Laboratory test results of confirmed COVID-19 cases in Tianjin and related influencing factors / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To study the characteristics and influence factors of laboratory test results of confirmed COVID-19 cases in Tianjin.Methods:Sample collection was conducted based on the standard operating procedure. Tianlong automatic magnetic bead nucleic acid extraction reagent was used for RNA extraction. Real-time RT-PCR was performed using four approved COVID-19 nucleic acid detection kits. Related epidemiological data of the cases were collected. One-way analysis of variance and non-parametric test for inter-group differences analysis were conducted using SPSS25.0 software.Results:A total of 162 PCR tests were completed for novel coronavirus nucleic acid detection in 123 confirmed COVID-19 cases. Eleven PCR results were positive for a single target gene and 10 of which were positive for nucleocapsid protein (N) gene. Nineteen cases were tested with two kinds of nucleic acid detection kits and the results of different detection kits were different. Different types of samples were collected form 13 cases for nucleic acid detection and the results showed that the Ct value of sputum sample was lower than that of throat swab sample. No significant difference in Ct values of throat swab samples was observed among patients with different clinical symptoms ( PCt-N=0.797, PCt-ORF1a/b=0.551). The 123 cases were divided into different groups according to the time interval between the onset date and the date of the first positive detection of viral nucleic acid. No significant difference in Ct values of throat swab samples was observed among different time interval groups ( PCt-N=0.373, PCt-ORF1a/b=0.058). Conclusions:Sputum samples were better than upper respiratory tract samples for viral nucleic acid detection. The sensitivity of N gene detection was higher, but re-sampling was needed when the result was positive for the single target N gene. Appropriate detection kits should be selected according to the actual needs, and samples should be collected at multiple time points, in multiple types and form multiple sites for detection.