A woman in her nineties from New South Wales has become the sixth person to die from a listeria outbreak linked to contaminated rockmelon.

Three people from New South Wales and three from Victoria have fallen victim to the disease so far.

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 total number of people affected nationwide remains at 19.

The woman, who had significant underlying health conditions, developed listeriosis before the outbreak was identified.

"It is still possible that more cases will be linked to the outbreak given the incubation period for the disease is up to 70 days," NSW Health said.

However, there have been no new cases of the disease since the outbreak was identified on February 19.

Consumers have been assured that there is no risk of listeriosis from rockmelons now on sale.

Listeria is found widely in the environment and rarely causes serious illness in the general population but for vulnerable people, such as those who are over 70, pregnant, or have diabetes or suppressed immune systems, it can be extremely serious or even life-threatening.

"Sadly, up to one-third of those who do contract the disease will die," NSW Health said.

"People at risk of listeriosis should always take care with handling and storage of food, including not purchasing pre-cut melons, salads, bagged lettuce, deli meats, raw seafood and sprouted seeds," said the director of communicable diseases, Dr Vicky Sheppeard.

Last Tuesday, authorities revealed that the rockmelon farm at the centre of the outbreak was Rombola Family Farms in the NSW Riverina region.

Farmers described the outbreak as a national disaster that will take the industry years to recover from.

Demand for melons in Australia has fallen by 90 per cent since deaths were announced and led to the closure of export markets in Indonesia and Singapore.

Australia's largest melon export market, the United Arab Emirates, has just re-opened access.

With very little demand for the fruit, rockmelons are now being stored or destroyed.

A class action involving Australians affected by the outbreak is likely, according to a United States legal expert.