Relating Numbers of Foodborne Pathogens to Human Illness: Question and Answer Sessions - Margaret Coleman
Food Safety Initiative Technical Workshop:
Relating Numbers of Foodborne Pathogens to Human Illness
Introduction | Program | Talks | Abstracts | Qs & As | Slides | Biographies
Tuesday, August
4, 1998
Atrium, Stamp
Student Union
University
of Maryland
College Park,
MD
Question and Answer Sessions
Margaret Coleman
DR. GAYLOR: Thank you, Peg. You certainly raised a lot of issues that we could spend the rest of the day discussing, whether it's thresholds or nonthresholds, linear, nonlinear, healthy versus susceptible, subpopulations and so on.
We have a couple of minutes here if anybody has a question they'd like to address now. Would you come to the mike and identify yourself?
MS. PUTZRATH: Resha Putzrath, Georgetown Risk Group.
Even though you just mentioned it in passing, Peg, since you did mention toxicity equivalency factors I have to make a comment, since I've spent the last several years working on it, which is that I urge caution if you want to go in that direction. In particular, if there are a lot of restrictions on the model and limitations for its use, one quick caution is if you believe in thresholds and do dose-response modeling with thresholds in them, you will often find that the dose-response curves cross, thus changing not only the magnitude of the proportional difference but the rank order.
MS. COLEMAN: Thanks, Resha.
MR. POWELL: I have a question for both Peg and Jim.
Given the evidence, the analysis that Peg and Harry have done regarding the magnitude of inter-individual variability that can be hypothesized, some three or four orders of magnitude greater than is conventionally used to account for inter-individual variability in chemical safety assessment and risk assessment, do you think that this might hasten, delay or have no effect on the transition from safety assessment to predictive consequence risk analysis in this arena?
MS. COLEMAN: I guess my general comment is that, for example, my title is still chemist within my agency, even though I've not done chemistry in years, so I came into the paradigm from the chemical risk assessment field and I've tended to shy away from the safety factors and assuming tenfold is sufficient across the board.
I think I'll take that one step further and agree with Jim that we ought to take our time in evaluating the evidence and I think case by case because personally, my opinion is that we don't have enough knowledge to really set defaults that could apply across the board to all pathogens.
I guess one other comment is maybe the time is now. Mark has raised issues about concerns from the international front for our agency of risk assessment that the U.K. is developing on hormones in beef, and that's going to be falling into our lap soon.
So I think even though this wasn't a direct answer to Mark's question, I think we do need to explore it.
DR. WILSON: The unidentified questioner was Mark Powell of the Food Safety Inspection Service.
First of all, Mark, even though our mutual friend Adam Finkel talks about assuming a tenfold span of human susceptibility, he's as ignorant as a post. In fact, when you expand the traditional process--the factor of 10 does not assume from the starting point as the median responsiveness or the median susceptibility of the population but something like 4 percent, okay?
So, in other words, the starting point of that safety factor is not the average susceptibility but a no effect or an observation where there is no observed effect, which is, at most, according to the work of our friend Dr. Gaylor, something around 4 or 5 percent in a typical experiment, okay?
So in the standard practice the inferred distribution of susceptibility is A, log normal or approximately log normal and B, and I'm not sure how you characterize it, say the difference between the first and the 99th percentiles is somewhere between three and four orders of magnitude.
Now, if you do back-of-the-envelope with a soft pencil eyeballing of the data that Peg presented, the span in the microbes, the susceptibility span is probably wider. That is to say, those response curves are shallower.
What was the other part of the question? Oh, the other thing you asked about is will we transition from safety assessment to risk assessment. My observation is that in microbial practice, they're not to safety assessment yet, let alone risk assessment.
