Methicillin-Resistant Staphylococcus aureus (MRSA) Exposure Assessment in Hospital Environment.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of healthcare-associated infections. Contaminated hands of healthcare workers (HCWs) are vectors of transmission, but the contribution of the contaminated environment is not well characterized. The goal of this dissertation is to provide insights into the role of the hospital environment in MRSA exposure to patients. First, a 20-month prospective study was conducted using nasal swab surveillance data in an intensive care unit (ICU) to examine MRSA acquisition risk associated with having MRSA-positive patients in the ICU during the ICU stay. The study showed that the more recent exposure to MRSA-positive patients in the ICU and the greater number of MRSA-positive patients in the ICU led to a greater hazard of MRSA acquisition among MRSA-negative patients. Second, we developed an MRSA fate and transport model for two hypothetical hospital rooms based on the Environmental Infection Transmission System (EITS) framework. We demonstrated a significant role of environmental surfaces in contaminating and re-contaminating HCWs. The model revealed the effect of S. aureus continuous shedding from the colonized patient onto room surfaces. The surfaces are quickly re-contaminated with MRSA even after the most efficacious decontamination. Our findings highlight the importance of decontamination frequency in addition to decontamination efficacy. Third, we constructed a stochastic agent based model using the same structure as the previous model, but with more realistic features. We demonstrated that HCW’s compliance is essential in determining the effectiveness of hand hygiene, although the time when it is performed and its efficacy are also important. The model emphasizes the significance of the hand hygiene opportunity before and after touching a patient’s surrounding environment, in addition to at the entry and exit of a patient’s room. Despite 100% compliance at the entry and exit of a patient’s room, we show that contaminated environmental surfaces are the dominant contamination sources to HCWs’ hands. Additionally, this model shows the value of hand hygiene efficacy. With 100% compliance and 70% efficacy, HCWs’ hands remain contaminated enough to subsequently contaminate the uncolonized patient’s environment, which later become another exposure route to the patient.