CDC still hopeful NDM threat can be contained
Trying to keep NDM out of E. coli
In a shrinking global village it seems a pathogen emerging anywhere is soon a threat everywhere, but public health officials are not conceding victory to the New Delhi metallo-β-lactamase (NDM) variety of carbapenem-resistant Enterobacteriaceae (CRE).
Having seen the widespread disbursement of another type of CRE — Klebsiella pneumoniae carbapenemase, (KPC) — they are still hopeful that the much less common NDM can be kept at bay. There are some favorable signs in surveillance data collected by the Centers for Disease Control and Prevention's National Healthcare Safety Network (NHSN).
"The thing that we are very encouraged about is that most places don't see this [NDM] organism very regularly," says Alexander Kallen, MD, MPH, a medical epidemiologist and outbreak response coordinator in the CDC Division of Healthcare Quality Promotion. "When we look at our data from the NHSN for health care associated infections, it's a vast minority of hospitals that are actually seeing these on a regular basis — within a six to 12 month period. So the time to act is now. There are certainly places in the United States where they are more common. But if you look kind of broadly across the whole U.S. in most areas [NDM-CRE] are relatively uncommon, and that's the time to intervene."
Since it was first reported in 2009, through 2012, only 27 patients with NDM-producing CRE were confirmed by CDC from isolates submitted by state laboratories. However, since January 2013 a total of 69 patients with NDM-producing CRE have been identified in the United States, 44 of them in the northeastern Illinois area where a hospital outbreak occurred. (See related story, cover.)
Enterobacteriaceae are a common cause of infections in both community and healthcare settings, meaning continuing emergence of carbapenem resistance could have considerable impact. An estimated 140,000 healthcare-associated Enterobacteriaceae infections occur in the United States each year; about 9,300 of these are caused by CRE, the CDC reports.1 The agency recently gave CRE its highest public health threat rating of "urgent." Given the long infamous reign of MRSA, it is hard to believe the CDC now gives it a lower threat rating than CRE. Make no mistake, MRSA still kills more than 11,000 patients annually, but invasive MRSA infections appear to be in decline and there are still some drug treatment options. The CDC is clearly concerned that CRE is going to continue to increase, as one of the factors used in designating threat status in the report was a 10-year projection of incidence.
"Over the last 10 years we have seen about a quadrupling of the percent of enterbacteriaceae that are resistant to carbapenens," Kallen says. "Our goal is to cut that as we move forward over the next 10 years or so, and I think we have a good chance of doing that. If you look across the board, across the main enterobacteriaceae — E. coli, Klebsiella, and enterobacter — almost all of the increase has been in Klebsiella, which has increased from about 1-2% to about 10%. So the other piece to this is that we are trying to prevent the emergence of [NDM] — trying to decrease the overall increase — while trying to keep it stable in Klebsiella."
It doesn't help that the drug resistance mechanisms in CRE may be genetically transferred via plasmids to other types of bacteria, creating the possibility of more and different bugs for which few treatment options are available. That said, some general tendencies are starting to become apparent.
"NDMs tend to be — at least outside the United States — found more commonly in E. coli, whereas KPCs in the U.S. are more commonly found in Klebsiella," says Kallen. "There are some KPCs in E. coli, but most are in Klebsiella. So the addition of NDM into the mix brings E. coli into the picture more. E. coli are a much more common cause of community infections. It raises the possibility of more spread of these bugs outside of health care facilities, where we see it now with KPC."
CDC laboratories have confirmed at least one type of CRE in healthcare facilities in 44 states. In addition, about 4% of U.S. short-stay hospitals had at least one patient with a serious CRE infection during the first half of 2012. About 18% of long-term acute care hospitals had one, the CDC reported.
A particularly daunting challenge going forward will be preventing CRE transmission in long term care and other non-hospital settings. As reported recently in San Francisco at the 2013 IDWeek meeting, public health investigators trying to stop an outbreak of CRE at a skilled nursing facility found that "patients with positive [CRE] infections were not on contact precautions and staff did not have knowledge of CRE or how it was transmitted. Deficiencies in hand hygiene and contact precautions were detected during the observational survey."2
- Centers for Disease Control and Prevention. Antibiotic Resistance Threats in the United States, 2013: http://1.usa.gov/15yIo29
- Sears J, Patel AS. Carbapenem-Resistant Klebsiella pneumoniae Cluster in a Long-term Skilled Nursing Facility Highlights the Role of Local Public Health in Prevention and Control. Abstract 1616. IDWeek 2013. San Francisco, CA; Oct. 2-6.