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101
Report of the Medical Officer of Health.
on the assumption that the outbreak was water-borne. I have, moreover, had the advantage of
conferring with Dr. Houston, the Director of Water Examinations. As a result of this conference
it appeared to me impossible to fit the facts of the outbreak with a hypothesis of water causation.
Milk.—The source of the milk consumed was investigated in all instances. In Bethnal Green
each retail supply was traced to the wholesale source. It was found that the milk partaken of by the
various sufferers came from widely separated parts of the country. There was no indication of common
origin for any notable percentage of the cases in any of the affected localities.
Spread of disease from case to case.—The outbreak was explosive. The dates of onset of
illness in Bethnal Green, and in most of the other localities affected, suggest that infection was contracted
on Auguat the 10th, 11th, or 12th; but there were other later (and much smaller) explosive
prevalences in some of the London boroughs, the time ot contraction of infection in the most marked
of these being about September 1st; there were, moreover, one or more earlier prevalences, contributing,
however, only a few cases. In the "multiple house invasions" the dates of onset were, as a rule, within
a few days of one another; and, though there are a few cases in which there may be some doubt on this
point, in the majority infection seems to have been introduced into the invaded households at one and the
same time. In 24 of the 31 London groups, the dates of onset of cases range from August 10th, or
11th to nearly the end of September (see Diagram). In seven other groups the dates of onset commence
and correspondingly terminate two or three weeks later. Cases belonging to the same house are connected
together on the Diagram by lines, and it will be seen that few of them admit of being regarded
(from the point of view of time of occurrence) as "secondary cases." Speaking generally, it was noted
that there was an almost absolute absence of intercourse, relationship, or association between the sufferers
in different houses which were invaded. Dr. Byett, Medical Officer of Health of Shoreditch, who
devoted careful attention to this question, was of this opinion, and my own detailed investigations, more
particularly in Bethnal Green, led me to a similar conclusion.
The possibility was considered of common visits to the hopping grounds in Kent, for example,
or to seaside resorts, such as Southend, Yarmouth, Ramsgate, Folkestone, etc., and the subject of
country outings generally was carefully enquired into. Incidentally the question of conveyance of
infection by bathing in the sea, or in canals, rivers, etc., and by the use of swimming baths was investigated,
but, generally speaking, in the 200 cases with entirely negative results. Throughout the
enquiry the possible operation of a carrier or carriers was prominently kept in mind. As facts, however,
were gradually accumulated, it became increasingly clear that none of these hypotheses could be
accepted in explanation of the outbreak.
Food infection.—In all instances, in Bethnal Green, enquiries were made as to the consumption of
shellfish, fish, uncooked vegetables and ice-cream, and questions were generally asked as to the drinking
habits of the sufferers (ginger-beer, aerated-waters, etc.). Two articles of food only (mussels and fried
fish) had been partaken of by a considerable percentage of the Bethnal Green patients within a month
preceding the onset of illness. As regards the former, among the total number of cases (79), occurring in
the whole of Bethnal Green, between 10th August and 18th October, it was found that there were at
least 45 in which mussels had not been consumed. Limiting consideration, however, to the cases
occurring in the area of special prevalence between the dates named, there are found to be, out of a total
of 50 cases, 26 with a negative history as regards mussels, and 24 with a positive history. It is thus
impossible to regard infection by mussels as the sole and sufficient cause of the special incidence in
Bethnal Green.
It will be seen, however, that the percentage of mussel eaters is a high one. From a calculation
made for me by Mr. Roberts, chief inspector at Billingsgate, it appears that nearly 300,000 Londoners
were every week consuming mussels at the time of the outbreak. This is considerably less than ten
percent. of the total population of London. But Bethnal Green consumes far more than its share
of mussels, and it may be assumed that, in a population such as that attacked in this outbreak, nearly
half would (at this time of year) give a history of eating mussels. In a number of instances the patients
themselves were found to be under the impression that their disease was due to their having eaten
mussels on a particular occasion. Examination of these instances and of other cases, in which, apart
from any belief on the patient's part, mussels might conceivably have been at fault, shows that it had
not infrequently happened that other persons as well as the sufferers had consumed the suspected
mussels, thus:—
In case (6), the mussels were shared with the patient's wife, who remained quite well.
In case (15), the mussels were shared with the rest of the family, who remained quite well.
In cases (20), the mussels were shared with other members of the family, who remained
quite well.
In case (24), the mussels were shared with the patient's wife, who remained quite well.
In case (27), the mussels were shared with the patient's wife, who remained quite well.
In case (39), the mussels were shared with the patient's mother, who remained quite well.
In case (47), the whole family ate mussels two or three times a week ; only one member
suffered.
In case (48), the mussels were shared with the patient's wife, who remained quite well.
In case (57), the mussels were shared with the patient's mother, who remained quite well.
This list must not be regarded as including all the cases in which more than one person had partaken
of a particular batch of suspected mussels, for the number of instances in which the patient was
definitely known to have purchased mussels not consumed by other members of the family was very
small. There was, moreover, no single instance of "multiple house invasion," in which all the members
of the family attacked gave a history of having eaten mussels.