The Department of Health and Human Services has warned consumers against eating the products, which were grown and distributed by the Victorian-based company Tripod Farmers.

The lettuce includes brands such as Coles 4 Leaf Mix, Woolworths salad mix, SupaSalad Supamix and Wash N Toss salad mix.

All these products have best before dates leading up to and including February 14.

Department senior medical advisor Finn Romanes said people with these products should either return them or discard them.

He said a link was made between the product and illness because of a higher than usual number of cases of the salmonella anatum strain.

“Normally we only see a handful of cases of this strain each year, but so far this year there have been 28 adult cases of salmonella anatum – mostly adults – notified to the department,’’ he said.

“As a result of following up the food histories of a number of people we have discovered a common source – the Tripod Farmers lettuce.

“Tests of three products from two batches have also tested positive for salmonella anatum bacterium.’’

Tripod Farmers is issuing a national voluntary product recall for these products and there will be ongoing testing and monitoring of all of its products.

Its premises has been inspected and a thorough clean-up carried out.

Salmonellosis is a form of gastroenteritis caused by the germ salmonella and can affect anyone.

The severity of symptoms depends on the number of bacteria ingested, age and general health.

The elderly, those with another medical condition such as a weakened immune system or are malnourished are more prone to the illness.

Symptoms of salmonellosis usually occur between six to 72 hours after the bacteria is ingested.

The most common symptoms include: diarrhoea, which might contain blood or mucous; fever; headache; stomach cramps; nausea; vomiting, and dehydration, especially among infants and the elderly.

In rare cases, septicaemia or local infection might develop as a complication of salmonellosis.