LONDON — At King’s College Hospital in the south of London, anyone who has blood drawn in the emergency department is automatically tested for hepatitis B and C.

Posters throughout the facility inform patients that the screening is routine, part of a new approach helping find and treat thousands of people who might otherwise never know they have the viruses, which can be fatal if left untreated.

“We pick up a lot of people who would never have actively accessed this kind of testing themselves — women in later life, people who’d never think they’re the sort of person who would have this condition,” said Dr. Oliver Mizzi, a consultant in emergency medicine at the hospital.

Across England, 90 hospitals now have opt-out testing for hepatitis, leading to thousands getting treatment and putting the country on the path to meeting its goal of eliminating the hepatitis C virus as a public health threat by 2030.

As Congress considers legislation to establish a national hepatitis C elimination program, experts say expanding opt-out testing in emergency departments is an indispensable way identify undiagnosed infections.