The growing threat of antibiotic resistance requires imminent action, the head of the U.S. Centers for Disease Control and Prevention (CDC) warned Tuesday.

Speaking at a National Press Club event, Dr. Tom Frieden said, “Antimicrobial resistance is a big problem and it’s getting worse.” It’s a problem that costs lives as well as $20 billion in healthcare costs, he said.

“We talk about a pre-antibiotic era and the antibiotic era. If we’re not careful, we will soon be in a post-antibiotic era. And in fact for some patients and some pathogens, we’re already there.”

The CDC issued a report last year to increase awareness of the problem of some infections becoming resistant to antibiotics as a result of both overuse and misuse in humans and farm animals. The World Health Organization also issued a warning earlier this year, stating that a post-antibiotic era, “far from being an apocalyptic fantasy, is instead a very real possibility for the 21st century.”

As the CDC has previously warned, Frieden said, “Antibiotic resistance could affect any of us,” noting that such infections strike 2 million Americans every year, with 23,000 of those being deadly.