With, the increasing Covid-19 infections in Delhi, caused by the new Omicron variant, doctors said that the rapid antigen test (RAT) was proving more efficient. A positivity rate of 50-70 % was reported in the capital when symptomatic and contacts of positive cases were being tested using the test. 

Dr Suresh Kumar, Medical Director, Lok Nayak Hospital, stated that during the current wave many people were testing positive on the RAT and confirmatory tests were being done for people going into surgery. But during the last wave, confirmatory RT-PCR tests had to be done. 

The RT-PCR test, CB-NAAT and TrueNat, are considered the gold standard for diagnosing Covid-19, while the RAT, just tests for viral particles in the patient sample. During the second wave, in Delhi in November 2020, the peak RT-PCR positivity rate stood at 30.2 %, while the RAT positivity rate was just 8.39 %.

Dr Sumit Ray, Medical Superintendent, Holy Family hospital said that for patients with ailments other than Covid-19 needing hospitalisation RAT, was being performed and it showed a positivity rate as high as 40 to 50%.

Dr Sandeep Buddhiraja, Group Medical Director, Max Healthcare, said, the Omicron variant reproduced well in the upper respiratory tract in contrast to the Delta variant, so patients with Omicron infection have a higher viral load in their throat and the nasal passage from where the sample was being collected, hence most patients test positive on the RAT itself. If the close contacts of patients and people with fever or other Covid symptoms were tested, the RAT positivity rate was about 70 %.

A study during the Omicron wave in December 2020, from the United States, compared RAT and RT-PCR positivity rate among 30 persons, found that the RAT turned positive nearly three days after the RT-PCR test turned positive.

Source: The Indian Express