In 2013, there was a foodborne outbreak caused by Listeria i…

In 2013, there was a foodborne outbreak caused by Listeria in prepackaged refrigerated spinach. An FDA investigation found the California plant producing the spinach product washed the spinach in lukewarm water prior to packaging.  Plant documentation showed the water was to be tested for pathogens every hour during production. However, the water had not been tested nor filtered the two days prior to the first outbreak case. What was the reservoir for this pathogen?