SYMPOSIUM Additionally, CDC is willing to
provide funding to support seven re- gional laboratories to deal specifically with antimicrobial-resistant bacteria, identify emerging antibiotic-resistant threats, conduct special threat as- sessments, and track changes in re- sistance. One of these laboratories is projected in Texas.
THE BACTERIAL THREATS
The list of antimicrobial-resistant hu- man pathogens is large and continues to expand. In an attempt to priori- tize efforts, CDC published a report outlining the most pressing drug- resistant organisms affecting the U.S. population. The agency categorized organisms based on the need to de- velop new therapies and the potential public health consequences as urgent, serious, and concerning. (See Figure 2.) The categorization helps prioritize surveillance strategies and prevention and assists in allocating funds to com- bat these organisms. Visit
www.cdc .gov/drugresistance/biggest_threats .html for a full description of all these bacteria. Some of the most important noso-
comial organisms affecting Texas hos- pitals include:
• Carbapenem-resistant Enterobac- teriaceae. The carbapenems are a group of potent, wide-spectrum antimicrobials considered to be the last resort against multidrug- resistant gram-negative organisms that cause a diverse array of serious human infections. Development of resistance against these compounds creates a major public concern. The Enterobacteriaceae family encom- passes a large group of organisms that include several important hu- man pathogens such as Escherichia coli, Klebsiella pneumoniae, and En- terobacter spp., among others. The most frequent and worrisome mechanism of resistance to carbapen- ems is the acquisition of enzymes that destroy the antimicrobial mol- ecule, rendering it ineffective. These
enzymes, called carbapenemases, are encoded by genetic elements that are readily transferable among members of the Enterobacteriaceae family, and antibiotic use usually stimulates the transfer mechanism. Many types and subtypes of such enzymes have been identified (and many others are likely to emerge), but the most widely disseminated en- zyme in the United States and Texas is the KPC ß-lactamase (for K. pneu- moniae carbapenemase). Carbapen- em-resistant Enterobacteriaceae have now been described all over the world, and their spread results in infections that are difficult, if not impossible, to treat.
In fact, recent data estimate about
50 percent of the patients who get a bloodstream infection with a carbapenem-resistant Enterobacteri- aceae while admitted in a hospital die from such infection.7
Additionally, in
a report in Houston, Aitken and col- leagues reported on the existence of carbapenem-resistant isolates carry- ing an enzyme known as NDM-1 (for New Delhi metallo-beta-lactamase), first described in Sweden in a patient coming from India and rapidly spread throughout the world.8
• Clostridium difficile. This organism can be found in the gastrointesti- nal tract of healthy humans without causing major issues. However, after the use of antibiotics and alteration of the gastrointestinal microbiome (a term for the community of microbes that inhabit the gastrointestinal tract of humans), this organism seizes the opportunity and becomes an aggres- sive pathogen, causing significant colon inflammation that can lead to severe disease and potentially death. C. difficile infections are most fre- quently seen in patients who have a history of recent antimicrobial use and/or current or previous contact with the health care environment (hospitalization, admission to long- term facilities, etc.). CDC estimates C. difficile is responsible for almost
half-a-million infections per year in the United States, becoming the most common cause of health care-associ- ated infections in the country.9
C. dif-
ficile carries economic burden calcu- lated to up to $4.8 billion each year in excess of health care costs for acute care facilities alone.9 The number of deaths directly at-
tributed to this infection is about 15,000 per year, and about 80 percent of these C. difficile-associated fatali- ties correspond to patients aged 65 years or older.9
Another challenge
posed by C. difficile infection is repeat infections with the same organism (recurrence). Indeed, a CDC study found 20 percent of patients diag- nosed with a health care-associated C. difficile infection experienced a re- currence of the infection after treat- ment,10
which exemplifies the impor-
tant therapeutic conundrum that this organism represents for clinicians in Texas and nationally.
• Methicillin-resistant Staphylococcus aureus. S. aureus is a major human pathogen that causes a wide range of infections (from mild skin infections to infective endocarditis), some of them life-threatening. The ability of S. aureus to adapt and develop resis- tance to virtually all antimicrobials used against it is concerning. In par- ticular, the dissemination of isolates harboring resistance to most beta- lactams (known as methicillin-resis- tant S. aureus [MRSA]) has become a major problem in hospitals and in the community. MRSA is a leading cause of hos- pital-associated infections and is the most common cause of soft-tissue in- fections requiring visits to emergency services in the United States.11
Ac-
cording to CDC estimates, each year, MRSA is responsible for more than 80,000 severe infections and causes more than 11,000 deaths in the Unit- ed States. Additionally, the develop- ment of vancomycin resistance (one of the most widely used drugs to treat MRSA infections) in a community-
February 2017 TEXAS MEDICINE 49
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