More than 900 workers at a single meatpacking plant in South Dakota were infected with the coronavirus over the course of just five weeks, showing how quickly it can rip through an essential workforce toiling away in close quarters.

Those numbers come from a report released Thursday examining the Smithfield pork facility in Sioux Falls, which was home to one of the worst COVID-19 clusters in the country this spring. The Centers for Disease Control and Prevention and state officials studied the outbreak to learn how it got so out of control.

The CDC report shows the outbreak was somewhat worse than previously believed. State officials had earlier put the total number of infections at 853, according to the Argus Leader . The actual number was 929, which translates into one of every four workers at the 3,635-person plant.

At the peak of the outbreak, the workforce was averaging 67 new cases a day. Two workers eventually died. In addition to the cases among employees, at least 210 contacts of workers contracted the virus. In total, 39 workers and nine contacts ended up hospitalized.

The CDC did not openly criticize Smithfield for its handling of the crisis and did not name the company in its report. But the findings suggest the pork producer was slow to deal with the situation and didnt put many controls in place until it was too late.

The researchers concluded that what happened at the Sioux Falls plant shows how the coronavirus can spread rapidly in meat processing facilities because of the close proximity of workstations and prolonged contact between employees. Employers need to have a robust mitigation program ... consistent with published guidelines in order to mitigate the spread of the virus.

Keira Lombardo, a Smithfield executive vice president, said in a statement that the companys coronavirus response has focused exclusively on keeping employees safe and maintaining the food supply. She said the company took aggressive action that preceded the guidance on meatpacking safety released by the federal government in late April.

Nationally, the coronavirus has hit the largely immigrant workforces inside meat and poultry plants particularly hard. So far, at least 65 workers have died and more than 14,000 have been infected or exposed to the virus, according to estimates from the United Food and Commercial Workers union, which represents workers at many plants.

Workers at meatpacking plants across the country have reported laboring practically shoulder to shoulder even during the pandemic. The CDC found that the attack rate the proportion of people in a given population infected with the virus was highest in departments where people could not work at least six feet apart.

Not surprisingly, hourly workers were nearly twice as likely to be infected as salaried workers inside the Smithfield plant. The latter, researchers wrote, typically had workstations that could be adjusted to maintain distancing and did not work in close proximity to other employees on the production line.

Showing just how rapidly the outbreak escalated, researchers found that the attack rate throughout the facility increased fivefold each week during the first three weeks. After Smithfield temporarily shuttered the plant, the rate of new infections dropped significantly among workers, to roughly 10 per day within a week.