In case of COVID positive patients, presence of corona virus is suspected only when the pathogen has produced a disease symptom. But when the symptoms of the disease has not appeared, the corona virus in the body can be detected by-

Reverse transcriptase Polymerase Chain Reaction (RT-PCR)

The correct answer is Option (3) - Reverse transcriptase Polymerase Chain Reaction (RT-PCR)

Currently, RT-PCR is used to diagnose COVID-19 and CT scans are used for screening. Each detection method has its own drawbacks. For RT-PCR-based diagnosis, the availability of RT-PCR kits cannot meet the demand, and the diagnostic efficacy depends on the presence of SARS-CoV-2 in the collected samples.

For CT-based diagnosis, the equipment is expensive and requires operation by professional doctors. Currently, real-time quantitative reverse transcription-PCR (rqRT-PCR) is popular for coronavirus detection due to its high specificity, simple quantitative analysis, and higher sensitivity compared with conventional RT-PCR.

It is a gold-standard test for diagnosing viral diseases like Ebola and SARS-CoV-2 virus infection. The RT-PCR is a sensitive test. It means that if someone has COVID 19 infection, higher are the chances of this test giving a positive result.

-The enzyme-linked immunosorbent assay (ELISA) is an immunological assay commonly used to measure antibodies, antigens, proteins and glycoproteins in biological samples. Some examples include: diagnosis of HIV infection, pregnancy tests, and measurement of cytokines or soluble receptors in cell supernatant or serum.

-A Widal test meaning is a sersology blood test that helps detect typhoid or enteric fever in the body. This test was first conducted in 1896 by Georges Ferdinand Widal and was named after him.