Day 107 - 24 Mar 95 - Page 40
1 not been destroyed by cooking, are all people who consume
2 that product likely to be affected in the same way or will
3 some people become ill and some not or degrees of illness?
4 A. All of those. There are enormous variations. There is
5 individual response, there is dose response and different
6 types of organisms have different effects at different
7 dose. In other words, you take a classic salmonella
8 outbreak, say, 100 people are exposed to an identical
9 amount of salmonella, it is unusual to get more than, say,
10 60 of those people to actually exhibit specific signs of
11 illness. That is called the "attack rate". So, rarely do
12 you get 100 per cent attack rate.
13
14 Secondly, the dose response, i.e. the amount of bacteria
15 consumed, or whatever infective organism it is, will
16 determine different levels of illness. So, therefore,
17 again using salmonella about which most is known, you get a
18 range from, say, a few thousand organisms ingested will
19 make you for a short time what is called an asymptomatic
20 carrier; you will be able to detect the organism in the
21 body but there will be no outward signs. Increase that
22 dose up to, say, typically 100,000 plus to several million,
23 and you will get a violent episode of diarrhoea, abdominal
24 pains, fever; increase it to several million and it may
25 well kill a small amount of people; increase it to a
26 hundred million and it will kill most of the people who are
27 exposed. So, those are the ranges.
28
29 Then, of course, the organisms: Salmonella I have
30 described earlier as the classic food poisoning that under
31 normal circumstances high dose, and the rule of thumb is
32 100,000 to 100 million, to draw out specific signs of
33 illness. This has actually been tested on human beings; a
34 series of experiments carried out in the 50s on American
35 prisoners who were fed varying doses of salmonella to see
36 what happened. Those same sorts experiments, for obvious
37 reasons, have not been repeated for other organisms.
38
39 But the evidence from outbreaks and subsequent food
40 sampling and enumeration of organisms found in food samples
41 and then calculations of the amount of food eaten, you can
42 extrapolate and determine roughly what infective doses give
43 rise to disease. On that basis, while salmonella takes an
44 enormous burden, we have good evidence to support an
45 assumption that campylobacter will produce overt signs of
46 disease in, say, 100 or so organisms and, similarly, E.coli
47 0157 also appears to be a very low dose to produce
48 infection.
49
50 MR. JUSTICE BELL: When you give these numbers, what do you
51 mean, total ingestion altogether of so many organisms?
52 A. Yes, total organisms ingested, yes, as a dose. So, you
53 might, my Lord, find two or three organisms per gramme in
54 the food and calculate that that person ate 200 grammes of
55 that food, and thereby work out they would have absorbed
56 400 and became very ill. You can also plot what is called
57 dose response, because severity of illness is related
58 loosely to the number of organisms ingested. Therefore, if
59 you get, say, somebody who is very seriously ill with the
60 ingestion of 400, it would be fair to extrapolate backwards
