Cases first came to the attention of health officials last month, with the source traced back to a farm in New South Wales (NSW) state.

"There have been two deaths in NSW and two in Victoria," NSW Health said in an update, adding that two new cases took the total affected nationally to 17.

Vicky Sheppeard, director of communicable diseases at NSW Health, said all contaminated rockmelons (cantaloupes) were recalled from the market on February 28.

"Typically around one third of people who fall ill with listeriosis die every year. Most of the cases are never related to an outbreak like this one we're seeing with the rockmelon contamination," she said.

Listeria is a commonly found bacteria and for many people who consume foods that contain it, it does not cause illness. But it can pose a threat to the elderly, pregnant women or those with conditions like diabetes or cancer.

Listeriosis begins with flu-like symptoms including chills, fever and muscle aches. It has an incubation period of up to 70 days.

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