A number of major retail and foodservice outlets in the US, including Wal-Mart and McDonalds, have opted to withdraw tomato varieties implicated in the recent salmonella scare, as the US Food and Drug Administration continues to search for the source of the outbreak.

The group has this week added Florida and California to the list of safe tomato sourcing states.

There are now 167 reported cases of almonella poisoning across 17 states, according to reports, with 23 people said to have been hospitalised as a result.