https://www.khou.com/article/news/health/coronavirus/meat-processing-plant-closed-after-employees-diagnosed-with-coronavirus/285-f18e80a6-0244-421b-9554-d76c81c53f07
"The plant, which employs about 3,700 people in the state's largest city, has become a hot spot for infections. Health officials said Sunday that 293 of the 730 people who have been diagnosed with COVID-19 in South Dakota work at the plant."
That's more than circumstantial evidence and the employer has to conduct an investigation itself for health and safety concerns. That will be handed over in discovery.