at the time. One outbreak in the UK provides a graphic illustration of
secondary contamination and also how the sudden onset of symptoms
can catch victims unaware and exacerbate the problem.
The outbreak occurred at a hotel in the UK where over 140 people
were ill. One chef vomited in the changing room lavatory and then
immediately returned to food preparation. Later that day he had an
episode of diarrhoea. Two days later another member of the kitchen staff
vomited into a bin outside the kitchen door and the following day two
staff vomited in the kitchen itself. The epidemiological evidence strongly
implicated the cold foods prepared by the chef who was found to be
excreting the NoV 48 h after his symptoms subsided. However, it is
clearly possible that several other foods may have been contaminated by
droplets from the vomitus from other affected kitchen workers.
In 1982 a huge outbreak in the Twin Cities area of Minnesota was
caused by a baker who was working during an episode of diarrhoeal
illness. Despite claiming to have washed his hands thoroughly after a
visit to the toilet, he transferred sufficient virus to the butter cream that
he mixed by hand to cause an outbreak which affected at least 3000
people. Shortly after, in the same area, a second outbreak affecting 2000
people occurred in which a food handler contaminated salads during
banquet catering.
There is no evidence yet of a persistent symptomless carrier state for
these viruses. They are no longer apparent in patient’s stools shortly after
recovery but this may simply reflect the insensitivity of electron micro-
scopy as a detection method.
8.5.5 Control
The problems of monitoring and control of foodborne viruses are very
different to those posed by bacteria. Testing foods for the presence of
pathogenic viruses is not possible since many cannot be cultured and the
numbers present are too low to be detected by techniques such as
electron microscopy. An alternative would be to use more readily cul-
tured viruses that are shed in the faeces, such as the vaccine polio strain,
as indicator organisms for the presence of pathogenic enteric viruses.
However, current extraction methods are very inefficient and the culture
techniques, based on observation of a cytopathic effect in cell monolay-
ers or plaques in cell monolayers under semi-solid medium, are far more
complex and expensive than bacteriological testing. Already though,
techniques based on immunoassay and nucleic acid probes with the
polymerase chain reaction promise to improve both the sensitivity and
speed of virus detection.
An interesting approach is to use coliphage, a bacteriophage which
infects the enteric bacteriumE. coli, as a viral indicator. Coliphages do
306 Non-bacterial Agents of Foodborne Illness