A coronavirus patient received care at Elmhurst Hospital in Queens last month.Credit...Erin Schaff/The New York Times

The desperately ill patients who deluged the emergency room at Detroit Medical Center in March and April exhibited the telltale symptoms of the coronavirus: high fevers and infection-riddled lungs that left them gasping for air.

With few treatment options, doctors turned to a familiar intervention: broad-spectrum antibiotics, the shot-in-the-dark medications often used against bacterial infections that cannot be immediately identified. They knew antibiotics are not effective against viruses, but they were desperate, and they feared the patients could be vulnerable to life-threatening secondary bacterial infections as well.

“During the peak surge, our antibiotic use was off the charts,” said Dr. Teena Chopra, the hospital’s director of epidemiology and antibiotic stewardship, who estimated that more than 80 percent of arriving patients were given antimicrobial drugs. “At one point, we were afraid we would run out.”

Dr. Chopra said the doctors, and others across the country who liberally dispensed antibiotics in the early weeks of the pandemic, soon realized their mistake.

“Many physicians were inappropriately giving antibiotics because, honestly, they had limited choices,” she said.

Now that the initial, terrifying flood of patients in hard-hit cities has subsided, doctors across the United States are seeking to draw lessons from their overuse of antibiotics, a practice that can spur resistance to the lifesaving drugs as bacteria mutate and outsmart the drugs.

Many critically ill patients on ventilators have developed serious secondary infections. But widespread fears that coronavirus patients were especially susceptible to drug-resistant infections — a concern first described in studies from China — appear to have been misguided, according to interviews with researchers and more than a dozen doctors who have been treating patients with Covid-19.

“The fears turned out to be overblown,” said Dr. Bruce Farber, the chief of infectious diseases at Northwell Health, which has cared for thousands of coronavirus patients at its 23 hospitals in New York.

For many doctors, the pandemic not only provides lessons about the judicious use of antibiotics, but it also highlights another global health threat that has been playing out in slow motion: the mounting threat of antimicrobial resistance that annually claims 700,000 lives as the world’s arsenal of antibiotics and antifungal medication lose their ability to vanquish dangerous pathogens.

In recent weeks, doctors, researchers and public health experts have been trying to turn the pandemic into a teaching moment. They warn that the same governmental inaction that helped foster the rapid, worldwide spread of the coronavirus may spur an even deadlier epidemic of drug-resistant infections that the United Nations suggests may kill 10 million by 2050 if serious action isn’t taken.

Without new antibiotics, routine surgical procedures like knee replacements and cesarean sections could become unacceptably risky, and the ensuing health crisis could spur an economic downturn to rival the global financial meltdown of 2008, the U.N. report, released last year, said.

“If there’s anything that this Covid-19 pandemic has taught the world, it is that being prepared is more cost-effective in the long run,” said Dr. Jeffrey R. Strich, a researcher at the National Institutes of Health Clinical Center and an author of a study published on Thursday in Lancet Infectious Diseases that seeks to quantify the growing need for new antibiotics to treat drug-resistant infections. “Antimicrobial resistance is a problem we cannot afford to ignore.”

The pipeline for new antimicrobial drugs has become perilously dry. Over the past year, three American antibiotic developers with promising drugs have gone out of business, most of the world’s pharmaceutical giants have abandoned the field and many of the remaining antibiotic start-ups in the United States are facing an uncertain future.

Such dreary financial realities are driving away investors at a time when new antimicrobial drugs are urgently needed.

“I’m worried the remaining small biotech companies won’t be here this time next year,” said Greg Frank, director of Working to Fight AMR, an advocacy group funded by the pharmaceutical industry. “The longer we wait, the deeper in the hole we’re in and the more expensive it’s going to be to solve the problem.”

The crisis, many experts say, calls for robust government intervention. In a report published in March, the U.S. Government Accountability Office documented a piecemeal federal response to antimicrobial resistance and said the Centers for Disease Control and Prevention was hobbled in addressing the problem by a lack of basic data about drug-resistant infections. As an example, it noted that the C.D.C. tracks less than 2 percent of the country’s annual half-million cases of drug-resistant gonorrhea. The data doesn’t even include cases affecting women.