BEIJING (BLOOMBERG) - A favourite pastime of elderly Asians has been implicated as a major driver of China's current outbreak of Delta virus cases, sparking the shutdown of tens of thousands of mahjong dens across the country.
The so-called chess and card rooms, where hundreds of elderly people gather in packed and poorly ventilated spaces primarily to play mahjong, were how a 64-year-old woman surnamed Mao spread the Delta variant in the eastern city of Yangzhou, seeding the biggest single outbreak in China's ongoing wave of infections.
Local officials in Jiangsu province, where Yangzhou is located, have now shut down more than 45,000 chess and card rooms, and the authorities in Beijing and at least four other hard-hit provinces - Henan, Zhejiang, Hunan and Heilongjiang - have followed suit.
The spread of the virus through these mahjong dens despite China's rigorous measures and fast vaccine roll-out reflects the challenges posed by underground social sites across the region.
From hostess bars in Japan, to social dancing clubs in Hong Kong and karaoke lounges in Singapore, these locales have stymied governments which are some of the most successful in the world at containment.
In China's case, Madam Mao had travelled from the nearby city of Nanjing, where China's Delta outbreak first started, to a relative's home in Yangzhou, where she played mahjong in several chess and card rooms before being diagnosed with Covid-19, said local media reports.
One of the rooms that Madam Mao visited had a nondescript facade and small entrance, but opened into a cavernous basement that could accommodate around 100 mahjong tables.
In the week after her diagnosis, nearly a hundred people in Yangzhou contracted the virus, with 64 per cent of them exposed in mahjong rooms, and nearly 70 per cent of them aged 60 years and older.
The Yangzhou cluster has escalated in severity because only 40 per cent of local elderly people were vaccinated; among the 448 people who have been sickened, 23 have developed severe disease and 12 are in critical condition, raising the prospect of China's first Covid-19 related fatality in nearly seven months.
The mahjong cluster is Yangzhou's first serious outbreak since the pandemic began, and inexperienced officials have already been punished for mishandling the response.
Mass testing efforts - the city's 4.5 million population has undergone six rounds of testing - resulted in more than 40 people infected while waiting in line to be swabbed.
The current Delta outbreak across China has seen more than 1,000 symptomatic infections in less than a month, with cases reaching as far south as Hainan and as far north as Heilongjiang.
Though more than 60 per cent of the population has been vaccinated, the government has defaulted to targeted lockdowns, transport controls and mass testing, insisting that China must stamp out all infection to protect lives, even as many other countries accept that the virus will be endemic.