Second test compulsory to declare COVID suspects negative: Experts

Hyderabad: More COVID-19 cases where patients were initially tested ‘negative’ are coming out. The latest instance is that of an 80-year-old paralysis patient from Neredmet in Hyderabad, who was initially tested negative from Gandhi Hospital and later found out to be positive.

To evaluate the reasons behind suspects initially testing negative for COVID-19 and testing positive subsequently, NewsMeter spoke to experts.

Responding to our query regarding the 80-year-old Neredmet patient, the nodal officer for coronavirus at Gandhi Hospital Dr. Prabhakar Reddy said the initial test on him could have been done at the incubation period of virus. “In such situations we ask people to go in for isolation and come back for another test if their condition aggravates,” the nodal officer told NewsMeter.

Multiple reasons can be attributed for a ‘false negative’

Meanwhile, Dr Raghu Kishore, cardiologist at KIMS opines that multiple reasons can be attributed for a ‘false negative’. From early testing, low viremia and low symptoms the reasons vary. “There are several reasons why a COVID-19 patient can initially test negative. One of the reasons is ‘early testing’. The incubation period of Coronavirus varies between 2-14 days. So, sometimes if the test is taken during the initial days of incubation period the result can be negative. Low viremia is the second cause. When the viral load inside the body of the patient is low, the test can come negative. Also the test result can show positive for high symptomatic patients than low symptomatic patients. After the pneumonia or other full-fledged symptoms are developed chances of the patient testing positive are higher,” he said.

Another reason for the negative result can be sensitivity of the test. The sensitivity of the nasal swab is around 66 per cent and pharyngeal swab is 33 per cent. So every second to third patient can be a false negative because of the low sensitivity of the swab. Also there can be technical problems while taking, processing, transferring and storing the sample.

Referring to a recent case where a man’s sample was sent for a second round test the doctor said, “A man with a travel history from Delhi came for COVID-19 test four days back. His first test was negative. But we have sent his sample for a second round of testing because he has high symptoms of viral pneumonia. We cannot rule out the possibility.”

Adding to Dr Kishore, Dr Suneetha Narreddy, an Infectious Diseases Physician from Apollo Hospital told NewsMeter, “The sensitivity ( i.e, what is the probability that a person will pick up that disease) for covid test is only 60-70 per cent. This means, if we have 100 people with coronavirus, the test will be positive only for 60-70 of them. Ideally we should have a test that can pick up all the people with the disease. But we have limited technology available and are forced to leave with it. So we need to understand the challenges in the test and work around interpreting it. Like PCR tests, anri-body tests also have their own limitations. It won't detect a patient at the initial stage of Covid-19. Also not every person will develop antibodies. Then what are we going to do with that test? So there are a lot of confusions going on.”

Community transfer

Telangana government denies any community transmission in the state, however there are atleast 20-30 per cent patients , daily wage labourers with no travel history, but tested positive . “So it's better to get tested again if the symptoms are recurring or if you have a travel or contact history, say doctors.”

The major concern with false negatives is someone who tests negative could unknowingly spread the virus into the community. Every one infected might not show symptoms of the infection says, Dr Ramesh Misra, director of CCMB (Centre for Cellular Molecular Biology). “The virus may enter a person’s body and he might be cleared of it without him realizing it.”

In a way this is good, he says and adds the person will not be infected again as he acquires immunity. But the person could still be a carrier of the virus and spread it.

“The covid test that we have today is only to identify whether the virus is there in the body or not. The virus may or may not cause the disease. A significant percentage of people (40 per cent) with Coronavirus are asymptomatic in India. If somebody is today negative and becomes positive after a week or 10 days it only means that either the test was not accurate or the person acquired the virus during the span of those many days,” Mr Mishra says.

The director says whether symptomatic or asymptomatic, the person tested negative needs to go in for self-quarantine and take a second test to confirm if he is infected or not.

“We are affected by various infections of fungus, bacteria among others on a daily basis. But our body’s immune system normally fights back and keeps the infections off. If the first test is negative, you need to send the person on quarantine for 14 days. A second test should be done even if they are asymptomatic after 14 days. If the result is negative then the person can be declared free of coronavirus.”