Broadening symptom criteria improves early case identification in SARS-CoV-2 contacts.

Introduction The success of case isolation and contact tracing for the control of SARS-CoV-2 transmission depends on the accuracy and speed of case identification. We assessed whether inclusion of additional symptoms alongside three canonical symptoms (CS) - fever; cough; loss or change in smell or taste - could improve case definitions and accelerate case identification in SARS-CoV-2 contacts. Methods Two prospective longitudinal London-based cohorts of community SARS-CoV-2 contacts, recruited within 5 days of exposure, provided independent training and test datasets. Infected and uninfected contacts completed daily symptom diaries from the earliest possible time-points. Diagnostic information gained by adding symptoms to the CS was quantified using likelihood ratios and AUC-ROC. Improvements in sensitivity and time-to-detection were compared to penalties in terms of specificity and number-needed-to-test. Results Of 529 contacts within two cohorts, 164 (31%) developed PCR-confirmed infection and 365 (69%) remained uninfected. In the training dataset (n=168), 29% of infected contacts did not report the CS. Four symptoms (sore throat, muscle aches, headache and appetite loss) were identified as early-predictors (EP) which added diagnostic value to the CS. The broadened symptom criterion "≥1 of the CS, or ≥2 of the EP" identified PCR-positive contacts in the test dataset on average 2 days earlier after exposure (p=0.07) than "≥1 of the CS", with only modest reduction in specificity (5.7%). Conclusions Broadening symptom criteria to include individuals with at least 2 of muscle aches, headache, appetite loss and sore throat identifies more infections and reduces time-to-detection, providing greater opportunities to prevent SARS-CoV-2 transmission.