View report page

80
There was no heightened autumnal prevalence in 1922, there being a steady
downward tendency in the notifications throughout the year, in striking correspondence
with 1894, which year was (like 1922) preceded by two years of exceptionally
high prevalence.
Rainfall and
flea prevalence.
In last year s report the influence of rainfall upon scarlet fever prevalence was
traced year by year through the period 1891-1921, and the conclusion was reached
that the influence of an excess or defect of rain is largely modified by the extent of
susceptibility of the population at the time. In 1922 the rainfall returned to
normal after two years of drought, accompanied with high scarlet fever incidence,
and the effect of merely average rainfall, coming upon conditions of depletion of
susceptible units in the population, was practically to obliterate the usual autumnal
wave of scarlet fever, as will be seen on reference to the diagram shown on page 81.
The rainfall of 1922 differed little from that of 1913 or 1919, but the scarlet fever
contours of these years are in marked contrast to 1922. The autumnal prevalence
of diphtheria in 1922 was also out of proportion to the high prevalence which
marked the early weeks of the year.
The relationship between flea prevalence and the incidence of scarlet fever is
shown in the diagram on page 81. With two exceptions, 1909 and 1922, there is
always a slight lag in the attainment of the scarlet fever maximum, which follows
from 2 or 3 up to 9 or 10 weeks after the flea maximum. In 1909 there was an
apparent exception to this rule, the highest number of notifications being attained
during a milk outbreak of scarlet fever in June, though a second peak occurred
later in September, 5 weeks after the attainment of the flea maximum. In 1922,
as already observed, there was practically no autumnal wave of scarlet fever, and
it is not, therefore, surprising that the lag of the maximum of scarlet fever upon
the flea maximum was not apparent in that year. The curve showing flea prevalence
is based upon the records of flea-marked beds in common lodging-houses
for the first four years shown; thereafter the curve shows the percentage of children
found in the course of medical inspection to have Seamarks. The common lodginghouse
records show a far greater autumnal prevalence than do the school figures,
and to this extent accord more with common experience. The weekly fluctuations
shown in the school records is noteworthy in view of the numbers upon which the
percentages are based; one important factor in these fluctuations is the great
contrast in the conditions in this respect found in different schools of the same
district, a circumstance which has to be borne in mind when following the weekly
contour of prevalence. The fluctuations from week to week may in part be
explained as resulting from differing character of the groups of children, entrants,
&c., dealt with in the course of school routine inspections at the time. The breaks
in the flea records after 1912 are due to holiday periods.
A noticeable point in regard to the contour of the flea prevalence in the last
two years is the comparative absence of seasonal fluctuation. The tendency is
downward throughout the course of the school records, i.e., 1913-22, but the last
two years do not show a minimum incidence in the winter season, and subsequent
autumnal rise, to the same extent as earlier years.
Dr. F. M. Turner, Medical Superintendent of the South-Eastern Hospital of the
Metropolitan Asylums Board, in a paper read recently before the Royal Society of
Medicine drew attention to multiannual fluctuations of the average age of scarlet
fever cases, and to the fact that there has been a slow but continuous increase
in the average age of cases in London during the past thirty years. The increase
occurs mainly among females; thus in the five years (1895-9) the average age of
notified cases was—males, 8.61 years; females 9.12 years. In the five years
(1916-20) the averages were 8.67 and 9.88 years. The difference in the average
for the two sexes has thus in the course of 21 years increased from .51 to 1.21
years. The difference is, apart from changes due to the war, not greater perhaps
than could be accounted for by the nature of the movement of population into