_______________________________________________________________ Healthcare-Associated Infections
the air, blood (or body fluid), contact (direct or indirect), fecal-oral route, food, animals, or insects. Once inside a host, micro-organisms thrive because of adherent properties that allow them to survive against mechanisms in the body that act to flush them out. Bacteria adhere to cell surfaces through hair-like projections, such as fibrillae, fimbriae, or pili, as well as by proteins that serve as adhesions [71]. Fimbriae and pili are found on gram-negative bacteria, whereas other types of adhesions are found with both gram-negative and gram-positive bacteria. Receptor molecules in the body act as ligands to bind the adhesions, enabling bacteria to colonize within the body. The virulence of the micro-organism will determine whether only colonization occurs or if infection will develop. With colonization, there is no damage to local or distant tissues and no immune reaction; with infection, bacterial toxins that break down cells and intracellular matrices are released, causing damage to local and distant tissues and prompting an immune response in the host. Bacteria continue to thrive within a host through strategies that enable them to acquire iron for nutrition and to defend against the immune response. These virulence factors enhance a micro-organism’s potential for infection by interrupting or avoiding phagocytosis or living inside phagocytes [71]. A healthcare environment increases the risk of infection for two primary reasons. First, it is likely that normally sterile body sites will become exposed, allowing pathogens to cause infection through contact with mucous membranes, nonin- tact skin, and internal body areas. Second, the likelihood of a susceptible host is high due to the vulnerable health status of patients. Especially in an era of decreased hospital stays and increased outpatient treatments, it is the sickest patients who are hospitalized, increasing the risk not only for infection to develop in these patients but also for their infection to be more severe and to be transmitted to others. Infection is transmitted in a healthcare environment primar- ily through exogenous and endogenous modes. Exogenous transmission is through patient-to-patient or staff-to-patient contact. Patients who do not have infection but have bacterial colonization can act as vectors of transmission. Staff members can also act as vectors because of colonization or contamina- tion. Endogenous infection occurs within an individual patient through displacement of commensal micro-organisms. In general, the spread of infectious disease is prevented by eliminating the conditions necessary for the micro-organism to be transmitted from a reservoir to a susceptible host. This can be accomplished by: • Destroying the micro-organism • Blocking the transmission • Protecting individuals from becoming vectors of transmission • Decreasing the susceptibility of potential hosts
Antiseptic techniques and antibiotics will kill micro-organisms, and proper hand hygiene will block their transmission. Gloves, gowns, and masks remove healthcare workers from the trans- mission cycle by protecting them from contact with micro- organisms. Contact precautions and isolation techniques help patients avoid being vectors of transmission. Lastly, ensuring that patients and healthcare workers are immune or vaccinated can help decrease the availability of potential hosts.
DEVELOPMENT OF DRUG- RESISTANT MICRO-ORGANISMS
The prevalence of drug-resistant micro-organisms has reached a critical level, and the inappropriate use of antibiotics is often cited as a primary cause of drug-resistant infections. As much as 50% of antimicrobial use is inappropriate [72]. The prophy- lactic use of antibiotics preoperatively and the empiric use of antibiotics have helped bacteria to develop resistance in the healthcare setting. To meet the challenge of drug resistance, the management of antibiotic use has been a priority recom- mendation in guidelines developed for infection control pro- grams in healthcare institutions, and review of the antibiotic formulary is required by institutions as part of compliance with Joint Commission standards [18; 26; 41; 73]. (Guidelines for preventing drug-resistant infections in the healthcare setting are discussed in the Infection Control section.) Although the inappropriate use of antibiotics is a major con- tributor to the development of drug resistance, other factors play an important role. These other factors include the natural ability of micro-organisms to adapt through genetic plasticity and rapid replication and the lack of antibiotic discovery and development over the past decades [74]. For example, when the efficacy of antibiotics was first demonstrated in the late 1920s, their development and manufacture increased rapidly, and they began to be widely used (too widely, perhaps). However, over the next 40 years, no new class of antibiotics was developed, and the number of new antibiotics decreased substantially between 1983 and 2014 [74]. In 2009, 16 antimicrobial com- pounds were in late-stage clinical development (phase II or later); however, these compounds represent only incremental advances compared with currently available options, and few address the most commonly resistant pathogens [75]. A 2013 IDSA report identified seven drugs in clinical development that were not included in the 2009 list, but indicated that these agents fell short of addressing the clinically relevant spectrum of resistance [76]. Only two new antibiotics were approved between 2009 and 2013, but five new antibiotics were approved in 2014–2015. Drug resistance typically emerges first in the healthcare setting, varies according to healthcare setting and geography, and subsequently extends to the community setting [26]. The transmission and persistence of resistant strains of pathogens in a healthcare setting depends on several factors: availability of vulnerable patients, selective pressure from use of antimicrobial agents, number of patients with coloniza- tion of infection, and presence and adherence to prevention efforts [26].
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