Nucleic acid packaging needs close contact with human saliva samples. If one of them is positive, it is probably infected.
The substance of nucleic acid detection is the nucleic acid of virus. Nucleic acid detection is to determine whether the patient is infected by COVID-19 by detecting whether there is nucleic acid of foreign invasive virus in respiratory tract samples, blood or feces. Once the nucleic acid is "positive", it can prove that there is a virus in the patient.