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London County Council.
Memorandum by the Medical Officer of Health on the Distribution of Enteric Fever
in London in 1894, considered in relation to water supply.
Public Health Department,
8th July, 1895.
I have for some time been engaged in the study of the distribution of cases of enteric fever in
London, and, inasmuch as I have observed an appearance of exceptional behaviour of this disease in
1894, I now beg to present to the Committee a memorandum on the subject.
The notification of cases of enteric fever has been obligatory in London since 1889. The results
therefore of notification during five whole years, 1890-4 inclusive, are now available for examination.
For the purpose of studying the behaviour of enteric fever as regards seasonal prevalence
in 1894, it is necessary to ascertain as far as possible the normal behaviour of the disease in this respect.
For this purpose Diagram I. has been prepared, based on the number of cases concerning which the
Metropolitan Asylums Board received copies of certificates in the four years 1890-3, and showing the
number of cases concerning which certificates were received in each week in relation to the mean
weekly number of the four years. For the purpose of comparison, the number of cases in each week
in the year 1894 is also shown in relation to the mean weekly number notified in that year.
Comparison may therefore be made between the curves thus prepared, and the point to which I
desire to direct attention is that whereas in the period 1890-3 there was decrease of the cases in the
49th, 50th and 51st weeks, in 1894 there was increase. If the distribution of the cases of each of the
five years be considered (see Table I.), it will be seen that only in the year 1894 did this increase
occur in these weeks. It is necessary that I should here state that I am not now discussing any large
prevalence of enteric fever, but a slight increase, a mere sprinkling of cases among the vast population
of London, which might readily occur at times when the disease is apt to be prevalent without exciting
observation.
It is desirable to ascertain whether this apparently exceptional behaviour of enteric fever
in London in 1894 has been shared by other communities. A curve has accordingly been
prepared based upon the number of cases notified in each week in 1894 occurring in a group of
districts from which the Local Government Board receives returns, and it will be seen that this
curve, which in Diagram 1. is described as the curve of " large towns," resembles that of London
for the period 1890-3 ; that is to say, there is decrease in the number of cases notified in the 49th,
50th and 51st weeks (see Table II.). It should be stated that in one respect the large town curve
is not strictly comparable with the others, for while the London curves are based upon the number of
cases, of which the Metropolitan Asylums Board each week receives copies of certificates from the London
medical officers of health, the large town curve is based upon the number of cases of which the provincial
medical officers of health each week receive certificates. There is, in fact, a little delay in the receipt
by the Metropolitan Asylums Board of a few certificates in each week.* If correction be made for this,
however, the effect in the diagram is so small that it in no way affects the fact that London in 1894
suffered from increased prevalence of enteric fever in the 49th, 50th and 51st weeks; whereas, in
London, in 1890-3, and in the large towns 1894, the number of cases in these weeks was decreasing.
It is, of course, necessary here to bear in mind that the normal behaviour of enteric fever in
London can now only be studied by the statistics of a few years, and the experiences of a longer period is
desirable for the purpose of construction of a mean seasonal curve as well as for the purpose of
ascertaining how far the curve of any one year may differ from this mean without suggestion of some
special factor of disease coming into operation in that year. It must also be remembered that the
mean seasonal curve of every community may not be the same, and that in considering how far the
curve of any one community in a particular year indicates exceptional behaviour of enteric fever, the
mean curve of that community affords a more reliable basis for comparison than that of other
communities. At the present time it is impossible to do more than state that the behaviour of enteric
fever in London in the weeks in question of 1894 was exceptional as compared with its behaviour in
the same weeks of four other years in which there has been notification of infectious disease.
In considering the circumstances which may have caused this apparently exceptional behaviour
of the disease in London in 1894, it is necessary to ascertain whether the increase in the 49th, 50th
and 51st weeks has been due to a purely local increase, its cause operating only on one or two districts,
or whether this cause has been operative over a large area of the county. A map has been prepared
showing by a spot each house newly invaded in these weeks. It is, of course, impossible to distinguish
in this manner between cases due to causes constantly operative and those due to any new factor of
disease which has come into operation; all that it can show is that the spots are distributed over a
wide area, and that there is no suggestion of local grouping.
An increased prevalence of enteric fever over a very wide area, at a time when enteric fever,
might be expected to decrease, raises question whether the disease has been disseminated
* In Diagram II., as the figures upon which the curves are based are very small, this correction has been made
in that part relating to the last 16 weeks.
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