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113
INFECTIOUS DISEASES.
The number of cases of infectious diseases which occur from year to
year is dependent on several factors, chief amongst which are the number
of susceptible persons and the risk they run of being infected. The
number of susceptibles is an unknown factor and must obviously vary
from year to year, but when it reaches a certain maximum (the risk of
infection being present), then it is that we experience what we term
epidemics. This maximum varies according to the type of disease; for
instance, in Measles it appears to occur every second year, and in Scarlet
Fever every seventh year, and so it is that epidemics of these fevers can
be fairly safely predicted and measures taken to combat them in advance
of their arrival.
The risk of infection varies according to the number of "carriers" of
the various diseases existing in a given population, and the amount of
overcrowding under which that population is living. It is obvious that
in the less crowded rural districts the chance of a "disease carrier"
spreading infection to a large number of persons and the spread of infection
from these to others is more remote than in a densely populated district
such as we have in Southwark. The fact that the number of infectious
disease cases is perhaps larger in the Borough than in some other less
crowded Boroughs is therefore not to be wondered at. The incidence or
"attack rate" will be lessened as and when overcrowded conditions are
abated.
During the year under review it will be seen from the tables following
hereafter that there was a rise in the incidence of certain of the infectious
fevers, and a fall in others.
Measles constituted the chief epidemic of the year, and was responsible
for 65 deaths, all of which occurred in children under 5 years of age.
Resulting from this, it will be found that the Infant Mortality rate has
increased.
The number of cases of Diphtheria also increased, and it is worthy of
note that there was a greater proportion of deaths than usual from this
cause, indicating that the disease was of a slightly greater virulence than
usual.
On the other hand, Smallpox gradually waned and towards the
summer entirely disappeared. Similarly, the outbreak of Scarlet Fever
experienced in 1933 gradually subsided.