If the C.D.C. — which the agency’s director, Dr. Thomas Frieden, called “the reference laboratory to the world” — had multiple accidents that could, in theory, have killed both staff members and people outside, there will undoubtedly be calls for stricter controls on other university, military and private laboratories.

In one episode last month, at least 62 C.D.C. employees may have been exposed to live anthrax bacteria after potentially infectious samples were sent to laboratories unequipped to handle them. Employees not wearing protective gear worked with bacteria that were supposed to have been killed but may not have been. All were offered a vaccine and antibiotics, and the agency said it believed no one was in danger.

In a second accident, disclosed Friday, a C.D.C. lab accidentally contaminated a relatively benign flu sample with a dangerous H5N1 bird flu strain that has killed 386 people since 2003. Fortunately, a United States Agriculture Department laboratory realized that the strain was more dangerous than expected and alerted the C.D.C.