Correlation Between Carbapenemase-Producing Enterobacterales Load, Environmental Contamination, and Transmission in Critical Care Units

Carbapenemase-producing Enterobacterales (CPE) represent a major global public health threat because of their extensive antimicrobial resistance and their ability to spread within healthcare facilities. Gastrointestinal colonization is recognized as the main reservoir for transmission. Previous studies have suggested that a subset of colonized patients, often referred to as "super-spreaders," carry a substantially higher bacterial burden and may account for a disproportionate share of environmental contamination and transmission events.

Although bacterial load can be quantified using culture-based and molecular methods, there is currently no validated cycle threshold (Ct) value from routinely used real-time PCR assays that reliably identifies patients with high dissemination potential. Establishing a correlation between Ct values and bacterial burden could provide a practical and accessible tool for infection prevention programs.

This prospective observational cohort study will be conducted in the Adult Intensive Care Unit of Hospital Italiano de Buenos Aires. All patients identified through the institutional surveillance program as colonized with CPE will be eligible for inclusion. For each CPE-positive patient, rectal swabs obtained as part of routine surveillance will undergo quantitative culture on selective chromogenic media and molecular testing using real-time PCR targeting carbapenemase genes. Bacterial load will be estimated using colony-forming unit counts and PCR Ct values.

Environmental contamination will be assessed through systematic sampling of high-touch surfaces in the patient's surroundings, including bed linen, bedside furniture, and medical equipment. Environmental isolates will undergo microbiological and molecular characterization. In selected situations, whole genome sequencing or pulsed-field gel electrophoresis will be performed to evaluate genetic relatedness among isolates recovered from patients, environmental samples, and secondary cases.

The primary outcome is the correlation between quantitative bacterial load and PCR Ct values. Secondary outcomes include the extent of environmental contamination associated with different bacterial loads and the occurrence of transmission events involving genetically related strains. Multivariable analyses will evaluate the influence of relevant clinical and epidemiological factors, including length of stay, fecal incontinence, prior antimicrobial exposure, immunosuppression, and other potential confounders.

The study involves minimal risk because all patient samples are obtained within the framework of routine infection control surveillance. Findings from this study may improve the identification of patients with increased transmission potential and support more targeted and efficient infection prevention strategies in critical care settings.

Inclusion criteria

• Age 18 years or older.
• Hospitalized in the Adult Intensive Care Unit of Hospital Italiano de Buenos Aires during the study period.
• Positive surveillance rectal swab for carbapenemase-producing Enterobacterales.

Exclusion criteria

-Patients colonized or infected with carbapenemase-producing Enterobacterales who remained in the same room for less than 48 hours.