NSW Health has defended its contaminated–food reporting process after it was revealed the investigation into rockmelons which contained fatal listeria began in January.

Pregnant women, the elderly and people with compromised immune systems have been warned to stay away from pre-cut rockmelon after the death of a third person from the bacteria linked to the contaminated fruit.

A total of 15 elderly people have now been diagnosed with listeria, with four Victorians and one Tasmanian joining 10 other confirmed cases.

NSW Health on Friday confirmed the death of a Victorian following two others from NSW earlier in the week.

The NSW Food Authority reportedly began investigations in January, which included collecting the hundreds of samples that eventually linked the outbreak to a rockmelon grower in Nericon, near Griffith.

Labor health spokesman Walt Secord, on Saturday, called on the Berejiklian government to explain why it took until February 23 to issue the first listeria warning.

But NSW Health defended their timeline, saying it followed established protocols and takes outbreaks “very seriously”.

“The identification of a source involves interviews with multiple patients, specialist laboratory testing of patient samples, trace-back of the source of food eaten and special testing of suspected foods,” NSW Health said in a statement on Sunday.

“As soon as the investigation indicated rockmelon from the Griffith area was the likely source, the NSW Food Authority issued a warning on Wednesday, 28 February.”

The producer voluntarily stopped production after being told of the contamination.

Crisis talks were held between the melon industry and retailers across the country on Thursday with the industry agreeing to review how it packs its fruit.

NSW Health expressed “sympathy to those affected by the outbreak”, but reassured the community that all appropriate process and procedures were followed.

Eating foods that contain the listeria bacteria does not cause illness in most people.

But for those with vulnerable medical conditions –  a compromised immune system, the elderly and pregnant women – it can result in severe illness and even death. Vulnerable people should avoid pre-cut melon.

Listeria starts with flu-like symptoms such as fever, chills, muscle aches, nausea and sometimes diarrhoea.

But the symptoms can take a few days or weeks to appear after eating contaminated produce.

People at risk should consult their doctor as soon as possible if symptoms appear.

– AAP