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Report of the Medical Officer of Health.
85

From these enquiries it is clear that more than one-third of the control populations in the areas
selected (and they were in each instance populations in which there might be expected to be a specially
large percentage of eaters of fried fish from a particular source) gave a history of not having eaten
fried fish from any single shop. This statement also holds good if the analysis be limited to persons
between 5 and 25 years of age, i.e., to persons of the ages which are specially apt to suffer in outbreaks
of fish typhoid. (See Report on outbreak of 1900, Ann. Rep. Med. Off. of Health, County of
London). It is therefore clear that the fact that a history of fried fish eating from a particular shop
(within a period which may be looked upon as covering the time of infection) is obtained in practically
all the persons who may be regarded as making up the special prevalence, strongly points to fried
fish as the source of the mischief, provided always, of course, that a number of persons sufficiently large
is concerned, to eliminate mere chance coincidence. It is in point of fact exceedingly improbable
that distribution of cases of typhoid fever among, say, fifty fried fish eaters, without involvement of
any persons who had not partaken of fried fish, could be the result of mere chance, unless, of course,
the fifty fried fish eaters had all been assembled together on a particular occasion upon which they
all partook of fried fish and also of some infected article of food such as cockles or mussels. This much
being premised, it remains to examine the results obtained in the Finsubry enquiry relating to control
populations from another point of view.
In Finsbury the enquiries as to fried fish were supplemented and controlled by similar questions
with reference to ice cream, and they were made in two control populations, one to the north, the
other to the south, of the two shops coming under suspicion. The results also admit of being
analysed according to the distance of the component populations from the particular centre in
question. "Inner radius" refers to a population living in some portion of an area within 220 feet of
a central point, taken midway between the ice cream shop and the fried fish shop, and situated some
30 yards from each shop. "Outer ring" refers to families living within the ring included between
two circles of 220 feet and 440 feet radius described from the same centre. The two control population
include merely sample families and not the entire population within the "inner radius" and
the "outer ring." The results obtained are exhibited in the annexed table.