March 13, 2015
State and local health officials, CDC, and FDA are collaborating to investigate an outbreak of Listeria monocytogenes infections (listeriosis). The joint investigation found that certain Blue Bell brand ice cream products are the likely source for some or all of these illnesses. 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 using techniques called pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). WGS gives a more detailed DNA fingerprint than PFGE. PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks.
The five ill people included in this outbreak investigation have been reported from Kansas and were each infected with one of four strains of Listeria monocytogenes identified by PFGE. All five people were hospitalized at the same hospital for unrelated problems before developing invasive listeriosis — a finding that strongly suggests their infections were acquired in the hospital. Isolates from four of these patients are highly related by whole genome sequencing. Illness onset dates for the five patients ranged from January 2014 through January 2015. Although some illnesses occurred more than a year ago, the cluster was identified in March 2015 after health officials noted that two patients who had been in the same hospital were infected with Listeria monocytogenes bacteria that were indistinguishable by PFGE. All five ill people are older adults, and three are women. Three deaths have been reported.
Investigation of the Outbreak
The information available at this time indicates that certain Blue Bell brand ice cream products are the likely source of this outbreak. Listeria can cause a serious, life-threatening illness. Of the four ill people for whom information is available on the foods eaten in the month before Listeria infection, all four consumed milkshakes made with a single-serving Blue Bell brand ice cream product called “Scoops” while they were in the hospital.
In an unrelated investigation, the South Carolina Department of Health and Environmental Control isolated Listeria monocytogenes from the following Blue Bell brand single-serving ice cream products collected from a distribution center in 2015: Chocolate Chip Country Cookie Sandwiches and Great Divide Bars. In response to the findings in South Carolina, the Texas Department of State Health Services collected product samples from the Blue Bell Creameries production facility in Brenham, Texas. These samples yielded Listeria monocytogenes from the same two products tested by South Carolina and also from the ice cream Scoops, which is made on the same production line. Listeria monocytogenes was not found in other Blue Bell brand ice cream products tested.
Three strains of Listeria monocytogenes isolated from the ice cream samples had PFGE patterns that were indistinguishable from those of Listeria bacteria obtained from samples from four patients. Listeria monocytogenes isolates with four other PFGE patterns were also isolated from the ice cream samples. Invoices provided by the hospital to the Kansas Department of Health and Environment indicate that the Blue Bell brand ice cream Scoops used in the patients’ milkshakes came from Blue Bell Creamery’s facility in Texas. Whole genome sequencing of the Listeria monocytogenes isolates obtained from the ice cream is in progress.
One patient’s Listeria monocytogenes strain has a PFGE pattern that does not match any identified in an ice cream sample. However, epidemiologic evidence, including acquiring infection at the same hospital as the other patients and consumption of the ice cream products, suggests that this illness may be related. CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify any additional ill persons whose illnesses may be related to this outbreak.
Blue Bell Creameries has reported removing from the market the Scoops ice cream product and other products made on the same production line. The company also has reported that it has shut down that production line.
Contaminated ice cream products may still be in the freezers of consumers, institutions, and retailers, given that these products can have a shelf life of up to 2 years. CDC recommends that consumers do not eat products that Blue Bell Creameries removed from the market, and institutions and retailers should not serve or sell them. A detailed list of products is available on the Advice page . State and local health officials, CDC, and FDA continue to work closely on this investigation, and new information will be provided on this website as it becomes available.