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Beijing Outbreak Shows Covid-19’s Insidious Ability to Hide
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Just as Beijing looked poised to claim victory over the coronavirus, a 52-year-old man with fever and chills showed how the pandemic can come roaring back from apparent obscurity.
The patient had shopped for meat and fish at a wholesale market in southern Beijing eight days before testing positive on June 11. His infection marked the Chinese capital’s first reported Covid-19 case in 55 days and scuppered hopes that months of physical distancing, meticulous testing and quarantining had driven the pathogen to extinction in the city of over 20 million.
Now, more than 200 people have tested positive across Beijing, schools are shut and thousands of domestic flights canceled. The resurgence offers a stark warning to countries that appear to have cut chains of transmission: The coronavirus’s ability to cause little or no symptoms in a large proportion of people enables it to spread silently for weeks — even months — creating viral reservoirs that can remain hidden until someone becomes sick enough to warrant testing.
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“Transmission could have started a month earlier, with already so many asymptomatic or mildly symptomatic patients shedding lots of the virus into the environment,” George Gao, head of the Chinese Center for Disease Control and Prevention, told government advisers at a meeting in Shanghai last week. It’s possible the virus lurked in dark, humid conditions before it was amplified in infected people, he said.
The flareup in China’s political center also reveals the difficulty of ridding the insidious contagion without an effective vaccine.
Some countries and cities that appeared to have tamed the virus are seeing cases start to increase again. Victoria, Australia’s second-most populous state, tightened control measures Monday after a spike in cases. New Zealand appointed a military leader last week to oversee the quarantining of citizens returning from abroad to head off fresh outbreaks. The country earlier this month removed physical distancing requirements after reporting zero active Covid-19 cases, indicating it had achieved its aim of eliminating the virus.
Elsewhere, countries from South Korea to Germany are battling new clusters, trying to stamp out sparks before they become raging fires.
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“We can’t assume it’s ‘eliminated’ anywhere,” said Peter Collignon, a professor of clinical medicine at the Australian National University Medical School in Canberra, who advises the Australian government on infection control.
A lull in reported cases may reflect transmission has been suppressed to very low levels, Collignon said. Still, the virus may continue to infect people, albeit with minimal symptoms, and “can then flare up and spread if given the opportunity,” he said.
Beijing health authorities probably identified the tip of an iceberg of cases when they diagnosed the 52-year-old market goer with Covid-19 earlier this month, said Raina MacIntyre, professor of global biosecurity at the University of New South Wales in Sydney.
“It’s possible that the outbreak itself started weeks before it was identified,” she said.
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Soon after the man’s infection was detected, more cases were found among merchants and those who shopped at the wholesale market. Health officials also identified the virus in environmental samples collected, including on a chopping board used to cut up imported salmon.
Genetic sequencing showed the virus isolated in the outbreak was similar to one that had spread in Europe, fueling speculation that the virus may have been introduced via imported salmon.
China CDC’s Chief Epidemiologist Wu Zunyou said the finding “doesn’t indicate much,” as the kitchen item may have been contaminated by respiratory droplets from an infected worker or shopper.
“I can imagine in meat packing plants, if there was an infected person, they could contaminate the environment and the virus could be there for a little while,” said Benjamin Cowling, head of epidemiology and biostatistics at the University of Hong Kong. “But there’s no evidence that leads to onwards transmission.”
Where transmission of the coronavirus has been studied, it appears to have mostly spread from one person to another directly, Cowling said.
Until this month, Beijing last detected a new case in mid-April, when a student returning from the U.S. fell sick after completing a 14-day stint in quarantine on arrival. He subsequently transmitted the virus to his mother, brother and grandfather, but transmission was contained within the family.
After the June 11 infection was reported, six cases were detected the next day, then dozens of cases daily emerged over the following week. China’s vice premier Sun Chunlan warned of the risks of further spread given the outbreak’s correlation with a thronging wholesale market.
Beijing quickly ramped up testing to detect, treat, and quarantine those infected by the virus and to trace their contacts to quell the growing cluster.
China CDC’s Wu said the outbreak in Beijing is under control, with new reported cases reflecting the lag between when people caught the virus and subsequently tested positive.
Even still, new cases will continue to emerge, Wu said. “By ‘under control,’ I don’t mean there will be no cases tomorrow or the day after tomorrow. The curve will continue for a while, with fewer and fewer cases.”
With new cases plateauing and no eradication of Covid-19 in sight, Beijing has refrained from resorting to a city-wide lockdown like that which curbed the contagion in Wuhan, where the pandemic emerged in late 2019.
Officials are instead restricting the movement of residents in identified hot spots -- an approach that seeks to halt transmission while causing the least economic disruption in the Chinese capital.
“In China, there’s a very clear strategy to get Covid-19 cases down to zero and to keep to zero as much as possible,” Hong Kong University’s Cowling said. “But the measures needed to bring it down to zero might just be too drastic and have too much knock-on effect on the longer term health of people, because of the economic consequences.”
Meantime, the rest of the world is watching to see if Beijing’s alternative approach can quash the outbreak without inflicting further economic damage. It’s yet another difficult predicament the pandemic is forcing governments worldwide to weigh up in the absence of lived experience.
“It’s unprecedented,” MacIntyre said. “Most people who are living today have not experienced anything like this.”