SECTION TWO: Understanding AMDR
Learning Objective: Explore the mechanisms responsible for the spread of AMDR.
According to the US Centers for Disease Control and Prevention (CDC), the number of antibiotic-resistant pathogens is on the rise, creating a major public health problem. AMDR is the ability of a specific microorganism to withstand a drug or a biocide preparation that interferes with its growth and functions (Meyers 1987; Russell 1999). Resistance is a complex phenomenon involving the microorganism, the drug, the environment, and the patient. It is important to note that resistance and virulence are not related; a resistant pathogen may be no more virulent than its antibiotic-sensitive parent strain (Holmberg et al. 1987; Berkowtiz 1995). The emergence of methicillin-resistant Staphylococcus aureus (MRSA), both hospital and community strains, as well as metallo-beta-lactamase–resistant Gram-negative pathogens, are two recent examples of how microbial resistance emerges and spreads through the global community (Liu et al. 2011; Walsh and Toleman 2011). Central to the emergence and proliferation of antimicrobial resistance in developed countries is the inappropriate use of antibiotics and patient contact with AMDR pathogens, whereas in emerging and developing countries, poor hygiene and crowded living conditions are important additional drivers (Walsh and Toleman 2011). Global mobility and socioeconomic problems such as overcrowding, sanitation, war, health disparities, poor public health literacy, and poor public health systems are intertwined with the spread of resistant infections.
In the United States, spending on antibiotic prescriptions increased 22% from 1980 to 1996, with a steep increase in resistance rates during the same period (Howard 2004). Studies in European countries also demonstrate a relationship between antimicrobial use and antimicrobial resistance rates (Livermore and Pearson 2007; Naber 2009). Infections caused by AMDR pathogens are associated with increased healthcare resource utilization. MRSA infections increase hospital length of stay (LOS), resource utilization, and cost, and are still associated with higher mortality (Cosgrove 2006). A similar pattern is noted for recently emergent Gram-negative antimicrobial-resistant strains (Walsh and Toleman 2011). Extended-spectrum β-lactamase (ESBL)–producing Enterobacteriaceae are associated with increased hospital LOS and costs, whereas bloodstream infections caused by ESBL-producing Enterobacteriaceae are associated with increased rates of mortality. Multidrug-resistant (MDR) Pseudomonas aeruginosa (resistant to 4 or more antibiotic drugs) is also associated with increased mortality and increased hospital LOS (Giske et al 2008). Overall, these resistance trends have prompted governments and professional associations to draft strong guidelines around the use of antimicrobial therapies (US Government Accountability Office 2011; World Health Organization 2011).