In the U.S. and across the world, concern about the coronavirus and the disease it causes, Covid-19, has triggered a run on global supplies of personal protective equipment, or PPE. Health care workers rely on that equipment — including gowns, gloves, and N-95 masks, which protect against the spread of respiratory pathogens — to protect themselves against infection. Data from other countries has shown that health care workers are particularly at risk of being infected with the coronavirus. Hospitals and health systems have their own stockpiles of PPE. They can also call on what’s known as the Strategic National Stockpile, a federal store of masks, medicine, and medical equipment. But the outbreak has already strained stockpiles.