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The actual mild cases in attendance are by far the most serious cause of spread, amounting to
80 per cent. This makes the detection and control of diphtheria easier than it otherwise would be,
as it is a simple matter, on rapid inspection, to single out those presenting clinical symptoms.
Another point of extreme importance is that in London an overwhelming majority of these cases
occur within certain age limits. It is rare to find a class whose average age is under 5 or over 8
spreading diphtheria. In not one single instance has a babies' class been found with diphtheria
spreading in it, nor has a class over 10 been found to do so.
Average Age
of Class.
Percentage of
Total Outbreaks.
3—4 —
4—5 2.7
5—6 13.5
6—7 43.2
7—8 19.
8—9 5.7
9—10 8.1
10—11 8.1
Over 11 —
This very remarkable fact which our investigations have brought out requires explanation.
In order to give a tentative explanation, other facts connected with diphtheria, as it is at present
occurring in London, must be taken note of. Briefly recapitulated they are these:—
1. When a school becomes a source of infection, it is generally found that the cases are connected
with a class or classes in which the average age of the children is between 5 and 8. Rarely do
classes below 5 or above 8 become sources of infection, and never has it happened in our investigations
that a class whose average age is less than 4 or above 10 has been found to be acting as a
disseminating centre.
2. These classes become sources of infection because the children at these ages appear to have
the power of partial resistance to the onslaught of diphtheria bacilli, and a large proportion of them
are capable of attending school while suffering from slight attacks. Many instances have occurred
in which the majority of the members of a class during this age period (5—8) have suffered from
slight attacks of diphtheria, to which attention is only drawn by the fact that younger children in
the family suffer from severe diphtheria and one or two members of the class are more severely
affected and are notified as diphtheria; thus, at Single-street School, in December, 1903, it was
found that a mild epidemic of sore throat had been slowly working its way through Standard I.
(aged 7) for six weeks, although there had been only 3 cases of notified diphtheria. It was
found that 29 out of 54 children had suffered from the illness of which the characteristic symptoms
were vomiting and sore throat, but in no case except those notified had the complaint been severe
enough to keep the child from school more than one day. It was very easy to tell on inspection of
the class which children had suffered, their pallor and listlessness contrasting with the ruddiness
and liveliness of those who were well. On bacteriological examination 2 children showed
diphtheria bacilli still, and on their exclusion the outbreak ceased.
3. Frequently it occurs that a new child admitted to such a class from another neighbourhood,
or a child who has been out of school for a long period on account of illness or residence in another
part of the country, suffers from diphtheria severely, while the others are having slight sore throats
and nasal discharge.
Thus at Church Manor Way School, in January, 1905, in one week two little girls suffered
from diphtheria; one had been out of school for the whole of the autumn and winter, and she
within three days of her return fell ill with diphtheria and died. The other case was her particular