Boston University (search) confirmed that three researchers who fell ill last year had been exposed to a potentially lethal bacterium, and a local health official said the city should have been notified sooner.

The three scientists recovered fully after receiving antibiotics.

The university said Wednesday that test results on Oct. 28 showed that the researchers, who were supposed to be working with a harmless form of the tularemia bacterium (search), had instead been working with material contaminated with a potentially lethal form of the bacteria.

Tularemia is not contagious, but left untreated, it can cause respiratory failure, shock and death. The harmless form is altered specifically to be safe for research.

The work was stopped Nov. 4 because of safety concerns. State health officials were notified Nov. 9 and the city's Public Health Commission a day later.

Dr. Anita Barry said Wednesday that under state law, confirmed or suspected cases must be reported to public health authorities "immediately, but in no case more than 24 hours" after being identified.

Dr. Thomas J. Moore, acting provost of the university's medical campus, said he could not explain the reporting delay. Laboratory personnel "must have assumed something was amiss" when they received the Oct. 28 test results, he told The Boston Globe.

Two of the researchers became ill in May, and the third in September. University officials declined to name them or describe their jobs, citing safety concerns.

Dr. Peter A. Rice was removed as chief of infectious disease, school officials said, citing inadequate leadership that they said contributed to lab safety lapses.

The tularemia exposures are being investigated by public health agencies and, as federal law requires, the FBI.

Officials said they do not yet know how the bacterium became contaminated but do not believe it was intentional.