SYDNEY (Reuters) - Three people have died and 12 others have fallen ill in a national listeria outbreak linked to contaminated rockmelons, and more cases are expected, Australian health authorities said.

The outbreak is linked to the melons, also called cantaloupes, from a grower in the eastern state of New South Wales, the state’s food authority confirmed on its website. The produce company, which has not been named, ceased operations and is investigating.

NSW Health said late on Friday that all 15 victims are elderly and are spread nationally from Victoria to Tasmania.

“We can confirm that 13 of the 15 cases consumed rockmelon before the onset of their illness,” said Vicky Sheppeard, director of communicable diseases for NSW Health, in a media release. “People vulnerable to listeriosis should discard any rockmelon purchased before 1 March.”

Health authorities have assured the public that all contaminated rockmelons have been removed from supermarket shelves.

Further cases are expected to surface as symptoms can take up to six weeks to appear after eating contaminated produce, and NSW Health told consumers to see a doctor if they experience symptoms.

The disease causes flu-like symptoms and can lead to nausea, diarrhea, infection of the blood stream and brain. Listeria bacteria does not cause illness in most people but it can result in sickness and death for those with weaker immunity such as the elderly, newborns and pregnant women.

The bacteria is found in soil, water and vegetation and can contaminate food anywhere during the production process from harvesting to serving.

Foods that can pose a risk of listeriosis include pre-cut melons, cold salads, raw seafood and smoked salmon, unpasteurized milk products, sprouted seeds and raw mushrooms, the New South Wales Food Authority said.

Listeria is rare in Australia but a deadly outbreak in South Africa has killed more than 170 people since January last year, the National Institute of Communicable Diseases said last month..