Like many other sectors, the meat and poultry industry has faced unprecedented disruption from the COVID-19 pandemic. The U.S. animal slaughter and processing industry employs an estimated 525,000 workers in approximately 3,500 facilities nationwide.1 It relies heavily on humans working in tight quarters on production lines, making it especially vulnerable. What is the current state of knowledge of the risk factors for workers?

One of the first reports of a COVID-19 outbreak in the industry was a Morbidity and Mortality Weekly Report from the U.S. Centers for Disease Control and Prevention (CDC) describing an outbreak of 929 cases among 3,635 employees of a South Dakota meat processing plant from March 16 to April 25, 2020.² CDC investigators were called to investigate at the request of the South Dakota Department of Health. Most of the cases (96%) had symptoms of COVID-19, including cough, fever, and shortness of breath. Thirty-nine of those individuals were hospitalized, 14 were eventually admitted to ICUs, and 2 died. Most of the cases (64%) were male, with a median age of 42. Those who became hospitalized were older, in their 60s. Nonsalaried employees (mostly line workers) were more likely to be infected than salaried employees (managerial or administrative staff). The facility harvested and processed animals during two shifts, with a third shift devoted to sanitizing the facility. Workers fell ill on all three shifts, however; those who worked in the cut, conversion, and harvest departments fell ill at a higher rate than other workers. In these departments, employees worked less than six feet (two meters) apart from each other. Investigators concluded that such factors as high employee density in work and common areas (e.g., cafeterias, locker rooms, and equipment-dispensing areas), prolonged close contact between employees during shifts, and COVID-19 transmission occurring in the local community all contributed to the outbreak. At the height of the outbreak, an average of 67 new cases occurred per day in plant employees. Within 7 days of the facility starting a phased closure, new cases had fallen to a rate of 10 per day. Investigators recommended using a system of control measures to reduce the risk of infection to employees, stressing that no one single control measure could prevent transmission. Controls could be engineering (e.g., modifying workstations), administrative (promoting social distancing or developing procedures to screen employees), and prophylactic (using face masks or coverings). The CDC is careful to note that face masks/coverings are not appropriate substitutes for personal protective equipment (PPE), such as N95 respirators or surgical face masks, in workplaces where such equipment is required.³ Also, in the challenging environment of a processing plant, workers probably can’t wear a single mask for an entire shift: Masks must be changed whenever they become wet or soiled.

Results and Indications from a Nebraska Plant

In late April 2020, workers at a Nebraska meat processing facility⁴ were invited by the facility, in partnership with the Nebraska Department of Health and Human Services, to be tested for SARS-CoV-2 (the virus that causes COVID-19). Testing took place at the worksite at no cost to the employees. Thirty-one percent of the 1,216 workers tested positive for the virus. Two hundred forty-one of these workers agreed to be interviewed by investigators: 57 percent were male, with a median age of 41 (similar to the South Dakota outbreak) and 46 percent were Hispanic. Seventy-eight respondents (32%) reported having had no symptoms. Workers were asked whom they may have been exposed to in the 2 weeks before their symptoms appeared or, if asymptomatic, before they got tested. Twenty-nine percent of workers reported being in close contact with a visibly ill person at work. Close contact had occurred in production areas and in cafeteria or break areas. Positive cases reported working in harvesting, processing, or rendering areas where they were in close contact (< 4 feet, or 1.5 meters) from others. Next, investigators questioned them about how they got to work and their living arrangements. Most reported arriving to work in a private vehicle rather than carpooling with fellow workers (considered a risk factor for transmission by CDC), and few reported crowded living conditions (another recognized risk factor). The investigators were concerned that one-third of workers with COVID-19 were asymptomatic, showing the limitations of relying on symptoms or temperature checks alone to prevent transmission within a facility.

Another CDC study⁵ examined aggregate data from confirmed COVID-19 cases and deaths among workers from 239 facilities in 23 states from April to May of 2020, hoping to draw conclusions. During that time there were 16,233 cases and 86 deaths among U.S. meat and poultry workers. In the 14 states that provided information about the total numbers of workers at affected facilities (needed to determine the overall infection rate), on average COVID-19 was diagnosed in 9 percent of the workforce; however, among individual facilities, infection rates ranged anywhere from 3.0 to 25 percent. The presence or absence of symptoms was recorded for 10,284 (63%) of all affected workers: Of these, 88 percent had symptoms, and 12 percent either never developed symptoms or only developed them shortly after testing positive for the virus. Twenty-one out of 23 states reported the demographic information of cases: 60 percent were male, 39 percent were white, 30 percent were Hispanic, 25 percent were Black, and 6 percent were Asian, with 46 percent between the ages of 40 and 59 years. Racial disparities in infection rates have been noted during the pandemic. One Utah workplace study showed that while only 24 percent of the workforce in 15 affected sectors (businesses ranging from manufacturing to construction) identified themselves as being Hispanic or nonwhite, ethnic minorities represented 73 percent of the cases in COVID-19 workplace-related outbreaks.⁶ 

Some distinctive risk factors found in the CDC aggregate data study were the following: prolonged close contact with coworkers over 8- to 12-hour shifts, shared workspaces, shared transportation to and from work, multifamily housing, and frequent community contact with fellow workers. Investigators examined the prevention efforts put in place by 111 affected facilities. The most commonly enacted measures were: screening workers upon entry to the facility (80%), requiring the wearing of face coverings (77%), increasing the number of hand hygiene stations (65%), educating workers about the spread of the virus in the community (63%), and installing physical barriers between workers (62%). Far fewer facilities reported offering virus testing for workers (37%) or temporarily closing (22%). Other reported interventions are shown in Table 1.¹ 

*Affected facilities defined as those having one or more laboratory-confirmed COVID-19 cases among workers.
†Based on data collected through May 31, 2020.
‡Because of rounding, row percentages might not equal 100 percent.
¶Testing strategies varied by facility.

The Risk Posed by a Single Infected Worker

German researchers investigating an outbreak in a large beef and swine processing plant7 found that a single infected worker transmitted the virus to 60 percent of their coworkers over a distance of more than eight meters (26 feet) while they worked together in a large room where air was constantly recirculated and cooled. The researchers performed a site visit, mapping out the positions on the processing line where the employee and their coworkers were stationed. Although they did not take quantitative measurements of airflow direction or air speed within the area where the employees worked, they noted that eight large air-conditioning units near the ceiling kept the room cool, and fans projected the air in a lateral direction, downwind from the first infected worker’s station. The researchers also conducted genetic analysis of positive viral test results, demonstrating that the viral strains found in the workers were identical to each other, implying a common infection source. The researchers noted that while the transmission of COVID-19 is thought to occur mainly via inhalation of infected droplets, aerosols are believed to play a role in so-called superspreading events, where a single individual transmits the virus to many other people. While droplets can usually only travel six feet (two meters), aerosols can stay suspended for long periods, traveling more than six feet, particularly indoors with low fresh-air exchange rates. The researchers’ findings suggested that low temperatures, low air-exchange rates, and constant air recirculation, in addition to close physical proximity, allowed for efficient aerosol transmission of the virus. To reduce the risk of spread, researchers suggested additional mitigation measures were needed, such as improved ventilation and airflow, installing air filtering devices, or using high-quality face masks.

Researchers from Columbia University and The University of Chicago⁸ used statistical modeling to determine whether there was a relationship between the presence of livestock-processing plants and increased numbers of COVID-19 cases and deaths within surrounding communities. Their estimates implied that an excess of 236,000 to 310,000 cases (6–8% of all total cases in the U.S.) and 4,300 to 5,200 excess deaths (3–4% of all U.S. COVID-19 deaths) occurred in areas where a plant was present, with most cases occurring among people not working at a livestock plant. They noted that the apparent association was found primarily with large processing facilities, rather than with medium or small facilities. They also found a relationship between increased cases in communities where poultry plants had received permission from the U.S. Department of Agriculture to increase their production line speeds. The researchers found no solid reason for why this might be but considered it notable, “given that these waivers were intended for plants with safe commercial production practices and microbial control.” (However, these microbial controls are probably intended more for food safety than human infection control.) Some possible reasons they posed for the apparent association were that workers were closer to each other or had greater difficulty maintaining PPE. Conversely, they found that closing plants led to lower rates of transmission in local communities. However, since most plant closures were only temporary (on average, lasting 9 days), they questioned whether this association was actually due to the closures themselves reducing COVID-19 transmission, or whether closures resulted in plants implementing safety protocols against COVID-19 once they reopened. The researchers also considered whether the presence of any type of manufacturing facility, not just a livestock plant, could increase community COVID-19 transmission and took this into account when they ran their modeling simulations. The relationship between livestock plants and increased COVID-19 transmission in local communities remained unchanged. However, they noted that there could be industries where, like processing plants, employees worked near each other and could not shut down in the face of infections, as they were critical to the nation’s supply chain (e.g., an Amazon distribution warehouse). The researchers concluded that particular aspects of large meat processing plants rendered them vulnerable to spreading respiratory diseases: They employed large numbers of people and provided a central location for moving products, meaning that an outbreak in the facility could have an outsized impact on disease transmission in the nearby community. Also, the physical characteristics of plants—large (where workers must travel a long distance to their workstations, increasing the number of possible interactions), noisy (necessitating that workers needed to shout to communicate, increasing the spread of respiratory droplets), and needing to maintain an environment for preserving meat (temperatures of 44 °F or less, low absolute humidity)—could encourage the transmission of airborne viruses, such as influenza or SARS-CoV-2. 

A Toolkit for Worker Safety

The National Institute for Occupational Safety and Health has developed tools tailored to meat and poultry processing facilities to help them reduce COVID-19 in their workforce, such as guidance on developing communication plans for employees,⁹ employee-focused graphics on how to avoid becoming infected (available in multiple languages),¹⁰ safety measures employees can take while carpooling,¹¹ and facility assessment toolkits for use by occupational safety and health professionals.¹² 

Modern humans live and work indoors in tightly clustered groups, a circumstance that SARS-CoV-2 has taken full advantage of. Although COVID-19 vaccines have now entered the picture, the reality is that it will be months before enough people are vaccinated to create herd immunity against the virus, so measures taken now to prevent infections from spreading to employees, their family members, and the community at large are important stopgaps until that day arrives.

References

1. Waltenburg, M.A., et al. 2020. “Update: COVID-19 Among Workers in Meat and Poultry Processing Facilities—United States, April–May 2020.” Morb Mortal Wkly Rep 69:887–892.
2. Steinberg, J., et al. 2020. “COVID-19 Outbreak Among Employees at a Meat Processing Facility—South Dakota, March–April 2020.” Morb Mortal Wkly Rep 69:1015–1019.
3. www.cdc.gov/coronavirus/2019-ncov/community/organizations/meat-poultry-processing-workers-employers.html.
4. Donahue, M., et al. 2020. “Notes from the Field: Characteristics of Meat Processing Facility Workers with Confirmed SARS-CoV-2 Infection—Nebraska, April–May 2020.” Morb Mortal Wkly Rep 69:1020–1022. 
5. Waltenburg, M.A., et al. 2020. “Update: COVID-19 Among Workers in Meat and Poultry Processing Facilities—United States, April–May 2020.” Morb Mortal Wkly Rep 69:887–892.
6. Bui, D.P., et al. 2020. “Racial and Ethnic Disparities Among COVID-19 Cases in Workplace Outbreaks by Industry Sector—Utah, March 6–June 5, 2020.” Morb Mortal Wkly Rep 69:1133–1138.
7. Gunther, T., et al. 2020. “SARS-CoV-2 Outbreak Investigation in a German Meat Processing Plant.” EMBO Mol Med 12: e13296.
8. Taylor, C., C. Boulos, and D. Almond. 2020. “Livestock Plants and COVID-19 Transmission.” Proc Natl Acad Sci USA 117(50): 31706–31715. 
9. www.cdc.gov/coronavirus/2019-ncov/community/organizations/meat-poultry-processing-workers-employers.html.
10. www.cdc.gov/coronavirus/2019-ncov/downloads/community/FS-MeatProcessing-EMPLOYEES.pdf.
11. www.cdc.gov/coronavirus/2019-ncov/downloads/community/organizations/carpooling-fs.pdf.
12. www.cdc.gov/coronavirus/2019-ncov/downloads/php/Meat-And-Poultry-Facility-Assessment-Checklist.pdf.

Deborah Carr, D.V.M., M.P.H., currently works for the U.S. Department of Defense. Her areas of interest include zoonotic diseases, food safety, public health, and biosurveillance.