Unmasked jogger infected 39 people with Omicron in Chinese park, study finds
- Dozens of cases were traced back to the 41-year-old man who spent half an hour running round a park in Chongqing in August
- Most of those who became infected during the man’s run were also not wearing masks, researchers from China’s CDC find
Only one of the people he infected had been wearing a mask.
The jogger spent about half an hour in the park, running four times round a lake on a 4-metre (13ft) wide jogging track. He did not talk to anyone, touch anything or use the toilet.
When the man reached home, he received a call from local health authorities and was told that a PCR test he had taken the previous day was positive.
The study, written by researchers from the Chinese Centre for Disease Control and Prevention in Beijing and Chongqing and published in the CDC’s weekly journal, said the patient had passed the virus to a total of 48 people, including his wife, four colleagues, two foot massage therapists and a breakfast server.
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But most transmissions occurred in the park. Security camera footage showed that more than a hundred unmasked people had come within a metre of the jogger. They were regarded as close contacts and sent to quarantine.
Thousands of people, who did not have any direct encounter with the jogger, were rated “at risk” and told to stay at home for three days.
Among the park visitors, 13 close contacts and 20 at-risk individuals produced positive test results. Further epidemiological investigations found no other exposure history in these people, and they did not know one another. Genetic sequencing suggested that they were infected by the same strain from patient zero.
Those infected also included six park employees, only one of whom was wearing a mask and was thought to have been given a secondary infection after coming into contact with two colleagues who worked as cleaners.
The researchers said they believed the jogger had been infected on a flight between Hohhot in Inner Mongolia and Chongqing on August 13.
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A day earlier, the plane carried four infected passengers from Tibet on a flight from Chongqing to Hohhot. The cabin was not disinfected overnight and the man sat in a seat close to where those passengers were sitting.
He was the only secondary infection reported on the flight, where wearing a mask was compulsory.
It is generally believed that the coronavirus spreads less easily outdoors, the researchers led by Zhang Lijie wrote.
Some studies have reported outbreaks in an open environment, but “these reports do not exclude the possibility of direct contact with cases in indoor spaces”, said Zhang and colleagues.
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But they wrote that the “only possible exposure” for many of those infected was that they were in the park at the same time as the jogger. “This transmission occurred in the park without directly contacting others,” they said.
The study said heavy breathing may have helped spread the virus, adding: “Patient zero jogged for 35 minutes, it is reasonable to assume that he may have emitted an abundance of virus-laden respiratory particles and spread Sars-CoV-2.”
They added although wearing a mask during exercise made it harder to breathe, “given the stronger transmission capacity and faster transmission speed of Omicron subvariants, the public should be encouraged to use good personal protection measures during the Covid-19 epidemic even while outdoors”.
