FDA & CDC investigate likely cause of Listeriosis in 4 states

On September 13, 2011, the Centers for Disease Control and Prevention (CDC) announced that they are working with public health officials in several states, including Colorado, and the U.S. Food and Drug Administration (FDA) to investigate a multi-state outbreak of listeriosis.

Listeriosis is a rare and 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.

At least 15 people infected with the outbreak strain of Listeria monocytogenes have been reported in Colorado, Nebraska, Oklahoma and Texas.  All illnesses started on or after August 15, 2011. The number of infected persons identified in each state is as follows: Colorado (11), Nebraska (1), Oklahoma (1), and Texas (2). Listeriosis illnesses in several other states are currently being investigated by state and local health departments to determine if these illnesses are part of this outbreak.

Among persons for whom information is available, illnesses began on or after August 15, 2011. Ages range from 38 to 96 years, with a median age of 84 years old. Most ill persons are over 60 years old or have health conditions that weaken the immune system. Seventy-three percent of ill persons are female. All 15 (100%) patients were hospitalized, and one death has been reported.

Ongoing collaborative investigations by local, state, and federal public health and regulatory agencies indicate the likely source of the outbreak is a type of cantaloupe, called Rocky Ford cantaloupes, which are grown in the Rocky Ford region of southeastern Colorado. These cantaloupes were harvested in August and September, distributed widely in the United States, and are currently available in grocery stores. Ill persons were interviewed about exposures during the month before becoming ill; investigators compared their responses to persons with listeriosis reported through the CDC Listeria Initiative, whose illnesses were not part of this outbreak. Preliminary results strongly suggest that illnesses are linked to consumption of cantaloupes. Several ill persons who remembered the type of cantaloupe said they were Rocky Ford cantaloupes. Product traceback information indicated these cantaloupes were marketed as cantaloupes harvested in the Rocky Ford region.

FDA investigators along with state health officials are working quickly to determine where in the supply chain the contamination most likely occurred and where potentially contaminated product may have been distributed.

Both FDA and state public health officials have collected product and environmental samples. Laboratory testing is underway.

A person with listeriosis usually has fever and muscle aches. Almost everyone who is diagnosed with listeriosis has “invasive” infection, in which the bacteria spread beyond the gastrointestinal tract.

Listeriosis can be fatal, especially in certain high-risk groups. These groups include older adults, people with compromised immune systems and certain chronic medical conditions (such as cancer). In pregnant women, listeriosis can cause miscarriage, stillbirth, and serious illness or death in newborn babies, though the mother herself rarely becomes seriously ill.

As FDA’s investigation continues, the agency will provide updates as warranted.

People who think they might have become ill should consult their doctor.