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7.—Dr. Hamer has, in the majority of instances, not experienced much difficulty in Southwark in
deciding which cases should be regarded as primary and which should be treated as secondary. Cases
occurring in the same house within a day or two of each other and not preceded by an earlier case in
the same house are necessarily regarded as primary, cases occurring a number of days after an
antecedent case in the same house have been classified as secondary. As matter of fact, however, the
number of cases occurring in September in which doubt can be entertained is so small as not to affect
the general result, and especially as the majority had eaten fried fish from the particular shop.
Concerning the exclusion of primary cases not regarded as associated with the special outbreak (9 in
number in the circle and 3 in number in the ring), the facts which led to such exclusion will be found in
the appendix to Dr. Hamer's report. Two of the nine, although notified as cases of enteric fever, were
not found after admission to hospital to be cases of that disease, two others, there was reason for
assuming, had contracted their disease outside London, and the remainder are not in larger proportion
than must often be found occurring during an autumn month in a population of 25,000 persons without
any common cause being assignable as explanation of their origin. So far, therefore, Dr. Hamer's
hypothesis meets the requirement that the whole of the increment of cases occurring at that time in
this population should have been subject to the particular cause which he is associating with the
outbreak.
8.—This hypothesis may, however, be examined in another way. The habit of consuming
particular articles of food is not shared equally by the population at all ages. An outbreak of enteric
fever, shown by Dr. George Turner to be due to the consumption of ice cream (Deptford, 1891), had, as
might be expected, a much greater incidence upon the younger ages, including children under 5 years
of age. The age incidence of an outbreak of enteric fever, shown by Dr. Theodore Thomson to be due to
water (Newport, 1894), had an age incidence different from that of an outbreak of this disease shown
by Dr. Davies to be due to milk (Plumstead, 1895). If Dr. Hamer's hypothesis be correct, the age
incidence of the Southwark outbreak should be exceptional if fried fish is not consumed equally at all
ages. This, indeed, is found to be the case, for, while inquiries by the Council's inspectors showed
that boys and girls, young men and young women, have been the principal customers of the particular
shop, it will be seen that infants and older persons have escaped disease, and young persons have
been especially affected, the incidence on the ages 10-20 years being particularly marked. This
peculiarity of the age incidence of the Southwark outbreak is not only conspicuous when comparison
is made with that of certain outbreaks due to food, but becomes much greater when comparison is
made with the age incidence of enteric fever in London generally, which must be regarded as the
total result of all the causes operating within the county.
9.—In conclusion of this part of the subject it may be said (a) that the behaviour of the outbreak
directly suggests that it was caused by the ingestion of an infected food; (b) that while all other food
supplies commonly known to be capable of conveying infection can be excluded and many other foods
also, fried fish cannot be thus excluded; that whether tested by the population in the circle or the
ring taken for consideration, practically the whole incidence of the disease has been on the consumers
of fried fish purchased at a particular shop, and that inquiries as to other articles of food pointed to no
similar result; (c) that the age distribution of the disease in the outbreak is explicable on the
hypothesis that infection was communicated by fried fish from the particular shop, having regard to
the ages of purchasers and consumers of fried fish from this shop. After careful examination of Dr.
Hamer's report, I am satisfied that these conclusions are well founded.
10.—While the positive evidence adduced by Dr. Hamer, that only fried fish eaters were attacked,
points directly to the fact that this cause was operative, not less important is the exemption from
attack of those who did not partake of this food, although the latter class constituted more than half
the population in the area involved in the outbreak. This fact, moreover, obtains greater significance
when the facts relating to particular families are considered, for Dr. Hamer found that, in numerous
instances, the disease singled out the fried fish eaters for attack, and left unaffected the other members
of the family who did not eat fried fish.
11.—It might be thought to be within the limits of possibility that explanation of the infection of
purchasers at this fried fish shop could be found in some circumstances incidental to visiting the shop,
but not necessarily including the consumption of the fried fish. Such hypothesis would, however,
not afford explanation of the attack of persons who did not visit the shop themselves, but who received
the fish in their own homes.
12.—In connection with the Lambeth outbreak it must be pointed out that the cases are less than
half as numerous as those which occurred in Southwark, and do not therefore so well lend themselves
to arithmetical statement. In the Lambeth outbreak, only one actual case of enteric fever occurred in
September in which fried fish from the suspected source was not eaten, while in particular streets
close to the shop, taken for the purposes of detailed inquiry, some 24 to 59 per cent. of the population
had not obtained fried fish from this source. The topographical distribution of the cases was
different from that of the Southwark cases, but Dr. Hamer's explanation of this circumstance is
probably the true one (see p. 16). While the facts ascertained in Lambeth do not by themselves
present the same amount of material for separate conclusion in their detail, they do not on any
material point differ from those obtained in Southwark.
13.—The facts obtained in Kensal-town cannot be said to be in close agreement with those either
of the Southwark or Lambeth outbreaks. A considerable proportion of the persons attacked had
obtained wet fish or shell fish from a particular source, and a slightly smaller proportion had also
obtained their milk from a common source. The proportion of cases which could not be associated
with a common supply of any sort of food was much larger than in either of the two other districts.