was recorded in a spreadsheet. The common characteristic among patients with positive cultures was a recent history of external double-lumen CVC installation.

The Instituto Nacional de Cancerología (INCan) in Mexico is a 133-bed referral hospital for oncologic adult patients. A team of nine nurses exclusively dedicated to standardized intravenous (IV) therapy, including assistance in CVC insertion, has been in place since 1990. Senior IV team nurses within our institution provide the training for these nurses. Additionally, our suppliers conduct specific training for the insertion of PICC lines. It's important to note that nurses must complete this training before they can join the IV-team. Regarding the location of CVC installations, while some are performed in the IV-team unit, others, particularly those for patients with difficult vascular access, are conducted in the Interventional Radiology Unit (IRU). This decision is based on clinical judgment and each patient's specific needs. In the IRU, the institutional standardized procedure for CVC placement involves insertion by an interventional radiologist and assistance throughout the installation process by a trained IV-team nurse to ensure adherence to sterile procedures [2,3,4]. Since 2020, the annual average number of CVCs installed has been 1869 (282 one-lumen, 512 double-lumen, 31 triple-lumen, 79 high-flux, and 966 implanted ports). The rate of CRBSI during the year preceding the outbreak was 1.92 per 1000/catheter days; during the month of the outbreak, it was 9.62.

A confirmed case was defined as any patient with a positive blood culture for Pseudomonas fluorescens after undergoing CVC insertion between June 21 and July 20, 2022, in the IRU of the INCan in Mexico City, Mexico.

Blood samples were cultured in BD BACTEC™ FX System (Becton Dickinson Microbiology Systems, USA), and plated on blood, and MacConkey agar. Isolated bacteria were identified using the Bruker Daltonics IVD MALDI Biotyper®. Identification scores of ≥ 2.0 were used to determine species-level identification, which were attained in every sample in which P. fluorescens was isolated. Antimicrobial susceptibility testing was determined in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines utilizing Vitek2™ semi-automated testing.

In July 2022, CR P. fluorescens were recovered from blood cultures from recently placed external double-lumen CVCs. The outbreak was confirmed by revision of the microbiologic culture archives, in which no P. fluorescens had been isolated from blood samples in the ten-year preceding period at our institution. The investigation was carried out by the hospital’s Infection Prevention and Control (IPC) team. It involved a comprehensive review of patient records and laboratory results and direct observation of the CVC placement procedure in the IRU, during which deviations in the standardized process were noted to request environmental cultures in an orderly manner.