Analysis in nucleic acid test results of patients with coronavirus disease 2019 in Yangzhou City of Jiangsu Province

Objective To analyze the nucleic acid test results of confirmed cases with coronavirus disease 2019(COVID-19)and asymptomatic infection cases reported by Yangzhou government. Methods The confirmed COVID-19 cases and asymptomatic infection cases were followed up continuously, and their pharyngeal swab specimens were collected during 6 weeks for virus nucleic acid detection. Results The results of virus nucleic acid test in the second, third and fourth weeks after exposure showed that the positive rates of confirmed COVID-19 cases were 100.00%, 61.54% and 8.33% respectively, and the average positive time of nucleic acid test was(24.08±1.17)d, while the positive rates of asymptomatic infection cases at the same time points were 100.00%, 66.67% and 20.00% respectively, and the average positive time of nucleic acid test was(25.21±1.28)d. There were no significant differences between two groups(P=0.42). At second and third weeks after exposure, the average values of circulation threshold(Ct)of novel coronavirus ORF1ab gene in confirmed - COVID-19 cases were(31.56±4.98)and(34.26±3.16), the average Ct values of the N gene were(30.88±4.82)and(34.40±2.86)respectively, and there were no significant differences(P=0.25, 0.15). Since the 4^th week, the number of positive cases for collection of pharyngeal swab specimen was less(n≤1), so they did not participate in the statistics. At second, third and fourth weeks after exposure, the average values of Ct of novel coronavirus ORF1ab gene in asymptomatic infection cases were(31.01±3.68),(32.64±3.74)and(29.05±2.96), the average Ct values of the N gene were(31.37±3.62),(32.90±3.51)and(28.40±4.19)respectively, and there were no significant differences(P=0.23, 0.12). Since the 4^th week, the number of positive cases for collection of pharyngeal swab specimen was less(n≤1), so they did not participate in the statistics. Since the 5^th week, the number of positive cases for collection of pharyngeal swab specimen was less(n≤1), so they did not participate in the statistics. There was one case with negative to positive result of pharyngeal nucleic acid in both confirmed COVID-19 cases and asymptomatic infection cases. Conclusion The positive rate of respiratory tract samples is high in the second week after the exposure in both confirmed COVID-19 cases and asymptomatic infection cases. There is no significant difference in the positive time of nucleic acid test between the two groups. There is a risk of reoccurrence of positive result of pharyngeal swab specimen in confirmed COVID-19 cases and asymptomatic infection cases after two negative results.