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45
beds have, therefore, during the war, been available for other much needed uses. Scarlet fever and
diphtheria reached the crest of one of their epidemic waves in 1907, and in that year scarlet fever was
just three times as prevalent as diphtheria. After the lapse of some seven years the next wave swelled
to a maximum in 1914; since that time both epidemic diseases have declined, but scarlet fever has
diminished more than diphtheria, so that in 1917 the scarlet fever notifications, for the first time on
record, were less in number than those of diphtheria; the same phenomenon was observed
in 1918.
In recent reports the relationship of scarlet fever to rainfall and flea prevalence was discussed.
The experience of 1918 has been in keeping with the views previously expressed with regard to
these Questions. (See p. 37 of the Annual Report for 1917.)
Comparison
of seasonal
prevalence
of Fleas
and Scarlet
Fever
The seasonal variations in the prevalence of fleas and scarlet fever are illustrated in diagram "A"
The seasonal incidence of diphtheria is also shown for purpose of contrast. The diagram is divided into
two sections, the first shows the monthly prevalence of fleas in relation to the monthly case rates of
scarlet fever and diphtheria during the ten years 1909-1918. A small inset diagram gives the mean
monthly rates for the ten years ; and, as the maximum seasonal incidence of scarlet fever cases is about
one month later than the maximum prevalence of fleas, the case rates are ante-dated one month to
facilitate comparison. The second section of the diagram is designed to illustrate how far a deviation
from the quarterly average of flea prevalence is associated with a corresponding deviation from the
average quarterly incidence of scarlet fever, as well at all ages as in certain age-groups; the averages
for diphtheria at all ages being also shown. The contour of flea prevalence is based upon figures which
post-date by one month the figures for cases of scarlet fever and diphtheria.
The first section of the diagram shows a greater measure of association of the annual prevalence
of fleas with scarlet fever than with diphtheria. The three years of highest prevalence of scarlet fever
and fleas (1913-15) are followed by three years of relatively low incidence, but in diphtheria the correspondence
is not so close. In some years there is a secondary prevalence of diphtheria following the
normal autumnal incidence, and in 1914 it will be seen that the February case rate of diphtheria exceeded
the normal autumnal maximum of the preceding October. There is no evidence of any similar secondary
prevalence in the case of scarlet fever, although the decline after the normal autumnal maximum is not
equally regular in all years.
The common lodging-house records are continuous throughout the period of ten years ; in the case
of school records the continuity is disturbed by holidays at Christmas, Easter, Whitsun and in August.
It will be noted that the former records correspond more closely than the latter with the scarlet fever
curve.
In the second section of the diagram the average figures for each quarter are taken as a basis in
order to eliminate the wide fluctuations of monthly records. The diagram shows the extent of deviation
in any first quarter from the average of nine first quarters in the period of 1910-18, and so on for
other quarters. The general similarity of the contours of the flea and scarlet fever prevalences is
significant, especially in view of the less marked correspondence shown in the case of
diphtheria.
Reverting to the interval, of one month or so, between the maxima of flea and scarlet fever
prevalence, the question arises whether this interval points to the fact that there are two distinct phenomena
controlled by one factor, (such, for instance, as meteorological conditions) or whether a part of
that interval can be taken to represent evolution of a scarlet fever germ. In either case the facts imply
that the conditions which favour flea prevalence are either identical or intimately associated with those
influencing prevalence of scarlet fever, and a presumption is raised that steps directed to the elimination
of fleas may loosen the foothold of scarlet fever. Effect is as far as practicable being given to this view
in London at the present time. Thus, as a case in point, reference deserves to be made here to a
prevalence of scarlet fever in Southwark in the summer of last year. The outbreak occurred at a
time when the amount of scarlet fever in London as a whole was exceptionally low. The area
affected was very limited but the incidence within the area was very high. Application was made to
the borough council to disinfect the infants' department of the Council's school central to the area, the
records of which showed a greatly excessive proportion of flea-bitten children. This was done, and in
addition the officers of the borough council visited homes and disinfected rooms and bedding associated
with scarlet fever cases. This action was followed by marked reduction of prevalence of scarlet
fever.
The prevalence
of
scarlet fever
in relation
to standards
of cleanliness
A point of some importance with regard to the flea hypothesis of causation of scarlet fever is the
fact that there is an undoubted tendency, at certain times and in certain localities for the disease to
occur in households and in schools in which the standard of cleanliness is not a low one. The question
was considered in the Annual Report for 1914, but, as it has especial importance as affecting the flea
hypothesis, further study has been devoted to it. Examination of the literature shows that there is
considerable difference of opinion with regard to the relation of the incidence of scarlet fever to "social
condition." There is apparently general agreement that mortality rates are almost always hgher
among the poor, but in the case of incidence rates, the facts are more difficult of ascertainment. In the
Annual Report for 1914 it was pointed out that the question is much complicated by the influences of
age and of school attendance and the conclusions reached may be briefly summarised.
(a) Contrasting poor with well-to-do boroughs the incidence of scarlet fever is excessive in the
former at ages under 5, but after that age the incidence in the two classes of boroughs is almost
exactly the same, indeed after 12 or 13 it becomes, if anything, higher in the richer than in the poorer
boroughs.