This article was last reviewed on
This article waslast modified on July 10, 2017.

Scientists are concerned about a rise in the number of infections caused by bacterial strains called "superbugs" because they are resistant to just about all antibiotics and have resulted in death in almost half of all patients who contracted them. They belong to a family of bacteria called CRE (carbapenem-resistant Enterobacteriaceae), according to the Centers for Disease Control and Prevention (CDC), which called them an "urgent public health threat" in a new report released in December.

In their natural form, Enterobacteriacae are a normal part of the digestive system (normal flora). As they grow and divide, some of these bacteria acquire a high level of resistance to several antibiotics, including carbapenems, developing into CRE. Carbapenems are often known as a "drug of last resort" to treat bacterial infections, so resistance to it is very concerning. If CRE spread to areas of the body like the blood or bladder, they can cause infections that are very difficult or impossible to treat.

Healthy people don't usually get CRE infections. The bacteria are more likely to infect seriously ill patients in healthcare settings such as hospitals or nursing homes. These patients often have weakened immune systems and have conditions that require devices where bacteria can breed, such as catheters and ventilators. The infection is typically spread person to person through contact with infected stool or a wound. Unwashed hands are a prime culprit for spreading the bacteria.

CRE have been a concern of scientists for more than a decade, but the number of CRE infections continues to rise. The emergence and rise of drug-resistant bacteria like CRE has even caught the attention of the White House, which released a "National Action Plan for Combating Antibiotic Resistant Bacteria" in March 2015.

These superbugs are actually more dangerous than other types of multiple-drug resistant bacterial species found in the healthcare system. They contain a "plasmid" or piece of DNA that can transfer resistance to multiple antibiotics into other bacteria normally found in the human body. The plasmid enables the bacteria to produce an enzyme that can make most antibiotics useless. Because the plasmid can be transmitted, antibiotic resistance can spread easily and quickly among bacteria.

In a recent interview with the Washington Post, CDC director Thomas Frieden, MD, MPH, said "this is a tricky drug-resistant bacteria, and it isn't easily found… [w]hat we're seeing is an assault by the microbes on the last bastion of antibiotics."

In the recent CDC report, the median age of patients who contracted the superbug was 70 and most had been treated previously outside of the US, many in India. Between June 2010 and August 2015, more than 40 patients in 19 states became infected with CRE, and the rate of infection appears to be growing. While only one CRE infection was reported in 2010, there were 11 new reports of infected patients each year in 2013, 2014, and 2015.

To test for CRE, samples are collected from sites of suspected infections and cultures are performed (e.g., blood culture or urine culture). Laboratories perform susceptibility testing on the bacteria that grow in the cultures to determine the ability of antibiotics to inhibit or kill the bacteria in question.

Detection of a CRE is challenging since there is not one simple laboratory test indicating that the bacteria are resistant to antibiotics in this class of drugs. That is changing, however, because of a new policy initiated by the CDC last year. According to a CDC spokesperson, the older definition of what constitutes a CRE relied on a pattern of susceptibility to carbapenems associated with resistance to another class of drugs (called extended-spectrum cephalosporins). The new definition says that even if bacteria are susceptible to (stopped by) extended-spectrum cephalosporins, they can still be classified as a CRE. The expanded definition should result in labs detecting and reporting more CRE cases, leading to healthcare practitioners initiating appropriate treatment sooner.

Coordinated efforts are needed from the federal, state, and local governments as well as from doctors, nurses, laboratorians, hospitals, nursing homes, and health departments to stop the spread of these deadly infections The CDC provides guidelines for these groups on actions that can be taken to help prevent the spread of CRE. Patients can also play a role:

  • Tell your healthcare provider if you have been hospitalized recently in another facility or country.
  • Take antibiotics only as prescribed.
  • Expect all doctors, nurses, and other health practitioners to wash their hands with soap and water or an alcohol-based hand solution before and after touching your body or tubes going into your body.
  • Clean your own hands often, especially before preparing a meal, or eating food; before touching your eyes, nose, or mouth; before and after changing wound dressings or bandages or handling medical devices; after using the bathroom and after blowing your nose, coughing, or sneezing.

(December 4, 2015) Sun, Lena. Superbug known as 'phantom menace' on the rise in U.S. The Washington Post. Available online at Accessed December 30, 2015.

(December 4, 2015) Centers for Disease Control and Prevention. Notes from the Field: Carbapenem-resistant Enterobacteriaceae Producing OXA-48-like Carbapenemases — United States, 2010–2015. Morbidity and Mortality Weekly Report. Available online at Accessed December 30, 2015.

Centers for Disease Control and Prevention. Carbapenem-resistant Enterobacteriaceae in Healthcare Settings. Available online at Accessed January 4, 2015.

(January 4, 2015) Correspondence with Melissa Browser, CDC Press Office.

(February 20, 2015) Centers for Disease Control and Prevention. Patients Face More Lethal Infections from CRE. Available online at Accessed January 6, 2016.

(March 2015) The White House. National Action Plan for Combating Antibiotic Resistant Bacteria. Available online at Accessed January 6, 2015.