Multistate Outbreak of Listeriosis Linked to Soft Cheeses Distributed by Karoun Dairies, Inc. (Final Update)

Final Case Count Update

Since the last update on September 23, 2015, six more people infected with one of the closely related Listeria strainswere identified using whole genome sequencing. These illnesses occurred in 2010 (3), 2012 (2), and 2015 (1). These illnesses have been added to the total case count.

Thirty people infected with one of the closely related Listeria strainswere reported from 10 states since June 16, 2010. The number of ill people reported from each state was as follows: California (18), Colorado (1), Illinois (2), Massachusetts (2), Michigan (1), New York (2), Ohio (1), Tennessee (1), Virginia (1), and Washington (1).

Dates of Listeria specimen collection ranged from June 16, 2010 to August 24, 2015. Ill people ranged in age from less than 1 year to 92, and the median age was 73. Seventy percent of ill people were female. Twenty-eight (93%) of 30 ill people for whom information was available reported being hospitalized. Six of the illnesses were pregnancy-related, and one illness resulted in a fetal loss. Three deaths were reported from California (2) and Ohio (1).

Investigation Update

Epidemiologic and laboratory information indicates that soft cheeses distributed by Karoun Dairies are the likely source of this outbreak. This investigation is ongoing.

State and local health departments continue to interview ill people about the foods they may have eaten or other exposures in the month before their illness began. Sixteen (67%) of 24 people with available information are of Middle Eastern or Eastern European descent or shopped at Middle Eastern or Eastern European-style markets. Of 23 ill people for whom information is available, 19 (83%) consumed soft cheese, and 18 (95%) reported eating Middle Eastern, Eastern European, Mediterranean, or Mexican-style cheeses, including ani, feta (e.g., Bulgarian feta), kefir cheese, Middle Eastern-style string cheese, nabulsi, and village cheese. Four of seven ill people who specified the brand of cheese eaten reported brands distributed by Karoun Dairies. An additional ill person was unable to name the brand of cheese eaten, but described the packaging and label of a Karoun product. No other brand of soft cheese was reported more than once.

FDA isolated Listeria monocytogenes from two environmental samples collected in September 2015 from the Central Valley Cheese, Inc. manufacturing facility in Turlock, California. Central Valley Cheese, Inc. manufactures cheese for Karoun Dairies. Whole genome sequencing showed that these isolates are closely related genetically to isolates from ill people. In addition, whole genome sequencing showed that five Listeria isolates collected in 2010 from the same facility are also closely related genetically to isolates from ill people.

CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill people and to interview them. Updates will be provided when more information is available.

Initial Announcement

CDC is collaborating with public health officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Listeria monocytogenes infections (listeriosis). Listeria can cause a serious, life-threatening illness.

Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA “fingerprinting” is performed on Listeria bacteria isolated from ill people by using techniques called pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. WGS gives a more detailed DNA fingerprint than PFGE. In the current outbreak, this additional detail was important. Five rare PFGE fingerprints of Listeria are included in this investigation. The sequencing showed that the Listeria strains with the five rare PFGE fingerprints are closely related genetically.

Twenty-four people infected with one of the closely related Listeria strains have been reported from nine states since August 8, 2010. The number of ill people reported from each state is as follows: California (14), Colorado (1), Illinois (1), Massachusetts (2), Michigan (1), New York (2), Ohio (1), Tennessee (1), and Washington (1).

Dates of Listeria specimen collection range from August 8, 2010 to August 24, 2015. The cluster was first identified in August 2015 after investigators saw an increase in one of the five rare PFGE  fingerprints reported to PulseNet. WGS found that the four other PFGE fingerprints were closely related genetically to the first PFGE fingerprint. Illnesses associated with those PFGE fingerprints were added to the investigation, including illnesses that occurred over 5 years ago. Additional illnesses are under investigation.

Ill people range in age from less than 1 year to 92, and the median age is 77. Seventy-five percent of ill people are female. Twenty-one (91%) of 23 ill people for whom information is available reported being hospitalized. Five of the illnesses were pregnancy-related, and one illness resulted in a fetal loss. One death was reported from Ohio.

The outbreak can be illustrated with a chart showing the number of persons who were diagnosed each day. This chart is called an epidemic curve or epi curve.

Investigation of the Outbreak

The investigation has not conclusively identified the source of this outbreak, but most ill people interviewed reported eating soft cheese before becoming ill. The investigation is ongoing.

State and local health departments are interviewing ill people about the foods they may have eaten or other exposures in the month before their illness began. Fifteen (63%) of 24 people with available information are of Middle Eastern or Eastern European descent or shopped at Middle Eastern-style markets. Of 22 ill people for whom information is available, 18 (82%) consumed soft cheeses, and 16 (89%) reported eating Middle Eastern, Eastern European, Mediterranean, or Mexican-style cheeses, including ani, feta (including Bulgarian feta), Middle Eastern-style string cheese, and nabulsi. Four (57%) of seven ill people who specified the brand of cheese eaten reported brands distributed by Karoun Dairies. No other brand of cheese was reported more than once.

On September 16, 2015, Karoun Dairies, Inc. voluntarily recalled [PDF – 2 pages] and ceased production of certain cheeses that the company distributes due to possible contamination with Listeria. The recall includes several brands and types of cheeses that were distributed to retail outlets in the United States. Products were sold under the following brands: Karoun, Arz, Gopi, Queso Del Valle, Central Valley Creamery, and Yanni. Products are vacuum packed, in jars or in pails. Weights vary from 5 ounces to 30 pounds. A full list of cheeses is available on the Advice to Consumers, Restaurants, and Retailers page.

CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill people and to interview them. Updates will be provided when more information is available.