Influenza versus COVID-19 cases among influenza-illness-like patients in travelers from Wuhan to Hong Kong in January 2020.

Abstract Objective The COVID-19 outbreak in Wuhan, Hubei, China followed the seasonal influenza epidemic. Since COVID-19 may be misdiagnosed as influenza in January 2020, before testing capacity was adequate, it is of significance to study the ratio of influenza cases and COVID-19 cases among influenza-illness-like patients and its temporal pattern. Results In this study we analyzed the record of the influenza-illness-like patients with a recent travel history to Wuhan arrived in Hong Kong between December 31, 2019 and January 21, 2020. We found that the ratio COVID-19 and influenza is much smaller than a study among ILI in Wuhan. This difference could be due to the difference in sampling. We argue that it is important to consider both samples when inferring number of COVID-19 cases from ILI patients.