In 2011, there was a multistate outbreak of listeria that infected 147 and killed 33, reports the Centers for Disease Control and Prevention (CDC).  One of the infected people was a pregnant woman, who also had a miscarriage.  The outbreak included five subtypes of listeria associated with the same outbreak and spread out over 28 states.  Illnesses started at the end of July 2011.

Listeriosis is a serious infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes.  CDC collaborated with public health officials in numerous states, including Colorado, as well as the U.S. Food and Drug Administration (FDA) to investigate.  Investigators used DNA analysis of listeria bacteria isolated from patients to identify cases of illness that may have been part of this outbreak.  The listeria bacteria were obtained from diagnostic testing; pulsed-field gel electrophoresis (PFGE) was used to determine DNA fingerprint patterns.

Among persons for whom information was available, reported illness onset ranged from July 31, 2011 through October 27, 2011.  The infected were up to 96 years of age, with a median age of 78 years.  Fifty-eight percent of ill persons were female.  Almost all of the infected were hospitalized.  Among the persons who died, ages ranged from 48 to 96 years, with a median age of 81 years, with one unborn child lost in a miscarriage.

According to USA Today, the listeria outbreak was linked to a Colorado farm, the now bankrupt Jensen Farms, run by two brothers.  Eric and Ryan Jensen, aged 37 and 33, were each charged with six counts of introducing adulterated food into interstate commerce.  If convicted of all six counts, they each face up to six years in prison.

The FDA found that Jensen Farms’ packing and storage facilities likely helped spread the listeria and directly contributed to the outbreak.  The FDA said one piece of equipment, a used potato washing machine bought just before the outbreak, was its possible cause and cited dirty water on the floor of the packing center as well.  Additionally, there were several areas on both the washing and drying equipment that appeared as if they could not be cleaned, with dirt and product buildup visible on some areas of the equipment.  The way the cantaloupes were cooled after being picked may have exacerbated the listeria growth.  Finally, a truck that frequently hauled cantaloupe to a cattle operation and was parked near the packing house could also have been a source of contamination.  Cases associated with the strain of listeria traced to Jensen Farms ended in December 2011.