But Dr. William Schaffner, chairman of the Department of Preventive Medicine at the Vanderbilt University Medical Center, estimates there are fewer than 250 cases every year in the United States.

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Though there is uncertainty about just how common such infections are since no clearinghouse compiles statistics on their incidence, Dr. William Schaffner, chairman of the Department of Preventive Medicine at the Vanderbilt University Medical Center, estimates there are fewer than 250 cases every year in the United States.

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Dr. William Schaffner, chairman of the Department of Preventive Medicine at the Vanderbilt University Medical Center, estimates that fewer than 250 such cases occur each year in the United States, though estimates are imprecise since doctors do not have to report the cases to health authorities.

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Dr. William Schaffner, chairman of the Department of Preventive Medicine at the Vanderbilt University Medical Center, estimated that fewer than 250 such cases occur each year in the United States, though estimates are imprecise because doctors do not have to report the cases to health authorities.

CNN: STORY HIGHLIGHTS