“I am scared I am going to die,” said Denni Asolini, the store’s union representative, who was Ms. Casanova’s colleague for 25 years. “It happened to Mariagrazia, but it could have been any of us.”

“We provide an essential good," he said. “So the good comes first and we are left behind.”

Italy has closed its schools, its restaurants and many of its factories to stop what has become the world’s most deadly coronavirus outbreak. As health care workers fight in the trenches against the virus, supermarket lines have become another front line.

“I think in particular before everything to doctors, nurses, but I also think of the police, the army, the men and women of the civil protection, supermarket clerks,” Prime Minister Giuseppe Conte said on Saturday night as he introduced still more restrictive measures to contain infections across the country.

About 12 miles south of Brescia — which had more than 6,000 reported cases as of Tuesday — Debora Bravo, a cashier at a supermarket in Leno, said that “stress and fear” accompanied her to work every day.

Last week she worked at the register as customers touched the products without wearing gloves. Many stood in checkout lines without wearing masks or keeping a safe distance apart.

On Saturday night, she got the news that one of her colleagues was hospitalized in an intensive care unit with coronavirus. “We are the only ones to be so exposed, together with doctors and nurses,” she said. “But we are not being protected.”

On March 1, a government decree allowed supermarkets to stay open provided that customers were allowed in small numbers. A subsequent agreement between unions and the state required companies to provide hand sanitizer and masks to employees.