N60 Sampling Presents Challenges

N60 sums up the latest in FSIS regulations for sampling of beef product in efforts to detect E. coli O157:H7 before it enters the food supply. The Beef Industry Food Safety Counsel's document containing the best practices for N60 states, "The N=60 sampling protocol uses an excision method to remove the surface of 60 pieces of product from throughout the defined lot. It is best to select samples from pieces of trim taken from the original surface of the beef carcass (i.e., exterior carcass surfaces). This sampling protocol has been accepted and is currently being used by FSIS personnel to conduct sampling of trimmings."

While the FSIS should be praised for moving toward an improved food safety system, MSI recognizes that the N60 process is fairly labor and cost intensive, especially in smaller plants, but propose the the M-Vac can make it easier.

Why use the M-Vac for N60? First, because the M-vac gets results similar to excision without the invasive process. It saves lab time and space, uses less media, and provides a cleaner sample. With all of these benefits,we are rapidly working to help plants use the M-Vac to reduce the high impact of such an important safety measure.

Sampling Trends from the FSIS

In the Powerpoint Document released by the FSIS ("FSIS Notice 65-07") it is stated:

"During the summer of 2007, a number of unfavorable trends emerged, causing concern about E. coli 0157:H7." They are as follows:

• The percent positive rate for E. coli O157:H7 in FSIS samples of beef products has recently gone up.
  
• The number of recalls for E. coli O157:H7 went up this summer.
  
• The number of illnesses caused by E. coli O157:H7 increased this summer.
  
• Food safety assessments at establishments producing product that tested positive by FSIS for E. coli O157:H7 raised questions about the decisions establishments made in the hazard analysis.
  

It goes on to make a list of "best practices," or things that, as the document states, "are essential to controlling E. coli O157:H7." These standards however are NOT mandatory.
No wonder we have a food safety problem. We know how to prevent the bacteria, but no one requires it.

Technology from 1917?

Following the string of recalls in foods ranging from pizza to ground beef, it is clear that something in the food safety process is not working. Sick consumers should not be the first indicator of bacteria located within a plant. The first step in any pathogen recovery method is to collect a surface sample, which is traditionally done with a swab or sponge. This sampling method may actually be the whole problem.

An article published in 2004 states, "The swab-rinse method was originally developed by Mannheimer and Ybanez in 1917 to assess the bacterial contamination of eating utensils. In 1944, the American Public Health Association included it in its recommended methods for food utensil sanitation monitoring."

In other words we have a big problem: prevalent sampling technology is 90 years old. The article goes on to state, "Historically, the number of organisms recovered from swabs used for environmental sampling has shown a poor correlation with the number of microbial contamination on surfaces."

We don't drive cars from 1917...maybe we shouldn't use equally dated sampling methods either.

Law of Equivalent Progression

To maximize the accuracy and confidence levels of laboratory results from rapid, ultra-sensitive bio-detection technology, and equivalent or higher level of sample acquisition technology is required. In other words, without a good sample, great detection systems don't have the chance to perform.

Sampling Proficiency

Sampling method proficiency or efficacy can be described as the overall sampling “probability of success” and is highly dependent on each of the three steps or segments of the sampling process: Location/Discovery; Extraction, and Elution. Since each step typically occurs in the same sequence, each prior step highly influences all subsequent steps. Additionally, a low probability coefficient for any of the three general steps significantly lowers the final probability that a true representative sample of the surface in question will be provided to the detection process.

For example, in the overall sampling process, if the probability of accurately locating an actual “hot spot” is low due to the limited sampling area allowed per sample, the success of the whole sampling process is in serious jeopardy. Obviously, if the first step is not successful, subsequent steps are meaningless. However, if the location step is successful but low, and if the second step of extraction of the pathogens from the surface is correspondingly low, perhaps due to harbored pathogens located below the immediate surface for example, the combined effects of these first two segments/steps of the sampling process are further reduced or biased downward. Consequently, the third step of elution or recovery of the contaminate from the sampling device inherits a predetermined lower probability of success because there are simply lower total numbers of bacteria present in that sample coming up for further lab processing.

The Sampling Proficiency (SP) can be calculated experimentally by determining the product of the combined probabilities (coefficients) of success of each of the three main sampling steps. That is, Location/Discovery (LD) x Extraction (Ex) x Elution (El) = Sampling Proficiency (SP). The final value of the SP reflects the true probability of an accurate analysis of the surface of interest. It is apparent that a higher SP values represent a greater efficacy of the overall sampling method or device.

"Zone" vs. "Spot" Contamination

The probability of bacterial contamination within a given general area of a particular production facility may form the basis of QC management for that facility. This “zone theory” concept simply divides the plant (physically or theoretically) into common areas based on similar probabilities of contaminated product or equipment. Measures are typically taken to restrict movement of materials and personnel from zones of higher contamination probabilities to “clearer” zones since “dirty” materials could increase the probability of cross contamination. Each zone may be further subdivided into “sub-zones” as needed to sensibly manage the QC of that area.

Individual swipe samples, taken from a single 4-16 sq in. surface area, would typically be considered a “spot” sample within a specified zone. Multiple spot samples, taken from a pre-determined specified large area (zone), and which are later combined or pooled by the lab would qualify as “zoned” samples. This procedure is followed in some facilities in order to more cost effectively “screen” zones within the facility. Management knows that by sampling larger surface areas within a zone, the probability of discovering contamination, if present, increases proportionally. Management would consider a positive pooled sample for the microbe(s) in question to be a good indicator that the entire zone or sub-zone was contaminated. That entire area (zone or sub-zone) would then be cleaned and sanitized as needed to correct the problem. This procedure is often used to reduce laboratory costs but also because managers know that any contaminated equipment, surface or material within a sub-zone, for example, will eventually spread to other areas within that zone or possibly to other locations throughout the facility. Further, he knows that all equipment, tools or work surfaces will be cleaned whether the positive came back from an individual sample or a pooled sample.

Surface Rinse Sampling

Wet-vacuum systems are routinely used in many private and industrial situations including some food surfaces but has not been readily used to collect surface bacteria for routine analysis. Liquid rinsing of surfaces has been proposed as a more efficient method of detaching and collecting surface pathogens, although convenient recovery of the rinse solution and suspended surface particles have presented numerous challenges in the past.

Some of the benefits of a liquid rinse, wet-vacuum collection device include consistent and repeatable volumes of formulated solutions applied and retrieved under constant application and vacuum pressures. Surface area covered per sample could be limited only by the size of the collection container, therefore would allow research or QC personnel to more effectively rinse and sample a larger surface area. Since rinse application and vacuum retrieval pressures remain consistent across the entire sampling surface, harmonization possibilities between users and facility locations could be improved. The combined affects of moving liquid (with or without surfactants or other additives) and air across the sampling surface would provide a multitude of interacting forces to improve bacterial detachment during collection. Vacuum retrieval of the surface suspension of bacteria would eliminate the elution (from the sampling device) by providing a liquid sample for the lab with pathogens already in suspension. These benefits to the laboratory would be far reaching and promote more efficient analysis, faster turn around of results and decreased probabilities of false negative results.