Vancomycin-Resistant Enterococci
Vancomycin-Resistant Enterococci
History and Scientific Foundations
Introduction
The World Health Organization (WHO) reports that drug-resistant germs infect more than two million people in the United States every year and that 14,000 die as a result. The rise of drug resistance among microorganisms is tied to the widespread use of antibiotics in humans and animals. Vancomycin-resistant enterococcus (VRE) is one of a group of drug resistant bacteria that were first reported in 1986, almost 30 years after the antibiotic vancomycin was introduced. Vancomycin has been a mainstay of hospital infection control since the emergence of microorganisms that are resistant to the original antibiotics developed in the early and midtwentieth century, such as penicillin, methicillin, and ampicillin.
History and Scientific Foundations
When large amounts of oral vancomycin are taken for an infection, some of the drug's proteins are not absorbed and remain in the gastrointestinal tract. This environment leads to colonization (the presence of microorganisms that normally do not cause disease) with vancomycin-resistant organisms when the antibiotic concentrations in the intestines are high enough to encourage resistant enterococci bacteria to grow, but not sufficiently high to kill these organisms.
WORDS TO KNOW
COLONIZATION: Colonization is the process of occupation and increase in number of microorganisms at a specific site.
ISOLATION: Isolation, within the health community, refers to the precautions that are taken in the hospital to prevent the spread of an infectious agent from an infected or colonized patient to susceptible persons. Isolation practices are designed to minimize the transmission of infection.
PATHOGEN: A disease causing agent, such as a bacteria, virus, fungus, etc.
PREVALENCE: The actual number of cases of disease (or injury) that exist in a population.
RESISTANT ORGANISM: Resistant organisms are bacteria, viruses, parasites, or other disease-causing agents that have stopped responding to drugs that once killed them.
For decades, vancomycin was the only effective therapy for potentially life-threatening infections with resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). Throughout the 1990s, there were few if any antimicrobial agents to treat VRE infections. In recent years, newly developed antibiotics have been effective against VRE and other multi-drug resistant organisms, but strains (types) of microorganisms that are resistant to these new agents have already emerged. Many of these strains are resistant not only to vancomycin, but are also to other antibiotics that have been widely used against infections with similar bacteria in hospital settings, a condition called cross-resistance.
The connection between VRE and MRSA is particularly alarming. In one study, almost 25% of hospitalized persons who were co-colonized with both bacteria (had growing populations of both bacteria present on their bodies) died. Another nearly 35% were discharged to other facilities and took with them significant risk of further transmitting the infection to other patients.
Most of the VRE recovered in the United States are one of two species of enterococcus bacteria E. faecium or E. faecalis. These enterococci occur naturally in the intestinal tract of all people and are not generally harmful, whether or not they are vancomycin-resistant, and most infections resolve without treatment. Nevertheless, infections with these microbes, especially with E. faecalis can be dangerous to immunocompromised persons (those receiving chemotherapy for cancer, organ transplantation, or who have weakened immune systems due to a variety of conditions such as AIDS).
From 1990 to 1997 the prevalence of VRE in hospitalized patients with infections arising from enterococi bacteria increased from less than one percent to about 15%. By 1999, VRE accounted for nearly a quarter of all enterococcus infections in hospital intensive care units (ICUs), as reported by the National Nosocomial Infection Surveillance System (NNIS). This figure rose to 28.5% in 2003.
Applications and Research
The Centers for Disease Control (CDC) publishes and revises guidelines for the management of VRE and other antibiotic resistant organisms in healthcare settings. Local advisories based on the CDC guidelines are now widely disseminated and public health agencies are attempting to increase public awareness of VRE. A notice on the website of the New York State Department of Health states, “Serious VRE infections usually occur in hospitalized patients with serious underlying illnesses such as cancer, blood disorders, kidney disease or immune deficiencies. People in good health are not at risk of infection, but health care workers may play a role in transmitting the organism, if careful handwashing and other infection control precautions are not practiced.” The notice goes on to say that VRE is usually spread by “direct contact with hands, environmental surfaces or medical equipment that has been contaminated by the feces of an infected person.”
Impacts and Issues
In the United States and around the world, VRE infections present a growing burden of illness with considerable economic impact. A recent analysis documented increased mortality (deaths), length of hospital stay, ICU admissions, surgical procedures, and costs for VRE patients compared to a matched hospital population. VRE prevalence in the United States has steadily increased over the past two decades.
During this time, public health officials as well as hospital-based infectious disease specialists and hospital pharmacists have become increasingly concerned with the spread of infection with VRE in hospitals, rehabilitation centers, and nursing homes. The CDC reports that concerted efforts involving the isolation of VRE-infected patients, active surveillance, use of a waterless hand disinfectant, and staff training have resulted in significant local decreases in VRE prevalence.
Hospitals are responding with strategies designed to limit the spread of VRE by limiting the use of vancomycin. Powerful new antibiotics such as piperacillin-tazobactam are often effective against VRE, but are expensive and require intravenous administration.
Such anti-VRE strategies can be highly effective across an entire health care system. Some hospitals in the Netherlands and Denmark, for example, pro-actively isolate all patients considered at risk for VRE until tests show them to be free of multi-drug resistant organisms. This step prevents carriers from passing infections to other patients and hospital workers. The strategy has significantly reduced VRE-related infections in these countries. Also in the European Union, the non-therapeutic use of antibiotics in animals was banned in 2006 in order to stop the transfer of resistant bacteria from farm animals to people. This prescription was on top of a pre-existing ban on the agricultural use of vancomycin-type drugs in animal feed.
The “tried and true” methods of infection control are not universally considered to be an adequate response to the antibiotic resistant infection crisis. Some observers are now advocating environmental strategies directed at farming practices such as restricting the use of antibiotics in farm animal feed that promote VRE and related cross resistant strains which multiply in dairy effluent lagoons. Such broad ranging strategies have a political and economic policy aspect, and have not yet been endorsed by the CDC, which continues to emphasize institutional infection control measures. However, as alarm spreads over the increase in antibiotic resistance, more comprehensive, environmentally based, and economy-wide measures may eventually be implemented in order to preserve the effectiveness of antibiotics as life-saving drugs.
See AlsoAntibiotic Resistance; Contact Precautions; Microbial Evolution; Resistant Organisms.
BIBLIOGRAPHY
Books
Shnayersen, Michael, and Mark J. Plotkin. The Killers Within: the Deadly Rise of Drug-Resistant Bacteria. Boston: Back Bay, 2003.
Periodicals
Rice, L.B. “Emergence of Vancomycin-resistant Enterococci.” Emerging Infectious Diseases, (March-April 2001):7(2)183–87.
Web Sites
Healthcare Infection Control Practices Advisory Committee. Centers for Disease Control and Prevention.“Management of Multidrug-Resistant Organisms In Healthcare Settings-2006.” <http://www.cdc.gov/ncidod/dhqp/pdf/ar/mdroGuideline2006.pdf> (accessed May 21, 2007.)
New York State Department of Health. “Vancomycin Resistant Enterococcus (VRE).” <http://www.health.state.ny.us/diseases/communicable/vancomycin_resistant_enterococcus/fact_sheet.htm> (accessed may 21, 2007).
Kenneth T. LaPensee