ATLANTA – COVID-19 can quickly spread among workers in a meat processing plant. But implementing control measures before, or soon after, the virus infiltrates a facility — especially in areas where employees have prolonged, close contact with others — might substantially reduce the risk for COVID-19 spread within facilities, the Centers for Disease Control and Prevention said in its Aug. 7 Morbidity and Mortality Weekly Report (MMWR).

The MMRW report documented how the coronavirus spread in a meat processing plant in Sioux Falls, SD, owned by Smithfield Foods and reinforced the agency’s guidance on how such facilities might reduce the risk of disease spread.

The facility, referred to as ‘facility A’ in the report, employed 3,635 individuals in 38 departments. Harvesting and processing of animals occurred during two shifts per day while a third shift sanitized the facility. On March 24, the South Dakota Department of Health notified that an employee had tested positive for COVID-19.

That employee last worked on March 14, developed symptoms on March 16, and was tested on March 22. On March 19, a first-shift employee in another became ill. The following day, two additional first-shift employees who worked in the same department as the first employee to test positive and one second-shift employee in a third department developed symptoms.

By March 21, a total of six COVID-19 cases were reported among employees. During March 22–28, 18 employees developed COVID-19 symptoms, resulting in the department’s temporary closure on April 3. The situation got worse from there as 15 cases in employees from nine other departments also occurred that week, CDC said.

“On April 3, facility A also began screening all employees for fever, installing physical barriers on the production line, and amending the employee dress code to include optional masks, which were required as of April 13, 1 day after the phased closure of facility A began,” the report stated. “By April 4, a total of 247 employees from 23 departments had developed COVID-19.”

During a five-week period, among 3,635 facility A employees, 929 (25.6%) met the COVID-19 case definition, including 895 (96.3%) who were symptomatic. During this period, plant employees represented 920 (41.8%) of the 2,199 COVID-19 cases identified among community residents, CDC said. Among 2,403 identified employee contacts, 210 (8.7%) had confirmed COVID-19. Illness onset date range was March 30 to April 25.

Among employees with COVID-19, 39 (4.2%) were hospitalized; two employees with COVID-19 had died as of June 14.

“The highest attack rates occurred in the Cut (30.2%), Conversion (30.1%), and Harvest (29.4%) department-groups,” the report said. “During the fourth week of the outbreak, an average of 67 employee COVID-19 cases were occurring per day. Within 7 days of facility closure, cases among employees declined to approximately 10 per day.”

CDC concluded that although cases were confined to three departments during the first week of the outbreak, the number of affected departments increased rapidly. CDC investigators believe that contact between employees in common areas such as cafeterias, locker rooms and equipment-dispensing locations might have facilitated the spread of COVID-19 among employees in different departments.

Based on its findings, CDC reiterated the importance of enforcing social distancing protocols, constructing physical barriers among workers on production lines and correct and consistent use of masks can help prevent pre-symptomatic or asymptomatic employees infected with the coronavirus from transmitting the virus to others.

“Visual cues to maintain physical distancing and staggered shifts and break times might reduce risk for transmission among employees in these areas,” the agency said in its report. “Transmission among employees who work in different departments might have also occurred outside the facility (e.g., carpooling, cohabitating, and socializing outside work).”

Read about mitigation measures Smithfield has implemented at company facilities here.