A VIRULENT strain of Escherichia coli that kills 60 people a year in
the US alone is more common in cattle than previously thought. The American meat
industry says cleaning carcasses will stop the spread of infection. But Canadian
scientists say meat is infected after the carcass is cleaned, because
meat-cutting equipment in packing plants cannot be disinfected.
The bacterium E. coliO157:H7 produces toxins that cause bloody
diarrhoea and can lead to kidney failure. Cattle pick it up from faeces in
drinking water, says Clell Bagley of Utah State University at Logan. But it has
not been clear how common it is, as surveys give differing results.
At a public meeting in Alexandria, Virginia, last week, the US Department of
Agriculture reported that a test developed by IGEN International of
Gaithersburg, Maryland—which is four times as sensitive as previous
tests—found E. coliO157:H7 in half the cattle being fattened up
during the summer for slaughter. This is twice as many as the highest rate
recorded before. The rate drops to 1 per cent in winter, and the seasonal effect
may have made earlier estimates too low.
Advertisement
“E. coliO157:H7 is far more widespread than we thought,” says Caird
Rexroad of the USDA. More than 80 per cent of 900 calves tested had already been
exposed to it, and in 13 of 15 herds tested at least one animal was infected.
“We can study how to limit infection,” says Bagley, “but we’ll never be able to
produce sterile animals.”
So the USDA is considering more stringent measures to keep bacteria from
spreading after slaughter. The American Meat Institute, an industry body,
presented data at the meeting showing that cleaning the entire beef carcass with
steam and weak acids after skinning reduces E. coli to almost
undetectable levels. James Hodges of the AMI says the regulators should ensure
carcasses are clean before they are cut up.
But infection spreads while the carcass is being cut up, says Colin Gill of
the Canadian government’s Lacombe Research Centre in Alberta. “Modern
meat-packing plants in North America and Europe have two or three kilometres of
conveyor belt made of hinged, interlocking plastic strips,” he says. One belt
carries carcasses past “cutters”, who toss beef cuts, trimmings and waste onto
further belts. “The surface is cleaned between shifts. But some belts are so
close to the floor you can’t clean under them, while the drive equipment has
shields that can’t be removed.”
The cutting plant is kept at 10 °C to discourage bacterial growth, but
the drive mechanisms heat up to temperatures E. coli love. “Populations
of bacteria can persist in this equipment for years,” says Gill. “When you turn
the belt back on the stuff comes out of the hinges and drive mechanisms.”
“The problem is that meat regulators are veterinarians,” says Gill. He adds:
“They don’t know anything about plant design.”