The U.S. Centers for Disease Control and Prevention has wrapped up its investigation on the multistate outbreak involving flour contaminated with Shiga toxin-producing Escherichia coli, warning not all recalled products may have been removed from households, so illnesses may persist.

Working alongside the U.S. Food and Drug Administration and officials from the states involved in the outbreak, the CDC used the PulseNet system in identifying illnesses that may be part of the incident. A national subtyping network of food regulatory and public health agency laboratories, PulseNet performed DNA fingerprinting on the STEC bacteria from the people who got sick, identifying the strains STEC O121 and STEC O26 as culprits.

According to the whole genome sequencing technique used by PulseNet, the strains found in those who were affected by the outbreak were genetically closely related, meaning they were likely to have come from a common infection source.

After traceback, laboratory and epidemiologic tests were carried out, it was discovered that flour from General Mills' Kansas City facility as the likely source of the outbreak.

Those who got sick were interviewed and 28 of 37 people revealed that they or someone in their home had used flour in the week prior to becoming ill, while 19 of 38 reported tasting or eating raw homemade batter or dough and three, all children, said they played with or ate raw dough while dining out in restaurants.

Based on the investigation, people started getting sick between Dec. 21, 2015 and Sept. 5, 2016. In May, General Mills initiated a recall of several variants of its Signature Kitchens Flour, Gold Medal Wondra Flour and Gold Medal Flour over possible E. coli contamination.

In June, a laboratory test showed that the STEC O121 strain found in General Mills flour samples collected from the homes of the people who got sick were genetically closely related to the STEC O121 isolates found in those who were ill.

In July, General Mills and the FDA carried out their own tests on samples of the recalled flour products and found the STEC O26 strain in the samples were genetically closely related to the STEC O26 present in those who were ill.

This prompted General Mills to expand its recall to include more production dates.

"Although the outbreak investigation is over, illnesses are expected to continue for some time," said the CDC.

This is because not only do the recalled flour products have long shelf lives, but it is also possible that some consumers are not aware of the recall so they'll continue eating the affected products.

Because of this outbreak, the CDC reiterated that it's not safe to consume raw batter or dough. Licking batter off a spoon may not seem much but it is enough to get someone sick.

Photo: Jessica Spengler | Flickr