Listeria Outbreak Linked To Cantaloupes
The U.S. Center for Disease Control is collaborating with public health officials in several states, including Colorado, and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of listeriosis. Listeriosis is a serious infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. Investigators are using DNA analysis of Listeria isolated from patients to identify cases of illness that may be part of this outbreak. The Listeria bacteria are obtained from diagnostic testing; pulsed-field gel electrophoresis (PFGE) is used to determine DNA fingerprint patterns. Investigators are using 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 35 persons infected with the outbreak-associated strains of Listeria monocytogenes have been reported from 10 states. All illnesses started on or after August 4, 2011. The number of infected persons identified in each state is as follows: California (1), Colorado (12), Illinois (1), Indiana (1), Montana (1), Nebraska (4), New Mexico (5), Oklahoma (6), Texas (3), and West Virginia (1). Listeriosis illnesses in several other states are currently being investigated by state and local health departments to determine if they are part of this outbreak.
Among persons for whom information is available, illnesses began on or after August 4, 2011. Ages range from 35 to 96 years, with a median age of 81 years old. Most ill persons are over 60 years old or have health conditions that weaken the immune system. Sixty-five percent of ill persons are female. Among the 28 ill persons with available information on whether they were hospitalized, all were hospitalized. Four deaths have been reported, one in Colorado, one in Oklahoma, and two in New Mexico.
The outbreak can be visually described with a chart showing the number of persons who became ill each day. This chart is called an epidemic curve or epi curve. Illnesses that occurred after August 28, 2011, might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported. Please see the description of the steps in a foodborne outbreak investigation for more details.
About 800 cases of Listeria infection are diagnosed each year in the United States, along with 3 or 4 outbreaks of Listeria-associated foodborne illness. The foods that typically cause these outbreaks have been deli meats, hot dogs, and Mexican-style soft cheeses made with unpasteurized milk. Produce is not often identified as a source, but sprouts caused an outbreak in 2009, and celery caused an outbreak in 2010.
Investigation of the Outbreak
Ongoing collaborative investigations by local, state, and federal public health and regulatory agencies indicate the source of the outbreak is cantaloupe. Among the 27 ill persons with available information on what they ate, 26 (96%) reported consuming cantaloupes. Ill persons were interviewed about exposures during the month before they became ill; investigators compared their responses to persons with listeriosis reported through the CDC Listeria Initiative, whose illnesses were not part of this outbreak. Several ill persons remembered the type of cantaloupe they had eaten and said they were Rocky Ford cantaloupes, which are grown in the Rocky Ford region of southeastern Colorado. Source tracing of the cantaloupes that ill persons ate indicated that they came from Jensen Farms, of Holly, Colorado, and were marketed as being from the Rocky Ford region. These cantaloupes were harvested in August and September, were distributed widely in the United States, and may still be available in grocery stores.
Laboratory testing by the Colorado Department of Public Health and Environment identified Listeria monocytogenes bacteria on cantaloupes collected from grocery stores and from an ill person’s home. Product traceback information from Colorado state officials indicated these cantaloupes also came from Jensen Farms. FDA is working closely with CDC, the firms involved, and public health authorities in states where illnesses occurred to determine the exact cause of contamination.
CDC advises persons throughout the mainland United States who are at high risk for listeriosis, including older adults, persons with weakened immune systems, and pregnant women, to not eat Rocky Ford cantaloupes from Jensen Farms. Other consumers who want to reduce their risk of Listeria infection should not eat Rocky Ford cantaloupes from Jensen Farms.
Clinical Features/Signs and Symptoms
Listeriosis is a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes. The disease primarily affects older adults, persons with weakened immune systems, pregnant women, and newborns. Rarely, persons without these risk factors can also be affected.
A person with listeriosis usually has fever and muscle aches, often preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has invasive infection (meaning that the bacteria spread from their intestines to their blood stream or other body sites).
Listeriosis is treated with antibiotics. Persons in the high-risk category, including older adults, persons with weakened immune systems, and pregnant women, who experience flu-like symptoms within 2 months after eating contaminated food should seek medical care and tell the physician or health care provider about eating the contaminated food.
The symptoms vary with the infected person:
High-risk persons other than pregnant women: Symptoms can include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions.
Pregnant women: Pregnant women typically experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
Previously healthy persons: People who were previously healthy but were exposed to a very large dose of Listeria can develop a non-invasive illness (meaning that the bacteria have not spread into their blood stream or other body sites). Symptoms can include diarrhea and fever.
If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for persons at high risk for listeriosis.
More general information about listeriosis can be found at the CDC’s Listeriosis webpage.