Analysis of temporal trends in potential COVID-19 cases reported through NHS Pathways England

Abstract

The National Health Service (NHS) Pathways triage system collates data on enquiries to 111 and 999 services in England. Since the 18th of March 2020, these data have been made publically available for potential COVID-19 symptoms self-reported by members of the public. Trends in such reports over time are likely to reflect behaviour of the ongoing epidemic within the wider community, potentially capturing valuable information across a broader severity profile of cases than hospital admission data. We present a fully reproducible analysis of temporal trends in NHS Pathways reports until 14th May 2020, nationally and regionally, and demonstrate that rates of growth/decline and effective reproduction number estimated from these data may be useful in monitoring transmission. This is a particularly pressing issue as lockdown restrictions begin to be lifted and evidence of disease resurgence must be constantly reassessed. We further assess the correlation between NHS Pathways reports and a publicly available NHS dataset of COVID-19-associated deaths in England, finding that enquiries to 111/999 were strongly associated with daily deaths reported 16 days later. Our results highlight the potential of NHS Pathways as the basis of an early warning system. However, this dataset relies on self-reported symptoms, which are at risk of being severely biased. Further detailed work is therefore necessary to investigate potential behavioural issues which might otherwise explain our conclusions.

Figure 1

Daily potential COVID-19 cases reported through NHS Pathways and reported COVID-19-related deaths, by NHS region. Pathways data include calls to 111 and 999, as well as 111-online reports. Dates correspond to the date of case report and death report, respectively, with x-axis labels corresponding to Mondays. The solid black line and grey ribbon correspond to a lowess smoother and its 95% confidence interval, calculated across all data points and NHS regions. The start of the lockdown in England (23rd March 2020) and date at which death data were truncated to avoid bias from reporting delay (21st April 2020) are highlighted by vertical lines.

Figure 2

Estimates of (A) daily growth rates (r) and (B) effective reproduction numbers (R_e) for potential COVID-19 cases reported through NHS Pathways. Dotted lines indicate the central estimate, and ribbons their 95% confidence intervals. Estimates are indicated at the end of the time window used for estimation, so that values of r and R_e provided on a given day correspond to the 2 weeks leading up to that day.

Figure 3

Pearson’s correlation between deaths and potential COVID-19 cases reported through NHS Pathways, lagged between 0 and 30 days. 95% confidence intervals are calculated by bootstrapping with 1000 replicates.

Figure 4

Daily total COVID-19 deaths reported in England between 3rd and 22nd April 2020, against the number of potential COVID-19 cases reported through NHS Pathways with a lag of 16 days (between 18th March and 6th April 2020). The black line and grey ribbon correspond to predictions from the regression model and associated 95% confidence intervals. The coefficient of determination indicates that 85.8% of the deviance in reported deaths is linearly explained by NHS Pathways reports.