THE food poisoning bacteriumEscherichia coli O157 is now officially
as dangerous as the agents that cause anthrax and rabies.
Alarmed by the plight of six microbiologists who became seriously ill in 1996
after working with E. coli O157, Britain’s Health and Safety Executive
(HSE) has pushed the European Union to introduce stricter safety rules for
anyone working with the bacterium in the lab. They must come into effect by 30
“Luckily no one died, but at least two were extremely ill with renal failure
and required kidney dialysis,” says Mark Bale, head of the HSE’s biological
agents policy section. “And these were not infants or elderly people seen as
specially vulnerable to the bug—they were young, healthy adults.”
E. coli O157 has been bumped up from a hazard group 2 pathogen to
hazard group 3. This means that the bacterium now commands the same degree of
caution as the pathogens that cause anthrax, rabies, AIDS, tuberculosis, typhoid
fever and BSE. This is one notch below the most dangerous
classification—hazard group 4—which includes the viruses that cause
Ebola, Lassa fever and smallpox.
Other strains of E. coli remain in hazard group 2, which also
includes most strains of Salmonella, viruses such as Herpes
simplex and the adenoviruses and rhinoviruses that cause common colds.
The infected researchers came from different parts of the country. None was
infected after working with samples taken from the most famous British E.
coli O157 outbreak, in Lanarkshire, Scotland, which emerged before
Christmas 1996 and killed 20 pensioners.
“People ought to be aware of how low the infective dose is,” says Bale.
“Fewer than 10 organisms can give you a life-threatening infection.”
The new rules will affect laboratory work on E. coli O157 in two
main ways. Workers at intermediate risk are clinical microbiologists in
hospitals and abattoirs who regularly analyse faecal samples to test for the
bacterium. From now on, they will be required to work in a separate room from
The researchers at highest risk are those who routinely culture the bacteria
and work with it. They must now operate in separate purpose-built laboratories.
The lab must have an inward air flow to prevent the escape of any airborne
E. coli O157. Researchers must use sealed glove boxes whenever they work
with aerosols containing the bacteria.
“There’s a big difference when people are culturing billions of these
organisms,” says Bale. “If any get on your lip, that’s it, you’re infected.”