Transient Dynamics of Infection Transmission in a Simulated Intensive Care Unit

Healthcare-associated infections (HAIs) remain a public health problem. Previous work showed intensive care unit (ICU) population structure impacts methicillin-resistant Staphylococcus aureus (MRSA) rates. Unexplored in that work was the transient dynamics of this system. We consider the dynamics of MRSA in an ICU in three different models: 1) a Ross-McDonald model with a single healthcare staff type, 2) a Ross-McDonald model with nurses and doctors considered as separate populations and 3) a meta-population model that segments patients into smaller groups seen by a single nurse. The basic reproduction number, R0 is derived using the Next Generation Matrix method, while the importance of the position of patients within the meta-population model is assessed via stochastic simulation. The single-staff model had an R0 of 0.337, while the other two models had R0s of 0.278. The meta-population model's R0 was not sensitive to the time nurses spent with their assigned patients vs. unassigned patients. This suggests previous results showing that simulated infection rates are dependent on this parameter are the result of differences in the transient dynamics between the models, rather than differing long-term equilibria.