OMAHA, Neb. (AP) — Some massive meat processing plants have closed at least temporarily because their workers were sickened by the new coronavirus, raising concerns that there could soon be shortages of beef, pork and poultry in supermarkets.

The meat supply chain is especially vulnerable since processing is increasingly done at massive plants that butcher tens of thousands of animals daily, so the closure of even a few big ones can quickly be felt by customers. For instance, a Smithfield Foods plant that was forced to close in Sioux Falls, South Dakota, after nearly 300 of the plant's 3,700 workers tested positive for the virus produces roughly 5% of the U.S. pork supply each day.

In addition, conditions at plants can be ripe for exploitation by the virus: Workers stand shoulder-to-shoulder on the line and crowd into locker rooms to change their clothes before and after shifts.

The virus has infected hundreds of workers at plants in Colorado, South Dakota, Iowa, Pennsylvania, Mississippi and elsewhere. The capacity of plants that remain open has also been hurt by workers who are sick or staying home because of fears of illness — though it's not clear by how much.

While company owners promise to deep clean their plants and resume operations as quickly as possible, it's difficult to keep workers healthy given how closely they work together.

"There is no social distance that is possible when you are either working on the slaughter line or in a processing assignment," said Paula Schelling, acting chairwoman for the food inspectors union in the American Federation of Government Employees.

The reduced production so far has been offset by the significant amount of meat that was in cold storage, said Glynn Tonsor, an agricultural economist at Kansas State University. Producers are also working to shift meat that would have gone to now-closed restaurants over to grocery stores.

Whether shoppers start to see more empty shelves or higher prices will depend on how many plants close and for how long.

At least half a dozen plants have closed temporarily, but that's across the pork, chicken and beef sectors, and Tonsor said the industry can manage for now.

"You could shut multiple plants down for a day or two, and we've got wiggle room to handle that," said Tonsor. "But if you took four or five of those big plants ... and they had to be down for two weeks, then you've got a game changer."

Still, the reduced meat processing capacity is already driving down the prices farmers and ranchers receive for cattle, hogs and chickens.

"It's like people on an escalator. Stopping the pork chain at the top of an escalator is just going to cause all sorts of tragedy and disaster all the way back up the system," said Dermot Hayes, professor of economics and finance at Iowa State University.

Farmers are being forced to kill baby pigs because the space in the barns where they were supposed to go is still filled by the pigs that should have been slaughtered last week, Hayes said. The meat from those baby pigs cannot be sold.

That has driven prices for those feeder pigs — which generally are fattened over the course of six months — to zero, Hayes said. The value of those big enough for the market is down about 50% from a month ago. The value of the meat is down about 30%.

Lower prices for producers could mean higher prices for consumers eventually, if production falls off, according to Chad Hart, an agricultural economist at Iowa State University.

Tyson, Cargill and other major meat processing companies say they are adopting several measures: taking the temperature of everyone entering plants, adding clear plastic shields between work stations and erecting tents to allow workers to spread out more at lunch. But critics worry that workers too often continue working in close proximity and that measures are being adopted piecemeal.

The League of United Latin American Citizens recently asked federal regulators to establish uniform rules after a number of immigrant workers complained to the rights group about tight quarters.

The new coronavirus is highly contagious. For most people, it causes mild or moderate symptoms, but for some, especially older adults and people with health problems, it can cause more severe illness and lead to death.

Federal health officials do not consider COVID-19 to be a food safety concern, but they recommend that workers maintain a safe distance from one another.

But Lily Ordaz Prado, who recently quit her job at the Smithfield plant in Sioux Falls, said she didn't see those recommendations being put into practice, noting the crowded conditions in locker rooms and on assembly lines. The 30-year-old called her decision to leave "the best decision that I have ever made."

Smithfield officials have defended operations in Sioux Falls and said the company is taking "the utmost precautions and actions to ensure the health and wellbeing of our employees."

Meanwhile, Hector Gonzalez, senior vice president of human resources at Tyson Foods, said the food giant is making important changes for its roughly 140,000 workers, such as slowing down production lines and adding plastic barriers between work stations.

Other meat companies say they have stepped up the cleaning of their plants and prohibited visitors. Several major meat companies are also paying workers more for continuing to work during the pandemic. For instance, JBS USA is paying workers a one-time $600 bonus. Cargill has temporarily boosted pay by $2 an hour.

Most major meatpacking companies also have relaxed attendance and sick leave policies to ensure that workers can receive at least some pay if they have to stay at home after testing positive or coming in contact with someone who has.

"Most of the employers that we deal with right now are really making a solid attempt to try and fix stuff," said Marc Perrone, president of the United Food and Commercial Workers union. "We're just working as hard as we can to protect as many people as possible right now and make sure that we keep the food supply open."

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Associated Press writers David Pitt in Des Moines, Iowa, and Stephen Groves in Sioux Falls, South Dakota, contributed to this report.