Health experts are on the alert for more incidents of salmonella poisoning following a spate of cases in Victoria and a national recall on some lettuce products.

Key points: 54 people in Victoria diagnosed with a rare strain of salmonella

54 people in Victoria diagnosed with a rare strain of salmonella 30 salad products recalled

30 salad products recalled Victorian Health Department investigating supplier

Fifty-four people in Victoria have been diagnosed with having a rare strain of the bacteria and two were hospitalised after eating leafy greens linked to Tripod Farmers, based in Bacchus Marsh, west of Melbourne.

Queensland Health is investigating whether eight cases of a rare strain of salmonella are linked to interstate pre-packaged lettuce.

South Australia is investigating seven suspect cases.

Tripod Farmers has withdrawn 30 products from supermarket shelves and is investigating the salmonella source.

The outbreak is believed to be linked to a fertiliser sourced from chickens and used to grow the lettuce.

Weight loss company Lite 'n Easy said some lunches on its menu were affected and customers were being contacted.

It said it had taken steps to replace its lettuce supplier.

Victoria's Department of Health and Human Services senior medical adviser Dr Finn Romanes said he expected more people to develop symptoms in the coming days.

The Department said it was confident the issue was contained, but would continue to investigate the source, along with the company and the local council.

Executive director of Health Protection for Queensland Health, Sophie Dwyer, said eight incidents have been reported over the past five weeks in Queensland.

"It's a type of salmonella that you don't see very often either in Queensland or in the rest of Australia which is why it would've been more obvious to authorities that something was going on," she said.

Tripod Farmers has recalled its affected products from major supermarkets in all states and territories, except Tasmania and Western Australia.

Food Safety Information Council spokeswoman Lydia Buchtman said it would take time to trace the source of the salmonella.

Tripod Farmers recalls products from: Coles and Bi-Lo supermarkets in Victoria, New South Wales, South Australia, Northern Territory and the ACT

Coles and Bi-Lo supermarkets in Victoria, New South Wales, South Australia, Northern Territory and the ACT Woolworths in the ACT, Victoria and NSW

Woolworths in the ACT, Victoria and NSW Other trade outlets in NSW, Queensland, Victoria, South Australia, Northern Territory and the ACT

Other trade outlets in NSW, Queensland, Victoria, South Australia, Northern Territory and the ACT No salad products recalled in Tasmania, Western Australia

"It could be a number of things — the irrigation water, the water the lettuce is grown with, it can be something in the washing process," she said.

"It can be someone who's ill who's actually handling the food."

The peak body for vegetable growers, Ausveg, defended the industry's quality assurance system and the farmers whose lettuce products were recalled.

It reassured consumers that fresh produce from Tripod Farmers had been cleared as safe to eat.

"We have every faith that this issue will be resolved extremely quickly," Ausveg's Jessica Lye said.

"Tripod Farmers have been investigated by the Department of Health yesterday and they found their system to be top notch and they cleared them for production and distribution."

Moorabool Shire Deputy Mayor Paul Tatchell said he hoped the issue would be resolved quickly.

"The drought conditions along with the recent fires have put Moorabool's agriculture under enormous stress, and it's obviously having a significant impact on the local economy," he said.

"Issues like this only add to the fire and we hope it can be resolved very very quickly."

A full list of recalled products can be found on the Food Standards website

Mass production of food increases salmonella risk, experts say

Australian National University epidemiologist Professor Martyn Kirk said Australia had one of the highest rates of salmonella in the industrialised world.

"The mass production of foods has led to the potential for the industrial scale of contamination," he said.

"So if there is a vegetable or a fruit that's been contaminated with salmonella, it can cause relatively large outbreaks to occur even in states quite some distance."

Richard Bennett from Fresh Produce Marketing Australia New Zealand said people expectations over food had changed.

"We expect greater convenience, we expect greater shelf life, we eat out a lot more," he said.

"We expect everything available everywhere at any time and so the food web is having to respond and that may well be the cause of an increase in salmonella."

Ms Buchtman said while overall rates of food poisoning had dropped in the last 10 years, salmonella poisoning was increasing.

"No-one's quite sure exactly why that's happened [but] one of the reasons is because we're doing a lot more fancy dishes, we're using raw eggs which are quite a source of salmonella," she said.

"It's great to eat salads but of course it's something that's not cooked and salmonella is killed if you thoroughly cook something."