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BACKGROUND: Listeriosis is caused by Listeria monocytogenes and is associated with significant morbidity and mortality among the elderly, those with weakened immune systems, and pregnant women. During 2014 and early 2015, the Kansas Department of Health and Environment (KDHE) investigated five cases of listerioisis all having hospitalizations at the same hospital prior to onset of illness.
METHODS: Food histories and medical records were obtained from the hospital. A case was defined as laboratory-confirmed Listeria monocytogenes infection in persons with hospital stays prior to their onset of illness from January 2014 to January 2015. Pulsed field gel electrophoresis (PFGE) on human isolates was performed by Kansas Health and Environmental Laboratories (KHEL) and whole genome sequencing (WGS) was performed by the Centers for Disease Control and Prevention (CDC). Kansas Department of Agriculture (KDA) inspected the hospital kitchen. KDHE and KDA, with guidance from Food and Drug Association (FDA), collected environmental samples and samples of ice cream from the hospital. KDA tested food samples, KHEL performed PFGE, and the FDA performed WGS.
RESULTS: Five persons were determined to be cases and all were over 55 years of age. Three deaths were reported. Food history was unknown for one person. Four persons consumed shakes made with Blue Bell ice cream scoops and either chocolate or strawberry ice cream. Four PFGE patterns were identified from five persons, two were indistinguishable and all four were highly related based on WGS. These four human isolates were highly related to isolates from ice cream samples collected during routine testing of ice cream products and samples collected from the production facility. All 22 hospital environmental samples were negative. One of 48 ice cream cups was positive for Listeria monotytogenes; this isolate was unrelated to the five Kansas cases based on PFGE pattern.
CONCLUSIONS: This listeriosis outbreak was associated with consuming shakes made with ice cream from Blue Bell Creameries. Examining hospital food history logs for patients was crucial for identifying a common food exposure. Multiple strains of Listeria monocytogenes from routine product sampling matched the PFGE patterns of human isolates in Kansas and helped to identify the cause of this outbreak. This along with positive product from the hospital led to the recall of multiple ice cream products from two Blue Bell Creamery facilities. The polyclonal nature of this outbreak caused a delay in the detection of this outbreak resulting in additional illnesses. WGS provided useful information in detecting this cluster of listeriosis.