Eating out is the most likely context for inadvertent gluten exposure in people with coeliac disease but the risk remains even when cooking and eating at home.

An analysis of 256 supposedly gluten-free foods obtained from supermarkets in Melbourne found seven samples (2.7%) had detectable levels of gluten up to 49 ppm.

The contaminated products included fruit/muesli bars, noodles, crackers, rice snacks and pasta.

A Research Letter published in the MJA said manufacturers of the offending foods were notified and one item had already been recalled.

“Repeat batches of five of seven contaminated foods also contained gluten, indicating that the initial results did not reflect isolated episodes of contamination,” the researchers said.

“As three of the seven items were produced in dedicated gluten-free factories, gluten contamination of ingredients supplied by outside sources should be examined.”

The researchers, including gastroenterologist Dr Jason Tye-Din from the Walter and Eliza Hall Institute, said the integrity of manufactured foods labelled gluten-free was imperative for people with coeliac disease.

However their findings, together with a 2016 study that found 14% of imported foods labelled gluten free were non-compliant with the Australian standard, suggest inadvertent exposure might be hard to avoid even at home.

“While the gluten content per standard food serve was generally low, the 3 mg gluten per serve of “gluten-free” pasta could be harmful, especially if consumed frequently,” they said.

Another study published earlier this year found 9% of meals promoted as gluten-free from food outlets also failed to meet the national standard of ‘no detectable gluten’.

“Our findings indicate that inadvertent gluten ingestion is more likely when dining out than when consuming manufactured “gluten-free foods”. Nevertheless, more frequent gluten testing, feasible for many companies, would reduce the risk for people with coeliac disease.”