The impact of testing and infection prevention and control strategies on within-hospital transmission dynamics of COVID-19 in English hospitals

Abstract

Nosocomial transmission of SARS-CoV-2 is a key concern, and evaluating the effect of testing and infection prevention and control strategies is essential for guiding policy in this area. Using a within-hospital SEIR transition model of SARS-CoV-2 in a typical English hospital, we estimate that between 9 March 2020 and 17 July 2020 approximately 20% of infections in inpatients, and 73% of infections in healthcare workers (HCWs) were due to nosocomial transmission. Model results suggest that placing suspected COVID-19 patients in single rooms or bays has the potential to reduce hospital-acquired infections in patients by up to 35%. Periodic testing of HCWs has a smaller effect on the number of hospital-acquired COVID-19 cases in patients, but reduces infection in HCWs by as much as 37% and results in only a small proportion of staff absences (approx. 0.3% per day). This is considerably less than the 20-25% of staff that have been reported to be absent from work owing to suspected COVID-19 and self-isolation. Model-based evaluations of interventions, informed by data collected so far, can help to inform policy as the pandemic progresses and help prevent transmission in the vulnerable hospital population. This article is part of the theme issue 'Modelling that shaped the early COVID-19 pandemic response in the UK'.

Keywords: SARS-CoV-2; coronavirus; mathematical model; nosocomial transmission.

Figure 1.

Schematic representation of the model. Parameter definitions and values, and model equations are given in the electronic supplementary material.

Figure 2.

Sources of COVID-19 transmission in hospital. (a–d) Effect of population incidence rates on nosocomial transmission. (a) New COVID-19 positive patients per bed per day, (b) cumulative proportion of all admissions that are COVID-19 positive, (c) cumulative proportion of susceptible admissions that acquire COVID-19 in hospital, (d) cumulative proportion of HCWs that are infected with SARS-CoV-2. (e–h) Sources of infection in patients (e,f) and HCWs (g,h) for a setting with a medium population incidence rate. (i,j) Cumulative count (i) and proportion (j) of infections by source.

Figure 3.

Effect of periodic testing of HCW on transmissions. (a) Cumulative number of transmissions by source (bars) and proportional reduction in transmissions to patients and HCWs (lines) when periodic testing is implemented from 9 March 2020 to 17 July 2020. (b) Total number of tests required under each testing scenario (bars) and overall reduction in transmissions per test (points) from 9 March 2020 to 17 July 2020. (c) Proportion of all infected staff that are absent from work under different testing scenarios (left), and the proportion of infected staff that continue to work each day (right). (d) Proportion of staff that are ever absent due to a COVID-19 infection (bars) and overall reduction in transmissions per absence (points) between 9 March 2020 and 17 July 2020.

Figure 4.

Effect of isolating suspected cases in single rooms versus cohorts. (a) Number of transmissions (bars) and proportional reduction in transmissions (lines) when patients are isolated in single rooms and transmission rates are reduced by various amounts. (b) Reduction in transmissions to patients and HCWs per single bed day over the entire simulation period. (c) Number of single rooms occupied per day by patients undergoing testing for COVID-19 who are susceptible, infected or exposed. (d) Proportion of rooms occupied by susceptible, exposed, infected and recovered patients over time.