The curious case of the recovered testing positive again

More than 4,250 people have recovered from covid-19 since India reported its first case at the end of January. But a fresh concern, based on the experience of China and South Korea, is that those who recover and test negative for SARS-Cov-2, the virus that causes covid-19, may later test positive again.

Doctors say India will need to do viral quantitative analysis to check the viral load in each positive case, closely monitor patients during the virus shedding or recovery stage, and compulsorily quarantine patients for two weeks even after full recovery to prevent this from happening.

“We don’t know the exact cause yet as research is still underway, but there are three possible reasons why people experience a relapse,” said Dr Sandeep Budhiraja, group medical director at Max Healthcare, who oversaw India’s first successful convalescent plasma therapy in a covid-19 patient.

One, the patient could contract a new infection. Two, the virus is mutating fast—there are currently three strains of SARS-Cov-2—and the person could contract another strain to which he has not developed immunity. The third reason Dr Budhiraja gave, while stressing that this is highly unlikely, was reactivation of the virus.

“There is a possibility of the virus remaining in the body, even after the person tests negative, and resurfacing,” he said.

Doctors in Wuhan, where SARS-Cov-2 first emerged in December 2019, have observed a number of cases in which patients tested negative for the virus after recovering, but then tested positive again 50 to 70 days later.

So far, there have been no confirmations of newly positive patients infecting others, according to Chinese health officials. China has not published figures for how many patients fall into this category.

In South Korea, more than 180 patients who recovered later tested positive, prompting health authorities to start an investigation. None of these were found to have infected anyone else. The prospect of people remaining positive, and therefore potentially infectious, is of international concern, as many countries seek to end lockdowns.

“If two subsequent tests within 24 hours prove negative for a person after treatment, we send them home,” said Dr Vijay Raju Krupesh, lead surgeon (intensive care) HCG, and member of Karnataka’s Covid Consultative Group. The American Society for Microbiology, however, recommends keeping a recovered patient in quarantine for two extra weeks. “We need to do viral quantitative analysis to know the load of the virus in the patient to ascertain why the infection came back,” he said.

There is the possibility of the test being so sensitive that it picks up small, potentially harmless levels of the virus, leading to positive results even if the person has recovered. Further, the test could be compromised if the sample is not collected properly.

“We need to carefully monitor the three stages of the disease—pre-symptomatic, asymptomatic and virus shedding. It appears that viral shedding takes time,” said Dr H. Sudarshan Ballal, chairman of Manipal Health Enterprises.

Closely monitoring the patient during the virus shedding period is crucial. “It varies from patient to patient, ranging from a fortnight to 45 days, depending on the underlying illnesses,” said Dr Rajani Bhat, a pulmonologist.

Ultimately, it emerges that immunity is key.

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