Abstract: Objective To compare the diversity of nucleic acid testing findings of COVID-19 in different prevention stages for scientific evidences to develop reasonable prevention and control strategies. Methods Pharyngeal swabs and sputum samples were obtained in the key population in Suzhou from January 22 to February 29,2020,and detected for the nucleic acid specific to COVID-19 using real-time RT-PCR. Then the testing results were compared among the samples tested in different prevention stages. Results A total of 1 182 samples were collected from 704 suspected subjects,in whom positive novel coronavirus nucleic acid was found in 46 subjects out of the 59 samples. The positive detection rate was 4. 99% (59 /1 182). Forty-one were finally confirmed as COVID-19,and 5 as asymptomatic infection. The highest positive rate of nucleic acid for COVID-19 was 14. 81% (12 / 81) in the early stage of the epidemic,followed by 6. 17% (24 / 389) in the second stage and 5. 71% (22 / 385) in the third stage,and the lowest positive rate was in the fourth stage(0. 31%,1 / 327) . The highest positive rate was seen in subjects with history of travelling or short-term stay in Hubei Province(10. 13%,31 / 306), followed by close contacts(3. 85%,28 / 727). Positive nucleic acid was not detected in local residents in observation at the outpatient due to fever. Conclusion Nucleic acid detection strategy was timely adjusted at different stages of COVID-19 endemic in Suzhou,which has ensured effective implementation of the prevention and control measures. However,sampling frequencies for the nucleic acid should be increased as many as possible in the key population including those from medium and high risk areas or close contacts,so as to reduce missed detection.

Key words: COVID-19, Nucleic acid detection, Suzhou City