More than four hours after the news emerged, the C.D.C. issued its first public statement about the outbreak, saying, “We are working closely with our international partners to provide technical assistance and guidance to mitigate risk.” It did not mention the Americans who were back in the country or efforts to monitor them.

It was only a day earlier, on Tuesday, that the agency had set up a team to respond to the outbreak, nearly a month after the first patient had died.

To some public health experts, the alarming thing about this situation is not the hantavirus, which they note spreads among people rarely, and only with close contact over a period of time rather than casual interactions. It is that the administration’s sluggish response and lack of communication suggest the United States is ill prepared for a larger health crisis, such as another pandemic.