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The findings suggest that giving antibiotics to children early in life might make them more susceptible to asthma by reducing levels of H pylori in the body.

Previous research has suggested that the cagA strain of H pylori can protect against gastro-oesophageal reflux disease (GORD) and could, therefore, protect against GORD-related asthma.

For the latest study, the link between H pylori and asthma was assessed in 7,663 adult asthmatics.

Each participant answered a questionnaire on medical history of asthma and allergy symptoms.

They were then tested for antibodies for H pylori and the cagA protein in their blood.

A sub-group of 2,385 participants also underwent skin testing for six asthma allergens, including ragweed and rye grass. The results were correlated with participants' H pylori status.

Those with the cagA strain of H pylori were found to be 20 per cent less likely to have ever had asthma compared with participants without H pylori.

This association seemed dependant on age. Those with the virulent cagA strain were 40 per cent less likely to have had asthma before the age of 15.

Lead researcher Martin Blaser, professor of microbiology at New York University School of Medicine, said: 'This study shows that H pylori is inversely associated with childhood onset but not adult onset asthma.

'H pylori plays a protective role in asthma and sensitivity to pollens and moulds, and its extinction might explain the rise in childhood asthma.'

Having H pylori in the stomach may skew the body's immune response in a particular direction, said Professor Blaser.

When GPs give antibiotics to children to treat infections, H pylori is removed from the stomach making them more at risk of asthma, he added.

sanjay.tanday@haymarket.com

Arch Intern Med 2007;167:821-7

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