The problem is that there are many different cultivars of oats.A study published in February 2011
demonstrated that there are diferences in the toxicity of the different varieties of oat. The oats may be "pure", but this means that cross-contamination is not the single reason for reactions in people.
Research into the prolamin (avenin) in oats indicates that it is the similarity of it's amino acid chains and structure that cause a reaction. But, there are different amounts of avenin present in different cultivars of oats.
Examination of the results show the effects of oats vary widely from being dangerous to almost harmless. There was no way to predict which coeliacs could/would be sensitive to avenins.
As one Scientific study concluded: -Coeliac patients can, to some advantage, include oats in a GFD although there may be the occasional patient who is also oats sensitive. Previous conflicting results may have been partly due to contamination of oats by wheat. Lest contamination is present and exceeds the safe threshold, we recommend that coeliac patients should only add oats to their GFD when they are established on a conventional GFD, and stop eating oats if they develop any symptoms.
In other words, you may or may not react: there's no way to tell: stop if you do react ...