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32
even when aware of its presence. There is evidence to show,
in the early part of the outbreak at any rate, the truth of the
above statement.
Attention has recently been drawn to the influence of
direct infection from one patient to another as the chief means
of maintaining Typhoid Fever in its endemic form. It may be
concluded that this influence may also be at work, though
probably to a lesser degree, when Typhoid Fever is epidemic.
Attention has also been drawn to the fact that Typhoid
infection may exist in a latent form in both children and
adults, and that the number of notifications received is not
always a correct measure of the amount of Typhoid infection
present in a given community.
An index of the influence of personal infection may be
obtained by working out the proportion of houses in any given
epidemic in which more than one case occurs.
Thus, taking as instances two extensive epidemics which
occurred in Belfast in 1898 and 1903, in which there were
about 5,000 and 800 cases respectively, the percentages of
houses with more than one case were 13.6 in the first
epidemic, and 7.1 in the second, showing that even in a
severe epidemic Typhoid Fever has not, as a rule, a very
marked tendency to spread to other members of the same
house.
In the outbreak at New Southgate, however, the percentage
of houses in which there were multiple attacks was
38.6; or deducting the 4 houses previously mentioned, in
which it was probable that the second attacks were simultaneous
with the first, even then the percentage was 25,
showing that in this outbreak the influence of personal
infection was much more at work than is usually the case.
Conclusion.—Taking all the above-mentioned facts and
features of the outbreak into consideration, and in the absence
of the evidence of any definite source of infection, such as
proved infection of the milk or water supply, or contaminated
shell-fish, the evidence, in my opinion, shows somewhat
conclusively that the origin and spread of outbreak was as
follows : —
One or more cases of sporadic or endemic origin having
occurred in this neighbourhood, and probably undetected till
late in the course of the disease, or not at all, and all the
factors favouring direct and indirect infection being present,
viz., the dust-shoot, the hot dry weather, the swarms of flies,
the dirty houses, the class of persons living in the infected
area and their habits, and the somewhat thickly-populated