Introduction

This was a complex multistate outbreak investigation of listeriosis cases occurring over several years. Public health investigators used the PulseNet system to identify illnesses that were 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 of enteric illness. Several PFGE patterns (strains) of Listeria were involved in this outbreak.

A total of 10 people infected with several strains of Listeria were reported from 4 states: Arizona (1), Kansas (5), Oklahoma (1), and Texas (3). Illness onset dates ranged from January 2010 through January 2015. The people with illness onsets during 2010–2014 were identified through a retrospective review of the PulseNet database for DNA fingerprints matching isolates collected from Blue Bell ice cream samples. All 10 (100%) people were hospitalized. Three deaths were reported from Kansas.

Investigation of the Outbreak

February 2015

In February 2015, the South Carolina Department of Health and Environmental Control isolated Listeria as part of routine sampling from Blue Bell brand single-serving ice cream products collected from a distribution center: 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, that made these products. Testing by Texas health officials yielded Listeria isolates from some samples of the same two products tested by South Carolina and from another Blue Bell ice cream product called “Scoops.” This product was made on the same production line as the Chocolate Chip Country Cookie Sandwiches and Great Divide Bars. PFGE was performed on the Listeria isolated from the ice cream samples; seven different PFGE patterns were identified and uploaded to PulseNet.

March 2015

In March 2015, Kansas health officials identified two people from the same hospital who were infected with Listeria bacteria that had the same PFGE pattern. Three additional listeriosis cases with three other PFGE patterns had previously been identified from the same hospital. All five people were hospitalized for unrelated problems before developing invasive listeriosis — a finding that strongly suggested their infections were acquired in the hospital. Listeria isolates from four of the five people had PFGE patterns that were also identified in ice cream tested by South Carolina and Texas. Although some of the illnesses occurred more than a year before this investigation began, all four people with available information consumed milkshakes made with the “Scoops” Blue Bell ice cream product while they were in the hospital. Isolates from four of these people were highly related to each other by whole genome sequencing. Listeria isolated from the fifth person was not related to isolates from the other four ill people. In addition, the PFGE pattern was not identified in any ice cream samples. However, this person was part of a recognized illness cluster at the hospital and consumed milkshakes made with “Scoops” while hospitalized. As a result, this person was included as a case in the outbreak. Illness onset dates for the five people ranged from January 2014 through January 2015. Three of these people died as a result of their Listeria infection.

On March 13, 2015, Blue Bell Creameries reported removing the “Scoops” ice cream product and other products made on the same production line from the market. The company also reported that it had shut down that production line at its Brenham, Texas, facility.

On March 22, 2015, the Kansas Department of Health and Environment (KDHE) reported that Listeria was isolated from a previously unopened, single-serving Blue Bell brand 3 oz. institutional/food service chocolate ice cream cupExternal collected from the Kansas hospital involved in the outbreak. Samples of Blue Bell brand 3 oz. institutional/food service chocolate ice cream cups collected from the company’s Broken Arrow, Oklahoma, facilityExternal also yielded Listeria. Listeria isolated from ice cream cup samples were indistinguishable from each other by PFGE, but were different from those isolated from people in Kansas and from other Blue Bell brand ice cream products previously sampled in Texas and South Carolina. On March 23, 2015, Blue Bell announced a recallExternal of 3 oz. institutional/food service ice cream cups (with tab lids) of several flavors produced at the company’s Broken Arrow, Oklahoma, facilityExternal .

April 2015

On April 3, 2015, CDC reported that illnesses might be linked to ice cream made in Blue Bell Creameries’ Oklahoma facility, but lacked sufficient information to include them as cases in the outbreak at the time. These illnesses were identified when investigators searched the PulseNet database and identified 6 people from Arizona (1), Oklahoma (1), and Texas (4) with listeriosis between 2010 and 2014 who had Listeria isolates with PFGE patterns indistinguishable from isolates from the chocolate ice cream cups made in the Broken Arrow, Oklahoma, facility. The four people reported from Texas were hospitalized for unrelated problems before developing listeriosis. Information available for one person indicated that they consumed ice cream in a Texas hospital before developing listeriosis; the Texas Department of State Health Services reported that the hospital had received Blue Bell brand ice cream cups. None of the four people in Texas died from Listeria infection. At this point in the investigation, CDC recommended that consumers not eat and institutions and retailers not serve any products made at the company’s Oklahoma facility, in addition to any previously recalled or withdrawn products. That day, Blue Bell Creameries reported that they had voluntarily suspended operations at their facility in Oklahoma.

On April 8, 2015, CDC reported that whole genome sequencing confirmed that three of the four isolates from people in Texas were nearly identical to Listeria strains isolated from ice cream produced at Blue Bell Creameries’ Oklahoma facility. These three people were added to the case count for the outbreak, bringing the total to 8. The fourth isolate was later determined not to be part of the outbreak by whole genome sequencing and this illness was not added to the case count.

On April 20, 2015, Blue Bell Creameries voluntarily recalledExternal all products currently on the market made at all of its facilities, including ice cream, frozen yogurt, sherbet, and frozen snacks.Blue Bell announced this recall after sampling by the company revealed that Chocolate Chip Cookie Dough Ice Cream half gallons produced on March 17, 2015, and March 27, 2015, contained Listeria.

On April 21, CDC reported that whole genome sequencing confirmed that the people from Arizona (1) and Oklahoma (1) were part of the outbreak, bringing the total case count to 10.

May 2015

On May 7, 2015, FDA released the findings from recent inspections at the Blue Bell production facilities in Brenham, Texas Cdc-pdf [PDF – 4 pages]External ; Broken Arrow, Oklahoma Cdc-pdf [PDF – 11 pages]External ; and Sylacauga, Alabama Cdc-pdf [PDF – 5 pages]External .

This outbreak investigation is over. However, people could continue to get sick because recalled products may still be in people’s freezers and consumers unaware of the recalls could eat them. Institutions should not serve and retailers should not sell recalled products. These products are frozen, so consumers, institutions, and retailers should check their freezers. Read the Advice to Consumers, Institutions, and Retailers.