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about 6th October, with early symptoms as before in some three cases, and later development of
symptoms in seven or eight cases, with tendency again, as before, to grouping of some of these cases
about a date approximately a fortnight later than 6th October.
Possible causes of the outbreak.
(1) Personal infection.—The fact that the outbreak was not an explosive one may be held to
support a hypothesis that, after introduction of a few cases of enteric fever into the area, infection
from case to case played a considerable part in promoting further spread of the disease. Against
this supposition is the fact that for the most part the persons attacked (who lived, as has been
noted, in an area covering nearly a square mile of ground) had no ascertainable relation or association
with one another. In four instances there were multiple house invasions—three houses yielded
two cases each, and one house four cases. It is impossible to be certain as to whether the cases in
these houses were simultaneously infected, or whether the later sufferers were infected by the earlier ones.
The balance of evidence seems to favour one, at any rate, of the groups of two cases, and the group
of four cases, having received infection on one and the same date. In the other two households the
two later cases may quite well, so far as dates of occurrence of symptoms are concerned, have been
true secondary cases. No information pointing to any common source of infection outside London,
such as visits to the seaside or to hop fields, could be elicited from inquiries made in the area and from
the patients themselves, who were seen after their removal to hospital.
(2) Water and food.—The geographical distribution of the cases does not admit of explanation
on a hypothesis of contamination of a local water main. Milk, too, can be definitely excluded, as
the source of milk supply to the cases was very varied.
The extent of consumption of water-cress, ice-creams, mineral waters, shell-fish and fish was
carefully considered. It soon became clear that as regards two articles only among those concerning
which inquiry was made, namely, mussels and fish, could any serious question arise.
The result of detailed inquiry showed that of the 28 patients concerned eight had almost certainly,
seven had possibly partaken of mussels at about the time when infection must have been contracted,
while 13 had not done so. In one instance, apart from the eight referred to (that of a
woman) the patient had washed mussels and prepared them for her husband's consumption but had
not eaten any herself. Her husband remained well; and it may be noted that in other instances
also, among those above referred to, in which mussels had been eaten by a person who was later
attacked by enteric fever, a number of persons had partaken of the same batch of mussels without
ill results.
With a view to ascertaining the normal percentage of mussel-eaters in the neighbourhood.
Mr. Henley (sanitary inspector of Bethnal Green) made inquiry with regard to 67 families, taken at
random, in the streets especially attacked, and found that 22 per cent, of the adults and 5 per cent,
of the children, or about 15 per cent, of the entire population, had partaken of mussels at one time
or another during August, September and October. Accepting these figures as a standard it would
follow that out of 28 cases (16 adults and 12 children) it might have been anticipated as a matter of
mere chance that some five or six would have eaten mussels.
It may be pointed out that the inquiries in the case of the 28 patients attacked were not quite
on all fours with those in the case of the 67 families. In the former case, in addition to making
inquiries at the home, the patient himself or herself was, as a rule, seen and questioned in the hospital ;
while in the latter case particulars were obtained at the home alone, no special inquiry being made
by a personal interview with each individual member of the families concerned. This is a point of
much importance in dealing with an article of food like mussels. It is probable, in the light of the
histories obtained from the patients in hospital, several of whom were able to give information
which could not have been obtained from their friends, that a higher or lower figure might
have been obtained, in the case of the unaffected families, if personal inquiry had been
made in all instances, as was in fact done in the case of the actual patients. But the incidence of
the disease upon mussel-eaters, viz., 9 or 10 out of 28, was not far removed from the incidence, 5 or 6
out of 28, which might a priori have been anticipated, having regard to the extent to which mussels
were consumed in the district. In fact, the slight excess may be held to have been, mathematically
speaking, within the limits of probable error. This analysis does not, therefore, attach any suspicion
to mussels.
Mussels may, indeed, be almost absolutely excluded as the source of infection, for it will be
noted that at least 13, and possibly 20, of the 28 persons attacked, did not at any time eat mussels.
Out of these 28 cases some 22 or more must, as has been seen, be taken as the number due to the
special cause, operating in the area during September and October, the remaining cases being regarded
as sporadic cases. Yet, even if all the mussel-eaters were included among the 22, the group would
still include at least 7 and possibly 14 persons who had not eaten mussels.
Turning now to the question of fish. A great deal of the fish consumed was obtained in the
form of fried-fish, and on inquiry it was found that 24 of the patients had probably, while the remaining
4 may have possibly, partaken of fried-fish at or about the time when they must have been infected.
Mr. Henley made inquiries, as he did in the case of mussels, with a view to obtaining a standard to
apply with regard to fried-fish eating. He found that 77 per cent, of the adults and 46 per cent, of
the children, or 63 per cent, of the whole population, had been in the habit of eating fried-fish during
August, September and October. Hence out of the 28 persons attacked, it might be assumed that
some 18 would be ascertained to be fried-fish eaters, had the question been one of mere chance coincidence.
The number 24, found as a matter of fact to have eaten fried fish among the 28 sufferers, is