It is frightening enough to have COVID-19. But imagine going to the emergency department (ED) with symptoms, testing positive, and then being sent home only to come back days later, sicker than before.

“We were surprised with the overall rate that [COVID] patients return and need admission, which is twice that of other illnesses,” said Austin Kilaru, MD, in an article in Penn Medicine News .

Dr. Kilaru, an emergency medicine physician at Penn Medicine in Philadelphia, is lead author of a study by researchers at the University of Pennsylvania’s Perelman Medical School. They found 8% of COVID patients who were well enough to go home after their initial emergency department visit returned to the hospital within a week.

The researchers followed some 1,400 patients who visited 5 U.S. emergency departments in March, April and May. Within 3 days of their initial visit, about 5% of the patients were admitted to the hospital. Around 4% returned but went home again. Patients who had a fever, low oxygen level or an abnormal chest X-ray were more likely to return to the hospital, as were older patients.

“[I]t can be difficult to make this diagnosis and send patients home without knowing if they will get sick in the coming days,” said Dr. Kilaru in the Penn Today article. “[T]his study gives clinicians a few signposts to know how often and when patients may need to return, and what risk factors to pay attention to.”

The study is a heads-up for doctors. “The concern is not that emergency physicians are making wrong decisions,” Dr. Kilaru said, “but rather that COVID can be unpredictable and turn severe rather quickly.”

Sabrina Emms is a science journalist. She got her start as an intern at a health and science podcast out of Philadelphia public radio. Before that she worked as a researcher, looking at the way bones are formed. When out of the lab and away from her computer, she's moonlighted as a pig vet's assistant and a bagel baker.