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Asymptomatic coronavirus cases may not be infectious, Wuhan study indicates

Christian Fernsby |
A mass screening programme of more than 10 million residents of Wuhan, China, performed after coronavirus was brought under control, has identified 300 asymptomatic cases of coronavirus, none of which was infectious.

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The findings cannot be extrapolated to countries where outbreaks have not been brought under control successfully, said the authors of the report, which was published in Nature Communications.

The researchers conducted a screening programme using PCR testing for viral RNA among the 10 million participants who were aged between 10 and 89. Trained staff interviewed participants on their history of coronavirus. Asymptomatic positive cases were those who had a positive result on screening with neither a history of coronavirus diagnosis nor any clinical symptoms at the time of the nucleic acid testing. The researchers found no “viable virus” in cultures from asymptomatic samples.

Further swab testing of 1174 close contacts of the 300 asymptomatic positive cases were all negative. The study population included 34 424 people with a history of coronavirus, 107 of whom (0.310%) had been re infected.

The researchers said that their findings did not show that the virus couldn’t be passed on by asymptomatic carriers, and they didn’t suggest that their findings were generalisable.

They said that strict measures—such as mask wearing, hand washing, social distancing, and lockdown—were successful in reducing the virulence of SARS CoV 2 in Wuhan and that asymptomatic people in Wuhan may have low viral loads. This means that the finding cannot be applied to countries where outbreaks have not been successfully brought under control.

Fujian Song, from UEA’s Norwich Medical School, who collaborated with colleagues in Wuhan on the research, said: “The asymptomatic cases identified in the screening programme were truly asymptomatic, as none of them showed clinical symptoms before or during their follow up isolation.” But, he added, “there is plenty of evidence elsewhere showing that people infected with coronavirus may be temporarily asymptomatic and infectious, before going on to develop symptoms.”

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