The bacterial infection - also known as H pylori - is a major cause of stomach disorders, ulcers and stomach cancer.

The infection was already 50-per-cent resistant to metronidazole, the original antibiotic group used to treat it, according to Prof Barry Marshall, the clinical microbiologist who proved that H pylori was the cause of most stomach ulcers and not stress, spicy food or too much stomach acid.

Marshall received the 2005 Nobel Prize for Medicine for those efforts. He received the 2001 Prince Mahidol Award for public health for the same discovery.

He said the bacteria had developed a 20-per-cent resistance to clarithromycin and a 10-per-cent resistance to amoxycillin.

Marshall was speaking at the Sixth Western Pacific Helicobacter Congress 2006, held in Bangkok between November 12 and today. Experts from 22 regional countries are attending.

He said only infected patients should be treated with antibiotics.

And, because the bacteria was starting to outsmart drugs used against it, researchers needed to find a new regimen, Marshall said.

Every second person worldwide has the bacteria yet many suffer only from chronic stomach ache, nausea and loss of appetite, explained Assoc Prof Udom Kachintorn, head of the Medicine Faculty at Siriraj Hospital.

A recent study by the hospital showed about 60 per cent of patients in Thailand complaining of stomach ache were found to have H pylori.

Asst Prof Sombat Treeprasertsuk, an expert from Chulalongkorn University, said the infection rate increased to between 70 per cent and 80 per cent in those with stomach ulcers.

The prevalence of H pylori was considerably higher in developing countries, said Assoc Prof Hoda Malaty of Baylor College of Medicine in Houston.

Furthermore, lower socio-economic groups tended to have greater infection rates, supporting the hypothesis that bacterial infections were transmitted through poor sanitation and personal hygiene, she said.

While it was certain the infection was passed person-to-person it remained unclear how, Udom said.

A Japanese study proved that rates of infection with the most virulent strain of H pylori dropped as sanitation and personal hygiene increased, Malaty said.

Marshall said it was unclear why strains of H pylori varied from one country to another. "We don't quite understand why."

There was considerable work to be done to better understand the bacteria. Discovery of a vaccine remained "far off".

"Maybe in about five years we will see something," said Marshall, explaining that the handful of drug companies working on one had, to date, failed.

Arthit Khwankhom

The Nation