CDC visual summary of the outbreak
People who work shoulder to shoulder indoors are at higher risk of respiratory infections, SARS-CoV-2 among them. In March and April 2020, a meat processing plant in South Dakota — "facility A," with 3,635 employees in 38 departments — showed how fast it can spread.
Five weeks
| Date (2020) | What happened |
|---|---|
| March 14–16 | the first known case — a first-shift worker in department A — last works on March 14 and falls ill on March 16 |
| March 19–21 | five more workers fall ill, in three departments and two shifts |
| March 22–28 | 18 workers in department B fall ill, plus 15 in nine other departments |
| March 24 | the South Dakota Department of Health learns of the first case and starts investigating: isolation for cases, tracing and quarantine for contacts, monitored by CDC's text-message system |
| April 2 | with 19 confirmed cases, testing opens to any worker with symptoms |
| April 3 | department B temporarily closes; the plant starts fever screening, installs barriers on the production line, and makes masks optional |
| April 4 | 247 workers in 23 departments have COVID-19 |
| April 11 | 369 confirmed cases |
| April 12 | the plant begins a phased closure; it does not reopen before April 25 |
| April 13 | masks become required |
| April 15 | a CDC team arrives to help |
At the peak, an average of 67 worker cases a day were diagnosed. In the first three weeks the attack rate grew about fivefold each week — 0.2%, then 1.2%, then 6.8%. Within a week of the closure, cases fell to about 10 a day; some decline began before closure, and testing also dropped once the plant shut.
The toll, March 16 – April 25
| Employees | Their contacts | Community residents | |
|---|---|---|---|
| Cases | 929 (25.6% of employees) | 210 (8.7% of 2,403 contacts) | 1,086 |
| Median age | 42 | 29 | 40 |
| Male | 64.2% | 41.0% | 45.5% |
| With symptoms | 96.3% | 97.1% | 95.1% |
| Hospitalized | 39 (4.2%) | 9 (4.3%) | 130 (12.0%) |
| Intensive care | 14 | 3 | 22 |
| Died | 2 | 0 | 25 |
Community residents: people in the two counties around the plant who were neither employees nor known contacts.
Hospitalized employees had a median age of 60. By June 14, 11 had been discharged after a median stay of 6.5 days; hospitalized contacts, median age 64, stayed a median of 10 days.
Who got sick at the plant
| Department group | Workers | Attack rate |
|---|---|---|
| Cut | 882 | 30.2% |
| Conversion | 575 | 30.1% |
| Harvest | 428 | 29.4% |
| Smoke meat | 357 | 24.1% |
| Bacon | 234 | 23.1% |
| Sausage | 151 | 21.9% |
| Other | 745 | 20.4% |
- The three hardest-hit groups are where many workers stood less than six feet (two meters) apart on the production line.
- Salaried employees, whose workstations could be spaced out and who did not work on the line, had a lower attack rate: 14.8%.
- The three shifts had similar rates — even the third, which cleans the plant with fewer people, distancing and protective gear — pointing to spread in common areas or outside work.
- Cases started in three departments but spread quickly through many. Cafeterias, locker rooms and equipment counters may have helped, as may carpooling, shared housing and socializing.
What plants should do
No single measure is likely to stop transmission, so the authors call for a layered program:
- Engineering controls — rearrange workstations to separate workers, add physical barriers.
- Administrative controls — keep workers in fixed groups, promote distancing, stagger shifts and breaks, mark distances in common areas.
- Masks, worn consistently and correctly, to stop workers who don't know they are infected from spreading it.
- Prompt isolation of cases and tracing of their contacts.
- If spread continues despite all that, temporary closure.
Acting before, or soon after, the virus arrives could greatly reduce spread.
Limits
- Workers got enhanced testing from April 2, while testing was scarce for everyone else, so more worker cases may have been found.
- Only department, shift and pay status were examined; other factors weren't.
- Race and ethnicity data were incomplete.
- People without symptoms were rarely tested, so the true number of infections was likely higher.
- Where each worker was infected — at the plant or in the community — could not be determined.
Sources
Based on Steinberg J, Kennedy ED, Basler C, et al., "COVID-19 Outbreak Among Employees at a Meat Processing Facility — South Dakota, March–April 2020," MMWR Morbidity and Mortality Weekly Report volume 69, number 31, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report's text counts 2,199 community cases, of which employees were 920 (41.8%), which does not fit its definition of community residents or its table (1,086); and it gives nonsalaried workers' attack rate as 26.8% in the text and 26.4% in the table. Those figures are left out.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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