原因就是在不同的州，不同的超市同时出现病例，患者发病前吃的并不是同一种东西。估计是一种在美东美西都有销售的熟肉品种被污染，然后进一步污染了Deli的切肉机和展示柜，所有的冷切的东西都被污染了。因此，有问题的恐怕绝不止是六州的几个超市而是多得多。
在找出关键污染产品之前只能做笼统的警告，高危人群应该高温加热后再食用。
CDC 官网这样解释：
Deli meats (cold cuts, lunch meats, hot dogs, and pâtés sold at the deli) and cheeses are known sources of Listeria illnesses. This is because Listeria can easily spread among food on deli countertops, deli slicers, surfaces, and hands. Listeria is a hardy germ that can be difficult to fully remove once it is in the deli. It can survive and grow at cold temperatures in the refrigerator.
Information collected so far shows that deli meat and cheese purchased at deli counters in multiple states are the likely sources of this outbreak.
It is difficult for investigators to identify a single food as the source of outbreaks linked to deli meats and cheeses. This is because Listeria spreads easily between food and the deli environment and can persist for a long time in deli display cases and on equipment. A contaminated food likely introduced the outbreak strain of Listeria into delis in multiple states. Investigators are working to identify any specific products or delis that may be contaminated with the outbreak strain.
