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On the other hand, in only four instances was there good ground for supposing that an infecting case,
suspected of causing mischief at home, had at a later date also done so at school, and in these four the
interval between return to school and development of the supposed secondary case was in one instance
less than 24 hours, and in the other three instances the intervals varied from ten days to three weeks;
in these three instances, moreover, scarlet fever was at the time prevalent among children attending
in those departments of the schools in which the secondary cases occurred.
The St. Pancras evidence generally confirms the view, which other considerations tend to support,
that the duration of potential infectivity in scarlet fever is not as a rule appreciably marked after three
or three and a half months from the date of original attack; it would further appear from the St. Pancras
experience that so far as return cases are concerned the mischief is as a rule done at home and not at
school—the part played by school infection is thus, at any rate under the St. Pancras conditions,
exercised rather through mild and missed than through recovered cases of scarlet fever.
The result of the nine years'study of the hypothesis that scarlet fever is commonly transmitted
by the flea is as follows :—
(i) There is very close correspondence in form between the last nine seasonal curves of scarlet
fever and of flea prevalence, and the autumnal maximum of the latter has invariably ante.dated that
of the former, the ante.dating being by periods of from one to eight or more weeks.
(ii) There is some correspondence between the contour of the curve of the latest major
wave of scarlet fever and that of the corresponding curve depicting annual flea prevalence.
(iii) Both scarlet fever and flea prevalence stand in close relationship with cycles of dry or wet
years.
(iv) Study of school influence in scarlet fever leads to the conviction that some factor, other
than immediate or direct personal infection from child to child, is concerned is maintaining the hold
which the disease not infrequently obtains upon particular departments or classrooms.*
(v) Study of the relation of scarlet fever to social status shows that among the well.to.do, attack
by scarlet fever may be often deferred until adolescence or adult age; in the best elementary schools
infection is common in the higher departments; in the poor schools the infants'departments especially
suffer; in the poorest schools it is not uncommon to find that the child has already suffered from scarlet
fever before coming to school at all. One of the conditions closely associated with this grading of
intensity of attack rate by scarlet fever is liability to suffer from fleabites.
(vi) In striking contrast to dissemination of scarlet fever in homes and in schools stands the
absence of any marked ability to spread in hospital wards, where susceptible children are undoubtedly
often present, but where flea prevalence is reduced practically to a vanishing point.
(vii) Study of return cases shows that the influence of hospitalism has been unduly exaggerated.
There is no doubt that cases of scarlet fever discharged from hospital, even when presenting no signs
of desquamation or of mucous discharge, are capable of producing return cases. As Mr. Thompson
originally pointed out and as Or. Arnold has conclusively shown, there is a special risk of return cases
in the poorer and more overcrowded homes, The St. Pancras figures strikingiy confirm the existence
of this special risk, and thus strengthen the conviction that some factor bound up with the natural
history of scarlet fever, the existence of which is not rendered apparent until the return of the hospital
case supplies the necessary materies morbi, must be present in these homes. It is submited that Mr.
Thompson's"obscure factor"may quite well have been the presence of fleas in several of the households
supplying return cases, and the close correspondence between the special extent of incidence ol
primary cases upon these poorer households and the special incidence of return cases upon them, is
compatible with the view that one and the same agency was concerned in the original diffusion of scarlatinal
infection and also in its later spread to return cases.
(viii) The supposed"recrudescence of infection"and the spread of infection by fomites or by
apparently healthy persons may find their real explanation on an appeal to a flea hypothesis.
(ix) Study of the geographical distribution of scarlet fever and of that of the human flea reveah
a general correspondence in the present day allocation of both; moreover, both have apparently spread
from Europe to other parts of the globe pari passu with the gradually increasing facilities of intercommunication
which have become available.
(x) The distribution, in time, of the fall in mortality from scarlet fever corresponds, so far as the
facts can be ascertained, with diminution of prevalence of fleabites in children. The period of decline
corresponds also, however, with increasing use of hospital isolation, so that the two factors, and not
one or the other exclusively, should be credited with the great improvement effected.
The question of possible influence of crowding in shelters in favouring spread of vermin and of
infectious disease was raised when, at the close of 1917, large use was made of tube railway stations
and other places of shelter on the occasion of air raids. This influence was especially suspected in connection
with the raids of September 24th—October 1st, the Zeppelin raid of October 19th.20th, the
raids of October 31st. November 1st, and those of the 5th, 6th and 18th of December; it has also been
examined in connection with those occurring, in 1918, on January 28th and 29th, on February 16th, 17th
and 18th, and on March 7th.
The flea curve constructed from the data available from medical inspections showed a rise in
1917 during the weeks ending 29th September and 6th October; again a slight rise in the week ending
27th October, possibly maintained in the following holiday week; again in the weeks ending 1st
December and 8th December; and then later a marked rise culminating in the week ending the 9th
* It may be incidentally mentioned that in London, during the past six years, special importance has been
attached to the adequate washing of floors in schools or class.rooms where persistent infection i>y scarlet fever or
diphtheria has been observed.
Summary.
Spread of
tleas and of
infectious
disease in
connection
with crowd.
inginshelters
during air
raids.