Europe assesses the risk of Salmonella and Norovirus in leafy greens

Rainfall, use of contaminated water for irrigation or contaminated equipment are among the factors that cause contamination of leafy greens with Salmonella and Norovirus. These are some of the findings of EFSA’s latest opinion on risk factors that contribute to the contamination of leafy greens at different stages of the food chain. The BIOHAZ Panel has lettuce.skull.e.coli.O145recommended that producers use good agricultural, hygiene and manufacturing practices to reduce contamination. The Panel has also proposed specific microbiological criteria at primary production.

Leafy greens eaten raw as salads are minimally processed and widely consumed foods. Risk factors for leafy greens contamination by Salmonella spp. and Norovirus were considered in the context of the whole food chain including agricultural production and processing. Available estimates of the prevalence of these pathogens (together with the use of Escherichia coli as an indicator organism) in leafy greens were evaluated. Specific mitigation options relating to contamination of leafy greens were considered and qualitatively assessed. It was concluded that each farm environment represents a unique combination of numerous characteristics that can influence occurrence and persistence of pathogens in leafy greens production. Appropriate implementation of food safety management systems, including Good Agricultural Practices (GAP), Good Hygiene Practices (GHP) and Good Manufacturing Practices (GMP), should be primary objectives of leafy green producers. The relevance of microbiological criteria applicable to production, processing and at retail/catering were considered. The current legal framework does not include microbiological criteria applicable at primary production which will validate and verify GAP and GHP. It is proposed to define a criterion at primary production of leafy greens which is designated as Hygiene Criterion, and E. coli was identified as suitable for this purpose.

A Process Hygiene Criterion for E. coli in leafy green packaging plants or fresh cutting plants was considered and will also give an indication of the degree to which GAP, GHP, GMP or HACCP programs have been implemented. A Food Safety Criterion for Salmonella in leafy greens could be used as a tool to communicate to producers and processors that Salmonella should not be present in the product. Studies on the prevalence and infectivity of Norovirus are limited, and quantitative data on viral load are scarce making establishment of microbiological criteria for Norovirus on leafy greens difficult.

MIT phage-based bacterial detection for produce

Ever wonder why fruits and vegetables sometimes hit the shelves contaminated by pathogenic bacteria such as listeria, E. coli, and salmonella?

According to Tim Lu, an assistant professor of electrical engineering and biological engineering at MIT, it boils down to the inefficient bacteria-750px-PhageExterior.svgdetection assays used in the food industry. In some cases, these aren’t accurate or speedy enough — sometimes taking several days to catch contaminated produce.

But now Lu’s startup, Sample6, is commercializing an advanced assay platform that “lights up” pathogenic bacteria for quick detection, with the ability to detect only a few bacteria. 

Based on Lu’s graduate school research at MIT, the assay uses biological particles called bacteriophages, or phages, which only target bacteria. In Sample6’s case the assay is engineered to inject pathogenic bacteria — specifically, listeria — with an enzyme that reprograms the bacteria to shine very brightly.  

To use the commercial assay, called the Bioillumination Platform, factory workers simply swab samples with a sponge, wait for the phages to do their work, and run the sample through a machine that detects any light emitted. Results can be plugged into the company’s software, which tracks contaminated products and can provide analytics on whether contamination correlates with certain days, people, or suppliers.  

Careful with that poop; stricter controls of wastewater reuse on crops needed to meet WHO guidelines

Wastewater used to irrigate agricultural crops in countries where water is scarce may contribute to significant public health risks such as diarrheal disease in children from rotavirus. A new study of these risks found that wastewater used to irrigate vegetable plots in Asian countries poses health risks that may exceed World Health Organization (WHO) wastewater.veg.chinaguidelines. The authors recommend that stricter wastewater regulation may be needed to protect the health of farmers and consumers worldwide.

The new findings come at a time when climate change and increasing population pressure requires the development of methods to produce more food with fewer irrigation resources. Wastewater reuse is an economical method to grow food, but wastewater carries microorganisms such as viruses, bacteria and protozoa that can contaminate food and cause disease. Asia accounts for the majority of the world’s reuse of wastewater in irrigation, and given that China is the world’s most populous country, millions of people may be exposed to health risks from contamination. However, normal cooking temperatures and food preservation strategies can reduce the risks posed by microorganisms and viruses.

Although health studies can trace the incidence of disease in a population, conducting extensive experimental work and collecting sufficient data can be cost-prohibitive. Food systems researchers Hoi-Fei Mok and Andrew J. Hamilton of The University of Melbourne in Australia instead created a statistical model to characterize the health risks posed by wastewater used to grow Asian vegetables. The reach of the Asian vegetable market extends well beyond Asia. Their paper, “Exposure factors for wastewater-irrigated Asian vegetables and a probabilistic rotavirus disease burden model for their consumption,” recently appeared in the electronic version of the journal Risk Analysis, published by the Society for Risk Analysis.

The researchers first determined the volume of water retained by three commonly grown Asian vegetables, and then used a statistical model to estimate rotavirus disease burdens associated with wastewater irrigation. Rotavirus is associated with diarrheal disease in children, and was chosen as the focus of the study because diarrheal disease is associated with 74 percent of wastewater-related deaths, 90 percent of which occur in children. According to the WHO, diarrheal disease is the second leading global cause of death in children under five years old, and is responsible for the deaths of approximately wastewater.china760,000 children each year. Diarrhea can last several days, and can leave the body without the water and salts that are necessary for survival. Most people who die from diarrhea actually die from severe dehydration and fluid loss.

Based on their findings, the researchers concluded that the probability curves of the annual disease burden “exceeded the WHO’s threshold for acceptable level of risk from wastewater reuse by two to three orders of magnitude.” Some vegetables posed greater risk than others, because leaf shape affects the amount of wastewater and contaminants that are retained. Vegetables such as bok choy posed the least risk and choy sum the greatest risk, whereas lettuce and gai lan had similar risk profiles. The viral decay rate also varies depending on the plant. The authors say that more research on the rate of viral decay on various crops would increase the accuracy of risk estimations.

The probability of rotavirus infection is affected by uncertainty in virus concentration and variation in vegetable consumption. For example, the mean daily per capita lettuce consumption in Australia is 21.81 grams lettuce/person day, compared to a mean of 171.94 grams lettuce / person day in China, although there is seasonal variation in consumption patterns.

The dose-response model, which characterizes the relationship between exposure level to contaminants and the probability of developing disease, is a source of uncertainty in the risk assessment. The rotavirus infection rates were based on data from an infectivity trial in adults, but rotavirus primarily affects children. Lower doses induce infectivity in children faster than adults, so the estimated disease burdens from the researchers’ statistical model may underestimate the actual risk to children. Collecting rotavirus infectivity data for children would improve the accuracy of risk assessments of the threat.

Although there are Chinese national standards and regulations for the reuse of wastewater, they present only threshold concentrations for bacteria such as E. coli, not viruses. Furthermore, while there are regulations relating to water quality, there is no guideline for risk management around wastewater reuse in China. The risk management approach involves more pro-active identification and management of risk, rather than relying on post-treatment testing for managing reuse schemes. Considering the global increase in wastewater use for agricultural irrigation, assessing the health risks from reuse schemes is necessary to develop better wastewater management policies to protect public health. 

Prevalence of shiga-toxin producing E. coli, Salmonella enterica, and Listeria monocytogenes

There’s a lot of STECs out there.

Cooley et al report in Frontiers that, produce contaminated with enteric pathogens is a major source of foodborne illness in the United States. Lakes, streams, rivers, and ponds were sampled with Moore swabs bi-monthly for over 2 years at 30 locations in the vicinity of a leafy green growing region on the Central California Coast and screened for Shiga toxin producing Escherichia coli (STEC), Salmonella enterica, and Listeria monocytogenes lettuceto evaluate the prevalence and persistence of pathogen subtypes. The prevalence of STEC from 1386 samples was 11%; 110 samples (8%) contained E. coli O157:H7 with the highest prevalence occurring close to cattle operations. Non-O157 STEC isolates represented major clinical O-types and 57% contained both shiga toxin types 1 and 2 and intimin. Multiple Locus Variable Number Tandem Repeat Analysis of STEC isolates indicated prevalent strains during the period of study. Notably, Salmonella was present at high levels throughout the sampling region with 65% prevalence in 1405 samples resulting in 996 isolates with slightly lower prevalence in late autumn. There were 2, 8, and 14 sites that were Salmonella-positive over 90, 80, and 70% of the time, respectively. The serotypes identified most often were 6,8:d:-, Typhimurium, and Give. Interestingly, analysis by Pulsed Field Gel Electrophoresis indicated persistence and transport of pulsotypes in the region over several years. In this original study of L. monocytogenes in the region prevalence was 43% of 1405 samples resulting in 635 individual isolates. Over 85% of the isolates belonged to serotype 4b with serotypes 1/2a, 1/2b, 3a, 4d with 4e representing the rest, and there were 12 and 2 sites that were positive over 50 and 80% of the time, respectively. Although surface water is not directly used for irrigation in this region, transport to the produce can occur by other means. This environmental survey assesses initial contamination levels toward an understanding of transport leading to produce recalls or outbreaks. 

Pathogens in produce, Netherlands edition

The Dutch have decided to estimate pathogens in their produce in two Journal of Food Protection papers.

Prevalence and concentration of bacterial pathogens in raw produce and minimally processed packaged salads produced in and for the Netherlands

Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 388-394(7)

Wijnands, Lucas M.; Delfgou-van Asch, Ellen H. M.; Beerepoot-Mensink, Marieke E.; van der Meij-Florijn, Alice; Fitz-James, Ife; van Leusden, Frans M.; Pielaat, Andannemarie

Recent outbreaks with vegetable or fruits as vehicles have raised interest in the characterization of the public health risk due to microbial contamination of these commodities. Because qualitative and quantitative data regarding prevalence and concentration of various microbes are lacking, we conducted a survey to estimate the prevalence and contamination level of raw produce and the resulting minimally processed packaged salads as sold in The Netherlands. A dedicated sampling plan accounted for the amount of processed produce in relation to the amount of products, laboratory lettuce.skull.e.coli.O145capacity, and seasonal influences. Over 1,800 samples of produce and over 1,900 samples of ready-to-eat mixed salads were investigated for Salmonella enterica serovars, Campylobacter spp., Escherichia coli O157, and Listeria monocytogenes. The overall prevalence in raw produce varied between 0.11% for E. coli O157 and L. monocytogenes and 0.38% for Salmonella. Prevalence point estimates for specific produce/pathogen combinations ranged for Salmonella from 0.53% in iceberg lettuce to 5.1% in cucumber. For Campylobacter, this ranged from 0.83% in endive to 2.7% in oak tree lettuce. These data will be used to determine the public health risk posed by the consumption of ready-to-eat mixed salads in The Netherlands.

Microbiological risk from minimally processed packaged salads in the Dutch food chain


Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 395-403(9)

Pielaat, Annemarie; van Leusden, Frans M.; Wijnands, Lucas M

The objective of this study was to evaluate the microbial hazard associated with the consumption of mixed salads produced under standard conditions. The presence of Salmonella, Campylobacter spp., and Escherichia coli O157 in the Dutch production chain of mixed salads was determined. Microbial prevalence and concentration data from a microbiological surveillance study were used as inputs for the quantitative microbial risk assessment. Chain logistics, production figures, and consumption patterns were combined with the survey data for the risk assessment chain approach. The results of the sample analysis were used to track events from contamination through human illness. Wide 95% confidence intervals around the mean were found for estimated annual numbers of illnesses resulting from the consumption of mixed salads contaminated with Salmonella Typhimurium DT104 (0 to 10,300 cases), Campylobacter spp. (0 to 92,000 cases), or E. coli (0 to 800 cases). The main sources of uncertainty are the lack of decontamination data (i.e., produce washing during processing) and an appropriate dose-response relationship.

Saudi Arabia greenhouse farms closed for using sewage water

Saad Al-Muqbil, general director of the General Administration of Agricultural Affairs in the Eastern Province, has said that the administration barred one farm from selling its produce due to its use of sewage water in irrigating crops.

The farm owner was fined SR50,000 and 14 greenhouses in his farm were dismantled. This resulted in an estimated loss of SR300,000 to the owner.
Local consumers had saudi.sewage.feb.14complained of vegetables sold in one of the well-known local grocery shops tasting foul and had voiced their concern about the quality of the crops. Shoppers demanded more intensive health control and supervision of fruits and vegetables sold in the province. 

Regardless of regulation, actually employing best practices matters

A lot of folks in the food system are concerned about the potential for FDA’s Food Safety Modernization Act (FSMA), and associated rules, to negatively impact businesses. There’s been a bunch of rhetoric and uncertainty around the final rules and what will be needed to comply. The majority of the content of the proposed Produce and Preventive Controls Rules summarizes the industry’s best practices and lists the references behind decisions.tomato_dump_tank

Not much in there that’s a surprise for folks who have been paying attention.

The focus of FSMA is on identifying hazards, putting steps in place to manage them and actually doing it. The best businesses are already doing this.

There are some specifics like manure incorporation and what a qualified individual is (who is supposed to be responsible for written plans) that need to be worked out. But employing practices and putting systems in place based on the best available science goes a long way in the absence of a regulation.

Back in the day when we were working with produce farmers and packers in Ontario (that’s in Canada) that’s what we tried to do – to stay ahead of the market requirements and regulation.

It’s not a unique approach – the almond industry took a similar path, so did Florida tomato growers and leafy greens producers in California and Arizona to some extent.

According to Lancaster Online, Pennsylvania farmers, through ag educators might be focusing on the uncertainty.

Ag educator Jeff Stoltzfus said he has learned a lot about food safety in the past five years.

But when it comes to the U.S. Food and Drug Administration’s efforts to overhaul food safety regulations, he’s still trying to figure out the impact it will have on the growers he works with.

“What we don’t know is more than what we do know,” he told a group of growers gathered recently at Yoder’s Restaurant for New Holland Vegetable Day.

Keeping good records, he said, could be the most important thing for growers to protect themselves in case a problem arises.

“Records are going to be very important and policies will be even more important, especially if you’re taking stuff from other growers.”

I disagree – actually employing the correct risk-reduction practices based would top my list. The documentation is nice and shows a regulator or a buyer that you know what you’re talking about – but doing it is more important.

33 scary things our moms didn’t know they had to be afraid of

I’ve had several people threaten to sue me over this image, and many others say how distasteful it is.

lettuce-skullBut I like it.

So, apparently, does BuzzFeed, which reprinted it without my knowledge a few days ago.

The time was 2005. Fresh produce outbreaks were mounting around North America, and the best leaders could come up with was cook, clean, chill, separate.

So we did our own take.

Or, a bunch of chats about what a bunch of bullshit passed for public discussion led to this: Christian did this on his own, in my house in Guelph, while I was off hanging out with this girl in Kansas.

He got it right.

We’re number 25.

Wouldn’t the dogs crap on the produce? Quantifying the sensitivity of scent detection dogs to identify fecal contamination on raw produce

Consumption of raw produce commodities has been associated with foodborne outbreaks in the United States. In a recent Centers for Disease Control and Prevention report outlining the incidence of food-related outbreaks from 1998 to 2008, produce of all kinds were implicated in 46% of illnesses and 23% of deaths. Methods that quickly identify fecal contamination of foods, including produce, will allow prioritization of samples for testing investigations and perhaps decrease the time required to identify specific brands or lots. We conducted a series of trials to characterize the sensitivity and specificity of scent detection dogs to accurately identify fecal contamination on raw agricultural commodities (romaine lettuce, spinach, cilantro, and roma tomatoes). Both indirect and direct methods of detection were evaluated. For the indirect detection method, two dogs were trained to detect contamination on gauze pads previously exposed to produce contaminated with feces. For the direct detection method, two dogs were trained to identify fecal contamination on fresh produce. The indirect method did not result in acceptable levels of sensitivity except for the highest levels of fecal contamination (25 g of feces). Each dog had more difficulty detecting fecal contamination on cilantro and spinach than on roma tomatoes. For the direct detection method, the dogs exhibited >75% sensitivity for detecting ≥0.25 g of feces on leafy greens (cilantro, romaine lettuce, and spinach) and roma tomatoes, with sensitivity declining as the amount of feces dropped below 0.025 g. We determined that use of a scent detection dog to screen samples for testing can increase the probability of detecting ≥0.025 g of fecal contamination by 500 to 3,000% when samples with fecal contamination are rare (≤1%).

Journal of Food Protection®, Number 1, January 2014, pp. 4-170 , pp. 6-14(9)

Partyka, Melissa L.; Bond, Ronald F.; Farrar, Jeff; Falco, Andy; Cassens, Barbara; Cruse, Alonza; Atwill, Edward R.


Wet is better for bacteria; produce cross-contamination in the kitchen

Rutgers food safety something Don Schaffner writes:

Every paper I’ve published has a history behind it. This one has its origins in Aberdeen Scotland in 2008.

Michelle Danyluk was a newly minted PhD out of Linda Harris’s lab at UC Davis and had just started as an assistant professor at the University of Florida. Like most good assistant professors Michelle was always on the lookout for grant opportunities, and she had recently seen a call for proposals from the U.S. Food and Drug Administration on schaffnerconsumer risk from fresh-cut produce. Michelle had offered to lead the grant writing efforts with Linda and I as co-principal investigators. The grant submission deadline fell during the Food Micro 2008 meeting in Aberdeen, Scotland and of course, as the deadline loomed closer, the proposal wasn’t finished.  Michelle and I were in Scotland, and Linda was back in Davis, California. Fueled by Scottish Thai food (actually not that bad), and beer, as well as a passible Internet connection and the occasional trans-Atlantic phone call, the three of us hammered out the details of who would do what in the proposal.  Somehow it all worked, and FDA decided to give us the money. And Michelle got tenure.

Three years later, the grant is mostly spent, and Michelle is sitting on a pile of data collected by super-technician Lorrie Friedrich. Michelle and Lorrie have amassed an astounding pile of cross-contamination data for four different surfaces (ceramic, stainless steel, glass, and plastic) and four types of fresh-cut produce (carrots, watermelon, celery and lettuce) under both dry and wet conditions, and considering transfer in either direction. Because Michelle was foolish enough to listen to me when I suggest we repeat each experiment 20 times to “capture inherent variability,” the entire dataset was composed of more than 600 observations. Enter graduate student Dane Jensen.

Dane is from the Jersey shore. The real Jersey shore, near Asbury Park. I pointed Dane at the pile of data and told him to come back when it was graphed and analyzed. He did a good job, and it was part of his Masters thesis, and our recent publication in the Journal of Food Protection.

What did we discover when we set off down this road in Aberdeen?  Mostly that surface moisture and direction of transfer have the greatest influence on microbial transfer rates: bacteria would rather be on a wet produce surface than a dry counter-top or cutting board.  Want to learn more? Order up some Thai food, crack open a beer and read the article.

Quantifying transfer rates of Salmonella and Escherichia coli O157:H7 between fresh-cut produce and common kitchen surfaces

Journal of Food Protection®, Number 9, January 2013, pp. 1488-1657, pp. 1530-1538(9), DOI:

Jensen, Dane A.; Friedrich, Loretta M.; Harris, Linda J.; Danyluk, Michelle D.; Schaffner, Donald W.


Cross-contamination between foods and surfaces in food processing environments and home kitchens may play a significant role in foodborne disease transmission. This study quantifies the cross-contamination rates between a variety of fresh-cut produce and common kitchen surfaces (ceramic, stainless steel, glass, and plastic) using scenarios that differ by cross-contamination direction, surface type, produce type, and drying level. A five-strain cocktail of rifampin-resistant Salmonella was used in transfer scenarios involving celery, carrot, and watermelon, and a five-strain cocktail of rifampin-resistant Escherichia coli O157:H7 was used in transfer scenarios involving lettuce. Produce or surface coupons were placed in buffer-filled filter bags and homogenized or massaged, respectively, to recover cells. The resulting solutions were serially diluted in 0.1% peptone and surface plated onto tryptic soy agar with 80 μg/ml rifampin and bismuth sulfite agar with 80 μg/ml rifampin for Salmonella or sorbitol MacConkey agar with 80 μg/ml rifampin for E. coli O157:H7. When the food contact surface was freshly inoculated, a high amount (>90%) of the inoculum was almost always transferred to the cut produce item. If the inoculated food contact surfaces were allowed to dry for 1 h, median transfer was generally >90% for carrots and watermelon but ranged from <1 to ∼70% for celery and lettuce. Freshly inoculated celery or lettuce transferred more bacteria (<2 to ∼25% of the inoculum) compared with freshly inoculated carrots or watermelon (approximately <1 to 8%). After 1 h of drying, the rate of transfer from inoculated celery, carrot, and lettuce was <0.01 to ∼5% and <1 to ∼5% for watermelon. Surface moisture and direction of transfer have the greatest influence on microbial transfer rates.