A methodology for using Lambda phages as a proxy for pathogen transmission in hospitals

Abstract

Background: One major concern in hospitalized patients is acquiring infections from pathogens borne on surfaces, patients, and healthcare workers (HCWs). Fundamental to controlling healthcare-associated infections is identifying the sources of pathogens, monitoring the processes responsible for their transmission, and evaluating the efficacy of the procedures employed for restricting their transmission.

Aim: To present a method using the bacteriophage Lambda (λ) to achieve these ends.

Methods: Defined densities of multiple genetically marked λ phages were inoculated at known hotspots for contamination on high-fidelity mannequins. HCWs then entered a pre-sanitized simulated hospital room and performed a series of patient care tasks on the mannequins. Sampling occurred on the scrubs and hands of the HCWs, as well as previously defined high-touch surfaces in hospital rooms. Following sampling, the rooms were decontaminated using procedures demonstrated to be effective. Following the conclusion of the simulation, the samples were tested for the presence, identity, and densities of these λ phages.

Findings: The data generated enabled the determination of the sources and magnitude of contamination caused by the breakdown of established infection prevention practices by HCWs. This technique enabled the standardized tracking of multiple contaminants during a single episode of patient care. Unlike other biological surrogates, λ phages are susceptible to common hospital disinfectants, and allow for a more accurate evaluation of pathogen transmission.

Conclusion: Whereas our application of these methods focused on healthcare-associated infections and the role of HCW behaviours in their spread, these methods could be employed for identifying the sources and sites of microbial contamination in other settings.

Keywords: Bacteriophage; Contamination; Healthcare workers; Hospital-acquired infection; Infection prevention; Lambda phage.

Figure 1.

Sampling design. Diagram of the simulated hospital environment with the sampling sites numbered. (Yellow inset) One simulated hospital room with sampling sites marked. (Green inset) Second simulated hospital room with sampling sites marked. (Blue inset) Two sampling sites located on the healthcare worker’s mobile workstation.

Figure 2.

Phage recovery experiments. Experimental results of the effect of antiseptics, time, and surface transfer in sprayed bacteriophage recovery. The density of each type of λ phage lysate that was used in the experiments was 1e⁸ PFU/mL. (A) Reduction rate of phage density on surfaces after exposure to products used to decontaminate simulations. (B) Reduction rate of phage density after exposure to cleaning and disinfecting products used by HCWs during simulations (C) Phage density of the lysate (blue) and the recovery 2 h post spray on a surface (purple) at room temperature. (D) Phage density of the lysate (blue), the density of the residual phage left on the sprayed surface (purple) after being touched and transferred to a new surface, and the density of phage recovered from the new surface (pink).

Figure 3.

Percentage of transmission event types originating from contamination sources. Data from ten randomly selected simulations are shown. Bars in dark blue are transmissions between the two patient rooms, in orange are transmissions within the patient’s own room, in grey recovery from the nurse, in yellow recovery from the workstation on wheels, and in light blue recovery of phage from a critical site on a patient. Bars of the same colour sum to 100% across the four sources of contamination.