Time from Symptom Onset to Hospitalisation of Coronavirus Disease 2019 (COVID-19) Cases: Implications for the Proportion of Transmissions from Infectors with Few Symptoms.

Robin N Thompson,Francesca A Lovell-Read,Uri Obolski

doi:10.3390/jcm9051297

Abstract

Interventions targeting symptomatic hosts and their contacts were successful in bringing the 2003 SARS pandemic under control. In contrast, the COVID-19 pandemic has been harder to contain, partly because of its wide spectrum of symptoms in infectious hosts. Current evidence suggests that individuals can transmit the novel coronavirus while displaying few symptoms. Here, we show that the proportion of infections arising from hosts with few symptoms at the start of an outbreak can, in combination with the basic reproduction number, indicate whether or not interventions targeting symptomatic hosts are likely to be effective. However, as an outbreak continues, the proportion of infections arising from hosts with few symptoms changes in response to control measures. A high proportion of infections from hosts with few symptoms after the initial stages of an outbreak is only problematic if the rate of new infections remains high. Otherwise, it can simply indicate that symptomatic transmissions are being prevented successfully. This should be considered when interpreting estimates of the extent of transmission from hosts with few COVID-19 symptoms.

Highlights

The coronavirus disease 2019 (COVID-19) pandemic continues to pose a significant threat to public health, with more than three million cases reported globally, including over 228,000 deaths
The expected number of infections arising from the infectious period with few symptoms was assumed unchanged during the outbreak, and is given by α0R0, where α0 represents the expected proportion of infections generated by infectious hosts in the period before clear symptoms near the beginning of the outbreak (i.e., t = 0)
The proportion of transmissions occurring from infectious hosts with few symptoms is a dynamic quantity that changes throughout the outbreak

Summary

Introduction

The coronavirus disease 2019 (COVID-19) pandemic continues to pose a significant threat to public health, with more than three million cases reported globally, including over 228,000 deaths (as of 30 April 2020). The proportion of transmissions occurring prior to symptoms has been noted as important [14] This is because individuals displaying few symptoms are harder to detect and isolate or treat effectively than those with clear, disease-specific symptoms. One of the key findings was that SARS-CoV-2 spreads too fast for containment by routine public health measures such as standard contact tracing and isolation of known infected hosts. This is partly because of the significant proportion of transmissions occurring prior to clear symptoms developing. It can show that some transmissions from infected individuals with clear symptoms are being prevented effectively

Time from Symptom Onset to Hospitalisation

Time-Varying Reproduction Number

Proportion of Transmissions from Individuals with Few Symptoms