Deaths caused by infections impervious to antibiotics and antifungal medications rose 15 percent during the first year of the pandemic compared to 2019, federal health officials found. Much of the increase was tied to the chaos wrought by the coronavirus as doctors and nurses struggled to treat waves of grievously sick patients whose illness they did not fully understand, before vaccines and treatments were widely available.

About 40 percent of the deaths were among hospitalized patients, with the remainder occurring in nursing homes and other health care settings, the C.D.C. report found. Early on, many frontline hospital workers mistakenly administered antibiotics for viral lung infections that did not respond to such drugs, according to the study. Many of the sickest patients spent weeks or months in intensive care units, increasing the chances for drug-resistant bugs to enter their bodies through intravenous lines, catheters and ventilator tubes.

The death toll is likely much higher, federal health officials said, because the public health labs that normally track drug-resistant infections have been swamped during the pandemic, leading to significant gaps in data for many of the most dangerous pathogens.