The bacteria would be dangerous to anyone who inhales or touches the contents of the vial, which bears a "biohazard" label, should it be opened or broken. The disease could easily be contracted and then passed on to other people.

If the vial is thrown away without being broken, it would pose no risk to the public because tuberculosis cannot be transmitted by water or soil.

Richard Lee of the San Francisco Department of Public Health said: "It can be a hazard to the person who has it now or someone who might open it."

Unwitting robber

It is unlikely that the burglar was after the gelatinous substance which holds the tuberculosis bacteria in the eight-inch vial and is unlikely to have any idea what it is.

The snatched black duffle bag was probably taken from the hotel room because it also contained clothes and jewellery.

Mr Lee said it was not illegal for the tuberculosis conference delegate to have the live bacteria in her luggage.

The woman intended to give the vial to a fellow researcher who planned to culture more of the bacteria.

In 1998, tuberculosis was listed by the World Health Organisation as the world's most deadly transmittable disease. The illness attacks mainly the lungs, intestines, skin and brain.