Sloppy laboratory practices at the Centers for Disease Control and Prevention caused contamination that rendered the nation’s first coronavirus tests ineffective, federal officials confirmed on Saturday.

Two of the three C.D.C. laboratories in Atlanta that created the coronavirus test kits violated their own manufacturing standards, resulting in the agency sending tests that did not work to nearly all of the 100 state and local public health labs, according to the Food and Drug Administration.

Early on, the F.D.A., which oversees laboratory tests, sent Dr. Timothy Stenzel, chief of in vitro diagnostics and radiological health, to the C.D.C. labs to assess the problem, several officials said. He found an astonishing lack of expertise in commercial manufacturing and learned that nobody was in charge of the entire process, they said.

Problems ranged from researchers entering and exiting the coronavirus laboratories without changing their coats, to test ingredients being assembled in the same room where researchers were working on positive coronavirus samples, officials said. Those practices made the tests sent to public health labs unusable because they were contaminated with the coronavirus, and produced some inconclusive results.