Americans returning from China landed at U.S. airports by the thousands in early February, potential carriers of a deadly virus who had been diverted to a handful of cities for screening by the Centers for Disease Control and Prevention…

But the effort was frustrated as the C.D.C.’s decades-old notification system delivered information collected at the airports that was riddled with duplicative records, bad phone numbers and incomplete addresses. For weeks, officials tried to track passengers using lists sent by the C.D.C., scouring information about each flight in separate spreadsheets…

The C.D.C., long considered the world’s premier health agency, made early testing mistakes that contributed to a cascade of problems that persist today as the country tries to reopen. It failed to provide timely counts of infections and deaths, hindered by aging technology and a fractured public health reporting system. And it hesitated in absorbing the lessons of other countries, including the perils of silent carriers spreading the infection.

The agency struggled to calibrate its own imperative to be cautious and the need to move fast as the coronavirus ravaged the country, according to a review of thousands of emails and interviews with more than 100 state and federal officials, public health experts, C.D.C. employees and medical workers. In communicating to the public, its leadership was barely visible, its stream of guidance was often slow and its messages were sometimes confusing, sowing mistrust.