Advice on Virus Transmission Vanishes From C.D.C. Website

“At this time, everybody knows that the stakes are extremely high, in terms of science communication,” said Dr. Abraar Karan, an internal medicine physician at Harvard Medical School.

The C.D.C. has suffered a series of blows to its reputation as the pandemic has spread in the United States. Only in April, for example, did officials recommend face coverings for the public, after initially saying masks were not necessary.

The C.D.C. said in August that people who have close contact with an infected person but no symptoms don’t need to get tested for the infection. But last week, after The New York Times reported that the guidance had been dictated by officials in the administration rather than by scientists, the agency reversed its position and said all close contacts of infected people should be tested regardless of symptoms.

That reversal came after Michael R. Caputo, the top spokesman at H.H.S., took a leave of absence “to focus on his health and the well-being of his family” after accusing federal scientists of “sedition” in a bizarre Facebook rant. Dr. Paul Alexander, an adviser to Mr. Caputo who was highly critical of C.D.C. research, also is leaving the department.

Mr. Trump last week lashed out at the agency’s director, Dr. Robert Redfield, after Dr. Redfield told a congressional hearing that a vaccine would not be widely available until the middle of next year. “It’s just incorrect information,” the president said.

The constant controversies make it “that much more difficult for the general public who are now looking at this guidance and wondering, ‘What the hell does this all mean?’” said Dr. Karan.

The latest incident concerns the spread of the virus by air through droplets and aerosols, which are tiny particles containing the virus that can stay aloft for long periods and travel farther than six feet.