BACKGROUND: As a highly contagious disease, coronavirus disease 2019 (COVID-19) 
is wreaking havoc around the world due to continuous spread among close contacts 
mainly via droplets, aerosols, contaminated hands or surfaces. Therefore, 
centralized isolation of close contacts and suspected patients is an important 
measure to prevent the transmission of COVID-19. At present, the quarantine 
duration in most countries is 14 d due to the fact that the incubation period of 
severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is usually 
identified as 1-14 d with median estimate of 4-7.5 d. Since COVID-19 patients in 
the incubation period are also contagious, cases with an incubation period of 
more than 14 d need to be evaluated.
CASE SUMMARY: A 70-year-old male patient was admitted to the Department of 
Respiratory Medicine of The First Affiliated Hospital of Harbin Medical 
University on April 5 due to a cough with sputum and shortness of breath. On 
April 10, the patient was transferred to the Fever Clinic for further treatment 
due to close contact to one confirmed COVID-19 patient in the same room. During 
the period from April 10 to May 6, nucleic acid and antibodies to SARS-CoV-2 
were tested 7 and 4 times, respectively, all of which were negative. On May 7, 
the patient developed fever with a maximum temperature of 39℃, and his 
respiratory difficulties had deteriorated. The results of nucleic acid and 
antibody detection of SARS-CoV-2 were positive. On May 8, the nucleic acid and 
antibody detection of SARS-CoV-2 by Heilongjiang Provincial Center for Disease 
Control were also positive, and the patient was diagnosed with COVID-19 and 
reported to the Chinese Center for Disease Control and Prevention.
CONCLUSION: This case highlights the importance of the SARS-CoV-2 incubation 
period. Further epidemiological investigations and clinical observations are 
urgently needed to identify the optimal incubation period of SARS-CoV-2 and 
formulate rational and evidence-based quarantine policies for COVID-19 
accordingly.