by Kate Devlin, medical correspondent (Editorial note: the writer refers in error to "hydrogen sulphate".)
A simple £13 test could be used to diagnose patients with Myalgic encephalopathy (ME), scientists believe, and potentially offer hopes of treatment for many.
re The researchers believe that the condition, thought to affect around 250,000 people in Britain, is triggered by an overabundance of certain bacteria in the gut and a build-up of toxins in the body.
Myalgic encephalopathy (ME), also known as Chronic Fatigue Syndrome, can leave sufferers bedridden for years.
Twice as common in women than men, it typically affects patients between the ages of 20 and 40 and common symptoms include severe fatigue, muscle pain, forgetfulness or trouble concentrating and difficulty sleeping.
Once dismissed as "yuppie flu" it has since been recognised as a disease by the Department of Health.
However, confusion has surrounded the cause of the condition, with some doctors believing its roots are viral or psychological.
Studies in Australia have shown that between 60 and 70 per cent of diagnosed patients suffer from large numbers of bacteria called enterococci and streptococchi in their gut.
Prof Kenny De Meirleir, from Vrije University, in Brussels, who created the new test, said that these bacteria, in combination with metals like mercury, stimulate the creation of high levels of a gas, Hydrogen Sulphate, in the body. This in turn sets off a chain of reactions which limit the body's ability to produce energy, he added, and creates a build-up of acid which muscles find difficult to break down.
In patients with severe symptoms the syndrome can cause large numbers of abnormal proteins in the body, which also inhibit the process of energy conversion, he added.
Prof De Meirleir, who has tried the new test on hundreds of patients, and who will present his findings at the Invest In ME conference in London on Friday, said: "We are seeing a positive result in 80 to 90 per cent of patients sent to us.
"I would say that if you do not have this bacteria, you do not have ME."
Many patients could be treated with a combination of a change in diet, probiotics and antibiotics, to alter the bacteria in their gut, he said.
However, patients with the most severe symptoms remained a "challenge" to treat, he added.
The test, which costs Euro 15 (£13) and will be available from the website of the manufacturers, Protea Biopharma, from Monday, will allow patients to test for the presence of this bacteria by analysing their urine.
Patients who screen positive are advised to see their family doctor.
Dr Charles Shepherd, medical adviser of the ME Association, said: "This is an interesting scientific observation which needs to be looked at in more detail and verified by independent researchers before we can conclude it is a diagnostic test for this illness."