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Vancomycin-Resistant Enterococci
Overview
Enterococci bacteria grabbed the attention of public health officials in the 1980s because of its ability to survive in humans and animals, and its knack for sharing those survival tricks with other bacteria.
While enterococci are not as familiar as staphylococcus (staph) or Escherichia coli (E. coli) bacteria, enterococci infections are among the most common type acquired by hospitalized patients. Enterococci, in general, are much less capable of causing disease than staph or E. coli but still can complicate and prolong hospital stays. Virtually the only people who develop illness from Enterococcus are those who are already ill, such as individuals in a hospital intensive-care unit, or those who are elderly, have diabetes, chronic kidney failure, and so forth. So, unlike other forms of resistant bacteria, there is little chance or concern among physicians of Enterococcus becoming epidemic in healthy populations.
But enterococci are of great interest because, as with many of its bacterial counterparts, it can resist and evade several forms of antibiotic therapy, including vancomycin, the antibiotic of last resort for resistant infections.
Enterococcal infections that result in human disease can be fatal, particularly those caused by strains of vancomycin-resistant enterococci (VRE). During 2004, VRE caused about one of every three infections in hospital intensive-care units, according to the Centers for Disease Control and Prevention (CDC).
In 1984, enterococci was given its own genus identity. In 1986, the first VRE strains appeared in Europe and, in 1989, the first case of vancomycin-resistant enterococci was reported in the United States. Between 1989 and 1993, the percentage of enterococcal tests that were positive for VRE in the United States rose from 0.3 percent to 7.9 percent.
Researchers seek to develop improved therapeutics, as well as gain a better understanding of VRE’s genetic survival characteristics, and how those resistance genes are passed to other pathogens.
Why is the latter element important? As of 2007, the United States had reported seven cases of vancomycin-resistant Staphylococcus aureus (VRSA) infection, a serious development that has healthcare providers fearful of losing ground in their attempt to control the spread of S. aureus. In one of the cases, scientists confirmed the transfer of a key antibiotic resistance gene from Enterococcus to Staphylococcus.
VRE Risks
Enterococci can survive for months. It primarily resides in the human digestive system and the female genital tract; the enterococci make up a significant part of the normal bacterial population of these sites in healthy people.
However, colonization can progress to infection, particularly for people with certain risk factors. The infection can lead to diseases of the urinary tract, bloodstream, heart valves (endocarditis), brain (meningitis), and to serious infections in open wounds.
Some of the risks for acquiring VRE infection are
- Persons who have been previously treated with vancomycin and combinations of other antibiotics, such as penicillin and gentamicin.
- Persons who are hospitalized, particularly when they receive antibiotic treatment for long periods of time.
- Persons with weakened immune systems, such as patients in intensive-care units, cancer, or transplant wards.
- Persons who have undergone surgical procedures, such as abdominal or chest surgery.
- Persons with medical devices that stay in for some time, such as urinary catheters or central intravenous catheters.
Transmission
VRE is transmitted from person to person most commonly by healthcare workers whose hands have inadvertently become contaminated, either from feces, urine, or blood of a person carrying the organism. It can also be spread indirectly via hand contact with open wounds or by touching contaminated environmental surfaces, where the bacterium can survive for weeks. Vancomycin-resistant enterococci is not transmitted through the air.
Of more than a dozen forms of enterococci bacteria, two are the primary concern for human disease: E. faecium and E. faecalis. E. faecium is the most frequent species of VRE found in hospitals.
Diagnosis
Enterococci have two types of resistance to vancomycin: acquired and intrinsic (natural). Some types of enterococci bacteria acquire the resistance when other bacteria come in contact with enterococci and share genetic information—scientists believe enterococci acquired the gene that resists vancomycin from bacteria in the digestive tract. Acquired resistance has been noted with two clinically important forms of enterococci: E. faecium and E. faecalis.
Of the dozen or so types of enterococci bacteria, some, such as E. gallinarum and E. casseliflavus, have an inherent, low-level resistance to vancomycin. These are very uncommon strains, however, and are of limited clinical significance.
If you have an enterococcal infection, it is crucial that your healthcare providers quickly identify the strain, so that they can determine how best to treat you and prevent patient-to-patient transmission. They will want to know if the strain infecting you is resistant to vancomycin, and if so, is the resistance intrinsic or acquired? If the resistance is acquired, does the strain contain specific genes that can share resistance traits with other bacteria, thus making it able to spread disease?
Tests are available to make those diagnoses.
Some healthcare practitioners, as part of their normal infection control procedures, will test you for the presence of VRE to learn whether you might be infected or colonized with the bacterium. This helps facilities know whether specific procedures should be used to reduce the potential spread of vancomycin-resistant enterococci.
Treatment
Most VRE infections can be treated with antibiotics other than vancomycin. Some of the antibiotics that fail to work because of intrinsic resistance include some types of penicillin, cephalosporins, clindamycin, and aminoglycosides. Treatments that are ineffective because of acquired resistance include vancomycin, some penicillins, macrolides (such as erythromycin), tetracycline, quinolones, and others.
The course of treatment is determined by testing different antibiotics in the laboratory to determine which ones might be most effective against the infectious strain. If you develop a VRE infection and have a urinary catheter, sometimes removing the catheter will clear the infection.
If you are colonized with VRE—the bacteria are present but have not caused an infection—you usually will not require treatment.
Prevention
Proper hand hygiene—thorough washing with soap and then drying—is the best way to prevent the spread of enterococci.
The CDC Hospital Infection Control Program encourages hospitals to develop their own institution-specific plans, which should stress
- Prudent vancomycin use by clinicians.
- Hospital staff education regarding vancomycin resistance.
- Early detection and prompt reporting of vancomycin resistance in enterococci and other gram-positive microorganisms by the hospital microbiology laboratory.
- Immediate implementation of appropriate infection control measures to prevent person-to-person VRE transmission.
Information obtained from National Institute of Health