Chinese researchers say they have discovered a new “chronic” mutation of the coronavirus in a patient who was contagious for a record-breaking 49 days.

The patient, a middle-aged man, had non-severe symptoms but had a prolonged ability to infect others, said the Chinese military researchers in Wuhan, according to the South China Morning Post.

He had an intermittent low fever and no cough, chills, shortness of breath or other typical symptoms of COVID-19.

CAT imaging showed lesions in both of his lungs, but they disappeared a few days after he was admitted to the hospital, and his body temperature also returned to normal.

But he kept testing positive for the illness, showing a high viral load similar to patients experiencing severe cases.

As signs showed that his body couldn’t eliminate the virus through normal therapy and that he could still be infectious, the patient was treated with a plasma transfusion from cured COVID-19 patients. Two days later, his test came back negative.

The rare case was the longest known duration of “viral shedding” in a patient. The previous record was 37 days.

Researchers warned there could be other “chronically infected patients,” who were more likely to be neglected but could spread the infection in their surroundings and cause a new outbreak.

The findings were published on March 27 on MedRxiv, a website for preliminary reports of scientific medical papers that have not yet been peer-reviewed and should not to be taken as a guide for clinical practice.