It appears that the same strain of Listeria has persisted in this plant for at least the last three years.
While corn has been the primary food associated with illness, it can be likely that more products are contaminated especially when similar equipment is used to pack the product. Perhaps there was more of a tendency to under-cook the corn before eating or using frozen corn in ready-to-eat applications, such as using it in a salad or fresh salsa.
https://www.efsa.europa.eu/en/press/news/180703
Listeria monocytogenes: update on foodborne outbreak
3 July 2018
Frozen corn and possibly other frozen vegetables are the likely source of an outbreak of Listeria monocytogenes that has been affecting Austria, Denmark, Finland, Sweden, and the United Kingdom since 2015.
https://www.efsa.europa.eu/en/press/news/180703
Listeria monocytogenes: update on foodborne outbreak
3 July 2018
Frozen corn and possibly other frozen vegetables are the likely source of an outbreak of Listeria monocytogenes that has been affecting Austria, Denmark, Finland, Sweden, and the United Kingdom since 2015.