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23
Report of the County Medical Officer—General.
to the aetiology of typhoid fever—in the Spanish-American and South African wars flies were believed
to be largely concerned in spreading the disease; in Germany the healthy carrier is held to be allimportant
; in Scotland, milk; in Belfast, cockles; in some of the large English towns, public water
services; in other towns, mussels; in London, fish has been held to be a not infrequent source of
infection.
A survey of the history of London typhoid suggests certain conclusions which may be formulated
as follows:—
The cases of typhoid fever in London particularly affect that section of the population which
buys and eats what Dr. Niven has termed "trash" in the streets; sometimes purchasers of pennyworths
and ha'porths of fried fish are apparently especially involved, sometimes eaters of mussels, more
rarely eaters of cockles, or consumers of watercress or of ice cream. At times of epidemic prevalence,
i.e., when from 10 to 15, up to 100 or more cases suddenly develop within a limited area, more precise
study can be made of the various kinds of "trash" consumed, and the question as to the exact origin
of the food implicated can be closely investigated. In 1900 it was thus possible to demonstrate that
in three simultaneously occurring outbreaks, in widely separated parts of London (120 cases, 50 cases
and 30 cases) the only sort of food material of common origin consumed by the sufferers was fish (which
in two of the affected areas was purchased already fried); this was eaten by all the persons who could
legitimately be regarded as making up the special prevalence in each area, and three single shops, one
in each area, supplied the fish, which, it may be noted, was in every case small plaice.
In 1903 there were two small outbreaks of 17 cases each, and similar conclusions were formed.
In 1908, 1910 and 1911 like results were again reached in connection with three further outbreaks. In
addition to the special point established in these outbreaks that an infected fried fish hypothesis, alone
of all suggested hypotheses, was capable of explaining the prevalences, certain important subsidiary
conclusions were reached. In one of the areas affected in 1900, and in the area affected in 1911, an icecream
hypothesis appeared, on a first cursory examination, to afford some likelihood of yielding an
adequate explanation of the outbreak, but a closer analysis of the facts clearly showed that ice-cream
from the suspected source had not been consumed by quite a considerable percentage of the sufferers.
Similarly, in the outbreaks of 1908 and 1910, a mussel hypothesis at first seemed promising, but close
analysis excluded it from further consideration. A similar failure to comprehend all the persons attacked
was encountered in an outbreak which it was found had been ascribed to watercress in 1903; the difficulty
is fully discussed in the report on watercress presented to the Council in 1905.
The conclusion is, therefore, forced upon the mind that in the case of these London outbreaks
very careful study is needed, if discrimination is to be properly made between the various suspected
kinds of food material, and unless the outbreak is of a certain magnitude no great degree of probability
can be attached to the conclusion reached. Thus, a common instance is the following: A group of five
or six cases occurs, and a particular source of infection seems a possible cause of the trouble; the
difficulty then arises as to deciding whether a further case, developing in the near neighbourhood of the
group and not associable with the suspected source, ought to be regarded as constituting part and parcel
of the special prevalence. If ten or twelve cases present themselves in a group, and all, or nearly all,
are associated with a particular source of infection, the probability of association meaning causation may
rise somewhat higher. In a recent instance, however, nine cases were reported as probably due to a
milk supply, and it was further found that two other patients not obtaining milk from this supply, but
who were living close to the nine milk consumers were almost simultaneously attacked. The evidence
against the milk was believed to be confirmed by discovery on the farm in the country from which the
milk came of a case of typhoid fever, and also of a man who some years before had suffered from typhoid
fever, and who, it was suggested, might therefore be a typhoid carrier. Question was raised as to
whether the milk supply should be stopped, but as the supposed carrier had left the farm, and his
whereabouts remained in doubt, there appeared no reason justifying drastic action with regard to the
London retail supply; the decision arrived at in this instance was justified by the event, for, as a
matter of fact, no further cases of typhoid occurred in the affected locality. Another case of like
difficulty is that of the dairy supplying the houses referred to at the top of page 21. In outbreaks
involving ten to twenty persons, and in which a precise analysis can be made of the facts as to food
supply, conclusions possessing a high degree of probability can be reached, witness for example,
Bulstrode'e very complete analysis of the Winchester and Southampton outbreaks, which were
proved to be due to oysters. In Southwark, in 1900, a still larger exceptional prevalence occurred,
and the facts analysed in this outbreak made it practically certain that in that case fried fish was at
fault.
The student of explosive outbreaks ascribed to water, shell fish, or fish, cannot fail to be struck
by the remarkable fact that after cessation of the special prevalence typhoid fever resumes its accustomed
behaviour in the community attacked. After the Maidstone and Lincoln and Worthing outbreaks
typhoid was not exceptionally prevalent in these towns ; after the Southwark outbreak the
disease soon assumed its wonted degree of prevalence. Thus the development of large numbers of typhoid
bacilli in an affected community and the presumed setting up of the carrier condition in a considerable
number of persons are seen to be incapable of causing post-epidemic cases of typhoid. A like phenomenon
was observed in this country on the return of many thousands of convalescents after the South African
war; again in Belfast disuse of cockles was followed by cessation of typhoid, despite the presumable
existence in the city of large numbers of bacillus carriers. The case of London is especially noteworthy,
for in 1898, 1899 and 1900 typhoid prevailed in very considerable excess, many hundreds of carriers of
typhoid bacilli must have newly appeared upon the scene, and to these were added in 1900 and 1901 appreciable
numbers of returned " carriers " from South Africa ; yet, in the succeeding years typhoid fever