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

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