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Tracking Pseudomonas Aeruginosa Transmissions Due to Environmental Contamination After Discharge in ICUs Using Mathematical Models
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A new publication on behalf of COMBACTE-MAGNET was published in bioRxiv.

Abstract. Pseudomonas aeruginosa (P. aeruginosa) is an important cause of healthcare-associated infections, particularly in immunocompromised patients. Understanding how this multi-drug resistant pathogen is transmitted within intensive care units (ICUs) is crucial for devising and evaluating successful control strategies.

While it is known that moist environments serve as natural reservoirs for P. aeruginosa, there is little quantitative evidence regarding the contribution of environmental contamination to its transmission within ICUs. Previous studies on other nosocomial pathogens rely on deploying specific values for environmental parameters derived from costly and laborious genotyping. Using solely longitudinal surveillance data, we estimated the relative importance of P. aeruginosa transmission routes by exploiting the fact that different routes cause different pattern of fluctuations in the prevalence. We developed a mathematical model including endogenous colonization, cross-transmission and environmental contamination. Patients contribute to a pool of pathogens by shedding bacteria to the environment. Natural decay and cleaning of the environment lead to a reduction of that pool. By assigning the bacterial load shed during an ICU stay to cross-transmission, we were able to disentangle environmental contamination during and after a patient’s stay. Based on a data-augmented Markov Chain Monte Carlo method the relative importance of the considered acquisition routes is determined for two ICUs of the University hospital in Besancon (France). We used information about the admission and discharge days, screening days and screening results of the ICU patients. Both cross-transmission and endogenous transmission play a significant role in the transmission process in both ICUs. In contrast, only about $1\%$ of the total transmissions were due to environmental contamination after discharge. Improved cleaning of the environment after discharge would have only a limited impact regarding the prevention of P. aeruginosa infections in the two considered ICUs. Our model was developed for P. aeruginosa but can be easily applied to other pathogens as well.