For risk modelling nerds: Deli meat

Fun observation: Most people think it’s safer to buy deli meat or cold cuts, fresh at the counter, than the pre-packaged stuff, which is probably safer because it contains antimicrobials (in the U.S.) and doesn’t come into contact with all that slicer shit at the deli counter.

Follow up: What’s the difference between a clean and a deep clean? Phallic hyperbole.

Ready-to-eat (RTE) deli meats sliced at retail are predicted to cause 83% of deli meat-associated listeriosis cases annually. While Listeria monocytogenes is commonly found in delis, environmental prevalence varies by store (0–40%).

A deep clean sanitation standard operating procedure (SSOP) executed by a third-party cleaning service immediately reduced L. monocytogenes prevalence in delis, but reductions were not sustained over time. The purpose of this study was to assess the efficacy of a L. monocytogenes predictive risk model and a subsequent deep-clean SSOP (deep clean) conducted by store employees and management complemented with training and facilities improvements all aimed to reduce L. monocytogenes prevalence in stores with known high L. monocytogenes prevalence and evidence of persistence.

Fifty delis among six states were screened using a predictive logistic regression model that estimates the probability of high L. monocytogenes prevalence in a deli. The model identified 13 stores with potentially high L. monocytogenes prevalence; seven stores were confirmed and enrolled for further study. Retail employees executed deep clean; additional interventions (e.g., facilities improvements, training) were incorporated in stores. Environmental samples (n = 20) were collected immediately before and after, and for six months post-deep clean. Deep cleans immediately reduced L. monocytogenes prevalence in six of seven stores tested.

A total of 21/138 (15.2%) samples before and 8/139 (5.8%) samples after deep-cleaning were positive for L. monocytogenes, with a marginal 16.0% decrease on non-food-contact surfaces (NFCS) immediately after deep clean (p = 0.0309, αadj = 0.0125) and a marginal 10.8% on NFCS during follow-up (p = 0.0337, αadj = 0.0125). Employee executed deep cleans with training, education, and maintenance programs can reduce environmental L. monocytogenes prevalence in retail delis, a pivotal part of preventing subsequent cross-contamination to RTE deli meats.

Predictive risk models combined with employee-and management-implemented SSOPs identified and reduced listeria monocytogenes prevalence in retail delis

Food Control

Sophie Tongyu Wua1, Susan R.Hammonsa1m Jingjin Wanga, Clara Assisia, Brittany DiPietrob, Haley F.Olivera

About those assumptions: The problem with models

This is the stuff that friend-of-the-barfblog Don Schaffner gets excited about: Modelling.

Belgian researchers attempted to predict future rates of specific foodborne illnesses to guide policy efforts and came up with this:

Salmonellosis, campylobacteriosis and listeriosis are foodborne diseases. We estimated and forecasted the number of cases of these three diseases in Belgium from 2012 to 2020, and calculated the corresponding number of disability-adjusted life years (DALYs). The salmonellosis time series was fitted with a Bai and Perron two-breakpoint model, while a dynamic linear model was used for campylobacteriosis and a Poisson autoregressive model for listeriosis.

The average monthly number of cases of salmonellosis was 264 (standard deviation (SD): 86) in 2012 and predicted to be 212 (SD: 87) in 2020; campylobacteriosis case numbers were 633 (SD: 81) and 1,081 (SD: 311); listeriosis case numbers were 5 (SD: 2) in 2012 and 6 (SD: 3) in 2014.

After applying correction factors, the estimated DALYs for salmonellosis were 102 (95% uncertainty interval (UI): 8–376) in 2012 and predicted to be 82 (95% UI: 6–310) in 2020; campylobacteriosis DALYs were 1,019 (95% UI: 137–3,181) and 1,736 (95% UI: 178–5,874); listeriosis DALYs were 208 (95% UI: 192–226) in 2012 and 252 (95% UI: 200–307) in 2014.

New actions are needed to reduce the risk of foodborne infection with Campylobacter spp. because campylobacteriosis incidence may almost double through 2020.

Burden of salmonellosis, campylobacteriosis, and listeriosis: a time series analysis



Maertens de Noordhout et al.

An avirulent Salmonella to better understand outbreaks on produce

Recurrent outbreaks of bacterial gastroenteritis linked to the consumption of fresh fruits and vegetables highlight the paucity of understanding of the ecology of Salmonella enterica under crop production and postharvest conditions.

tomatoThese gaps in knowledge are due, at least in part, to the lack of suitable surrogate organisms for studies for which biosafety level 2 is problematic. Therefore, we constructed and validated an avirulent strain of Salmonella enterica serovar Typhimurium.

The strain lacks major Salmonella pathogenicity islands SPI-1, SPI-2, SPI-3, SPI-4, and SPI-5 as well as the virulence plasmid pSLT. Deletions and the absence of genomic rearrangements were confirmed by genomic sequencing, and the surrogate behaved like the parental wild-type strain on selective media. A loss-of-function (phoN) selective marker allowed the differentiation of this strain from wild-type strains on a medium containing a chromogenic substrate for alkaline phosphatase. Lack of virulence was confirmed by oral infection of female BALB/c mice. The strain persisted in tomatoes, cantaloupes, leafy greens, and soil with the same kinetics as the parental wild-type and selected outbreak strains, and it reached similar final population levels. The responses of this strain to heat treatment and disinfectants were similar to those of the wild type, supporting its potential as a surrogate for future studies on the ecology and survival of Salmonella in production and processing environments.


There is significant interest in understanding the ecology of human pathogens in environments outside of their animal hosts, including the crop production environment. However, manipulative field experiments with virulent human pathogens are unlikely to receive regulatory approval due to the obvious risks. Therefore, we constructed an avirulent strain of S. enterica serovar Typhimurium and characterized it extensively.

Development of an avirulent Salmonella surrogate for modeling pathogen behavior in pre- and postharvest environments

Marcos H. de Moraes a, Travis K. Chapin b, Amber Ginn c, Anita C. Wright c, Kenneth Parker a, Carol Hoffman d, David W. Pascual d, Michelle D. Danyluk b and Max Teplitski a

A Soil and Water Science Department, Genetics Institute, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), Gainesville, Florida, USA

B Department of Food Science and Human Nutrition, Citrus Research and Education Center, UF/IFAS, Lake Alfred, Florida, USA

C Department of Food Science and Human Nutrition, UF/IFAS, Gainesville, Florida, USA

D Department of Infectious Diseases and Pathology, University of Florida, Gainesville, Florida, USA

Applied and Environmental Microbiology, Volume 82, Number 14, July 2016, Pages 4100-4111, doi:10.1128/AEM.00898-16

Predictive models to estimate Listeria spp. growth on baby spinach leaves

Leafy vegetables such as spinach may be contaminated with Listeria monocytogenes during pre-harvest and postharvest management.

listeria.spinachRecent Listeriosis outbreaks associated to contaminated leafy vegetables have marked the need for technologies to minimize safety issues in fresh and fresh-cut produce.

US scientists at Texas A&M University have studied the effectiveness of washing treatments as a postharvest practice to minimize the growth of the pathogen and L. innocua on fresh baby spinach leaves under different storage temperatures and to evaluate the feasibility of using L. innocua as a surrogate to the pathogen. The objectives of the study were:

1. to determine the response of L. monocytogenes and L. innocua to different washing treatments with or without chlorine (200 mg/L) at room temperature (∼22°C);

2. to assess the effect of natural microbiota load on growth of both microorganisms at different storage temperatures, from 5 to 36°C;

3. to validate the use of L. innocua as a surrogate of L. monocytogenes for further studies with fresh baby spinach leaves.

Scientists developed predictive models to investigate the effect of simulated storage temperature on the growth patterns of L. monocytogenes and L. innocua.

Results showed that each microorganism had a different significant response to the type of washing treatment at room temperature and the pathogen was harder to remove from the leaves than the L. innocua was.

Although, the natural microflora on fresh baby spinach leaves affected the growth parameters (Maximum grow rate, lag time, maximum population density) for both bacteria, the effect was not significant. Thus, in the specific case of spinach leaves, the study shows that L. innocua may be a suitable surrogate for L. monocytogenes in growth studies.

Growth data for L. monocytogenes and L. innocua on fresh baby spinach leaves at 5–36 °C were modelled using the Baranyi and Ratkowsky (secondary) models which were validated by comparing the root mean square error (RMSEs) and biases between the growth data and model predictions. The secondary models showed good agreement between observed and predicted values.

The validation results show that these models could provide reliable estimates for growth of L. monocytogenes and L. innocua as a function of temperature. These models may be used by processors to evaluate the impact of postharvest practices such as storage and washing on the growth of Listeria in baby spinach leaves evaluated in this study. These models can provide useful input to quantitative risk assessment models.

Basri Omac, Rosana G. Moreira, Alejandro Castillo, Elena Castell-Perez, “Growth of Listeria monocytogenes and Listeria innocua on fresh baby spinach leaves: Effect of storage temperature and natural microflora”, 2015, Postharvest Biology and Technology, Vol. 100, 41–51.