BEIJING (AP) — Meron Mei, a sophomore at Wuhan University in the Chinese city at the heart of a viral outbreak, went back to his home village and started to cough.

So he went to the hospital and got checked. Doctors determined it was a common cold, not the new coronavirus, he says, and he returned home. Then a week ago, he says, five officers showed up at his house in Xishui County, a two hour drive from Wuhan. They wore masks and wielded blue, gun-shaped thermometers.

Now Mei finds himself under constant surveillance by plainclothes police. His doorstep has been posted with a red warning: “Do not approach – patient with suspected pneumonia.” Doctors in gowns, goggles and masks check his temperature three times a day, and the government calls him constantly to monitor his condition — despite tests that he says show his body is free of the coronavirus. His phone is constantly checked; its camera has been disabled and his photos deleted. He relayed his story to The Associated Press via messages in English to prevent officers from reading them.

“I am in prison,” said Mei, whose story could not be independently verified by the AP. “I’m so angry. I feel physically and mentally exhausted.”

As China institutes the largest quarantine in human history, locking down more than 50 million people in the center of the country, those who have recently been to Wuhan are being tracked, monitored, turned away from hotels and placed into isolation at their homes and in makeshift quarantine facilities.

The information available to regular people is uneven. Uneasy residents have circulated lists of hundreds of people from Wuhan containing sensitive personal information including addresses, phone numbers, national ID numbers, dates of birth and occupations.

One list sent by a Shanghai resident to the AP lists 174 people in the city’s Putuo district, including a foreigner, some city natives, many people from other parts of China, and an apartment where the resident lives. The identification numbers were authentic and matched other data on the list, according to a Chinese ID reference tool.

“Inside information! Accurate and reliable!” said one post sharing the list, in a screenshot shared with the AP. “Putuo friends please pay attention, the people listed here have all gone to Wuhan, and they aren’t allowed into hospitals, so they’re being forcibly isolated at home! Neighbors, don’t go outdoors under any circumstances!”

During the past decade, the Chinese government crafted a rigorous system of social control, which it calls “stability maintenance.” Through methods high-tech and low, from face-scanning cameras to neighborhood informants to household registration, Beijing keeps track of its 1.4 billion citizens, managing them via community-level officials.

Such monitoring doesn’t typically bother most people in China. Usually only political dissidents or minorities are subject to overt state control. But in times of extraordinary stress, such as the virus outbreak, these systems swing into action nationwide.

On Jan. 25, an extraordinary televised meeting of the Politburo Standing Committee, China’s ruling inner circle of power, ordered officials to carry out “prevention and control work” with special emphasis on “monitoring, screening and warning.” Since then, millions of local officials and officers have mobilized to monitor, screen and warn — and restrict, to varying degrees — in a governance approach that Beijing calls “blanket-style tracking.”

“We must effectively manage people from Wuhan according to the principles of ‘tracking people, registering them, community management, inspecting them at their door, mass transfers, treat abnormalities,’” Li Bin, deputy director of the Chinese National Health Commission, said at a news conference the next day.

Officials say — and some experts agree — that the stringent measures are necessary. “This epidemic is spreading quite quickly, which presents challenges and is putting pressure on our control and prevention work,” said Ma Xiaowei, director of the Chinese National Health Commission. “The country has adopted more powerful measures, which should be able to control the epidemic at a lower cost and faster speed.”

A woman who works in education in Wuhan said she had been back in her hometown in China’s Inner Mongolia region for nearly two weeks when friends and relatives forwarded her an Excel sheet that contained not just her name but her ID number, address, and occupation. At first, she said, she felt shock, then fury.

“It listed a bunch of people in the whole city who had come back from Wuhan,” said the woman, Na. Like many Chinese, she gave only her last name so she could speak openly on a sensitive topic. Police are vigilant about cracking down on information spread through unofficial channels, and many people are often hesitant to speak to the foreign press.

“I was so angry,” Na said. “This could affect me later in life.”

Unlike Mei, Na’s hometown is more than 1,000 kilometers (600 miles) from Wuhan, and she wasn’t confined to her home. But Na said she began to receive calls from the police, community officials and a newly established epidemic prevention center.

Because government departments often fail to share or coordinate data collection, many calling Na asked the same questions. On the first day, she said, she got a dozen calls , possibly more, asking a slew of questions: Where are you? When are you going home? Who’d you come into contact with?

“It’s so bothersome,” she said. “I made it clear that I didn’t want my personal information leaked.”

Others upset at leaks took to Weibo, a Chinese social media platform, and demanded to know what was going on. Most posts were deleted, but the censors left up a post by Cui Baoqiu, the vice president of Chinese cellphone maker Xiaomi, who criticized the leaks for stigmatizing people from Wuhan.

“Sick people are not criminals,” Cui said. “This data must be managed by a few people in the government. They need to tighten to their controls.”

Whether the leaks were intentional is unclear. Various government departments gather reams of data from cameras, cellphones, and social media, as well as through transportation records and queries from health and security officials.

In one case, Nick, who asked to be identified by only his English name, said he had merely driven through Wuhan but later found his name on a leaked list. In other cases, people were told to report on anyone suspected of having gone to Wuhan by ringing a hotline. A woman who answered a hotline for Baoshu, a village in Fujian province, confirmed they were offering a 1200 RMB ($173) reward for information. And in a news conference Thursday, a China State Railway Group representative said it is providing passenger data to the government.

Many of the more than 9,600 confirmed cases are in Wuhan and surrounding cities in Hubei province. Virtually the entire province was locked down last week. But even Wuhan natives who slipped out before the trains and planes stopped running are finding there’s no escape.

An IT worker from Wuhan who also asked only to be identified by his English name, Andy, to protect his family’s privacy, was sightseeing in Beijing with his wife and two children when he heard the government was closing off his hometown. The family went to Nanjing, a city near China’s coast, but the Intercontinental Hotel turned them away after seeing their national ID cards, which include their Wuhan addresses. Andy finally found a room at the five-star Shangri-La hotel and settled in, planning to stay until it was safe to go back home.

On Monday, reception called: Police were kicking them out. It didn’t matter that Andy’s family hadn’t been in Wuhan for more than a week, or that they’d been wearing masks for nearly two. Everyone from Wuhan was being ordered to stay at an isolated Home Inn for 14 days.

When they saw their room at the new hostel, Andy panicked: it was drafty. He stuffed wet towels in the cavity underneath his door, but worried it was futile since doors were opened for meals. He was awake until 2 a.m., fretting over his two young children and imagining potentially virus-filled air from the hallways, swirling into their room.

Andy says he “totally understands” and “trusts” the government, and appreciates the hard work of doctors and nurses on the front lines. He’s grateful, but he can’t stop worrying.

“I understand that in such a big country you don’t want this to spread further,” he said. “What I can’t accept is, what about my children? Who’s going to guarantee our safety?”