ANTIMICROBIAL RESISTANCE

WHAT  IS ANTIMICROBIAL RESISTANCE?

Antimicrobial  resistance is one of the most serious global public health concerns today.  Approximately 1.7 million patients in the United States acquire an infection in  the hospital each year, about 99,000 of whom will die as a result. Seventy  percent of the bacteria causing such infections are resistant to at least one  antimicrobial commonly used to treat these infections.1 Antimicrobial resistance  occurs when microorganisms adapt so that they are no longer able to be treated  with antimicrobial drugs that once were effective.

In  some of the most difficult cases, organisms become resistant to nearly all  available antimicrobials, leaving health care providers with few treatment  options for their patients. This is called multidrug resistance (MDR). One of  the most urgent MDR threats is carbapenem-resistant Enterobacteriaceae, or CRE.  CRE is resistant to almost all available antimicrobials. According to the  CDC’s 2013 Threats Report, CRE  causes 600 deaths per year in the United States.2 CDC is planning to release an  updated AR Threats Report in fall 2019 and CRE is expected to remain at or near  the top of the list. Clostridioides difficile is another significant threat  which can cause life threatening diarrhea and colitis and often occurs in people  who have been recently treated with antimicrobials. Widespread antimicrobial use  over many years has contributed to increasing numbers of infections due to both  MDR and C. difficile.

HOW  IS ANTIMICROBIAL RESISTANCE BEING COMBATTED?

Essential  to the fight against antimicrobial resistance is the implementation of an  antimicrobial stewardship program (ASP) which focuses on responsible use of  antimicrobials in health care facilities and in the community. Effective ASPs  reduce unnecessary and inappropriate antimicrobial usage which can lead to a  reduction in the development and spread of resistant bacteria and ultimately  improve patient outcomes. Clinical microbiologists are involved with developing  and implementing ASPs and design their antimicrobial susceptibility testing  (AST) and reporting protocols to meet the needs of the ASP. In doing so, it is  essential for each laboratory to utilize the most current AST and reporting  standards.

WHAT  ARE ANTIMICROBIAL SUSCEPTIBILITY TESTING STANDARDS?

Standards  for AST guide clinical microbiologists and others in using the best practices in  their laboratories to assess the in vitro activity of antimicrobials. Standards  organizations such as Clinical and Laboratory Standards Institute (CLSI) develop  and publish standards based on the most currently available information and data  provided to them by individuals involved in all aspects of antimicrobial  development, testing, and use. Recommendations for selection of the most  appropriate agents for testing and reporting and for interpretation of test  results are updated and published regularly. In January of each year, CLSI  publishes a new edition of its most widely used AST standard, Performance  Standards for Antimicrobial Susceptibility Testing, also known as  M100.3

When  clinical microbiologists examine bacterial cultures, they first identify the  organism or organisms likely contributing to a patient’s infection. If the organism has  unpredictable susceptibility to the antimicrobials that might be used in  treating the suspected infection, the laboratory then performs AST using one or  more of several test methods available. Subsequently, results are interpreted  based on criteria listed in M100, enabling the laboratory to inform health care  providers of those drugs that might be effective in treating the  patient’s infection.  Organisms can acquire antimicrobial resistance rapidly, and a drug that was  previously effective for a specific type of organism might no longer be,  highlighting the importance of reevaluating and updating AST standards  regularly.

HOW  ARE AST STANDARDS DEVELOPED?

CLSI’s M100 and other AST standards are  written by volunteer experts who are involved with developing, approving,  prescribing, and testing of antimicrobials, and/or reporting of bacterial  culture susceptibility results. These experts make up the CLSI Antimicrobial  Susceptibility Testing Subcommittee. Multiple working groups within this  subcommittee address very specific aspects of AST, such as determining which  antimicrobials to consider for testing and reporting for a specific type of  bacterium, assigning breakpoints to newer antimicrobial agents, and defining  appropriate quality control protocols. To ensure fairness, the subcommittee is  comprised of an equal balance of experts from health care, industry, and  government. Health care experts include clinical microbiologists, pharmacists,  and infectious disease specialists. Government participants include  representatives from the FDA and CDC. Industry members include pharmaceutical  and in vitro device manufacturers and statisticians. All work together to ensure  that the most up to date and useful information is available to help health care  providers prescribe the most effective treatment for their  patients.

PATIENT  CARE AND ANTIMICROBIAL RESISTANCE IS IMPROVED THROUGH THE USE OF AST STANDARDS  IN THE MICROBIOLOGY LABORATORY

The  responsible use of antimicrobials can be achieved through the implementation of  an antimicrobial stewardship program and the use of the most current AST  standards in the clinical microbiology laboratory. Responsible use of  antimicrobials improves patient care outcomes and contributes to the global  fight against antimicrobial resistance.