The Medical Mystery of Positive Covid-19 Tests in Recovered Patients
Doctors and scientists are still grappling with the mystery of patients who continue testing positive for the Covid-19 virus weeks after recovery, even as China declared the pandemic’s initial epicenter Wuhan free of cases.
More than 30 patients in Hubei province, including Wuhan, have recovered from disease but continue to test positive, said Jiao Yahui, an inspector at the National Health Commission, in an April 24 interview with the state broadcaster.
Most patients who recovered from the coronavirus tested negative on nucleic acid throat swabs around 20 days after the disease was first detected. But some took an excessively long period of more than 40 days to get negative readings, doctors said. And some patients who tested negative later returned to positive without showing symptoms, doctors found.
The emergence of recovered patients remaining positive in tests for the virus raises the questions of whether they can still be infectious and how long such people can continue spreading the virus. It also poses challenges to global efforts to continue containing the disease while bringing society back to normal as the outbreak seemingly wanes.
Caixin’s coverage of the new coronavirus
Wuhan, the central China city of 11 million where the virus first emerged in December, declared zero remaining Covid-19 cases April 26, three weeks after the city lifted its unprecedented 76-day lockdown to control the spread of the disease. The city recorded 50,333 cases as of April 27, including 46,464 people who recovered.
Patients can be deemed fully recovered and discharged from hospitals after they test negative in two consecutive tests for the virus.
But a doctor at Jinyintan Hospital, one of the hospitals designated for Covid-19 patients in Wuhan, said there are still some recovered patients who continue showing positive results in tests. Such patients are no longer counted as confirmed cases and will be transferred to isolation sites in their communities after hospital assessment, the doctor told Caixin.
Several Chinese epidemiologists said recovered patients who continue to test positive are unlikely to be strongly infectious, and there is little possibility that humans can be lifelong carriers of the virus.
Rong Meng, an infectious disease expert at Beijing Ditan Hospital, said that although the virus can still be detected in some recovered patients, studies found it is much less contagious and can hardly become a new infection source.
According to Rong, some recovered patients, many of them children, remained positive in virus tests for more than 40 days since they showed symptoms, compared with the average of 20 days for most recovered patients. But positive results in nucleic acid testing don’t necessarily mean the virus is active, Rong said.
Cai Weiping, an infectious disease doctor at Guangzhou No. 8 People's Hospital, told Caixin that there is no consensus on whether such patients can be infectious and more studies are underway. Before a conclusion is made, patients with continued positive results should be placed under isolation and observation, Cai said.
Genome sequencing for remaining virus from some recovered patients showed that the virus was dead, said Zhang Boli, president of Tianjin University of Traditional Chinese Medicine. That may indicate that only traces of the virus’s genetic material remained in patients’ bodies, Zhang said.
Doctors in China and abroad are puzzled by some patients’ longer process of of viral shedding. In late March, a preprint essay by Wuhan military doctors Wang Qingshu and Niu Hongming discussed a patient who remained positive in virus tests for 49 days.
The patient, a middle-aged male, showed fever and other symptoms Jan. 25 but recovered after a week of medication. He tested positive for the virus Feb. 8 after one of his family members was confirmed with the infection. The man took nine nucleic acid tests in the following weeks, and only one test on March 11 showed negative.
He also received two antibody tests in late February and mid-March, reading positive for one form of immunoglobulin but negative for another. Such results suggest that the infection has lingered for a while and faded from the acute phase, the doctors wrote.
The patient received plasma therapy March 15, which involves transfusing antibody-rich blood components into patients. He had high fever hours after the infusion, but his temperature returned to normal the next day. His virus tests on the following two days turned negative.
“Without plasma therapy, this patient may turn to a chronic infection case,” the doctors wrote in the paper. “We want to know how many patients have similar situations.” The authors said they were unable to conclude whether such patients could infect others or how long their infections could last.
The patient was part of a family cluster, the researchers wrote. One of his infected family members, an elderly female, also took a longer-than-normal period to test negative. The authors said the cases suggested that family-cluster infections may be less virulent but lead to longer periods for patients to resolve the virus.
Contact reporter Han Wei (firstname.lastname@example.org) and Bob Simison (email@example.com)
Jiang Moting and Zeng Yukun contributed to this story.
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