Multistate outbreak of listeriosis caused by imported cheese and evidence of cross-contamination of other cheeses, USA, 2012

Abstract

Listeria monocytogenes is a foodborne pathogen that can cause bacteraemia, meningitis, and complications during pregnancy. In July 2012, molecular subtyping identified indistinguishable L. monocytogenes isolates from six patients and two samples of different cut and repackaged cheeses. A multistate outbreak investigation was initiated. Initial analyses identified an association between eating soft cheese and outbreak-related illness (odds ratio 17·3, 95% confidence interval 2·0-825·7) but no common brand. Cheese inventory data from locations where patients bought cheese and an additional location where repackaged cheese yielded the outbreak strain were compared to identify cheeses for microbiological sampling. Intact packages of imported ricotta salata yielded the outbreak strain. Fourteen jurisdictions reported 22 cases from March-October 2012, including four deaths and a fetal loss. Six patients ultimately reported eating ricotta salata; another reported eating cheese likely cut with equipment also used for contaminated ricotta salata, and nine more reported eating other cheeses that might also have been cross-contaminated. An FDA import alert and US and international recalls followed. Epidemiology-directed microbiological testing of suspect cheeses helped identify the outbreak source. Cross-contamination of cheese highlights the importance of using validated disinfectant protocols and routine cleaning and sanitizing after cutting each block or wheel.

Determination of Evolutionary Relationships of Outbreak-Associated Listeria monocytogenes Strains of Serotypes 1/2a and 1/2b by Whole-Genome Sequencing

“…This data set comprises 52 genomes for isolates of serotypes 1/2a and 1/2b and phylogenetically related serotypes (1/2c and 3). These 52 genomes include 20 outbreak-associated isolates representing 11 outbreaks and isolates from clinical, food, and environmental sources, for example, one isolate from an implicated production facility (ricotta salata) that matched a human case (12). We also included 17 additional genome sequences from isolates of serotypes 4b, 4d, and 4e to root the phylogenetic tree.…”

Utilization of Foxtail Millet Starch Film Incorporated with Clove Leaf Oil for the Packaging of Queso Blanco Cheese as a Model Food

“…Listeria monocytogenes, in particular, is frequently known to contaminate fresh cheese products, such as queso blanco cheese during their processing and post‐processing . It has been reported that L. monocytogenes can grow in commercial cheese products wrapped with polyethylene (PE) or low density polyethylene (LDPE) . In addition, cheese products without food preservatives such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) can be easily oxidized during storage …”

Infectious Dose ofListeria monocytogenesin Outbreak Linked to Ice Cream, United States, 2015

“…We estimate that 1 of 10,000 milkshakes would have a load >26,000 L. monocytogenes cells (95% CrI 15,600–240,000 L. monocytogenes cells). Assuming there was no initial contamination of the milkshake machines and no growth of the pathogen in the milkshakes, the mean contamination level of L. monocytogenes in the milkshakes (8 cells/g of ice cream) was relatively low compared with contamination levels in some other outbreaks ( 9 – 12 ). However, in the absence of leftovers from the actual implicated milkshakes, we cannot rule out the possibility that the 4 susceptible patients received some of the highest contaminated products from the factory line, triggering infection.…”