The researchers compared 160 men and women who were treated for deep vein
thrombosis (DVT) with 160 patients treated for other conditions. The DVT
patients were four times as likely to have made a journey of four hours or more
in the preceding four weeks (Chest, vol 115, p 440). Ferrari and his
team believe the problem may be even more widespread, because many DVT cases are
never reported.

Of the 39 DVT patients who had made a long journey in the month before being
hospitalised, two had travelled by train, nine by aircraft and 28 by car.
Airlines have been quick to point out that other forms of transport are also
implicated. “This is an issue for the transportation industry in general, not
just the airline industry,” says a spokesman for British Airways.

However, there is some evidence that air travel poses additional dangers. In
1994, a team at Frankfurt University Hospital reported that simulated 12-hour
flights increased blood plasma thickness and fluid retention in healthy people
(Aviation, Space & Environmental Medicine, vol 65, p 930). They
concluded: “Alterations produced by long-distance air travel could intensify the
risk of developing deep venous thrombosis in passengers with predisposing risk
´Ú˛ął¦łŮ´Ç°ů˛ő.”

Concerns that surgeons’ instruments might pass on new variant
Creutzfeldt-Jakob disease (vCJD), the human form of BSE, intensified last month
with news that the infection is present throughout the lymph tissue of victims,
not just in the central nervous system
(This Week, 23 January, p 5).
Because there is no sure way of sterilising instruments contaminated with prions, the
discovery prompted calls for surgeons to use disposable instruments for
operations involving lymph tissue. But so far the British government has not
committed itself because of the high costs.

Now there is evidence that attempts to disinfect instruments by “pressure
cooking” them at high temperatures in an autoclave might do more harm than good.
David Taylor of the Institute for Animal Health in Edinburgh found that
increasing the temperature of the autoclave actually made it harder to destroy
CJD prions. In one experiment, infected tissue samples were heated at 134 °C
for 9, 18 and 30 minutes. The treated samples were not infectious. However, when
the experiment was repeated at 138 °C, the tissue was still infectious. In
Britain, the standard temperature range for autoclaving instruments is 134 to
138 °C.

Taylor believes the slightly higher temperature “fixed” the prion, allowing
chemical links to form that made the molecules more stable. He is preparing his
results for publication.

Mark Pepys, who specialises in the chemistry of brain disorders at the Royal
Postgraduate Medical School in London, says Taylor’s explanation “involves a lot
of speculation because we just don’t know enough about the agent that causes CJD
yet”. But the suggestion doesn’t surprise him. Even very small temperature
changes can cause changes in a protein molecule’s shape, he says. This might
involve bonds that by themselves are quite weak. “But if there were enough of
them, perhaps hundreds, the effect of strengthening the molecule could be
dramatic,” he says.

“Taylor’s work highlights the difficulty in inactivating prions,” says John
Barbara, a microbiology consultant to Britain’s National Blood Authority. He
says the findings strengthen the case for developing ways of physically
excluding prions from blood products.

In terms of surgical instruments, Taylor says that a strong solution of
sodium hydroxide for one hour followed by autoclaving at 136 °C for one hour
is fairly effective. “If we combine alkali solutions with the right grade
surgical steel that can stand up to it, it will be possible to improve
sterilisation,” he says.

For now, though, he says that the only completely safe way to deal with
contaminated items is to throw them away.