Is there any risk of illness from eating onions?

As with any vegetable, improper storage (without air) can lead to contamination with toxins that cause botulism.  Therefore, it is important to wrap all vegetables loosely.  These toxins can form only in an environment that contains no air.

Produce can be contaminated in many other ways, for example,  by dirty water, animal droppings, handlers with illnesses or dirty hands, and factory equipment that hasn’t been properly cleaned.  There are possibilities for contamination all along the food chain, even in your kitchen.  (In 2006, onions were suspected of  causing an outbreak of E.coli 015:H7.)  Therefore, it’s important to wash all produce well immediately before use.  Don’t wash it before refrigerating. That can lead to the development of mold.

Source(s):

Satin, Morton.  Food Alert! The Ultimate Sourcebook for Food Safety.  2008.

Susan  Brewer, Ph.D.  University of Illinois, Department of Food Science and Human Nutrition