At a Senate Estimates hearing, officials from the Department of Agriculture revealed Tripod Farmers, at the centre of the outbreak, had exported 23 consignments of the "same sort of product" to three important trading partners.

In response to questions by Senator Rachel Siewert, they said Thai authorities had heightened inspections at the border, but no bans had been put in place.

"We have written to those three countries involved, with 23 identified consignments that may contain lettuce from that particular establishment," said Chris Parker, assistant secretary of the department's plant export operations branch.

"This is regular business that we would clearly notify our trading partners when issues may or may not arise and it is something they would do for us as well."

Fourteen consignments (a mix of fresh fruit and vegetables) were exported to Singapore, seven to Hong Kong and two to Thailand.

So far, 128 people are believed to have contracted the rare strain of salmonella anatum after eating Tripod Farmers' pre-packaged salad leaves - 10 confirmed and 118 probable.

The affected products, now under recall, were sold at supermarkets Coles and Woolworths, and used in ready-to-eat meals by Lite n' Easy.

The outbreak has potential to rock Australia's $8.6 billion fresh fruit and vegetable industry and undermine our "clean and green" reputation.

Horticulture heavyweight Frank Costa has previously told Fairfax Media the contamination was "a great concern" to the industry.

Such is the sensitivity in China – Australia's biggest export partner - on food safety that it temporarily banned imports from New Zealand dairy company, Fonterra, in 2013 after it recalled products following a positive test for botulism.

This was despite that test eventually proving to be false.

Vegetable growers' body AusVeg said the recall was limited to one supplier and not indicative of a systematic food safety problem in Australia.

"Australian produce has an international reputation for being high quality and safe to eat. At this stage our trading partners are continuing to import Australian produce," said Jessica Lye, AusVeg's national manager of scientific affairs.

"It is important to note ... all affected product stocked domestically and internationally has been recalled, with products available for purchase being safe to eat."

Senator Siewert said she was concerned that products had been exported from a farm that was grappling with a major contamination issue.

"The Australian Government does not have export certification for salmonella, and the only action the Department is aware of is heightened inspection at the Thailand border," she said.

"This represents another gap in our export/import biosecurity and health protections, I urge the Government to look at how this can be addressed".

During Senate Estimates, the Department of Agriculture said it did not test for contamination that could lead to food poisoning.

"In regards to exports, the Australian government's responsibility is around meeting importing countries' requirements and providing certification against those requirements," said Mr Parker.

"I'm not aware of there being certification requirements by the Australian government when we export plant products for things like salmonella."

Tripod Farmers, based in Bacchus Marsh, west of Melbourne, said it was still investigating the cause of the contamination.

"We are continuing to work closely with health authorities to determine the cause and extent of the problem, and with our customers to manage an effective recall," said managing director Frank Ruffo.

David Ironside, the department's assistant secretary of compliance arrangements, said lettuce could get salmonella by being exposed to contaminated water or other sources of contamination between harvest and retail.

"So we don't really know?" asked Senator Bill Heffernan.

"No, it's very difficult with microbiological contamination to identify exactly where the contamination happened," replied Mr Ironside.