CRE Infection: Causes, Symptoms & Treatment
This image shows two rod-shaped bacteria called Klebsiella pneumoniae that are resistant to treatment with the “last resort” antibiotic drug called carbapenem. In this image, the mustard-colored bacteria are interacting with the green-colored human white blood cells.
Credit: National Institute of Allergy and Infectious Diseases (NIAID)

CRE are a type of bacteria that are highly resistant to many antibiotics. They have earned the name "killer bacteria" and "nightmare bacteria" for good reason. The death rate for those infected with CRE, or carbapenem-resistant enterobacteriaceae, is greater than 40 percent, according to the California Department of Public Health (CDPH), and could be as high as 50 percent, according to the Centers for Disease Control (CDC). 

Infections usually occur in hospitals, nursing homes and other health care settings, the CDC said. Members of the general population are generally not at risk.

Enterobacteriaceae are "normal" bacteria that have acquired the ability to produce enzymes that work against most antibiotics. Klebsiella and E. coli are types of Enterobacteriaceae, and are found in the intestines or in the environment. If these bacteria get into areas of the body other than the intestines, they can cause infections such as bloodstream infections, wound infections, pneumonia, urinary tract infections and meningitis, according to the CDC. 

Broad-spectrum antibiotics called carbapenem are used to kill Enterobacteriaceae. When carbapenem is overused, the bacterium becomes resistant to the antibiotics, forming CRE, according to the North Dakota Department of Health. This means that antibiotics can no longer kill the bacteria. Some types of CRE can create an enzyme called Klebsiella pneumoniae carbapenemase that can actually destroy antibiotics. 

CRE are spread when the bacteria are transferred through touch. For example, a doctor may touch the wound or stool of an infected patient, and then touch another patient, infecting the second patient with the bacteria. These bacteria can also be spread by touching a contaminated surface, such as a medical tool or hospital bed. It is unclear how long the bacteria can remain alive on surfaces, according to the Government of Australia Department of Public Health.

Healthy people generally are not at risk of becoming infected with CRE. It is those with compromised immune systems who are at risk. Patients using catheters and ventilators or taking antibiotics have the highest risk of becoming infected, according to the CDPH. 

"Most of the people who contract these bacteria are patients in hospitals, nursing homes, and come-and-go surgical clinics," said John R. Palisano, a professor of biology at the University of the South in Sewanee, Tennessee. "These people are exposed to these carbapenem-resistent bacteria while they are on ventilators or [involved in] medical procedures involving catheters or endoscopies, with instruments that were not properly cleaned and sterilized." 

The symptoms of CRE can be different for each patient. "The symptoms of infection can vary depending on the organs (like lungs or bladder) that are involved, but usually include fever and chills," Palisano told Live Science. Other symptoms to look for are sores that do not heal, especially if treated with over-the-counter antibiotic treatments. 

"However, most of these infections occur in health care settings," said Mary B. Farone, a professor of biology at Middle Tennessee State University. "For caregivers in these situations, they should also look out for fever and lethargy in patients. It is also important to monitor any areas of swelling, redness or soreness — under the skin, not necessarily open sores — that persists." 

A doctor will diagnose an infection by doing a lab culture. CRE are a type of bacteria called gram-negative, making them easy to identify using lab cultures. "Bacteria are categorized as either gram-negative or gram-positive, based on how they react with certain dyes for diagnostic purposes," said Shahriar Mobashery, a life sciences professor at the University of Notre Dame. "Members of both groups could be antibiotic resistant, and they are problematic in their own ways." 

There are only a few antibiotics that can kill CRE. This is why the mortality rate with CRE is so high. According to the U.S. National Library of Medicine, the only antibiotics that are used to treat CRE are polymyxins, aminoglycosides, tigecycline, fosfomycin and temocillin. The group of antibiotics called carbapenems has been serving as a "last resort" for treatment of gram-negative bacteria, Mobashery told Live Science. "With the emergence of CRE, which now have become resistant to carbapenems, the option of treatment of infection by carbapenems has been eliminated." 

A microbiology laboratory must run tests to determine which antibiotic will work to cure a particular case of CRE, according to the West Virginia Department of Public Health. Taking antibiotics after the recovery process begins can make the CRE bacteria grow, so these drugs must be taken with caution.

There are some experimental drugs being developed to fight CRE. For example, the company Actavis is developing a new antibiotic called ceftazidime-avibactam. Actavis submitted a New Drug Application (NDA) to the Food and Drug Administration for ceftazidime-avibactam in September 2014. In December 2014, an FDA advisory committee recommended that the FDA approve the drug for the treatment of patients who have limited or no alternative treatment options, and the drug is currently under review at the FDA.

According to North Dakota Department of Health, once a person is infected with CRE, he or she is immune to future infections with CRE. 

Prevention can minimize the spread of CRE. Cleanliness is a key part of prevention. Palisano said that medical devices should be scrupulously cleaned and sterilized before use. Once cleaned and sterilized, devices should only be handled by properly trained personnel to maintain a clean and sterile workspace. At home, proper hand washing and sanitization of surfaces can help to prevent the spread of CRE.

The use of antibiotics should also be limited. "Antibiotics should be carefully used only under conditions that warrant their use and should always be used as prescribed," said Palisano. 

Farone agreed and told Live Science that the best way to prevent the emergence of such deadly bacteria is to follow physician/health practitioner instructions when taking medication, especially antibiotics. "If you do not understand the proper way to take your antibiotics or why you need to completely finish a prescription, ask your pharmacist or health care provider," said Farone.