ABSTRACT
Objective: To investigate the value of anal swabs positive for 2019-nCoV in patients with COVID-19 and the clinical features of the patients. Methods: Throat swabs, sputum and blood samples, and anal swabs were collected from 104 patients with COVID-19 at admission to test for 2019-nCoV nucleic acid. Clinical characteristics and hematological indexes were compared between viral nucleic acid-positive and -negative groups of different sample types. Fifteen patients whose anal swabs were positive for viral nucleic acid were selected to analyze the length of time before the nucleic acid turned negative in different specimens. Results: Compared with the patients having negative anal swab test results, those having positive test results showed decreased lymphocytes, increased lactate dehydrogenase (LDH) and high-sensitivity C-reactive protein (HsCRP), and higher incidence of severe COVID-19. The levels of HsCRP and IL-6 and the incidence of severe COVID-19 were significantly higher in patients with positive throat swab test results than in those with negative results. No significant difference in hematological indexes or the proportion of severe cases was detected between the patients with positive and negative sputum test results. Only 1.92% of the patients had positive blood test results, but all of them were severe patients. The positive rate of sputum test was the highest, which was 46.15%. Patients with positive results of both throat and anal swab test had significantly decreased lymphocytes, increased HsCRP and IL-6 levels, and higher incidence of critical COVID-19. It took longer time for patients to have negative anal swab and sputum test results. Moreover, it should be noticed that the viral nucleic acid in sputum might become positive again after it turned negative. Conclusions: Patients with positive anal swab test results had reduced lymphocytes, enhanced inflammatory response and higher incidence of severe COVID-19, suggesting that a positive anal swab test might be an indicator of severe COVID-19. Moreover, the time of 2019-nCoV nucleic acid turning negative in anal swabs was longer than that in throat swabs. The combined detection of throat swabs and anal swabs would help to predict the occurrence of severe COVID-19.
ABSTRACT
OBJECTIVE: To evaluate a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and compare it with RT-PCR. METHODS: We designed primers specific to the orf1ab and S genes of SARS-CoV-2. Total viral RNA was extracted using the QIAamp Viral RNA Mini Kit. We optimized the RT-LAMP assay, and evaluated it for its sensitivity and specificity of detection using real-time turbidity monitoring and visual observation. RESULTS: The primer sets orf1ab-4 and S-123 amplified the genes in the shortest times, the mean (±SD) times were 18 ± 1.32 min and 20 ± 1.80 min, respectively, and 63°C was the optimum reaction temperature. The sensitivities were 2 × 101 copies and 2 × 102 copies per reaction with primer sets orf1ab-4 and S-123, respectively. This assay showed no cross-reactivity with 60 other respiratory pathogens. To describe the availability of this method in clinical diagnosis, we collected 130 specimens from patients with clinically suspected SARS-CoV-2 infection. Among them, 58 were confirmed to be positive and 72 were negative by RT-LAMP. The sensitivity was 100% (95% CI 92.3%-100%), specificity 100% (95% CI 93.7%-100%). This assay detected SARS-CoV-2 in a mean (±SD) time of 26.28 ± 4.48 min and the results can be identified with visual observation. CONCLUSION: These results demonstrate that we developed a rapid, simple, specific and sensitive RT-LAMP assay for SARS-CoV-2 detection among clinical samples. It will be a powerful tool for SARS-CoV-2 identification, and for monitoring suspected patients, close contacts and high-risk groups.