Epidemiological testing — where the contacts of infected people are identified, tested in turn and isolated as needed — is the only way to fully break the chains of transmission, says Adhanom Ghebreyesus Tedros, head of the W.H.O. Without it, the virus will come roaring back as soon as social distancing guidelines are relaxed.

American officials have not absorbed that lesson. Even as some cities and states enter a phase of exponential spread, with the number of confirmed cases doubling every few days or so, social distancing is not being paired with the basic epidemiology that’s needed. Contact tracing — the practice of identifying and testing every person that an infected person came into contact with after they themselves contracted the virus — has not been prioritized. Almost no efforts are underway to develop the infrastructure for quarantining the exposed or isolating the infected outside their homes, away from their families. In some places, as the case counts surge, doctors who think they’ve been exposed are being advised to keep on working.

Worst of all, widespread testing — the foundation of both clinical care and broader containment efforts — has been disastrously slow to come online in the United States. President Trump and his team have repeatedly assured the country that tens of thousands of tests will soon be available in convenient locations across the country. But media reports make clear that confusion still reigns: It can take days and dozens of phone calls to access a test — at least it can if you don’t play professional basketball or star in the movies — and it still takes at least a few days to obtain results. In some cases, that’s because of backlogs; in others, it’s because of shortages.

The federal government’s mind-boggling failure has bred an apathy that’s as virulent as any microbe. With coronavirus outbreaks in the states of New York and Washington stretching into their second months, some experts have all but given up on testing, saying that the virus has probably spread well beyond our ability to contain it. Based on that logic, people who are known to have been exposed are being advised to isolate themselves at home but are not being tested to determine whether they pose a risk to roommates or relatives, nor are they being monitored for symptoms in any consistent or meaningful way. It also means those who have immunities can’t know it, and thus can’t know they are in a position to safely help those who are high risk.

In China, when officials realized that some 80 percent of Covid-19 cases involved infected people passing the virus to their family members, the government built large-scale isolation units where those people could be cared for a safe distance from their loved ones. In South Korea, when an early outbreak was pegged to one large church, health workers began tracing the contacts of more than 200,000 of that church’s members. They quarantined all of the people who were exposed, monitored them and sent anyone who became symptomatic to an isolation center.