Symptom profiles and accuracy of clinical definitions for COVID-19 in the community. Results of the Virus Watch community cohort. (preprint)

ABSTRACT

Background: Understanding the symptomatology and accuracy of clinical case definitions for COVID-19 in the community is important for the initiation of Test, Trace and Isolate (TTI) and may, in future, be important for early prescription of antivirals. Methods: Virus Watch is a large community cohort with prospective daily recording of a wide range of symptoms and self-reporting of swab results (mainly undertaken through the UK TTI System). We compared frequency, severity, timing, and duration of symptoms in test positive and test negative cases. We compared the test performance of the current UK case definition used by TTI (any one of new continuous cough, high temperature or loss of or change in sense of smell or taste) with a wider definition that also included muscle aches or chills or headache or loss of appetite. Findings: We included results from 8213 swabbed illnesses, 944 of which tested positive for COVID-19. All symptoms were more common in swab positive than swab negative illnesses and symptoms were also more severe and of longer duration. Common symptoms such as cough, headache, fatigue, muscle aches and loss of appetite occurred early in the course of illness but were also very common in test-negative illnesses. Rarer symptoms such as fever or loss or altered sense of smell or taste were often not present but were markedly more common in swab positive compared to swab negative cases. The current UK definition had a sensitivity and specificity of 81% and 47% respectively for symptomatic COVID-19 compared to 93% and 26% for the broader definition. On average cases met the broader case definition one day earlier than current definition. 1.7-fold more illnesses met the broader definition than the current case definition. Interpretation: COVID-19 is difficult to distinguish from other respiratory infections and common ailments on the basis of symptoms. Broadening the list of symptoms used to encourage engagement with TTI could moderately increase the number of infections identified and shorten delays but with a large increase in the number of tests needed and in the number of people and contacts who do not have COVID-19 but might need to self-isolate whilst awaiting results.