Can someone who has overcome COVID-19 develop the illness again? Technically, yes.

Reports that a recovered coronavirus patient in Japan tested positive for a second time have sparked debate about the possibility.

Experts note that test results suggesting recurrent infections may result from erroneous diagnoses linked to a limited testing capacity, but they also caution that there is possibility of the virus reactivating.

The Osaka Prefectural Government said Wednesday that a woman in her 40s from Osaka tested positive for COVID-19 after what appeared to be a recovery earlier in February.

According to the prefecture, the woman first tested positive on Jan. 29 after joining a tour in which visitors from the Chinese city of Wuhan — where the virus is thought to have originated — also took part. She was discharged from the hospital on Feb. 1 after her condition improved. The woman tested negative during a monitoring period a few days after her release, but she was still symptomatic. She tested positive again on Wednesday after multiple visits to the hospital.

So are recurrent infections possible?

Virologists and epidemiologists say it’s too soon to say with regards to the new coronavirus, officially named SARS-CoV-2.

But Masaya Yamato, director of the Infectious Diseases Center at the Osaka-based Rinku General Medical Center, rejects the possibility in the Osaka woman’s case.

“I believe the virus has reactivated,” Masaya said by telephone on Thursday. Such a scenario, Yamato said, is likely in patients who have not yet produced antibodies, which protect the body against the virus.

In healthy people with fully developed antibodies, reactivation is rather unlikely, he said.

“A patient who contracts the virus needs about 14 days, or longer in some patients like the elderly, to produce the antibodies,” he said. “A recovery doesn’t mean the virus is gone — it is dormant.”

He explained that like other viruses, including SARS in 2003, SARS-CoV-2 remains latent in certain cells in the body, for instance, in gastrointestinal tissues. Once reactivated, the virus may again attack the respiratory tract and intestines, he added.

Experts say the body’s immune response determines whether coronavirus patients believed to have overcome the disease later develop serious illnesses.

Earlier this month, Hitoshi Oshitani, a professor of virology at the Tohoku University Graduate School of Medicine, said coronavirus reinfections are possible but that they would likely be less severe.

Marc Windisch, head of the Applied Molecular Virology Lab at the Institut Pasteur Korea, who made clear he was speaking in a personal capacity, agrees. He said that reinfections are usually either asymptomatic or accompanied by only mild symptoms because adaptive immune systems immediately take on the pathogen.

He said, however, that COVID-19 can be fatal in immunodeficient patients — transplant patients or those infected with HIV — “because the adaptive immune system is missing.”

Experts also point to vague criteria allowing doctors to discharge patients who have not overcome the disease and suggest that test results may be misleading.

An official from the Osaka Prefectural Government’s medical section said the woman who tested positive after a recovery was released before the government issued guidelines for medical institutions treating coronavirus patients.

Before Feb. 3, the government had not required doctors to perform polymerase chain reaction (PCR) tests when discharging patients. Doctors could decide to release patients if their temperatures hadn’t gone higher than 37.5 degrees Celsius during a 24-hour period, their symptoms showing respiratory infection had shown improvement and blood cell analysis had shown signs of recovery.

The health ministry later in February asked all medical institutions accepting COVID-19 patients to conduct PCR tests until two negative tests were recorded.

“My question would be why do they keep testing,” David Fisman, a professor of epidemiology at the University of Toronto, asked rhetorically in an email to The Japan Times. He said he would regard a positive result after a negative as a false positive likely due to persistent viral material.

But Yamato, of the Infectious Diseases Center, stressed that without a blood antibody screening, tests of saliva or sputum collected from the patient’s throat won’t be sufficient to detect the virus.

Conducting all possible tests for viral infection would be “unrealistic,” he said.

Contributing writer Enzo DeGregorio assisted with this report

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