A drug-resistant "superbug" just overtook NYC's most common antibiotic-resistant threat

In 2024, a particularly dangerous type of antibiotic-resistant bacteria quietly crossed a milestone in New York City: infections caused by New Delhi metallo-β-lactamase–producing carbapenem-resistant Enterobacterales (NDM-positive CRE) outnumbered those caused by the strain that had dominated for decades. The shift matters because the two types require different treatments, and doctors who assume the old enemy is still the main one could reach for the wrong drug.

From 58 cases to 388 in five years

Between 2019 and 2024, the NYC Health Department tracked CRE cases reported by laboratories across the city. Among 7,114 total CRE cases reported during that period, 3,293 (46%) had carbapenemase test results attached—the proportion ranged from 40% in 2021 to 54% in 2024.

Within that tested group, NDM-positive CRE cases climbed steeply:

• 2019: 58 cases
• 2024: 388 cases

Meanwhile, cases caused by Klebsiella pneumoniae carbapenemase (KPC)—the carbapenemase that has dominated U.S. Enterobacterales infections since 1996—stayed relatively flat, ranging between 277 and 332 cases annually. By 2024, NDM had surpassed KPC as the most frequently reported carbapenemase among CRE cases in NYC.

Annual CRE cases in New York City by carbapenemase type, 2019–2024. Credit: CDC/MMWR

Why this is harder to treat

Enterobacterales—a large group of gram-negative bacteria that includes Escherichia coli and Klebsiella species—normally require treatment with broad-spectrum carbapenem antibiotics when they cause serious infections. CRE strains produce enzymes called carbapenemases that make those antibiotics ineffective.

The NDM enzyme creates an extra layer of difficulty: it also confers resistance to ceftazidime-avibactam, a combination antibiotic commonly used to treat KPC-positive CRE. That means a patient infected with NDM-positive CRE cannot simply receive the drug that would work against the KPC strain. Providers treating NYC residents at risk for CRE may need to consider empiric therapy effective against NDM-producing organisms—such as cefiderocol or ceftazidime/avibactam plus aztreonam—especially for patients with severe infection, adjusting based on carbapenemase or susceptibility test results.

What's driving the increase—and what's still unknown

The reasons behind the rise are not fully understood. NDM-positive CRE had previously been associated mainly with returning international travelers and with long-term care facilities (LTCFs). The newer data show an increase in NDM-positive CRE among people without known LTCF exposure, which raises the possibility of transmission in community settings beyond traditional health care environments. However, the available disease data did not allow investigators to pinpoint exactly where individual infections were acquired.

Incomplete carbapenemase testing and reporting—possibly due to limited laboratory resources and complex reporting requirements—contributed to gaps in the data. Still, the relatively stable prevalence of other carbapenemases over the same period suggests the NDM increase is not simply an artifact of more testing.

What comes next

The NYC Health Department is implementing prospective whole genome sequencing of CRE isolates to improve detection of transmission clusters, including NDM-positive CRE, and to better understand how the bacterium is spreading locally. Health officials in other jurisdictions are encouraged to watch for similar increases in NDM-positive CRE cases.

Laboratories in NYC have been required since a 2018 amendment to the NYC Health Code to electronically report CRE cases among city residents, including organism identification and antimicrobial susceptibility results. Carbapenemase testing—covering KPC, NDM, oxacillinases, imipenemase, and Verona integron–encoded metallo-β-lactamase—is increasingly performed by clinical laboratories directly, with public health laboratories filling in for those that lack that capability.

Sources

This article is based on "Notes from the Field: Increase in New Delhi Metallo-β-Lactamase–Producing Carbapenem-Resistant Enterobacterales — New York City, 2019–2024," published in the CDC's Morbidity and Mortality Weekly Report; it is a work of the United States government and is in the public domain.