About Listeria

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Jensen Farms Rocky Ford Cantaloupe Listeria Outbreak

In September and October, 2011 the Centers for Disease Control and Prevention (CDC) and public health agencies from multiple states identified at least 147 people from 28 states who had become ill with Listeria monocytogenes infections after consuming Jensen Farms Rocky Ford cantaloupes.  At least 33 people died as a result of their Listeria infections (known as listeriosis) and 1 miscarriage was linked to Jensen Farms cantaloupe.

States where cantaloupe Listeria cases were reported included:

Alabama (1), Arkansas (1), California (4), Colorado (40), Idaho (2), Illinois (4), Indiana (3), Iowa (1), Kansas (11), Louisiana (2), Maryland (1), Missouri (7), Montana (2), Nebraska (6), Nevada (1), New Mexico (15), New York (2), North Dakota (2), Oklahoma (12), Oregon (1), Pennsylvania (1), South Dakota (1), Texas (18), Utah (1), Virginia (1), West Virginia (1), Wisconsin (2), and Wyoming (4).

7 of the illnesses were related to a pregnancy; 3 were diagnosed in newborns and 4 were diagnosed in pregnant women.

Listeria found on cantaloupes, in Jensen Farms processing plant

Lab testing by the Colorado Department of Public Health and Environment identified Listeria monocytogenes bacteria on cantaloupe collected from grocery stores and from an ill person’s home.  A traceback investigation led to Rocky Ford-grown melons from Jensen Farms, which issued a recall of all whole cantaloupes shipped between July 29, 2011 and September 10, 2011 on September 14. 

FDA officials said samples taken from the Jensen Farms fields and irrigation water, as well as cantaloupes picked directly from the fields, were negative for the deadly outbreak strains of Listeria, but samples collected inside the packing plant, as well as cantaloupes in cold storage, were positive for the bacteria.  FDA officials pointed to several factors they say likely caused Listeria to grow and spread inside the packing plant to lethal levels:

  • A truck used to haul culled cantaloupes shuttled to and from a cattle operation. Employees may have tracked Listeria into the plant from the truck, which was parked adjacent to the packing facility.
  • Water was pooled on the floor next to equipment and employee walkways inside the packing plant. Listeria harbors in standing water and wet places, and perhaps spread to conveyors and other packing equipment. Samples collected from the pooled water tested positive for an outbreak strain of Listeria.
  • The packing equipment could not be easily cleaned and sanitized. Inspectors saw “visible product buildup” on food contact surfaces.
  • Recently purchased used washing and drying equipment was corroded and hard to clean, and previously had handled other raw produce.
  • Natural moisture or increased water from washing the cantaloupes could have encouraged the growth of Listeria on the cantaloupe rind. Moreover, melons warm from the field were not pre-cooled before going into cold storage, so the condensation on the melons likely created conditions ideal for Listeria growth.

At least 5 different outbreak-associated strains of Listeria monocytogenes were isolated from outbreak victims through laboratory testing.