Conagra Brands Inc. has recalled four varieties of Duncan Hines cake mix as authorities investigate possible salmonella contamination at a manufacturing plant.

People who bought Duncan Hines’ Classic White, Classic Golden Butter, Signature Confetti or Classic Yellow cake mix with certain sell-by dates are being advised not to use or eat the products and to return them to the stores where they were bought.

The recall comes as the Food and Drug Administration and the Centers for Disease Control and Prevention investigate salmonella illnesses in five people, several of whom said they ate cake mix. Some may have eaten it raw.

A retail sample of the Classic White cake mix tested positive for Salmonella Agbeni bacteria, and its DNA footprint matched the salmonella in the ill people, according to the FDA. Conagra voluntarily recalled that mix as well as three others made during the same time period.

The FDA is reminding people not to eat raw batter, which can contain raw eggs, and to take care to wash hands and utensils that touch raw batter.

The Duncan Hines cake mixes being recalled are those with best-if-used-by dates of:

Classic White: March 7, 8, 9, 10, 12 and 13 of 2019.

Classic Yellow: March 9, 10, 12, 13 of 2019.

Classic Butter Golden Cake: March 7, 8 and 9 of 2019.

Signature Confetti: March 12 and 13 of 2019.