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The number of cases, rather less than half the total, in which particulars were forthcoming as
to possible sources of infection, was as follows: Fish, shell.fish, etc., are referred to in 85 instances;
15 cases were soldiers or sailors; in 28 cases the disease was said to have been contracted outside
London; 26 were ascribed to contact infection (this number included 10 nurses, 4 of whom sickened
between 3rd November and 2nd December; they were engaged in nursing in a ward in an institution
and their illness was suspected to have been contracted from a patient who had old Potts disease, and
who was found to give a positive Widal reaction); two cases were ascribed to river bathing; 2 to drains
and bad smells; 3 to water; in 3 there was a history of previous typhoid fever; 5 were attributed
to "other causes," and 57 were found not to be cases of typhoid fever.
The year 1916 was the fifth in succession in which there was a marked smoothing out of the
autumnal rise in London. Before entering upon a critical examination of this phenomenon, it is desirable
to state briefly the historical sequence of events. Typhoid fever has shown fairly steady decline in
London since its first appearance in medical returns; moreover, examination of mortality figures
indicates roughly a fourfold division based upon the statistics available:—
(i.).—1869.1884.—High mortality, averaging about .25 per 1,000 per annum.
(ii.).—1885.1902.—Lower mortality, averaging about .14 per 1,000 per annum.
(iii.).—1903.1911.—Still lower mortality, averaging about .05 per 1,000 per annum.
(iv.).—1912.1916.—Still lower mortality, averaging about .025 per 1,000 per annum.
Study of notification figures, which afford a much more precise test than mortality figures, shows
that the year 1909 was the first in which a marked smoothing out of the autumnal rise was observed;
in the September and October of both 1910 and 1911 there were distinct exacerbations of prevalence
due in the main, as was shown (see the Annual Reports for those years), to localised outbreaks of the
disease traced to fish; since 1911 the autumnal rise has, again, been inconspicuous.
It should be added that in the Annual Report for 1914, account was given of an outbreak due
to infected food—possibly fish. In commenting upon this prevalence, attention was called (page 22)
to the tendency to lay stress on one or other of two types of theory of causation of typhoid fever—the
theory of Koch and the food theory properly so called. In both types infected food materials are believed
to play an important role; but on the theory of Koch and his followers the food is supposed to become
infected by healthy carriers at the place of local distribution, and great importance is therefore attached
to dealing with these healthy carriers; while, on the other theory, incriminated foods (generally speaking
—shell.fish or fish), are held to have been infected on the gathering ground, or in the well, lake, river,
or estuary, and little importance is attached to the healthy carrier. Some epidemiologists are inclined,
indeed, to doubt the causal significance of the typhoid bacillus altogether; to suspect, in fact, that it
may prove to be no more than an epiphenomenon, the result of changes brought about in the intestinal
organisms consequent upon invasion of the body by the as yet undiscovered virus which produces
typhoid fever.
When war was declared in 1914, the believers in the causal role of the bacillus and in the healthy
carrier hypothesis, strongly advocated protective inoculation, more especially of soldiers, though in some
instances of civilians also; they further laid stress upon the possible risk to civilians due to the return
of soldiers from abroad, and urged the need of practising segregation methods. Study of facts observed
during the South African War casts doubt upon both these articles of faith; it shows that the results
of the inoculations then practised were not so definitely favourable as could have been desired, though
it must, on the other hand, of course, be admitted that a great deal has been learnt concerning the
typhoid bacillus in the last 15 or 16 years, and that improvements in the technique of inoculation have
been made. As regards widespread infection by returned convalescents and healthy carriers, there
are many reasons for being altogether sceptical; thus, it will be remembered that typhoid, which had
attained an unusually high level just prior to the South African War, notably declined during the years
succeeding it (loc. cit. p. 23). It was argued accordingly (loc. cit. p. 24) that all the evidence goes
to show that London itself is "an eminently unfavourable field for growth and cultivation of the typhoid
poison; the areas from which infection is derived are no longer near at hand, but are to be found in
distant polluted foreshores and in remote estuarial waters . . ." On this hypothesis, fears as to
spread of disease by returning soldiers and refugees are held to be alarmist and groundless, but on the
other hand" disturbances of the operations of the fishing fleet in the North Sea, and possible interference
with the shell.fish industry brought about by the war," require to be closely scrutinised in their relation
to altered behaviour of typhoid fever.
The experience of 1916 confirms that of 1915 in respect of absence of any evidence of notable
increased dissemination of disease by direct human agency; indeed, as has been already seen, after
making due allowance for the absence abroad of large numbers of susceptible male persons, the prevalences
of typhoid in London, in 1915 and 1916, were actually lower than ever before previously known, despite
the addition to the population of an appreciable number of returned typhoid convalescents, and
presumably also of healthy carriers from abroad.
The phenomena tally quite well, however, with the rival theory of food causation. Here, to
begin with, the fact that since 1909 the weather conditions have been those usually associated with
low typhoid fever rates, finds more ready explanation on a theory of maturation of a virus in the
estuary or on the foreshore than on that of storing up of infective potentiality in the healthy carrier. It
should be borne in mind, moreover, that steady improvement as regards elimination of dangerous shell.
fish, has been brought about during the last twenty, and especially during the last ten, years. A
full account of the conditions formerly existing is given in Dr. H. T. Bulstrode's earlier report of 1896
on oysters, and in his later report of 1911 on shell.fish other than oysters in relation to disease. Moreover
in 1900, a fish outbreak occurred in London, and the suspicion was soon after confirmed that the