Tag Archives: transfer

A systematic look at the five-second rule: Miranda and Schaffner edition

Posted on by
2

When I meet someone who asks what I do the conversation usually turns to restaurant grades, foods I avoid and the famed 5-second rule. Most have an opinion that confirms their actions (where benefit may outweigh risk depending on what was dropped).

Paul Dawson and colleagues looked at the five-second rule in 2007 showing greater transfer with longer drying times with an 8 hour drying period of the floor contaminant. In 2014 a group of students at Aston University in Birmingham, U.K conducted some science-fair type experiments and reported the non peer-reviewed research on their university website. It got picked up all over the place and for 15 minutes the question was answered; everyone could go back to dropping their food on the floor and setting the critical limit at <5 seconds.giphy

Rutgers graduate student Robyn Miranda and friend of barfblog (and podcast co-host extraordinaire) Don Schaffner tackled the 5-second rule in a more systematic way and put out a press release today after the paper went through peer-review and was published (cuz that’s how Schaffner rolls). The quick answer to whether the oft-cited risk prevention step is a myth? ‘The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food. Bacteria can contaminate instantaneously.’

Turns out bacteria may transfer to candy that has fallen on the floor no matter how fast you pick it up.

Rutgers researchers have disproven the widely accepted notion that it’s OK to scoop up food and eat it within a “safe” five-second window. Donald Schaffner, professor and extension specialist in food science, found that moisture, type of surface and contact time all contribute to cross-contamination. In some instances, the transfer begins in less than one second. Their findings appear online in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.

“The popular notion of the ‘five-second rule’ is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer,” Schaffner said, adding that while the pop culture “rule” has been featured by at least two TV programs, research in peer-reviewed journals is limited.

“We decided to look into this because the practice is so widespread. The topic might appear ‘light’ but we wanted our results backed by solid science,” said Schaffner, who conducted research with Robyn Miranda, a graduate student in his laboratory at the School of Environmental and Biological Sciences, Rutgers University-New Brunswick.

The researchers tested four surfaces – stainless steel, ceramic tile, wood and carpet – and four different foods (watermelon, bread, bread and butter, and gummy candy). They also looked at four different contact times – less than one second, five, 30 and 300 seconds. They used two media – tryptic soy broth or peptone buffer – to grow Enterobacter aerogenes, a nonpathogenic “cousin” of Salmonella naturally occurring in the human digestive system.

Transfer scenarios were evaluated for each surface type, food type, contact time and bacterial prep; surfaces were inoculated with bacteria and allowed to completely dry before food samples were dropped and left to remain for specified periods. All totaled 128 scenarios were replicated 20 times each, yielding 2,560 measurements. Post-transfer surface and food samples were analyzed for contamination.

Not surprisingly, watermelon had the most contamination, gummy candy the least. “Transfer of bacteria from surfaces to food appears to be affected most by moisture,” Schaffner said. “Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”

Perhaps unexpectedly, carpet has very low transfer rates compared with those of tile and stainless steel, whereas transfer from wood is more variable. “The topography of the surface and food seem to play an important role in bacterial transfer,” Schaffner said.

So while the researchers demonstrate that the five-second rule is “real” in the sense that longer contact time results in more bacterial transfer, it also shows other factors, including the nature of the food and the surface it falls on, are of equal or greater importance.

“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” Schaffner said. “Bacteria can contaminate instantaneously.”

The paper can be downloaded here, abstract below.

 

WORLD: Longer contact times increase cross-contamination of Enterobacter aerogenes from surfaces to food
02.sep.16
Appl. Environ. Microbiol. DOI: 10.1128/AEM.01838-16
Robyn C. Miranda and Donald W. Schaffner
Bacterial cross-contamination from surfaces to food can contribute to foodborne disease. The cross-contamination rate of Enterobacter aerogenes was evaluated on household surfaces using scenarios that differed by surface type, food type, contact time (<1, 5, 30 and 300 s), and inoculum matrix (tryptic soy broth or peptone buffer). The surfaces used were stainless steel, tile, wood and carpet. The food types were watermelon, bread, bread with butter and gummy candy. Surfaces (25 cm2) were spot inoculated with 1 ml of inoculum and allowed to dry for 5 h, yielding an approximate concentration of 107 CFU/surface. Foods (with 16 cm2 contact area) were dropped on the surfaces from a height of 12.5 cm and left to rest as appropriate. Post transfer surfaces and foods were placed in sterile filter bags and homogenized or massaged, diluted and plated on tryptic soy agar. The transfer rate was quantified as the log % transfer from the surface to the food. Contact time, food and surface type all had a highly significant effect (P<0.000001) on log % transfer of bacteria. The inoculum matrix (TSB or peptone buffer) also had a significant effect on transfer (P = 0.013), and most interaction terms were significant. More bacteria transferred to watermelon (~0.2-97%) relative to other foods, while fewer bacteria transferred to gummy candy (~0.1-62%). Transfer of bacteria to bread (~0.02-94%) and bread with butter (~0.02-82%) were similar, and transfer rates under a given set of condition were more variable compared with watermelon and gummy candy.

 

Why proper glove use is important: Norovirus transfers nicely from inoculated gloves to surfaces and fruit

Posted on by
Reply

No bare hand contact rules are often rebutted with "people do dumb things with gloves on."

One of my favorite glove use stories is something a greenhouse manager told me 10 years ago. It goes something like this: the guy had convinced the business owner that food safety was really important and he installed full restrooms in the greenhouse — and fully stocked a closet with latex gloves. The manager trained all the employees on why clean hands and gloves were important.  A week after the training session he saw an employee urinating on the outside of the restroom. With his gloves on.

In this month’s Journal of Food Protection, my friend Jen Cannon’s group has a paper that shows some great data to back up why proper glove use is important: Dirty gloves are pretty decent at transferring norovirus. After looking at multiple donor/recipient surfaces (stuff like dirty gloves to berries, or dirty gloves to food contact surfaces) Sharps and colleagues showed transfer rates from 20%-70% under wet conditions and although less, still showed transfer of up to 12% under dry conditions.

From the discussion, "After a restroom visit, a food worker, not respecting hygienic practices, may immediately or within a short period of time (<30 min) begin to handle foods, not allowing sufficient time for contaminated hands to dry." or take the gloves in to the restroom with them.

Abstract is below.

Human Norovirus transfer to stainless steel and small fruits during handling

Journal of Food Protection®, Volume 75, Number 8, August 2012 , pp. 1437-1446(10)

Sharps, Christopher P.; Kotwal, Grishma; Cannon, Jennifer L.

Human noroviruses (NoVs) cause an estimated 58% of foodborne illnesses in the United States annually. The majority of these outbreaks are due to contamination by food handlers. The objective of this study was to quantify the transfer rate and degree of contamination that occurs on small fruits (blueberries, grapes, and raspberries) and food contact surfaces (stainless steel) when manipulated with NoV-contaminated hands. Human NoVs (genogroups I and II [GI and GII]) and murine norovirus (MNV-1) were inoculated individually or as a three-virus cocktail onto donor surfaces (gloved fingertips or stainless steel) and either immediately interfaced with one or more recipient surfaces (fruit, gloves, or stainless steel) or allowed to dry before contact. Viruses on recipient surfaces were quantified by real-time quantitative reverse transcriptase PCR. Transfer rates were 58 to 60% for GII NoV from fingertips to stainless steel, blueberries, and grapes and 4% for raspberries under wet conditions. Dry transfer occurred at a much lower rate (<1%) for all recipient surfaces. Transfer rates ranged from 20 to 70% from fingertips to stainless steel or fruits for the GI, GII, and MNV-1 virus cocktail under wet conditions and from 4 to 12% for all viruses under dry transfer conditions. Fomite transfer (from stainless steel to fingertip and then to fruit) was lower for all viruses, ranging from 1 to 50% for wet transfer and 2 to 11% for dry transfer. Viruses transferred at higher rates under wet conditions than under dry conditions. The inoculum matrix affected the rate of virus transfer, but the majority of experiments resulted in no difference in the transfer rates for the three viruses. While transfer rates were often low, the amount of virus transferred to recipient surfaces often exceeded 4- or 5-log genomic copy numbers, indicating a potential food safety hazard. Quantitative data such as these are needed to model scenarios of produce contamination by food handling and devise appropriate interventions to manage risk.
 

How long does norovirus last on surfaces and foods, and is norovirus easily transferred?

Posted on by
Reply

Leading lights of Britain’s food safety junta have issued a call for research into norovirus, specifically how the virus continues to survive when it comes into contact with the surfaces that food is prepared upon or with food itself.

They should have just given the money to LeeAnn.

As in LeeAnn Jaykus of North Carolina State University, who was one of the authors of a paper in this month’s issue of my favorite bath time reading, Journal of Food Protection. The authors write:

“Foods become contaminated with HuNoV by direct contact with fecal matter on the hands of food workers who have not practiced adequate personal hygiene and by transfer of virus via contact with contaminated surfaces. Intuitively, this makes sense, as HuNoV are shed in high numbers in the feces and vomitus of infected individuals, and shedding can precede illness, occur in asymptomatic individuals, and/or be prolonged for days to weeks after symptom resolution.

Our results confirm that HuNoV can persist on commonly used food contact surfaces and on a model food for long periods, as evaluated by the only reliable method to detect these viruses, RT-qPCR. This our work confirms that moisture, pressure, and recipient surface were key factors influencing transferability (reviewed in (24) ). For example, transfer of HuNoV and MNV-1 from stainless steel surfaces to lettuce was more efficient when the virus inoculum was still wet (time 0), an observation consistent with previous studies using FCV (8) and rotavirus.

Persistence and transferability of Noroviruses on and between common surfaces and foods
02.may.12
Journal of Food Protection®, Volume 75, Number 5, May 2012 , pp. 927-935(9)
Escudero, B.I.; Rawsthorne, H.; Gensel, C.; Jaykus, L.A.
http://www.ingentaconnect.com/content/iafp/jfp/2012/00000075/00000005/art00016
Abstract:
Human noroviruses (HuNoV) are the leading cause of foodborne disease, and poor personal hygiene practices of infected workers are the most common mode of contamination. The purpose of this study was to characterize the persistence and transferability of representative noroviruses Norwalk virus (NV), Snow Mountain virus (SMV), and murine norovirus 1 (MNV-1) on and between solid surfaces and foods. Changes in virus concentration on artificially inoculated solid surfaces (stainless steel, ceramic, and Formica) or lettuce were monitored over a period of 14 to 42 days. Virus transfer was evaluated from donor (solid surface) to recipient (food, e.g., lettuce and sliced turkey deli meat) for up to 2 h postinoculation. Viruses were recovered by elution and titered with reverse transcription quantitative PCR (RT-qPCR) and/or infectivity assay, as appropriate. Based on RTqPCR, the concentration of NV and SMV on surfaces dropped gradually over time, with an average reduction of 1.5 to 2.0 and 1.8 to 2.3 log, respectively, after 42 days, with no statistically significant differences by surface. When inoculated onto lettuce stored for 2 weeks at 4°C and room temperature, the titers of NV and SMV dropped by approximately 1.0 and 1.2 to 1.8 log, respectively. Comparatively, the RT-qPCR signal associated with purified HuNoV RNA placed on the same surfaces was more rapidly lost to degradation. Transfer efficiency ranged from 0 to 26 % for lettuce and from 55 to 95 % for sliced turkey deli meat, with statistically significant differences (P ≤ 0.05) in transferability as a function of contact pressure (100 and 1,000 g/9 cm2) and inoculum drying time. When similar experiments were done with MNV-1, infectious virus failed to be detected on solid surfaces after storage day 21, although the virus did persist on lettuce. This study provides much needed quantitative data for use in risk assessment efforts intended to characterize the transmission of HuNoV during food preparation and handling.