The hygiene mythbuster

25 July 2014

This issue Seán Derrig, scientific director at Chemex International, puts antimicrobial surfaces under the microscope

We were shopping for a new fridge at the weekend. I was having real difficulty finding anything without ‘antimicrobial’ surfaces "conforming to ISO 22196”. When I started questioning this I’m not sure who was more uncomfortable: the doomed salesman or my long-suffering wife.

There are plenty of different surfaces on the market for which all sorts of germ-killing properties are claimed, but do they really work and how are they tested? A good example is the NHS spending a fortune on brass handles and taps despite the most recent research undermining their utility even further.

There are two intrinsic flaws in all ‘antimicrobial’ surfaces. First and foremost is that You Can't Disinfect Dirt: surfaces need to be physically clean before you can disinfect them. That’s why alcohol foams and rubs can’t be used on dirty hands.

The second flaw is more subtle; once you tell people a surface is self-sterilising they are far less diligent in cleaning it. Why waste time cleaning something in a hospital that’s ‘proven’ to kill germs on contact? One argument is ‘antimicrobial’ surfaces can’t hurt and might do some good but I’ve also seen claims that they can reduce cleaning cycles. This is dangerous nonsense.

Let’s go back to ISO22196. One could be forgiven for thinking that something with an ISO standard must be effective. Surely no-one would claim conformance to an irrelevant standard? But having looked it up that’s just what that standard is. It’s nonsense. You put some bugs in – essentially – distilled water and leave them in contact with the test surface. If 99.9% are gone 24 hours later it’s a pass. So a huge test time, a very low standard to achieve a pass, no organic matter – I suspect the bugs die of starvation or boredom.

What might this standard mean in a hygiene or infection control setting? Unless hospitals can get patients to pass on infections in distilled water this test is quite simply irrelevant.

In contrast BSEN1276 (a standard test for disinfectants) requires a hundred-fold greater kill rate in under five minutes. For my money that’s a far more relevant test when killing bugs is critical.