Relating Numbers of Foodborne Pathogens to Human Illness: Question and Answer Sessions - Kirk Smith, DMV, PhD
Food Safety Initiative Technical Workshop:
Relating Numbers of Foodborne Pathogens to Human Illness
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Tuesday, August
4, 1998
Atrium, Stamp
Student Union
University
of Maryland
College Park,
MD
Question and Answer Sessions
Kirk Smith, DMV, PhD
DR. SMITH: Do we have questions?
DR. WILSON: Jim Wilson. I got the impression from what you were saying that the various chocolate samples were rather heterogeneous, that there was not, at least in the one that I heard you characterize in a little more detail, there were not organisms recovered from all the samples and there was only a small fraction of those from which organisms were recovered where the number could be quantified.
If that is characteristic, that suggests that A, you're sampling from the tail of the exposure median. You know you're sampling from the tail of the distribution of people affected because, of course, you don't ever find those who are not affected. And that makes me worry a little bit about using the means or even the medians of those numbers to draw conclusions about how many organisms were required to cause the infection.
I mean, there's certainly some reasonable probability that all those affected got a lot more because they got the hot candies.
DR. SMITH: Maybe somebody could speak to the distribution of Salmonella contamination in chocolate. There's probably somebody here that knows a lot more about it than I do. In the one outbreak I know they did look at 100 10-gram chocolate balls, and six were contaminated.
DR. WILSON: Have you estimated the number of subjects that would be required to get a reliable estimate of an ID-1?
DR. SMITH: I know it's a whole lot.
DR. WILSON: You can imagine doing a volunteer trial with 1,000 volunteers.
MS. SILBERMAN: I'm Jennifer Silberman with BNA. I wanted to know how do Salmonella strains get into cheddar cheese and chocolate in the first place?
DR. SMITH: I don't so much know the chocolate. I can speak to the cheddar cheese. The cheddar cheese outbreaks are usually due to some defect in pasteurization of the milk that goes into the cheese.
The chocolate, I think, is somehow contaminated at its source, the cocoa beans.
MS. COLEMAN: I'm Peg Coleman, USDA.
I haven't thought very much about cheese and if you have a one-pound block of cheese, are you likely to have organisms all throughout or are they mostly on the surface?
DR. SMITH: I Think I'm going to have to defer to Dr. Tatini on that. I think probably they're not all on the surface, that they're probably throughout--
DR. TATINI: [Inaudible.]
DR. SMITH: So there is heterogeneous distribution, and organisms are not just on the surface.
QUESTIONER: You are discussing other host factors. Does that mean that the data simply are not available yet?
DR. SMITH: Yes, I think that is the case. Usually we'll get sex and age data and I think predisposing conditions. Antibiotic use is certainly being looked at now but really hasn't in the past, and exactly how much people ate. I think those kinds of detailed questions really aren’t being routinely asked. You investigate, find out what the product is and get it pulled.
But I think certainly we're headed in that direction and can do a lot more of that.
DR. LEVINE: Kirk, both in the volunteer studies and in epidemiologic investigations where you go into an outbreak situation and maybe culturing contacts who are not clinically ill, one could be talking about infectious dose, meaning including subclinical infection, or clinical infectious disease dose.
In your last bullet, what are you referring to? Clinical ID or literally infectious dose?
DR. SMITH: I would think maybe a clinical ID is more useful for our purposes but again that's going to take even more people, obviously.
