Health authorities believe a food-borne illness caused a gastroenteritis outbreak at a Blue Mountains nursing home, during which 10 elderly people died.

More than 80 people were struck down by gastroenteritis at the Endeavour Nursing Home in June.

New South Wales Health communicable diseases director Jeremy McAnulty says some of the 10 deaths during the period appear unrelated to the outbreak but it cannot be ruled out as a contributing factor.

"Certainly, some of those deaths seem unrelated in that they didn't have any diarrhoea at all," he said.

"Others were people who did have some diarrhoea that seemed to have gone away before they died of some other reason.

"But we can't rule out that some deaths in the frail people, on top of their underlying condition, having diarrhoea may have contributed to that, so we don't know that for sure."

Food Authority inspectors have given the nursing home the all clear and Dr McAnulty says there is no ongoing risk.

"We have found toxin that's commonly found in food-borne outbreaks that's called clostridium perfringens," he said.

"That's a toxin produced by bacteria that's found in food after it's been sitting around for a while, so that plus the nature of the outbreak - that sudden sharp increase and it going away - all adds up to a food-borne outbreak."