A revolutionary material that can remove bacteria from swimming pool water could prevent the spread of an unpleasant stomach bug.

Present pool filters occasionally have problems removing the infectious form of the Cryptosporidium.

This is a protozoan - a single celled organism - which is often passed into poolwater by infected infants brought for a swim.

It is so infectious that one person with the bug could theoretically infect 100,000 others.

The most infectious form of the Cryptosporidium during one phase of its reproductive cycle, when it becomes something called an oocyst.

These are resistant to the chlorine in swimming pools which kills many infectious bacteria.

Contaminated water

Water-treatment plant use sophisticated filters to remove oocysts from reservoir water contaminated by manure and sewage overflow.

But these do not always work, and do nothing to prevent individuals using pools passing on the bug.

Chemists Ric Pashley and Marilyn Karaman of the Australian National University in Canberra have identified a crystalline material which actually attracts the oocysts and holds on to them.

The researchers, reports New Scientist magazine, found that the surface of the oocyst was scattered with phosphate and carboxylic acid molecules.

They then found a materials which naturally attract them, and picked one which not only did this, but also cracked the shell of the oocyst, destroying the contents.

Chemist James Quirk, of the University of Western Australia in Perth, said: "They've found a chink in the Cryptosporidium armour.

"The material sucks the oocyst onto its surface with such force that it collapses the whole thing."

A filter using the material would be cheap to make, says the team, and would not require any change in water flow.

They are now applying for a patent to start producing the material.

There were 4,759 reported cases of Cryptosporidium in England and Wales in 1999, although many more cases would go unreported.

The main symptoms are stomach cramps and diarrhoea, although infections in the very old, the very young, the week, and those with suppressed immune systems, such as those receiving chemotherapy were far more vulnerable.

A spokesman for the Public Health Laboratory Service said that there were simple steps that people could take to limit the spread of the illness.

He said: "It's important that if you have diarrhoea, or your child has it, you should not go in the swimming pool.

"You should also consider taking a shower before having a swim."