Microbiological Diagnosis of COVID-19

Various tests are used to detect the severe acute respiratory syndrome-coronirus-2 (SARS-CoV-2) virus causing Coronavirus disease-19 (COVID-19) disease. Today, the realtime (RT) -PCR test combined with the reverse-transcription reaction is the gold standard method used to diagnose SARS-CoV-2. This method is referred to as quantitative realtime PCR (RT-qPCR) because it determines not only the presence of SARS-CoV-2 but also the amount of virus in the specimen. Due to the use of virus-specific primers, the specificity of the tests is considered to be 100%. For this test, swab samples taken from the upper respiratory tract such as nasopharyngeal and throat, samples from the lower respiratory tract areas such as sputum and bronchoalveolar lavage fluid, rectal swab, feces, serum and urine samples are preferred. Correct use of personal protective equipment (PPE) by healthcare professionals during sampling and testing is important. Rapid antigen tests used in addition to RT-qPCR test for the diagnosis of SARS-CoV-2 are advantageous due to the theoretical rapid result time and low cost, but the sensitivity of this method is known to be very low. Virus detection in cell cultures can be used to detect SARS-CoV-2, but it is not for routine diagnostic because the results take a long time, require labor, and expertise. Serological tests are frequently used in the diagnosis and follow-up of this disease. These are mainly ELISA, CLIA, immunofluorescence test (IFA), western blot (WB), protein microarray (microarray) and neutralization. ELISA based immunoglobulin (Ig)M and IgG antibody tests have more than 95% specificity in the diagnosis of COVID-19.