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China data shows vast majority of asymptomatic coronavirus carriers never get sick

April 15, 2020, 11:30 AM UTC

China for the first time publicized a breakdown of people testing positive for the novel coronavirus without outward signs of being sick, revealing that those among them who remain symptom-free throughout infection are in the majority.

Among 6,764 people who tested positive for infection without showing symptoms, only one fifth of them — 1,297 — have so far developed symptoms and been re-classified as confirmed cases, China’s National Health Commission spokesman Mi Feng said at a briefing in Beijing Wednesday.

Some 1,023 are still being monitored in medical quarantine to see if they develop symptoms. The rest — 4,444 — have been discharged from medical observation after recovering from the virus.

The phenomenon of asymptomatic transmission is a puzzling feature of the virus that’s allowed the pandemic to spread wider and faster than previous outbreaks. While researchers earlier thought that most patients ultimately end up developing symptoms, the indication from China’s data that a sizable group remains symptom-free throughout infection underscores the challenge of containing the widening pandemic.

Researchers are still struggling to understand asymptomatic cases: there’s a possibility that patients who appear to be symptom-free are actually just manifesting symptoms that doctors don’t know yet to look for. For months, a fever and dry cough were understood to be the disease’s main markers, and it’s only recently emerged that a loss of smell and taste is also a sign of infection. China has not disclosed the range of symptoms it looks for.

China continues to detect asymptomatic infections even after new confirmed cases dropped to zero for the first time in March. The virus, which emerged from the central Chinese city of Wuhan last December, has officially sickened some 82,000 and killed over 3,000 in the country.

The number of asymptomatic infections is likely higher than the 6,764 China has detected. These cases were found through efforts to test the contacts of confirmed patients. Otherwise, those who show no signs of being sick have no reason to seek out testing on their own.

Once found, asymptomatic patients are placed under isolated quarantine for monitoring and discharged only when they no longer tested positive for the virus. Those who develop symptoms during the two-week quarantine period will be re-classified as confirmed cases under China’s counting method and treated in hospital.

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