1. Introduction
Since December 2019, the severe acute respiratory syndrome coronavirus (SARS-CoV-2) causing severe lower respiratory tract infections (COVID-19) was firstly reported in Wuhan China (Zhu et al., 2020). In the past three months, SARS-CoV-2 has spread to over than 200 countries rapidly. On March 11, 2020, the WHO has declared a global pandemic.
The clinical symptom of COVID-19, including fever, cough and myalgia, has similarities to that of other infectious diseases such as influenza (Bordi et al., 2020; Guan et al., 2020). The SARS-CoV-2 also co-infected with influenza A virus (IAV) (Wu et al., 2020). And some people who seemingly died from influenza were later tested positive for SARS-CoV-2 in the United States (Redfield, 2020). Maybe, SARS-CoV-2 has appeared among human for a long time and been misdiagnosed as influenza virus. In order to trace the occurrence time of SARS-CoV-2, we conducted a retrospective detection of SARS-CoV-2 and influenza virus in human throat swab samples in influenza epidemic season (from January to May of 2019) in Guangzhou, China.