Some patients who have met tough hospital discharge requirements after recovering from Covid-19 could still be breathing out the coronavirus in high volumes, according to an international study led by Chinese scientists.
These patients tested repeatedly negative with throat swabs, their lung images were back to normal, and symptoms such as fever had disappeared.
But each minute, some could still exhale thousands of particles of Sars-CoV-2, the formal name for the coronavirus, the study found.
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“[There is] an urgent need to revisit current hospital discharge guidelines to minimise the public risk,” the researchers led by Peking University professor Zhang Yuanhang said in a peer-reviewed paper published in the Journal of Aerosol Science on Thursday.
The qualifications for discharge vary from one hospital to another, and country to country. In China, the health authorities need to see at least three negative PCR tests for a pass, among other requirements.
Nine patients who met these requirements in the central Chinese city of Wuhan, in Hubei province, took part in Zhang’s study. They were asked to breathe into a tube for five minutes. Breath condensate from two patients – one 71 years old and the other 81 – tested positive, with one producing about 7,350 copies of the novel coronavirus per minute and the other and 7,770 copies.
These amounts were about 10 per cent of that generated by some patients during the peak of their disease in Beijing, according to the study. But still the number was alarmingly high.
“This potential of hidden spread represents a serious airborne infection risk from the recovering Covid-19 patients,” the researchers said.
It remained unclear if the exhaled viral strains were infectious. One possibility is that the PCR test only detected fragmented viral genes rather than complete virus.
The study was conducted during an intensive outbreak in China and the researchers said they did not test if the virus could infect and replicate in human cells due to resource constraints.
A government epidemiologist in Shanghai said the coronavirus genes, in single-stranded ribonucleic acid, were highly unstable. “RNA fragments degrade quickly” so the chance that these viral particles were complete could be high, said the researcher who was not involved in the study.
One previous study on the coronavirus collected from hospital air suggested that more than 60 per cent of the virus particles remained infectious.
“But the patients could be breathing harder into the tube than they normally did, so how serious the risk can be remains somewhat uncertain,” said the scientist who requested not to be named because they needed authorisation to speak to the media.
Zhang’s team also collected samples from the environment in the hospital ward housing these recovering patients. They used a robot to collect air samples in different rooms and public areas. In positive samples, the number of viruses varied from nine to 219 per cubic metre of air, and only three per cent of the samples collected from environmental surfaces produced positive results.
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“This finding implies that direct surface contact, even in high risk areas ... may not represent a major route of transmission,” they said.
The researchers said they believed the virus in breath came from the lung of the recovering patients. Their findings confirmed a previous study by researchers in the southwestern municipality of Chongqing that found intact viral strains from deep inside a woman’s lungs who had recovered from Covid-19 and then died.
In some Chinese cities, health authorities have extra requirements for hospital discharge, according to doctors who worked at these hospitals.
One doctor in Beijing said at his hospital “you are not allowed to go home until your faeces tests negative”.
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This article Coronavirus: researchers call for review of hospital discharge guidelines first appeared on South China Morning Post