The definition of a close contact is getting broader in China, where authorities hunting down every potential COVID-19 infection now consider people who are far away and virtually unknown to each other as potentially at risk.

People who happen to be in the same general area at about the same time as a person who is found to be infected may need to be tested or even quarantined, according to notices issued by local health authorities. The “spacial-temporal overlap,” a term mentioned frequently by Chinese officials, means people don’t actually have to be in direct contact with a COVID-19 case to be impacted. Simply overlapping with someone carrying the virus is enough.

While authorities have been using mobile phone surveillance to identify close contacts throughout the pandemic, the latest effort appears to have expanded the criteria for contacts as the more infectious delta variant continues to spread. China has committed to fighting the virus at every step, and is taking more aggressive measures, including closing schools, entertainment venues and some forms of transportation, in its effort to regain a “Covid zero” status.

There were 99 new locally transmitted infections reported on Monday, including 34 that were asymptomatic. The number remains low compared to outbreaks in other parts of the world, with fewer than 1,000 people diagnosed during the latest wave. Still, 20 of China’s 31 provinces have seen cases during the latest flare-up, making it the broadest since the virus was first detected in the city of Wuhan in 2019.

China’s success thus far in fighting the pandemic is a source of pride, with politicians using it as a comparison to other countries that struggled to contain the virus and experienced high levels of disease and death. Experts believe China will continue to pursue a zero-tolerance approach for the foreseeable future, particularly with the Winter Olympics in Beijing slated to begin in February.

The definition of “spacial-temporal overlap” varies among provinces. In the city of Chengdu, two criteria must be met. A person whose mobile phone appeared to be within the same 800-meter (2,600 feet) grid square as the phone of someone with a confirmed infection for more than 10 minutes checks the first box. If either person’s phone was in the city for more than 30 hours in the last 14 days, the second box is checked and the two are considered a potential contact, state media CCTV reported, citing local health officials.

Police have detected 82,000 people who are at risk using the new methodology.

The Beijing health commission previously urged residents to refrain from returning to the capital city if they overlapped with any confirmed patients using the new criteria. Those who already returned were told to immediately self-quarantine at home and report their status to their residential compounds and employers.

The rule sparked complaints on social media among those who now find themselves stuck in other cities.

In the southern province of Hunan, the definition is even broader. If someone intersects with an infected person, whether it was a physical connection or simply bypassing a communication signal, he or she might be identified as a spacial-temporal companion. Officials in Fujian, a southern coastal province, used the new criteria to change some people’s electronic health codes to yellow starting in September, signifying they were regarded as being at risk of being infected and therefore limiting their movements.

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