In 2007 the American Heart Association changed the guidelines so that only people at highest risk for developing infective endocarditis are now advised to receive prophylactic antibiotics before invasive procedures.

CNN: Why do I no longer need an antibiotic before teeth cleaning?

About 50 people who were in Daschle's office at the time the letter was opened have begun a prophylactic regimen of antibiotics, Nichols said.

CNN: daschle