There has been a third death linked to a national outbreak of listeria related to rockmelons.

Victoria's deputy chief health officer said five Victorians had been infected, and that one of those people had died after being hospitalised.

Dr Brett Sutton confirmed the victim had been diagnosed with listeriosis and subsequent testing linked them to the outbreak strain.

Dr Sutton would not provide the age or gender of the victim.

At least 15 people around Australia have now been affected.

Victims have been reported in Victoria, Queensland, New South Wales and Tasmania.

What is listeriosis? Listeriosis is a serious and sometimes fatal bacterial infection

Listeriosis is a serious and sometimes fatal bacterial infection Symptoms can include fever, headaches, cramps, aches and pains, nausea and diarrhoea

Symptoms can include fever, headaches, cramps, aches and pains, nausea and diarrhoea It can be fatal in newborns, elderly people and people with a weakened immune system

The Victorian cases range in age from 65 to 88, and included three men and two women.

All affected melons, also known as cantaloupes, have been withdrawn from sale and distribution.

Dr Sutton said all states and territories were continuing to work together to investigate the national outbreak.

Two elderly people in New South Wales have also died.

The outbreak has been traced to a farm at Nericon, near Griffith in the Riverina in NSW.

Pregnant, elderly most at risk

Dr Sutton said listeria infection was "particularly dangerous" for pregnant women, their unborn babies and elderly people.

He said it could cause death in people with compromised immune systems.

Symptoms of infection in pregnant women may be mild and include a temperature before or during birth.

However, the infection can be transmitted to the foetus through the placenta which can result in stillbirth or premature birth.

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

"In immunosuppressed patients, listeriosis usually presents as a brain inflammation, brain abscess or blood poisoning. Pneumonia, and heart valve infections have also been described," Dr Sutton said.

Authorities say if people are unsure about the origin of a rockmelon, it should be disposed of in the waste bin, not into compost bins, to avoid further contamination.