'Secondary infection' is a familiar concept among celiac patients. This refers to the contamination created as a result of preparing food in an environment that is not gluten-free. In such a case, even if it is a gluten-free dish, a celiac will not be able to eat it. for example:
Cutting a salad on a cutting board on which bread has been cut, frying chips in the oil in which schnitzels were fried and making gluten-free toast in a regular toaster