A total of 29 persons were infected with the outbreak strain of STEC O26 linked to clovers sprouts served on sandwiches served at Jimmy John’s in 11 U.S. states.

The Centers for Disease Control reports in its final update today that among 29 ill persons, illness onset dates ranged from December 25, 2011 to March 3, 2012. Ill persons range in age from 9 years to 57 years old, with a median age of 26 years. Eighty-nine percent of ill persons are female. Among the 29 ill persons, 7 (24%) were hospitalized. None have developed HUS, and no deaths have been reported.

Based on previous outbreaks associated with sprouts, investigation findings have demonstrated that sprout seeds might become contaminated in several ways. They could be grown with contaminated water or improperly composted manure fertilizer. They could be contaminated with feces from domestic or wild animals, or with runoff from animal production facilities, or by improperly cleaned growing or processing equipment. Seeds also might become contaminated during harvesting, distribution, or storage. Many clover seeds are produced for agricultural use, so they might not be processed, handled, and stored as human food would. Conditions suitable for sprouting the seed also permit bacteria that might be present on seeds to grow and multiply rapidly.

In 1999, FDA released guidance to help seed producers and sprout growers enhance the safety of their products. Specific measures recommended in the guidelines include a seed disinfection step and microbiologic tests of water that has been used to grow each lot of sprouts. The microbiologic tests currently recommended under this guidance would not identify the presence of STEC O26.