Bacteria that are difficult to treat due to the so-called NDM gene primarily drove the increase, CDC researchers wrote in an article published Monday in the Annals of Internal Medicine. It's likely many people are unrecognized carriers of the drug-resistant bacteria, which could lead to community spread, the CDC scientists said. In recent years, the CDC has drawn attention to "nightmare bacteria" resistant to a wide range of antibiotics. But the rate of NDM cases rose from around 0.25 to about 1.35 — an increase of 460%, the authors said. A CDC report published in June noted an increase in NDM cases in New York City between 2019 and 2024.