The latest statistics reflect how the contagious respiratory illness, COVID-19, has spread widely through slaughterhouses where large groups of employees often work shoulder to shoulder in difficult conditions.

Major meat processors like JBS USA and Tyson Foods Inc have indefinitely shuttered beef and pork plants due to outbreaks among workers, limiting US production as demand has increased at grocery stores.

Companies said they are checking workers' temperatures, working with local health officials and taking other steps to prevent the spread of the virus.

The United Food and Commercial Workers International Union is pushing government officials to provide more protective equipment like masks for plant employees, after saying workers did not have enough.

The union has 250,000 members who are meat and food-processing workers, and represent about 80 percent of US beef and pork production and 40 percent of poultry production.

Plant workers on a conference call organised by the union said they are afraid of falling ill, although meat processors have been bleaching hallways and doorways for safety, and installing dividers to separate employees.

"As far as social distancing, it's almost impossible," said Margarita Heredia, who works in a JBS pork plant in Marshalltown, Iowa. "There's no room."

Brazilian-owned JBS did not respond to a request for comment. Cargill Inc expressed sympathies for employees affected by the virus, while Tyson Foods said it was deeply saddened by employees' deaths.

"We’re working hard to protect our team members during this ever-changing situation, while also ensuring we continue fulfilling our critical role of helping feed people," Tyson spokeswoman Liz Croston said.

The US Department of Agriculture is separately trying to obtain face masks for federal inspectors who work in meat plants, according to the agency. Supplies are limited due to high demand, requiring some inspectors to provide their own masks, the USDA said.

As a result, the USDA authorised a one-time reimbursement of $50 to Food Safety and Inspection Service employees who must work away from home.