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Multistate Outbreak of Listeriosis Linked to Imported Frescolina Brand Ricotta Salata Cheese

Posted September 11, 2012 9:15 PM ET

At a Glance:

Latest Case Count Map
Latest Epi Curve


Initial Announcement

September 11, 2012

CDC is collaborating with public health and regulatory officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Listeria monocytogenes infections (listeriosis). Joint investigation efforts indicate that ricotta salata cheese is the likely source.  

Public health investigators are using DNA “fingerprints” of Listeria obtained through diagnostic testing with pulsed-field gel electrophoresis, or PFGE, to identify cases of illness that may be part of this outbreak. They 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 14 persons infected with the outbreak strain of Listeria monocytogenes have been reported from 11 states and the District of Columbia. The number of ill people identified in each location is as follows: California (1), Colorado (1), District of Columbia (1), Maryland (3), Minnesota (1), Nebraska (1), New Jersey (1), New Mexico (1), New York (1), Ohio (1), Pennsylvania (1), and Virginia (1).

Among persons for whom information is available, dates that illness was diagnosed range from March 28, 2012 to August 30, 2012. All 14 ill persons were hospitalized. Four of the illnesses were related to a pregnancy; two of these were diagnosed in newborns. The other 10 ill persons ranged in age from 56 years to 87 years, with a median age of 79 years, and 55% were female. No fetal losses have been reported. Three deaths have been reported; one each in Minnesota, Nebraska, and New York. Listeriosis contributed to at least one of the deaths in Nebraska and New York, but did not contribute to the death in Minnesota.

The outbreak can be visually described with a chart showing the number of persons who were diagnosed each day. This chart is called an epidemic curve or epi curve. Clinical specimens that were collected after August 26, 2012 might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported.

About 800 laboratory-confirmed cases of listeriosis are reported each year in the United States and typically 3 or 4 outbreaks are identified and reported to CDC. Some foods that have been linked to outbreaks in recent years are Mexican-style soft cheeses, cantaloupe, sprouts, celery, and ready-to-eat deli meat. 

Investigation of the Outbreak

Epidemiologic, laboratory, and traceback investigations conducted by officials in local, state, and federal public health, agriculture, and regulatory agencies indicate that imported Frescolina brand ricotta salata cheese distributed by Forever Cheese, Inc. is the likely source of this outbreak of listeriosis. In interviews, ill persons answered questions about foods consumed and other exposures in the month before becoming ill. Twelve (86%) of 14 ill persons interviewed reported consuming a soft cheese. All six ill persons who could provide information about packaging of cheeses reported consuming cheese that had been cut and repackaged at a retail location. The investigation is complex because ill persons reported consuming many different cheeses from many different retail locations. No one cheese was reported by the majority of ill persons, suggesting that cross-contamination of other cheeses through cutting boards and utensils may have played a role. The investigation focused on identifying intact cheeses shipped to multiple retail locations where ill persons purchased cut and repackaged cheese.

FDA identified the outbreak strain of Listeria monocytogenes bacteria in a sample of uncut imported Frescolina brand ricotta salata cheese distributed by Forever Cheese, Inc. FDA is working closely with CDC, the firm involved, and public health authorities in states where illnesses occurred to determine the exact cause of contamination.

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