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17 samples of raw meat from the slaughter houses operating within the Borough were submitted
for bacteriological examination, counts ranging from 400 organisms per gramme at 35°C
to 3.5 million were obtained. All the specimens were free from salmonella organisms. A further 31
samples of raw meat and chicken were submitted from wholesalers and manufacturers premises
the counts ranging from 100 to 13 million organisms per gramme at 35°C. Salmonella organisms
were isolated from 3 samples. They were typed as S. derby, S. typhimurium U71 and an unnamed
strain.
SPECIAL LABORATORY INVESTIGATIONS
Bacillus cereus
During July and August complaints were received from members of the public who had become
ill after eating food prepared at a Chinese take-away restaurant. The clinical symptoms included
vomiting and nausea and were mostly of short duration, twenty-four to forty-eight hours. The incubation
period was very short, forty-five minutes in one instance. On tracing the food consumed it was
found that everyone affected had eaten fried rice as part of their meal. There was close collaboration
between the Central Public Health Laboratory at Colindale and the health department and numerous
samples of food were examined including boiled and fried rice, beaten egg, sweet and sour vegetables
beef curry, flour, breadcrumbs and seasoning. Bacillus cereus, an aerobic sporing bacillus, was
isolated from the remains of the meal consumed and from boiled and fried rice obtained at the
restaurant. Bacillus cereus is common in soil, on vegetation and in many raw or processed foods.
Methods of preparation of the rice were investigated in great detail and it was found that it was
the custom to boil the rice at 8.30 a.m. approximately. This was then piled in large colanders and
left to cool at ambient temperatures. A crust formed over the surface which prevented the interior
of the pile of rice from cooling. At no time was cooled rice refrigerated. Before the premises opened
to deal with customers' orders, quantities of the cool, boiled rice were mixed with beaten shell eggs
and fried. This was then kept warm on a tray near the stove and reheated quickly in small quantities
as required. A bowl of beaten egg left uncovered in the kitchen was replenished as the initial quantity
was used, and any remaining at the end of the day was refrigerated for use next day. Further rice
was boiled during the afternoon to meet the evening requirements but this was usually sold as
"boiled rice". Any which was left was reclaimed to use as fried rice the following day. It is believed
that this method of rice preparation is a traditional practice in Chinese restaurants. A further similar
outbreak occurred shortly afterwards. In this case a different restaurant was concerned but the
methods of preparation of the rice were almost identical.
Following these outbreaks improved methods of rice preparation were discussed with Dr.
Betty Hobbs of the Central Public Health Laboratory and were then translated into Chinese. The
recommended methods were put into operation at the restaurant where the original outbreak occurred
and frequent check samples of the rice are continuing. If the new methods are practical and successful,
efforts will be made to enforce their use in all restaurants where rice is boiled and fried.
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