Specimens of stomach tissue were also taken to search for viral proteins and compared with specimens taken from healthy people and patients with other gut diseases none of whom had been diagnosed with ME.
Patients with ME often have intermittent or persistent gut problems, including indigestion and irritable bowel syndrome.
And viral infections, such as Epstein Barr virus (glandular fever), cytomegalovirus, and parvovirus, among others, produce many of the symptoms associated with chronic fatigue syndrome.
Enteroviruses, which infect the bowel, cause severe but short lasting respiratory and gut infections.
There are more than 70 different types, and they head for the central nervous system, heart and muscles.
Most of the biopsy specimens from patients with gut problems showed evidence of mild long term inflammation, although few were infected with Helicobacter pylori, a common bacterial infection associated with inflammation.
But more than 80% of the specimens from the ME patients tested positive for enteroviral particles compared with only seven of the 34 specimens from healthy people.
In a significant proportion of patients, the initial infection had occurred many years earlier.