NEW YORK (NYTIMES) - Having worked for nearly 30 years at City Fresh Market in Bushwick, Brooklyn, perched on her stool at cash register No. 4, Cecilia Nibbs knew customers by the things they bought, keeping a mental list of their spending habits, much like taking stock of the store's inventory.

In March, some of them started disappearing, one by one. They had died, other residents told her. The news got grimmer: They had fallen victim to a new and incurable disease.

"People came to tell me: 'Oh Ceci, remember that guy? He died,'" Nibbs said. "'Oh Ceci, remember that one? He died.'"

Their deaths were ominous early signs of the arrival of the coronavirus pandemic.

Suddenly, going to work felt like walking into a war zone where the enemy was invisible and could be carried by any person whose groceries she packed and into whose hands she placed change.

What used to be a mundane job became fraught with anxiety, nearly overnight.

"When you're working in the store, you interact with a lot of people. You don't know which one is the sick one," Nibbs, 58, said. "You don't know which one is the good one.

"I tell you, it's scary," she added.

Supermarkets do not usually stand out as providers of essential services like hospitals, police precinct houses or fire stations do. But they have emerged as vital to the city, keeping New Yorkers fed and communities together. At the same time, they are places of danger for workers because of the waves of customers shuffling in and out.

At City Fresh - like at most grocery stores - workers' rituals have changed in ways they never could have imagined.

There are the usual tasks - turning on cash registers, stocking the cereal aisle, setting up the cold cuts at the deli counter. But now they protect themselves behind plastic shields and cloth masks, slipping on gloves and carrying disinfectant wherever they go. When the store ran out of Lysol, they had to make their own disinfectant out of alcohol, eucalyptus oil and aloe vera.

Before social distancing requirements were imposed, customers clogged the aisles, sparring over toilet paper, disinfectant and frozen pizza. At City Fresh, which is open 24 hours, the number of customers quintupled in March from the previous month, including a surge in shoppers after midnight.

"They were panicked," said Dulce Simono, 32, who works as a cashier and in the back office. "That's when we realised there were too many people, and we started wearing face masks and gloves."

Nibbs said that she had counted at least 10 customers who had died. But so far only one worker is believed to have gotten the virus.

Despite the health risks, workers continue to show up, in part because they consider their colleagues to be family, but also out of a sense of duty.

"We need to make people feel good," Nibbs said, describing how she listens attentively to customers, who, in the throes of a cooking frenzy because of the city's stay-at-home order, demand out-of-season ingredients, like chestnuts.

"You want to be here; you want to be with the customers; you want to help," she said. "It's like a service. If you don't live to serve, you lose. Some people be a doctor, some people be a teacher, and some people be like me, a worker."

While no precise data is available, at least 32 grocery workers have died of Covid-19 across the United States, according to estimates by the United Food and Commercial Workers Union. At least 4,687 have tested positive for the virus or missed work because they have self-quarantined.

But those numbers are believed to be higher because major chains like Walmart and Whole Foods have not made infection data public, the union said.

Juan-Pablo Polanco, also known as Pablito, a tall and taciturn 66-year-old from Santo Domingo, has worked at City Fresh for 20 years after harvesting coffee in the Dominican Republic.

His wife pleaded with him to stop working. "I told her that the rent and bills didn't pay themselves," he said.

The staff was terrified when Ricardo Caiche, 65, who has worked at the supermarket for 34 years, caught what everyone thought was the coronavirus. "I was so scared," said Arturo Payamps, 38, the manager, clutching his chest. "I was calling him every day." (Caiche had the flu and tested negative for COVID-19.)

Simono, one of the store's younger employees, says she misses being able to see customers' facial expressions. "We don't get to see their smile; they don't get to see our smile," she said. "Everybody is so sad."

Kenneth Santana, 34, an assistant manager, prefers staying at the supermarket longer than he needs to because, he says, it's better than the boredom of being alone at home. "I like hanging out here," he said. "At least I get to see and talk to people."

City Fresh sits on Knickerbocker Avenue, which threads through Bushwick and Ridgewood along Brooklyn's border with Queens. It has been a neighborhood mainstay, even as the mostly black and Latino community has started to gentrify.

Its staff of about 50 is largely immigrants, with workers from the Dominican Republic, Colombia, Mexico, Ecuador and Honduras. Their wages start at US$15 (S$21) per hour and increase with more years of experience.

They said that the pandemic has made them less invisible and more appreciated, a sentiment echoed by customers like Koory Mirz, 31, a web developer.

"They're amazing. Normally we don't think of thanking people in supermarkets," he said as he walked the store's aisles around 1am. "I couldn't do it if my boss called me to do a shift here."

Aside from maintaining a healthy environment, a major challenge for the supermarket is keeping its shelves stocked amid increased demand. Toilet paper and disinfectants are in short supply, as well as other products that were not popular in normal times, like eucalyptus oil.

One hurdle has been getting new stock, as vendors say some of their drivers have gotten sick from the coronavirus.

"We're trying to do our best, but now it's getting complicated," Payamps said.

Still, the store has hired more workers to keep shelves filled because of the influx of customers. "If you restocked every other hour, you're restocking every 30 minutes," Santana said.

Well before the virus started overwhelming New York, store managers got a sense of how serious the disease was from the chatter in some of the Chinese-owned stores on the block.

Chinese workers were sending large packages of face masks to their families in China to protect against the growing outbreak.

"If the one country that provides masks to the world has a shortage, there was going to be a shortage everywhere," Santana said.

City Fresh managers, in turn, began ordering them, and Payamps told his workers they had to wear masks and gloves weeks before the city made it a requirement. "In the beginning, everybody took it as a joke," he said.

He also gathered workers one day in early March and urged them "not to cough on anybody or let anybody cough on you." Now a professional cleaning company disinfects the store every day, and employees regularly wipe down shopping baskets. Tape has been put on the floor to turn aisles into one-way corridors and space out customers.

Payamps put up plastic barriers, costing at least $200 each, to separate cashiers from customers. Workers wear plastic shields in addition to face masks. And the piped-in music that usually plays is regularly interrupted by announcements admonishing customers to maintain social distancing.

The early intervention, Payamps believes, helped shield his workers even as the virus was coursing through the neighbourhood.

Still, one cashier, Susly Jimenez, did get sick. Though she was unable to get tested, she said she had all the symptoms of Covid-19, including a fever that started March 25 and remained very high for several days.

But her conditions eased. She was back to work this week.