Bacteria normally linked to stomach ulcers and even cancer may turn out to actually protect children from dangerous infections.

Diarrhoeal diseases kill many thousands of children each year, mainly in developing countries.

German scientists are suggesting that the Helicobacter pylori bacterium, which is carried by a large swathe of the population from childhood onwards, may help the body fight off the other bugs which cause them.

A study published in the Journal of Infectious Diseases tested almost 2,500 children aged between five and eight to detect the presence of H. pylori.

They found that while 54% of H. pylori positive children had suffered some sort of diarrhoeal illness in the previous three months, more than 76% who were not carrying the bacteria had suffered an infection.

This roughly meant that the H. pylori children were only half as likely to get such an infection.

Eradication debate

Experts are currently debating whether it is worth using antibiotics to eradicate H. pylori infected children and adults.

Although a large number of people carry the infection, a very small number go on to develop stomach ulcers as a result.

And in a tiny number, H. pylori has been implicated in the development of gastric cancer.

The study results add weight to the argument that, if eradication therapy is warranted, it should at least be left until after childhood, so that children could benefit from the "protection" offered by H pylori.

Dr Dietrich Rotherbacher, who led the study, said: "It may well be that the benefits of colonization in most carriers outweigh the costs, since only a small proportion of H. pylori carriers develop clinically-related diseases during any time during their life."

However, a UK expert suggested that the study results did not offer concrete proof that H. pylori infection could be beneficial.

Dr John Atherton, a senior research fellow for the Medical Research Council based at Nottingham University, said that a separate study had in fact suggested H. pylori carriers were in fact more vulnerable to diarrhoeal infections.

He said: "The data is still a bit unclear. It's potentially an important study. There is a big argument about whether H.Pylori should be eradicated to prevent ulcers later in life."