BBC Health Correspondent Richard Hannaford reports

They said that the actual levels of contamination found in the soft drink were not high enough to cause the illnesses reported.

Instead, anxiety following the recent dioxins scare and high media coverage of the issue may have caused people to react badly to small amounts of the smell of contamination not in the drink itself.

Professor Nemery and colleagues at the University of Leuven in Belgium and the University Catholique de Louvain in Brussels published their theory in a letter to The Lancet medical journal.

Heightened anxiety

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Declaring that they have no conflicts of interest, they said the widespread reports of Coca-Cola "poisoning" were in fact symptoms of mass sociogenic illness (MSI) - brought about by society's heightened sense of anxiety over the safety of products.

"Many features of this outbreak point to MSI, described as 'a constellation of symptoms of an organic illness, but without identifiable cause, which occurs among two or more persons who share beliefs related to those symptoms'," they said.

They said such outbreaks were identifiable by the kind of people reporting symptoms - schoolgirls.

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This combined with the absence of the illness in other groups of people in the same area, and a high level of unusual physical or mental stress.

Also characteristic was that information was spread through the media, health professionals, family or social networks.

The situation in Belgium fitted these criteria, they said.

Complaints snowballed

Outlining events, they said that after it was reported on the evening news that 26 children from one school were taken to hospital, similar episodes of illness after drinking Coca-Cola drinks were reported in other schools.

"Most complaints consisted of vague constitutional symptoms and were transient," they said.

After the health authorities banned Coca-Cola products from sale, hundreds of complaints of "poisoning" arrived at the National Poison Centre.

However, laboratory analysis showed that many of these complaints were unsubstantiated.

What analysis of the first - genuine - instance revealed was the presence in some bottles of very low, but odorous, amounts of hydrogen sulphide.

Harmless smell

The further complaints were linked with a fungicide that was found in small amounts on the outside of some cans.

The doctors say it is unlikely that these chemicals, in such small concentrations, could have had any toxic effect on those who consumed them, but may have given the drink an abnormal odour or taste.

This was enough, in the population's state of anxiety, to trigger psychosomatic symptoms, the researchers said.