Three members of family A, who had diarrhoea on 20 October, lived
on
a small arable farm
which had 10 cattle. Manure from the animals was used to fertilize the
ground for growing
potatoes which were then offered for retail sale, unwashed, directly from
the farm. The mother
from family B bought potatoes, which were covered with manure, from
family A in early
November and over the subsequent 10 days she became ill with diarrhoea
and
her daughter and son both became ill with bloody diarrhoea. The mother
from family C
visited family B
while the daughter from the latter family was symptomatic; the mother
developed diarrhoea
several days later. The mother and two sons from family D visited family
B while the son from
the latter family was symptomatic; the first son developed bloody diarrhoea
6 days later which
progressed to development of haemolytic-uraemic syndrome. Direct culture
of faecal samples
onto cefixime rhamnose sorbitol MacConkey agar failed to isolate E.
coli O157 from any of
the symptomatic patients, and direct culture onto cefixime tellurite
sorbitol MacConkey agar
isolated the organism from only one patient. In contrast, a combination
of
isolation of E. coli
O157 by immunomagnetic separation and detection of E. coli
O157-specific secretory IgA,
suggested E. coli O157 infection in all eight symptomatic patients,
but not in any of the family
members who were not ill. Two children who excreted the organism for 60
and 89 days
respectively were the only two patients who did not develop a secretory
IgA response. E. coli
O157 was not isolated from potatoes from the farm and faecal samples from
the farm animals were not available for examination. The study illustrates
the need to use the most sensitive
methods available during the investigation and follow up of cases of
E. coli O157 infection.
An outbreak of infection due to verocytotoxin-producing
Escherichia coli O157 in four families: the influence of
laboratory methods on the outcome of the investigation
