Simulacra & Simulation(& Health Care-Associated Infections)

Michael Rubin, MD, PhDSection Chief, Epidemiology

VA Salt Lake City Health Care System

Military Simulations

• Models in which theories of warfare can be tested and refined without the need for actual hostilities

• Provide insights that can be applied to real-world situations– a non-prescriptive attempt to inform the decision-

making process

Military Simulations

• Exist in many different forms, with varying degrees of realism

• Are they really useful?

Models in Healthcare Research

• Familiar models– Statistical regression models:• Linear, Logistic, Poisson, etc.

– Used for prediction, inference, hypothesis testing, and modeling of causal relationships• Rely heavily on the underlying simplifying assumptions

being satisfied

Models in Healthcare Research

• Familiar models– Equation-based models• Compartmental models, Differential Equation models

S(t) R(t)I(t)βI(t) r

S I R

Models in Healthcare Research

• Less familiar models: simulations– Many different types of simulations• Continuous Dynamic simulations• Discrete Event simulations• Monte Carlo simulations

– Agent-based simulations

Agent-Based Models

• Agent-based models– Individual-based models/Individual-agent models– System is modeled as collection of autonomous

decision-making entities (agents) which exist/interact within an environment or framework

– Each agent assesses its situation and makes decisions based on a set of rules (behaviors) and characteristics (parameters)

– System-level observables emerge from individual actions

Agent-Based ModelsS I R

Susceptible

Infected

Recovered

Each individual agent exists in a particular “state”(“Statechart”)

States correspond to the different compartments in the SIR model

Transitions between states are governed by rates

Agent-Based Models

• Agent-based models: Benefits– Can explore dynamics out of the reach of pure

mathematical methods– Events occur stochastically rather than

deterministically– Can exhibit complex behavior patterns, sometimes

unanticipated– Captures emergent phenomena– Provides a natural description of a system– What-if experimentation is accommodated

Agent-Based Models

• Situations appropriate for simulation– questions that are too expensive, complicated, or

difficult to answer in meatspace– situations where it is impossible (or extremely

difficult) to know the absolute "truth"– systems with complex interactions or behaviors

that are difficult to express with mathematical equations

MRSA Simulation

• Detailed simulation of hospital setting– Patient admissions, transfers, discharges– ICU and non-ICU wards; private and double rooms– Healthcare worker (doctor, nurse) contacts with

patients– Environmental contamination– Performance of surveillance testing

Model Components

• Patient• Room• Ward/ICU• Nurse• Physician• Network structure• Surveillance

Transmission pathways

– Patient nurse patient– Patient physician patient– Patient environment nurse patient– Patient environment physician patient– Patient environment roommate– Patient environment subsequent occupant

roomroom

patientpatientADMISSIONADMISSION

DISCHARGEDISCHARGE

COLONIZATION EVENT

colonizedcolonized

not colonizednot colonized

CLINICAL EVENTS

asymptomaticasymptomatic

symptomaticsymptomatic

off antibioticsoff antibiotics

on antibioticson antibiotics

node-colonization

node-colonization

de-colonizationde-colonization

unoccupiedunoccupied

occupiedoccupied

uncontaminateduncontaminated

contaminatedcontaminated

no isolationno isolation

contact isolationcontact isolation

nursenurse

physicianphysician

uncontaminateduncontaminated

contaminatedcontaminated

uncontaminateduncontaminated

contaminatedcontaminated

Agents and states

Contact Networks

Model animation

• Alternative surveillance approaches• Reduce (or increase) antibiotic use• Improve hand hygiene • Modify health care worker - patient contact

networks• Expedite discharge • Selectively screen contacts• Decolonize– Carriers versus high-risk patients– Health care workers

Types of Interventions

MRSA Simulation

• Types of questions that can be addressed:– Time to observe decrease in MRSA acquisition?– Do interventions exhibit threshold effects?– How long will it take for a policy to exhibit an

effect?– Better to decolonize at admission or discharge?– Time course for effects on community prevalence?

These questions cannot be fully addressed by clinical trials

Rural Health Care Access

• Can simulation be used to study and optimize access to care in rural settings?

• How to optimize access to care across a population in a catchment area

• Goal is to design an interactive agent-based simulation model that can be used by researchers and planners to test varying strategies of addressing access in their system