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. In recent years, the CDC has drawn attention to "nightmare bacteria" resistant to a wide range of antibiotics. They counted 4,341 cases of carbapenem-resistant bacterial infections from those states in 2023, with 1,831 of them the NDM variety. But the rate of NDM cases rose from around 0.25 to about 1.35 — an increase of 460 percent, the authors said. A CDC report published in June noted an increase in NDM cases in New York City between 2019 and 2024.