NAATs such as RT-PCR for SARS-CoV-2 are designed to detect viral RNA. A positive result is very specific for the presence of viral nucleic acid; however, it does not distinguish between viable and non-viable viruses. Therefore, a positive test does not necessarily indicate that a person is infectious and requires isolation. Clinical samples submitted to the CDC for SARS-CoV testing that tested positive were confirmed by a TaqMan real-time RT-PCR test based on three different sets of primers and probes (Table 1). This test was performed independently in a separate laboratory using nucleic acid newly extracted from a second aliquot sample. The confirmatory test used the SuperScript One-Step RT-PCR (Invitrogen Corp., Carlsbad, CA) and the Multiplex Mx4000 quantitative PCR system (Stratagene, La Jolla, CA). Because the PCR test is so sensitive, it can detect very small amounts of viral material. This means that the test can continue to detect fragments of the SARS-CoV-2 virus even after you have recovered from COVID-19 and are no longer contagious. So you can still test positive if you`ve contracted COVID-19 in the distant past, even if you can`t transmit the SARS-CoV-2 virus to others. Overall, in this prospective study to assess the feasibility of saliva samples, the majority of patients with SARS-CoV-2 positive nasopharyngeal swabs also had positive saliva samples, but the sensitivity of the latter test was lower. Higher viral loads were found in nasopharyngeal smears. Guidelines for health care workers testing for SARS-CoV-2. The clinical sensitivity of a NAAT is influenced by the detection limit of the test, the time elapsed since the onset of infection and the type of sample.
Since patients with symptoms tend to appear earlier in the course of their infection, there is an increased sensitivity to testing in symptomatic people compared to asymptomatic people. Traditionally, the nasopharynx has been the body`s preferred site for sampling, but given the patient`s discomfort and the need for serial testing, many hospitals and public health programs now use anterior nars, or saliva, as a primary sample type. This frequently updated page contains information on specific tests for which the FDA has identified potential effects on performance due to genetic MUTATIONS in SARS-CoV-2. Evaluation of the accuracy of various respiratory tract samples in laboratory diagnosis and viral shedding surveillance of 2019-nCoV infections (Yang, February 2020). 213 patients hospitalized for COVID-19 in China provided 866 clinical samples from the respiratory tract, including nasal swabs and throat swabs, sputum, and bronchoalveolar lavage fluid. Sputum samples were most likely to test positive for RT-PCR, regardless of the clinical severity of the disease. PCR is one of the most widely used diagnostic tests to detect pathogens, including viruses that cause diseases such as Ebola, African swine fever and foot-and-mouth disease. Since the COVID-19 virus contains only RNA, real-time or conventional RT-PCR is used for detection. Nucleic acids were obtained from clinical samples using the NucliSens (bioMérieux) automated extraction system. According to the manufacturer`s instructions, the samples obtained in the NucliSens lysis buffer were incubated at 37 ° C for 30 min with intermittent mixing, and 50 μL of silica suspension contained in the extraction kit were added and mixed.
The contents of the tube were then transferred to a nucleic acid extraction cartridge and processed at an extraction workstation. Approximately 40 to 50 μL of total nucleic acid eluvite was recovered from nuclease-free vials and tested immediately or stored at -70°C. Prolonged infection in immunocompromised people can occur if they excrete infectious viruses for months. Even healthy people can become infected again. If your SARS-CoV-2 test is positive, but you think you have already recovered from COVID-19, please discuss this with a health care provider. Polymerase chain reaction (PCR) tests are a fast and highly accurate way to diagnose certain infectious diseases and genetic changes. Tests work by finding the DNA or RNA of a pathogen (pathogenic organism) or abnormal cells in a sample. A negative test result means that you probably did not have a SARS-CoV-2 infection at the time you took your sample. However, it is possible to have COVID-19 but not have the virus detected by the test. For example, this can happen if you`ve recently been infected but don`t have any symptoms yet – or it can happen if you`ve had COVID-19 for more than a week before being tested. A negative test does not mean that you are safe for long periods of time: you can be exposed to COVID-19 after your test, become infected, and transmit the SARS-Cov-2 virus to others. .