Analyses of the nucleic acids of SARS-CoV-2 from pharyngeal swabs and fecal specimens in COVID-19 patients and asymptomatic SARS-CoV-2 infected persons at different exposure times

ABSTRACT

The coronavirus disease 2019 (COVID-19) pandemic has become a public-health crisis worldwide. Accurate identification of the virus that causes COVID-19, SARS-CoV-2, carriers of SARS-CoV-2, and infected people is crucial for the prevention and control of this pandemic. Detection of the nucleic acids (NAs) of SARS-CoV-2 is one of the main criteria for COVID-19 diagnosis. Pharyngeal swabs (PSs) and fecal specimens (FSs) tend to be positive for SARS-CoV-2. However, there have been no reports of differences in the detection results of SARS-CoV-2 NAs in PSs and FSs of COVID-19 patients and asymptomatic SARS-CoV-2 infected persons at different exposure times. Forty-six patients diagnosed with COVID 19 in Nanyang City, China, from 2 February to 17 February 2020 and 27 asymptomatic SARS-CoV-2 infected persons screened through epidemiologic history and PSs and FSs at different exposure times were evaluated through detection of SARS-CoV-2 NAs. COVID-19 patients and asymptomatic SARS-CoV-2 infected persons had the highest positive rate of NAs in PSs at week 2 and the highest positive rate for NAs in FSs at week 3. The positive rate of NAs in PSs was significantly higher than that of FSs (P < 0.05). The difference in the positive rate of NAs in PSs between the two groups at 1, 3, and 4 weeks was significant (P < 0.05). The difference in the positive rate of NM in FSs between the two groups at 1-4 weeks was not significant (P > 0.05). The time for SARS-CoV-2 NAs to test positive in FSs lagged behind that for SARS-CoV-2 NAs to test positive in PSs (P > 0.05). The time for SARS-CoV-2 NAs to test positive in the PSs and FSs of asymptomatic SARS-CoV-2 infected persons lagged behind that for COVID-19 patients (P > 0.05). There was no significant difference in the average cycle threshold (Ct) value of the ORFlab gene and N gene of PSs and FSs between COVID-19 patients and asymptomatic SARS-Cov-2 infected persons at each exposure time tested (P > 0.05). The more severe the COVID-19, the higher was the positive rate of SARS-CoV-2 NAs in PSs and FSs, and the shorter was the time taken for SARS-CoV-2 NAs to test positive (P < 0.05). The re-positive rate of asymptomatic SARS-CoV-2 infected persons was 14.81% (4/27), higher than that of COVID-19 patients (6.52%;3/46), and the difference was significant (X2=8.193, P=0.016). Our study suggests that SARS-CoV-2 has a fecal mouth transmission route. The time taken for SARS-CoV-2 NM from FSs to turn positive lags behind that for SARS-CoV-2 NAs in PSs to turn positive, and the positive rate is lower. Test specimens should be selected according to different exposure times. Attention should he paid to younger asymptomatic SARS-CoV-2 infected persons.