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Table 1 Key parameter values in the baseline scenario

From: Impact of non-pharmaceutical interventions on SARS-CoV-2 outbreaks in English care homes: a modelling study

Key baseline scenario parameters

Value

Source

Number of residents and staff at the start of each simulation

Residential care home: 29, nursing care home: 47

Average care home sizes in England [4]

Visitors

Number of visitors per resident per day ~ \(Beta(\mu =0.24, se=0.1)\)

Personal communication from expert opinion trustee of the Residents and Relatives Association & CEO of Social Care Forum (see Additional file 1: Table S1)

Admission of residents

Admissions only from hospital, no new admissions from the community

Assumed

Previous exposure to SARS-CoV-2 of care home residents and staff at the start of the simulation

No previous exposure in residents, previous exposure in staff according to community prevalence assumed (baseline scenario: medium community prevalence: 13% recovered)

Mathematical model of SARS-CoV-2 transmission in the community[14] (see Additional file 1: Table S1)

Testing probabilities and frequencies

p(symptomatic residents tested) ~ \(Beta(\mu =0.9, se=0.0{5)}\);

p(residents without symptoms tested every 28 days) ~ \(Beta(\mu =0.85, se=0.0{5)}\);

p(staff without symptoms tested every 7 days) ~ \(Beta(\mu =0.95, se=0.0{5)}\)

All symptomatic hospitalised residents were tested in hospital upon discharge

Testing probabilities assumed. Frequency of testing from previous national policy [9, 15]

Test characteristics

PCR p(false negative test in a care home) ~ \(Beta(\mu =0.2, se=0.0{5)}\);

PCR p(false negative test in a hospital) ~ \(Beta(\mu =0.1, se=0.0{1)}\);

PCR test 100% specificity

Approximately 90% PCR tests are positive in individuals with early stage COVID-19 clinical infection [10, 11]. Sensitivity in care homes assumed

Infection prevention and control

p(residents isolated following symptom onset or positive test) ~ \(Beta(\mu =0.8, se=0.0{8)}\);

relative infectiousness of isolated residents vs not ~ \(Beta(\mu =0.25, se=0.1{5)}\)

Assumed

Delay to isolation (in residents) or absence (in staff)

delay to isolation/absence in residents/staff with symptoms ~ 

\(Gamma(\mu =1, k=4)\) (days);

delay to isolation/absence in residents/staff without symptoms ~ \(Gamma(\mu =2, k=4)\)(days)

Assumed

Transmission rates

The transmission rates between staff and residents, residents and residents and staff and staff are the same

\({{R0}_{a}}\)(\(R0\) pathway a) ~ \(Gamma(\mu =2, k=8)\);

\({{R0}_{b}}\)(\(R0\) pathway b) = \({{R0}_{a}}\times {mR0}_{b}\);

\({mR0}_{b}\)~ \(Beta(\mu =0.5, se=0.1)\)

All transmission rates are halved at timepoints when a case is detected (i.e. there are one or more care home residents isolated or staff absent)

Assumed. In line with the R0 estimated for SARS-CoV-2 in healthcare facilities with 5–10 average contacts per day [16]

Proportion of hospital discharges to the care home by infectious state (if admitted as non-COVID-19 hospitalisation)

Baseline (medium prevalence) scenario:

% infected ~ \(Beta(\mu =0.01, se=0.0{01)}\), of which 69% exposed, 13% infectious preclinical, 18% asymptomatic;

% recovered ~ \(Beta(\mu =0.05, se=0.0{3)}\);

% susceptible = 1-(% recovered + % infected)

All residents are tested upon discharge, and, if positive, are isolated upon their return

Mathematical models of SARS-CoV-2 transmission in the community [14] and in hospital [17] (see Additional file 1: Table S1)

Care home staff working at another site

p(original staff work at an additional care home) ~ \(Beta(\mu =0.01, se=0.00{5)}\);

p(replacement staff work at an additional care home) ~ \(Beta(\mu =0.2, se=0.07{)}\)

Personal communication from lead of Thames Valley care home survey (see Additional file 1: Table S1)