FDA Publishes Report on Factors Potentially Contributing to the Contamination of Fresh, Whole Cantaloupe Implicated in the Multi-State Listeria monocytogenes Foodborne Illness Outbreak

On October 19, 2011, FDA released a document which provides an overview of factors that potentially contributed to the contamination of fresh, whole cantaloupe with the pathogen Listeria monocytogenes, which was implicated in a 2011 multi-state outbreak of listeriosis. In early September 2011, the Food and Drug Administration (FDA), in conjunction with the Centers for Disease Control and Prevention (CDC) and state health departments, began to investigate a multi-state outbreak of listeriosis. Early in the investigation, cantaloupes from Jensen Farms in the southwest region of Colorado were implicated in the outbreak. 

On September 10, 2011, FDA, along with Colorado state officials, conducted an inspection at Jensen Farms during which FDA collected multiple samples, including whole cantaloupes and environmental (non-product) samples from within the facility, for laboratory culturing to identify the presence of Listeria monocytogenes. Of the 39 environmental samples collected from within the facility, 13 were confirmed positive for Listeria monocytogenes with pulsed-field gel electrophoresis (PFGE) pattern combinations that were indistinguishable from three of the four outbreak strains collected from affected patients. Cantaloupe collected from the firm’s cold storage during the inspection was also confirmed positive for Listeria monocytogenes with PFGE pattern combinations that were indistinguishable from two of the four outbreak strains.

As a result of the isolation of outbreak strains of Listeria monocytogenes in the environment of the packing facility and whole cantaloupes collected from cold storage, and the fact that this is the first documented listeriosis outbreak associated with fresh, whole cantaloupe in the United States, FDA initiated an environmental assessment in conjunction with Colorado state and local officials. FDA, state, and local officials conducted the environmental assessment at Jensen Farms on September 22-23, 2011. The environmental assessment was conducted to gather more information to assist FDA in identifying the factors that potentially contributed to the introduction, growth, or spread of the Listeria monocytogenes strains that contaminated the cantaloupe.

FDA identified the following factors as those that most likely contributed to the introduction, spread, and growth of Listeria monocytogenes in the cantaloupes:


There could have been low level sporadic Listeria monocytogenes in the field where the cantaloupe were grown, which could have been introduced into the packing facility

A truck used to haul culled cantaloupe to a cattle operation was parked adjacent to the packing facility and could have introduced contamination into the facility


The packing facility’s design allowed water to pool on the floor near equipment and employee walkways;

The packing facility floor was constructed in a manner that made it difficult to clean

The packing equipment was not easily cleaned and sanitized; washing and drying equipment used for cantaloupe packing was previously used for postharvest handling of another raw agricultural commodity.


There was no pre-cooling step to remove field heat from the cantaloupes before cold storage. As the cantaloupes cooled there may have been condensation that promoted the growth of Listeria monocytogenes.

FDA’s findings regarding this particular outbreak highlight the importance for firms to employ good agricultural and management practices in their packing facilities as well as in growing fields. FDA recommends that firms employ good agricultural and management practices recommended for the growing, harvesting, washing, sorting, packing, storage and transporting of fruits and vegetables sold to consumers in an unprocessed or minimally processed raw form.

FDA has issued a warning letter to Jensen Farms based on environmental and cantaloupe samples collected during the inspection. FDA’s investigation at Jensen Farms is still considered an open investigation.

Jensen Farms’ Recall

Jensen Farms voluntarily recalled its whole cantaloupes on Sept. 14 in response to the multi-state outbreak of listeriosis. Cantaloupes from other farms have not been linked to this outbreak.

FDA has successfully audited the majority of Jensen Farms’ direct and secondary accounts. The recalled cantaloupes were produced from the end of July to September 10, 2011. Given that the Jensen Farms’ recall has been in effect for more than a month and that the shelf life of a cantaloupe is approximately two weeks, it is expected that all of the recalled whole Jensen Farms cantaloupes have been removed from the marketplace.

FDA has verified that the following states received recalled cantaloupes directly from Jensen Farms: Arizona, Arkansas, Colorado, Idaho, Illinois, Indiana, Kansas, Louisiana, Minnesota, Missouri, Montana, Nebraska, New Jersey, New Mexico, New York, North Dakota, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Wisconsin and Wyoming. There is no indication of foreign distribution.

Consumer Safety Information

Listeria can grow at refrigerator temperatures, about 40◦ Fahrenheit (4◦ Celsius). The longer ready-to-eat refrigerated foods are stored in the refrigerator, the more opportunity Listeria has to grow.

It is very important that consumers clean their refrigerators and other food preparation surfaces. Consumers should follow these simple steps:

Wash hands with warm water and soap for at least 20 seconds before and after handling food.

Wash the inside walls and shelves of the refrigerator, cutting boards and countertops; then sanitize them with a solution of one tablespoon of chlorine bleach to one gallon of hot water; dry with a clean cloth or paper towel that has not been previously used.

Wipe up spills in the refrigerator immediately and clean the refrigerator regularly.

Always wash hands with warm water and soap following the cleaning and sanitization process.

FDA advises consumers not to eat the recalled cantaloupes and to throw them away. Do not try to wash the harmful bacteria off the cantaloupe as contamination may be both on the inside and outside of the cantaloupe. Cutting, slicing and dicing may also transfer harmful bacteria from the fruit’s surface to the fruit’s flesh.

Listeriosis is rare but can be fatal, especially in certain high-risk groups. These groups include older adults, people with compromised immune systems and unborn babies and newborns. In pregnant women, listeriosis can cause miscarriage, stillbirth, and serious illness or death in newborn babies, though the mother herself rarely becomes seriously ill. A person with listeriosis usually has fever and muscle aches. Persons who think they might have become ill should consult their doctor.

For more information on the epidemiologic investigation, please refer to CDC’s Investigation on the Multi-State Listeriosis Outbreak.


Mr. Ryan D. Jensen, Co-Owner/Partner
Mr. Eric S. Jensen, Co-Owner/Partner
Jensen Farms
31 North Cline
Granada, Colorado
Dear Messrs. Jensen:
On September 10, 2011, investigators from the Food and Drug Administration (FDA) inspected your produce packing facility located at 31 North Cline, Granada, Colorado. FDA conducted this inspection under its authority in section 704 of the Federal Food, Drug, and Cosmetic Act (the Act) [21 U.S.C. § 374] as a result of epidemiological and traceback investigations that implicated cantaloupe grown at your farm and packed at your facility with a nationwide outbreak of listeriosis.
Specifically, on September 2, 2011, the Colorado Department of Public Health and Environment (CDPHE) notified the Centers for Disease Control and Prevention (CDC) of seven cases of listeriosis reported since August 28, which was a significant increase from the average number of listeriosis cases reported in Colorado each month. By September 6, all seven Colorado patients reported eating cantaloupe in the month before illness began, and three reported eating cantaloupe marketed as “Rocky Ford,” which is produced by a number of farms in the Rocky Ford region of Colorado, including Jensen Farms.
CDC has stated that this is one of the largest outbreaks of listeriosis in the history of the United States. As of October 11, 2011, 116 people from 25 states were sickened and 23 people have died. Four widely differing strains and two serotypes (1/2a and 1/2b) have been associated with the outbreak. CDC defined clusters of illnesses (clusters 1-4) based on the four strains. You may read more information about the outbreak at the following web address: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6039a5.htm?s_cid=mm6039a5_w.
Infection with Listeria monocytogenes causes a spectrum of illness, ranging from febrile gastroenteritis to invasive disease, including sepsis and meningoencephalitis. Invasive listeriosis occurs predominantly in older adults and persons with impaired immune systems.  Listeriosis in pregnant women is typically a mild “flu-like” illness, but can result in fetal death, premature labor, or neonatal infection.
During the September 10 inspection, FDA sampled cantaloupes from cases on four pallets in the cold storage in your packing facility. FDA conducted laboratory analyses, including pulsed-field gel electrophoresis (“PFGE”), on these samples. Five of the ten cantaloupes FDA analyzed were positive for Listeria monocytogenes. The PFGE analysis determined that four of the ten cantaloupes matched the strain of Listeria monocytogenes representing cluster #2, and one of the cantaloupes matched the strain of Listeria monocytogenes representing cluster # 4. Consequently, these cantaloupes from your facility are adulterated within the meaning of Section 402(a)(1) of the Act [21 U.S.C. § 342(a)(1)] in that they bear or contain a poisonous or deleterious substance that may render them injurious to health. You can find the Act and the regulations through links in FDA’s homepage at www.fda.gov.
During the inspection, we also collected environmental swabs from various locations and surfaces throughout your packing facility. FDA conducted laboratory analyses which determined that 13 of the 39 total environmental swabs were positive for outbreak strains of Listeria monocytogenes. PFGE analysis determined that eleven of the positive swabs matched the strain of Listeria monocytogenes represented by cluster #2, one positive swab matched the strain of Listeria monocytogenes represented by cluster #4, and one positive swab matched the strain of Listeria monocytogenes represented by cluster #3. Further, one swab was positive for a strain of Listeria monocytogenes that did not match any of the outbreak strains. These positive swabs were taken from different locations throughout the washing and packing areas in your facility, all of which were either food contact surfaces or areas adjacent to food contact surfaces. This significant percentage of swabs that tested positive for outbreak strains of Listeria monocytogenes demonstrates widespread contamination throughout your facility and indicates poor sanitary practices in the facility.
Accordingly, the cantaloupe packed in your facility are adulterated within the meaning of Section 402(a)(4) of the Act [21 U.S.C. § 342(a)(4)] in that they have been prepared, packed, or held under insanitary conditions whereby they may have been rendered injurious to health. A summary of the PFGE results from samples collected during this investigation that tested positive for Listeria monocytogenes is attached for your information.
FDA may take further action if you do not promptly correct these violations. For instance, 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.
Please notify this office in writing within fifteen (15) working days from the date you receive this letter of the specific steps you have taken to correct the noted violations, including an explanation of how you plan to prevent these violations, or other similar violations, from occurring in the future.  Include documentation of the corrective actions you have taken. If your planned corrections will occur over time, please include a timetable for implementation of those corrections.  If corrective action cannot be completed within 15 working days, state the reason for the delay and the time within which the corrections will be completed.
This letter may not list all the violations at your facility. You are responsible for ensuring that your facility operates in compliance with the Act and all applicable regulations.
FDA acknowledges receipt of the letter, dated October 17, 2011, from your counsel, Michael W. Callahan. In this letter, Jensen Farms agreed, among other things, to FDA inspection of its growing, packaging, and cold storage operations before it resumes food harvesting, packaging, or processing. Jensen Farms also agreed to correct all objectionable observations noted during said FDA inspections.
We note that, in our Draft Guidance for Industry, Guide to Minimize Microbial Food Safety Hazards of Melons, we recommend a number of practices to minimize microbial food safety hazards associated with melons throughout the entire melon supply chain. Specifically, we recommend, among others, the following postharvest practices:
• Using packing equipment designed to facilitate cleaning and sanitation of melon contact surfaces and constructed of materials that may be easily cleaned and sanitized;

• Validating and verifying that melon wetting and brushing operations are not a potential source of melon contamination or cross-contamination; and

• Cooling and cold storing melons as soon as possible after harvest because delays in cooling when melons with netted rinds (such as cantaloupe) are wet from washing operations may allow for multiplication of human pathogens on the rind surface.

Please send your reply to FDA, Attention: Carolyn A. Pinney, Compliance Officer, at the above letterhead address. If you have any questions regarding this letter, please contact Carolyn A. Pinney at (303) 236-3024.
La Tonya M. Mitchell
Denver District Director