Contact tracing — along with robust testing, isolation, and care of cases — is a key strategy for interrupting chains of transmission of coronavirus disease 2019 (COVID-19), caused by COVID-19 virus also known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and reducing mortality associated with COVID-19 (1-2). Close contacts are defined as individuals who have had contact, without effective protection, with one or more suspected or confirmed COVID-19 cases any time starting 2 days before onset of the suspected or confirmed cases’ symptoms or 2 days before sampling for laboratory testing of asymptomatic infected persons (3-4). At the early phases of COVID-19 pandemic, the finding of COVID-19 cases usually began from suspected cases due to delayed testing capabilities (5).
On January 9, 2021, the first case (Patient A) of a COVID-19 outbreak arrived unknowingly infected in Dongchang District, Tonghua City, Jilin Province, China. He gave three product promotion lectures in Location A and infected audience members during the lectures. By January 31, 2021, 74 lecture participants were confirmed to have been infected and were considered first-generation cases. The Tonghua CDC led an investigation of this outbreak that ultimately identified 140 cases (6). In this article, we focused on the 74 first-generation cases, which all had known exposure times and locations. Once Patient A had been diagnosed using polymerase chain reaction (PCR) testing as being infected, lecture participants were located and placed in quarantine where they were tested with PCR and evaluated for COVID-19 symptoms every day. This careful observation period under quarantine provided an opportunity to assess infectivity period, incubation time, the time between becoming PCR positive and developing symptoms. We report results of our study of first-generation cases to further improve investigation and management of close contacts of COVID-19 cases.