I am always a bit shocked that we seem never to be able to learn from history – even if it is recent.

Largest Death Toll in Decades

In September 2001, a total of 147 persons infected with any of the five (5) outbreak-associated strains[1] of Listeria monocytogenes were reported to CDC from 28 states.  The number of infected persons identified in each state was as follows:  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).

Among persons for whom information was available, reported illness onset ranged from July 31, 2011 through October 27, 2011.  Ages ranged from <1 to 96 years, with a median age of 77 years.  Most cases were over 60 years old.  Fifty-eight percent (58%) of cases were female.  Among the 144 ill persons with available information on whether they were hospitalized, 142 (99%) were hospitalized.

Thirty-three deaths[2] were reported:  Colorado (9), Indiana (1), Kansas (3), Louisiana (2), Maryland (1), Missouri (3), Montana (1), Nebraska (1), New Mexico (5), New York (2), Oklahoma (1), Texas (2), and Wyoming (2).  Among persons who died, ages ranged from 48 to 96 years, with a median age of 82.5 years.  In addition, one (1) woman pregnant at the time of illness had a miscarriage.  Seven (7) of the illnesses were related to a pregnancy; three (3) were diagnosed in newborns and four (4) were diagnosed in pregnant women.

On September 10, 2011, with Colorado state officials, the FDA conducted an inspection at Jensen Farms and collected multiple samples, both product and environmental, for laboratory testing.  Of the 39 environmental swabs collected from within the Jensen Farms packing facility, 13 were confirmed positive for Listeria monocytogenes with PFGE pattern combinations that were indistinguishable from three (3) of the six (6) outbreak strains.  Of the 13 positive environmental swabs, 12 were collected at the processing line and one was collected from the packing area.  Cantaloupe collected from the firm’s cold storage during the inspection also tested positive for Listeria—in fact, five (5) of the ten (10) samples collected were positive for Listeria—with PFGE pattern combinations that were indistinguishable from two (2) of the six  (6) outbreak strains.

After finding evidence of extensive contamination at Jensen Farms, the FDA, again, with the assistance of Colorado state officials, conducted an environmental assessment at the facility in an effort to identify the practices and conditions that lead to such widespread contamination.  The results of the assessment, which occurred on September 22 and 23, 2011, were disclosed in a report dated October 19, 2011.  Among other things, the report notes:

a.         Facility Design:  Certain aspects of the packing facility, including the location of a refrigeration unit drain line, allowed for water to pool on the packing facility floor in areas adjacent to packing facility equipment.  Wet environments are known to be potential reservoirs for Listeria monocytogenes and the pooling of water in close proximity to packing equipment, including conveyors, may have extended and spread the pathogen to food contact surfaces.  Samples collected from areas where pooled water had gathered tested positive for an outbreak strain of Listeria monocytogenes.  Therefore, this aspect of facility design is a factor that may have contributed to the introduction, growth, or spread of Listeria monocytogenes.  This pathogen is likely to establish niches and harborages in refrigeration units and other areas where water pools or accumulates.

Further, the packing facility floor where water pooled was directly under the packing facility equipment from which FDA collected environmental samples that tested positive for Listeria monocytogenes with PFGE pattern combinations that were indistinguishable from outbreak strains.  The packing facility floor was constructed in a manner that was not easily cleanable.  Specifically, the trench drain was not accessible for adequate cleaning.  This may have served as a harborage site for Listeria monocytogenes and, therefore, is a factor that may have contributed to the introduction, growth, or spread of the pathogen.

b.         Equipment Design:  FDA evaluated the design of the equipment used in the packing facility to identify factors that may have contributed to the growth or spread of Listeria monocytogenes.  In July 2011, the firm purchased and installed equipment for its packing facility that had been previously used at a firm producing a different raw agricultural commodity.

The design of the packing facility equipment, including equipment used to wash and dry the cantaloupe, did not lend itself to be easily or routinely cleaned and sanitized.  Several areas on both the washing and drying equipment appeared to be un-cleanable, and dirt and product buildup was visible on some areas of the equipment, even after it had been disassembled, cleaned, and sanitized.  Corrosion was also visible on some parts of the equipment.  Further, because the equipment is not easily cleanable and was previously used for handling another raw agricultural commodity with different washing and drying requirements, Listeria monocytogenes could have been introduced as a result of past use of the equipment.

The design of the packing facility equipment, especially that it was not easily amenable to cleaning and sanitizing and that it contained visible product buildup, is a factor that likely contributed to the introduction, growth, or spread of Listeria monocytogenes.  Cantaloupe that is washed, dried, and packed on unsanitary food contact surfaces could be contaminated with Listeria monocytogenes or could collect nutrients for Listeria monocytogenes growth on the cantaloupe rind.

c.         Postharvest Practices:  In addition, free moisture or increased water activity of the cantaloupe rind from postharvest washing procedures may have facilitated Listeria monocytogenes survival and growth.  After harvest, the cantaloupes were placed in cold storage.  The cantaloupes were not pre-cooled to remove field heat before cold storage.  Warm fruit with field heat potentially created conditions that would allow the formation of condensation, which is an environment ideal for Listeria monocytogenes growth.

The combined factors of the availability of nutrients on the cantaloupe rind, increased rind water activity, and lack of pre-cooling before cold storage may have provided ideal conditions for Listeria monocytogenes to grow and out-compete background microflora during cold storage.  Samples of cantaloupe collected from refrigerated cold storage tested positive for Listeria monocytogenes with PFGE pattern combinations that were indistinguishable from two of the four outbreak strains.

After conducting this environmental assessment, the FDA issued a warning letter to Jensen Farms, indicating, “we may take further action to seize your product(s) and/or enjoin your firm from operating.  Additionally, the receipt of this warning letter and any action taken to correct the violations cited in it do not preclude a subsequent criminal prosecution by the United States Department of Justice.”  To date, despite 38 deaths, one miscarriage, and 147 confirmed illnesses nationally, no criminal indictments have been issued in this outbreak—yet.

Another Listeria Cantaloupe and Melon Recall

Just less than one year latter – August 13, 2012: Burch Equipment LLC (Burch Farms) of Faison, N.C., expanded its recall to include all of this growing season’s cantaloupes and honeydew melons that may remain on the market.

Consumers who think they may have purchased these melons should contact the store where they made their purchases and ask for information about whether their melons originated from Burch Farms. The cantaloupes and honeydew melons involved in this expanded recall were sold to distributors in the states of Florida, Georgia, Illinois, Kentucky, Massachusetts, Maryland, Maine, Michigan, North Carolina, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, South Carolina, Virginia, Vermont and West Virginia, who may have further distributed them to other states.

The recall expansion was based on the FDA’s finding of Listeria monocytogenes (L. mono) on a honeydew melon grown and packed by Burch Farms. The recall expansion is also a result of the agency’s finding of L. mono in the environment of the firm’s packing facility.

Why Can’t We Learn from History?

About a month later, the CDC collaborated with public health officials in many states and the U.S. Food and Drug Administration (FDA) to investigate a multi-state outbreak of Salmonella Typhimurium and Salmonella Newport infections linked to cantaloupe originating from Chamberlain Farms Produce, Inc. of Owensville, Indiana.

Public health investigators used DNA “fingerprints” of Salmonella bacteria obtained through diagnostic testing with pulsed-field gel electrophoresis (PFGE) to identify cases of illness that may be part of this outbreak.  They used data from PulseNet, the national subtyping network made up of state and local public health laboratories and federal food regulatory laboratories that performs molecular surveillance of foodborne infections.

A total of 261 individuals infected with the outbreak strain of Salmonella Typhimurium and Salmonella Newport were reported from 24 states:  Alabama (25), Arkansas (6), Florida (1), Georgia (13), Illinois (36), Indiana (30), Iowa (9), Kentucky (66), Maryland (1), Michigan (8), Minnesota (2), Mississippi (7), Missouri (17), Montana (1), New Jersey (2), North Carolina (5), Ohio (5), Oklahoma (1), Pennsylvania (2), South Carolina (4), Tennessee (8), Texas (2), Virginia (1), and Wisconsin (9).

Among 257 persons for whom information was available, illness onset dates ranged from July 6, 2012 to September 16, 2012.  Ill persons ranged in age from less than 1 year to 100 years, with a median age of 47 years.  Fifty-five percent (55%) of ill persons were female.  Among 163 persons with available information, 84 (51%) reported being hospitalized.  Three deaths were reported in Kentucky.  Results of antibiotic susceptibility testing indicated that this strain of Salmonella is susceptible to commonly prescribed antibiotics.

From August 14-16, 2012 investigators from the U.S. Food and Drug Administration (FDA) collected samples of cantaloupe at Chamberlain Farms.  They also took samples in the farm’s cantaloupe packinghouse from surfaces that would likely harbor bacteria.  This action was taken in cooperation with the Indiana State Department of Health.  FDA samples of cantaloupe collected at Chamberlain Farms showed the presence of Salmonella Typhimurium with an indistinguishable DNA fingerprint as the outbreak strain.  These samples also showed the presence of Salmonella Newport with a DNA fingerprint that was from the same outbreak strain that sickened 30 people in the states of Illinois, Indiana, Michigan, Missouri, Ohio, Virginia, and Wisconsin.  The link was supported by trace back information collected by state officials in Indiana and Illinois which showed that patients consumed cantaloupe bought at stores supplied by Chamberlain Farms.[3]

On October 3, 2012 the FDA released FDA Form (Inspectional Observations) for Chamberlain Farms.  Federal inspectors observed poor sanitary practices at the firm’s cantaloupe packing shed.  A third Salmonella serotype, Anatum, was isolated in samples obtained via environmental swabs collected from various locations and surfaces in the shed.  FDA inspectors noted that food contact surfaces were not constructed or designed in a manner to allow appropriate cleaning.  Multiple locations of the conveyor rollers and belts had accumulated black, green and brown buildup.  There was standing water in the shed.  The firm’s garbage receptacle was overflowing with garbage constituting an attractant, breeding place, or harborage for pests.[4]

This is another it what will be a long – too long – series of outbreak investigations where we have represented consumers in what I hope will be a cautionary tale, and a learning experience, for manufacturers of food.