Several types of “nightmare” drug-resistant bacteria are lurking within healthcare settings across the country, according to the Centers for Disease Control and Prevention’s latest surveillance data. But the data also suggests that recently implemented control efforts are helping to squelch the deadly germs.

The data, published Tuesday in the CDC's Morbidity and Mortality Weekly Report , focused on bacteria resistant to a group of antibiotics called carbapenems , which are often used as drugs of last resort. Carbapenem resistance often shows up in bacteria in the Enterobacteriaceae family, which includes common gut pathogens such as E. coli and Klebsiella. These carbapenem-resistant Enterobacteriaceae (CRE) burst onto the clinical scene starting in the early 2000s and they’ve tended to carry resistance to many or nearly all other antibiotics , in addition to carbapenems. In fact, CRE cause dreadful infections with mortality rates as high as 50 percent—aka, nightmare cases, as the CDC likes to call them. For this reason, CRE are considered among the biggest microbial threats by the CDC and the World Health Organization

In 2009, the CDC created a CRE-specific guidance to try to monitor and effectively control and eliminate CRE cases from healthcare settings, where they often cause blood, catheter, and central line infections. The guidance instructs healthcare workers to do things like use laboratory testing to surveil clinical isolates, screen healthcare workers that may be asymptomatically carrying the deadly germs, place infected patients in single rooms and under contact precautions, and up hand-washing.

Last year, the agency also boosted its laboratory surveillance game in healthcare centers, performing more detailed analyses on collected CRE isolates as well as a similarly concerning germ, carbapenem-resistant Pseudomonas aeruginosa (CRPA). The increased analyses included looking at each isolate’s resistance levels and what types of genes were responsible for that resistance—there are many genetic elements that can help bacteria evade carbapenems.

In the first nine months of 2017, the agency’s network of laboratories collected and analyzed 5,776 isolates from a variety of healthcare facilities in 32 states. Of those isolates, about 25 percent produced carbapenem-thwarting enzymes called carbapenemases. There were 1,401 CRE and 25 CRPA identified.

Scary numbers and good news

Of those carbapenem-resistant isolates, 1,205 (84.5 percent) defeated the last-resort antibiotic by encoding the common carbapenemase, dubbed KPC, short for Klebsiella pneumoniae carbapenemase. The other 221 strains (15.5 percent) carried at least one of four less-common-but-concerning genes that encode different carbapenemases. Those enzymes are New Delhi metallo-beta-lactamase (NDM), Verona integrin encoded metallo-beta-lactamase (VIM), imipenemase (IMP), and oxacillinase-48-like carbapenemase (OXA-48).

The agency highlighted these genetically rarer carbapenem isolates in a press release and a teleconference with reporters, which led to some confused headlines. From an epidemiological standpoint, the agency wants to catch these less-common strains before they become more common, like the KPC-carrying CRE. But that’s not to say that these are necessarily increasing or more dangerous than the common KPC-carrying CRE—both in terms of killing a higher percentage of patients or spreading their drug-resistance more freely to their brethren.

In the teleconference, CDC Principal Deputy Director Dr. Anne Schuchat noted that the surveillance data did not include mortality rates associated with those 221 less-common types of CRE. And the molecular data didn’t include an assessment of whether the enzymes were encoded on genetic elements that bacteria can easily share among themselves. (Earlier work suggests many of them, including KPC, can be found on these). Also, this level of surveillance is in its relative infancy, so there isn’t enough data to say how prevalent these less-common strains are overall or whether they’re increasing or decreasing. There is no trend data yet for specific types of CRE.

The good news, however, is that there is enough data on CRE generally to say that they may be decreasing overall. Based on data collected from CDC’s National Healthcare Safety Network (NHSN) between 2006 and 2015, the percentage of carbapenem resistance among Enterobacteriaceae isolates from short-stay, acute-care hospitals fell from a peak of 10.6 percent in 2007 to 3.1 percent in 2015.

Researchers compared that fall to the rates of another concerning type of drug-resistance in Enterobacteriaceae, extended-spectrum β-lactamases (ESBLs). The agency keeps track of germs that have this type of resistance, too, but it hadn’t implemented a guidance for controlling ESBLs as it had done for CRE. In the same period of 2006 to 2015, rates of ESBLs remained relatively stable, ranging from 17.6 percent in 2006 to 16.5 percent in 2015.

The CDC concluded that “these data suggest that an early aggressive response, as outlined in CRE-specific infection prevention recommendations released beginning in 2009, can slow emergence and even decrease the occurrence of infections from resistant pathogens.”