(Reuters) - General Mills Inc GIS.N on Tuesday issued a voluntary recall of about 10 million pounds of flour, saying it was working with health officials to investigate an outbreak of E. coli that had sickened 38 people in 20 U.S. states.

The General Mills logo is seen on a box of Cheerios cereal in Evanston, Illinois, June 26, 2012. REUTERS/Jim Young

The bacteria strain behind the outbreak has not been found in any of General Mills’ Gold Medal, Wondra and Signature Kitchens flour or their manufacturing plant, the company said. Consumers have not contacted it directly to report any illnesses, the Minneapolis-based company added.

“Out of an abundance of caution, a voluntary recall is being made,” General Mills said.

U.S. and state health authorities are probing an outbreak of E. coli O121 from Dec. 21 to May 3, General Mills said. The potentially deadly strain can cause bloody diarrhea and dehydration, mostly among the elderly, very young children and people with weak immune systems.

The Centers for Disease Control and Prevention found that about half of the 38 sickened people reported cooking with flour before becoming ill, General Mills said. About half of this group reported using a General Mills brand, a company spokesman said in a phone interview.

Additional recall information can be found at www.generalmills.com/flour.

Kashi Co, owned by General Mills' rival Kellogg Co K.N, also announced a recall of one variety each of its granola and granola bars on Tuesday.

Kashi said the bars contained ingredients made from sunflower seeds distributed by SunOpta SOY.TO that had the potential to be contaminated with Listeria monocytogenes bacteria.

The bacteria can cause serious and sometimes fatal infections in young children, frail or elderly people, and others with weakened immune systems.

SunOpta this month recalled some of its sunflower kernel products produced at its Crookston, Minnesota facility between Feb. 1 and Feb. 19, citing the potential to be contaminated with listeria.