Modeling the Impact of Staff to Patient Ratios on MRSA Acquisition in an Intensive Care Unit

Primary Author: Stephanie Sikavitsas Johnson

Faculty Sponsor: Eric Lofgren


Primary College/Unit: College of Veterinary Medicine

Category: Medical and Life Sciences

Campus: Pullman




Staff-to-Patient ratios in hospitals impact several hospital acquired infections (HAIs). Intuitively, increasing the number of nurses and doctors in an intensive care unit (ICU) should impact rates of HAI transmission by reducing the number of patients per provider, allowing less patient-patient interaction. Designing a study to determine how different staffing ratios would affect HAIs is difficult to in person because of lots of different factors that make each hospital and unit unique. Mathematical modeling can be used instead to simulate how staffing ratios affect methicillin-resistant S. aureus (MRSA) being acquired in a 15-bed ICU.


We varied the number of doctors in the ICU from one to three. For each doctor scenario, the nurse -patient ratio was 1:1, 1:2.5, 1:3. And 1:5. We ran each model 1000 times, with each time simulating 1 year in the ICU. The outcome was the mean number of MRSA acquisitions in one year for each of the 12 models. Our baseline model we compared everything to was the single doctor, 1:3 nurse-patient ratio model.


Adding more doctors slightly decreased the number of acquisitions, with the steeper decline going from one doctor to two. Going from a 1:3 nursing ratio to 1:1 ratio decreased MRSA acquisition by 64%. Increasing to a 1:5 ratio raised acquisitions 21.5%. These results suggest reduction in provider contact may have an impact on HAI rates. Appropriate staffing should be considered in infection control guidelines, and the cost of staffing be weighed against its impact on infection prevention.