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cases were obtained 10 days and 5 days after the date of onset
respectively. One of the three, V.B., with a positive specimen was
seized with very severe symptoms less than 10 hours after eating
a boiled duck egg. The other two had eaten Russian salad containing
hard-boiled duck eggs approximately 16 hours before. V.B. fed in
a separate dining room from the other two and the onset in her case
was so violent that the infecting agent was almost certainly ingested
within a matter of hours.
In these circumstances investigation was focused more intensely
on the domestic supply of duck eggs. The whole of two days' layings,
36 eggs from 31 ducks, were submitted for examination and the
laboratory reported that one egg yielded a heavy growth of S. typhimurium.
Duck eggs were thereafter excluded completely from the
dietary and no further cases occurred.
Having established a source of infection the subsequent investigation
was devoted to confirming the source by phage-typing and to
identifying the infected bird or birds. By a process of segregation,
one duck was found to be laying infected eggs after the examination
by the Epsom Public Health Laboratory of 142 duck eggs. The last
laboratory examination of an infected egg from this duck showed that
whilst the yolk was heavily infected the albumen was sterile. Of the
first three eggs from this bird, after identification, laid on consecutive
days, the first was sterile and the succeeding two infected. Cultures
from two of the patients (one from the first group of cases and one
from the second group) and from two infected eggs were referred for
phage-typing to Dr. Felix at the Central Enteric Reference Laboratory
who reported that all four were Vi Strain, Group 2.
The question now arose as to what should be done with the domestic
flock of ducks, a consideration which depended on the extent to which
the flock was infected. Was it safe to eliminate the offending bird only ?
To assist in deciding this question, the help of the Ministry of Agriculture
and Fisheries Veterinary Laboratory Service at Weybridge was enlisted.
Blood from all the 31 ducks and 1 drake was tested for agglutination
against S. typhi-murium with the following results:—
6 negative;
6 only slightly doubtful;
20 positive or very doubtful and should be destroyed.
(Eight of these positive in very high titre.)
The duck which had been found to be laying infected eggs was not one
with a high blood titre to S. typhi-murium, but was in the slightly
doubtful group.
In view of this evidence of extensive infection, 23 of the birds were
destroyed and the remaining 9 with the highest titre were transferred
to the Ministry of Agriculture and Fisheries Laboratory at Weybridge
where routine bacteriological examinations were carried out on faeces
and on the eggs laid by the ducks until they went out of production.
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