The number of people testing positive to salmonella linked to custard-filled cakes has risen to 97.

Vili’s custard berliners and St George Cakes and Gelati custard eclairs and cannolis were withdrawn from sale on February 4, after SA Health established they were the common link in the reported cases.

SA Health’s director of public health Dr Kevin Buckett said an extensive investigation was yet to identify a common source.

"All of the environmental and product samples from both manufacturing plants have had negative results for salmonella contamination," Dr Buckett said. "We will continue to work with both companies prior to the products returning to the shelves."

Tindall Gask Bentley partner Tim White said the personal injury firm had received more than 30 calls since it placed an advertisement urging victims to come forward to find out their legal and possible compensation options.

"This significantly increases the likelihood of a class action," Mr White said.