Prevention and Control of Health Care–Associated Infections

The Burden of Health Care–Associated Infections

Epidemiology

The Centers for Disease Control and Prevention (CDC) defines health care–associated infections as infections that patients acquire during the course of receiving health care treatment for other conditions. Nosocomial infection is a term that refers specifically to a health care–associated infection that develops in association with hospital care. The development of infection during the course of health care is not, however, limited to the acute care hospital setting. Thus, health care–associated infection , which is the preferred term, refers to the broader spectrum of infections that develop during the course of health care, wherever that care may be provided, including acute care hospitals, long-term care facilities, rehabilitation facilities, dialysis facilities, infusion centers, outpatient practices, and even the patient’s home during the receipt of home care services.

The most extensive data regarding the incidence of and outcomes associated with health care–associated infections come from acute care hospital settings. Each year, an estimated 700,000 or so health care-associated infections occur in U.S. hospitals ( Table 261-1 ), a huge number but a significant reduction from 4% to 3.2% of admitted patients since 2011. Approximately 1 of every 30 patients admitted to U.S. hospitals develops a health care–associated infection, thereby making health care–associated infection one of the most common complications associated with the receipt of health care. Moreover, these data indicate that health care–associated infections are one of the top 10 causes of death in the United States. Whereas many of these health care–associated infection-associated deaths occur among patients who are already severely ill and who have a high likelihood of death due to their underlying disease, a substantial proportion of health care–associated infection-related deaths occur among persons who were otherwise expected to survive their hospitalization. In one study, about 30% of unexpected in-hospital deaths were determined to be possibly or probably related to health care–associated infections. In addition to an increased risk of death, patients who develop health care–associated infections suffer a number of other adverse outcomes, including prolonged hospital stays, additional medical interventions and antibiotic treatment, discomfort, and loss of function and income. These statistics are particularly concerning when they are considered with the knowledge that many of these infections are preventable. In fact, a systematic review found that 55 to 70% of four of the most common types of health care–associated infections are preventable through the use of currently available, evidence-based preventive strategies (see Table 261-1 ).

TABLE 261-1

ESTIMATES OF THE BURDEN, COSTS, AND PREVENTABILITY OF COMMON HEALTH CARE–ASSOCIATED INFECTIONS IN U.S. HOSPITALS

TYPE OF INFECTION	ESTIMATED NUMBER OF INFECTIONS PER YEAR ^†	AVERAGE ATTRIBUTABLE COST ∗ PER INFECTION ^‡	CASE-FATALITY RATE ^§	PROPORTION PREVENTABLE ^‖
Urinary tract infection Catheter-associated urinary tract infection	62,700 39,188	$749-$1007	2.3%	65-70%
Surgical site infection	110,800	$11,087-$34,670	2.8%	55%
Pneumonia Ventilator-associated pneumonia	176,700 63,532	$14,806-$28,508	14.4%	55%
Blood stream infection Central line–associated blood stream infection	83,600 61,170	$6461-$29,156	12.3%	65-70%
C. difficile infection	106,759	$5682-$9124	2.9%

∗ In 2007 U.S. dollars.

† Magill SS, O’Leary E, Janelle SJ, et al. Changes in prevalence of health care-associated infections in U.S. hospitals. N Engl J Med . 2018;379:1732-1744.

‡ Scott RD. The direct medical costs of healthcare-associated infections in U.S. hospitals and the benefits of prevention. Centers for Disease Control and Prevention; 2009. Available at: http://www.cdc.gov/hai/pdfs/hai/scott_costpaper.pdf . Accessed July 25, 2021.

§ Klevens RM, Edwards JR, Richards CL, Jr., et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Rep . 2007;122:160-166.

‖ Umscheid CA, Mitchell MD, Doshi JA, et al. Estimating the proportion of healthcare-associated infections that are reasonably preventable and the related mortality and costs. Infect Control Hosp Epidemiol . 2011;32:101-114.

Although the majority of health care–associated infection statistics come from acute care hospitals, data demonstrate that health care–associated infections are significant problems in other health care settings as well. Point prevalence surveys conducted in European and the U.S. Veterans Affairs system long-term care facilities found that the prevalence of health care–associated infection among long-term care facility residents ranged from 2.4 to 5.2%. The overall burden of health care–associated infection among long-term care facility residents has been estimated to be 1.64 to 3.83 million infections per year in the United States and at least 2.6 million infections per year in Europe. Vascular access–related infections are the most common health care–associated infections among patients requiring chronic hemodialysis for end-stage renal disease, with a reported incidence ranging from 0.16 per 100 patient-months for patients with arteriovenous fistulas to 1.83 episodes per 100 patient months for patients with central venous catheters, and they are associated with increased morbidity, hospitalization, and death. The magnitude of health care–associated infections related to care provided in other settings, such as ambulatory surgery and endoscopy centers, has not been as thoroughly studied, but such infections have been well described.

Pathobiology

Health care–associated infections can be caused by organisms that are a part of the patient’s normal microbiota (i.e., endogenous infection) or by pathogens acquired during exposure to health care (i.e., exogenous infection) through the contaminated hands of health care providers, the environment, contaminated medical equipment, other patients, or visitors. A variety of factors can contribute to the development of health care–associated infections, and in many cases, these infections are multifactorial in nature. These factors can be related to the pathogen, the host, the specific health care interventions that a patient receives, the setting in which health care is received, and the methods by which these interventions are implemented. Health care–associated infection prevention strategies focus on eliminating, reducing, or modifying one or more of these risk factors.

Pathogen-Related Factors

The pathogen-related factors that contribute to the ability of an organism to cause infection include the organism’s normal reservoir, mode of transmission (e.g., direct or indirect contact transmission, respiratory droplets, airborne particles), ability to survive on inanimate objects and surfaces, ability to produce biofilm, virulence factors, and resistance to antimicrobial agents or disinfectants.

Host-Related Factors

The host-specific factors that are associated with an inherent increased risk of one or more types of infection, regardless of the receipt of health care, include age (with older adults having an increased risk of infection because of senescence of the immune system), obesity, smoking, severity of illness, and certain comorbid conditions (e.g., burns [ Chapter 97 ], end-stage liver [ Chapter 140 ] or renal disease [ Chapter 117 ], poorly controlled diabetes [ Chapter 210 ], some cancers, congenital or acquired immune deficiency [ Chapter 231 ]). These factors reflect suppression of the immune system or breaches of other normal host defense mechanisms. Whereas many of these factors are not amenable to intervention or cannot be effectively modified in the short term, interventions that address remediable risk factors (e.g., obesity, smoking, poorly controlled diabetes mellitus) have the potential to reduce the risk of health care–associated infection during future episodes of health care.

Health Care–Related Factors

Health care–related infection risk factors result from interventions that are intended to treat or otherwise provide benefit for a patient’s existing medical conditions but that also introduce an increased risk of infection. These factors may disrupt normal host defenses or alter the patient’s normal microbiota ( Chapter 257 ). Health care–related risk factors include the use of invasive devices (e.g., intravascular catheters, urinary catheters, endotracheal tubes), surgical procedures, exposure to antibiotics, receipt of immunosuppressive medications, and prolonged hospitalization. Because each of these interventions poses at least some degree of increased risk of infection, the risk-to-benefit ratio of each intervention must frequently be reassessed so that patients are not exposed to unnecessary risk. For example, central venous catheters and indwelling urinary catheters are major risk factors for primary blood stream infection and urinary tract infection, respectively. In a patient who has a true medical need for one of these devices, the benefits of the catheter exceed the risk of infection. However, once the patient recovers from the condition that necessitated use of the catheter, the risks associated with the device then outweigh the benefits.

Exposure to antibiotics is a well-established risk factor for colonization and infection with multidrug-resistant organisms and development of Clostridioides difficile ( Chapter 271 ) infection through a mechanism known as antibiotic selection pressure. Antimicrobial use is common in acute care hospitals and other health care settings, such as long-term care and dialysis facilities and ambulatory care practices. About one third of hospitalized European patients receive one or more antimicrobials during their hospital stay, as do about 50% of hospitalized patients in the United States. The rate is even higher, over 70%, in surgical critical care units. Unfortunately, studies have shown that 25 to 75% of antimicrobial use in acute care, long-term care, and hemodialysis facilities is unnecessary or inappropriate because the regimen is broader in spectrum or longer in duration than necessary, the antibiotics do not provide activity against the causative pathogen, the patient does not actually have a bacterial infection (e.g., specimen contamination, asymptomatic colonization), or the prescribed dose is inappropriate. Misuse and overuse of antimicrobial agents in the outpatient setting are also well-recognized problems in the United States and other countries, including many countries where antimicrobials can be obtained without a prescription. This inappropriate use of antimicrobial agents introduces unnecessary risk for the development of complications of antibiotic therapy, including C. difficile infection, the emergence of multidrug-resistant organisms, and drug toxicity, and represents an important target for intervention.

Health Care Delivery–Related Factors

Health care delivery–related risk factors do not offer any potential benefit to patients but rather are associated only with risk. Such factors include but are not limited to failure to perform hand hygiene when indicated or to use aseptic or sterile technique during invasive procedures; unsafe injection practices (e.g., entering a multidose vial with a used needle); and failure to clean, disinfect, or sterilize the patient environment, medical equipment, and instruments. All these risks are potentially modifiable and are thus important targets for prevention initiatives. Antibiotic use, which is also a patient-specific health care–related risk factor, can also be considered a health care delivery–related risk factor because misuse of antibiotics in one patient or population can introduce risks among the larger population through changes in microbial ecology (i.e., selection and increased prevalence of antimicrobial-resistant pathogens).

Many of these health care delivery–related factors are the result of poor adherence to recommended, evidence-based infection prevention practices. Despite recognition that poor hand hygiene practice is a leading cause of pathogen transmission, the existence of major national and international guidelines, and initiatives to improve hand hygiene practices among health care providers, compliance with recommended hand hygiene practices among health care personnel remains unacceptably low. In the United States, average rates of health care provider compliance with recommended hand hygiene practices have been reported to be less than 50%, with some individual studies reporting rates as low as 20% in some intensive care units (ICUs). Similarly, unsafe injection practices continue to be identified as the cause of health care–related transmission of blood-borne pathogens, such as hepatitis B and C viruses.

Environmental contamination can also contribute to the transmission of health care–associated pathogens. For example, environmental contamination with C. difficile has been detected in up to 100% of hospital rooms occupied by patients with C. difficile infection, and methicillin-resistant Staphylococcus aureus (MRSA) has been detected on environmental surfaces in approximately 70% of hospital rooms housing patients infected and colonized with MRSA. Some, but not all, studies have identified similarly high rates of environmental contamination with multidrug-resistant gram-negative pathogens. This environmental contamination has been shown to result in patient-to-patient transmission through transient contamination of hands and equipment or by direct contact of the patient with the contaminated environment. Environmental contamination is, however, a potentially modifiable risk factor for health care–associated infection. Cleaning and disinfection of the environment and portable medical equipment that is shared among patients are often suboptimal. For example, one multicenter study conducted in 36 acute care hospitals in the United States found that at baseline, only 48% of high-risk environmental surfaces were cleaned during routine cleaning after discharge of the patient. Improvement in cleaning practices and other interventions to reduce the microbiologic burden in the health care environment can reduce the microbial burden of organisms in the environment and has been associated with a reduction in the risk of acquisition of multidrug-resistant organisms and C. difficile infection. Outbreaks of infection due to contaminated medical devices (e.g., duodenoscopes, heater-cooler devices used in cardiothoracic surgery procedures) highlight the critical role that cleaning, disinfection, and sterilization of medical equipment play in preventing health care–associated infections. In addition, environmental interventions are important to prevent patients from acquiring pathogens due to exposure to water (e.g., Legionella species; Chapter 290 ) and air (e.g., environmental fungi) within health care settings.

Pathogens in Health Care–Associated Infections

The organisms most commonly identified in device- and procedure-associated infections (i.e., central line–associated blood stream infection, catheter-associated urinary tract infection, ventilator-associated pneumonia, and surgical site infection) vary somewhat among the different types and sites of infection. Overall, in the United States 10 pathogen groups accounted for more than 75% of pathogens identified in device- and procedure-related infections reported to the CDC through the National Healthcare Safety Network between 2015 and 2017. These pathogen groups and the proportion of reported pathogens that they represented include Escherichia coli (18%), Staphylococcus aureus (12%), Klebsiella species (9%), Pseudomonas aeruginosa (8%), Enterococcus faecalis (8%), coagulase-negative staphylococci (7%), Enterobacter species (5%), Enterococcus faecium (4%), Proteus species (3%), and Candida albicans (3%).

Multidrug-Resistant Bacteria

An increasingly concerning problem is the emergence of acquired antimicrobial resistance among many of the bacterial pathogens that are common causes of health care–associated infections ( Table 261-2 ). Multidrug-resistant organisms represent a significant health threat because infections caused by many of these multidrug-resistant organisms have been associated with worse outcomes than those caused by antimicrobial-susceptible strains of the same organism, including excess length of hospital stay, increased health care costs, and higher mortality, with mortality rates approaching 50% in some studies. Possible explanations for the observed increased rate of adverse outcomes associated with multidrug-resistant organism infections include the presence of more severe underlying disease, delays in initiating effective therapy, and the use of more toxic or less effective therapy for treatment of the infection. Regardless of their cause, the poor outcomes associated with multidrug-resistant organism infections highlight the critical need for effective preventive measures and development of new antibiotics with activity against them, particularly multidrug-resistant gram-negative bacilli.

TABLE 261-2

RATES OF ANTIMICROBIAL RESISTANCE AMONG PATHOGENIC ISOLATES FROM HEALTH CARE–ASSOCIATED INFECTIONS

		PROPORTION OF ISOLATES RESISTANT TO ANTIBIOTIC
ORGANISM	ANTIBIOTIC CLASS	United States (2015-2017) ∗	ICUs in 45 Asian, African, European, and Latin American Countries (2013-2018) ^†	ICUs in 14 European Countries (2017) ^‡
Staphylococcus aureus	Anti-staphylococcal penicillins (e.g., oxacillin, methicillin)	44%	56%	24%
Klebsiella species	Extended-spectrum cephalosporins Carbapenems	19% 6%	76-78% 49%	40% 15%
Pseudomonas aeruginosa	Carbapenems	16%	53%	26%
Enterococcus faecium	Glycopeptides (vancomycin)	72%	29%	NR
Acinetobacter baumannii	Carbapenems	39%	92%	64%
Escherichia coli	Extended-spectrum cephalosporins Carbapenems Fluoroquinolones	20% 0.7% 36%	66-68% 17% 62%	16% 0.8% NR

ICUs = intensive care units; NR = not reported.

∗ Weiner-Lastinger LM, Abner S, Edwards JR, et al. Antimicrobial-resistant pathogens associated with adult healthcare-associated infections: summary of data reported to the National Healthcare Safety Network, 2015-2017. Infect Control Hosp Epidemiol . 2020;41:1-18.

† Rosenthal VD, Duszynska W, Ider BE, et al. International Nosocomial Infection Control Consortium (INICC) report, data summary of 45 countries, for 2013-2018, adult and pediatric units, device-associated module. Am J Infect Control . 2021;49:1267-1274.

‡ European Centre for Disease Prevention and Control. Healthcare-associated infections acquired in intensive care units. In: ECDC. Annual epidemiological report for 2017. Stockholm: ECDC; 2019. Available at: https://www.ecdc.europa.eu/sites/default/files/documents/AER_for_2017-HAI.pdf . Accessed June 9, 2021.

Organisms can develop resistance to antimicrobial agents to which they were previously susceptible through a variety of mechanisms, including induction, genetic mutation, and acquisition of new genetic material (e.g., conjugation with cell-to-cell transfer of genetic material by plasmids or transposons). In health care settings, however, patient-to-patient transmission of multidrug-resistant organisms is more common than de novo development of resistance in a previously susceptible organism within the patient’s existing microbiome. Identified risk factors for acquisition of multidrug-resistant organisms include exposure to antibiotics, frequent or prolonged exposure to health care facilities (e.g., hospitals, nursing homes), poor infection control practices among health care providers, environmental contamination with multidrug-resistant organisms, and prevalence of multidrug-resistant organisms among other patients within a health care facility.

Among the pathogens reported to the CDC between 2015 and 2017 as causes of device-associated infections and surgical site infections in adults, acquired antimicrobial resistance was relatively common (see Table 261-2 ). For example, 72% of Enterococcus faecium isolates were vancomycin resistant, and 44% of S. aureus isolates were resistant to methicillin (MRSA). Multidrug resistance among gram-negative pathogens also is a growing global health threat among persons receiving health care ( Chapter 281 ). Approximately 10% of the most common gram-negative pathogens reported to the CDC in 2015-2017 demonstrated acquired resistance to at least one drug in three or more antibiotic classes. For example, 39% of Acinetobacter baumannii isolates, 11% of Klebsiella and P. aeruginosa isolates, and 9% of E. coli isolates met this definition of multidrug resistance.

Although the lack of a standardized definition of multidrug resistance limits direct comparisons of data from different populations, antimicrobial resistance is an important problem in many regions of the world. For example, International Nosocomial Infection Control Consortium data from device-associated infections in ICUs in 45 countries in Asia, Africa, Europe, and Latin America collected between 2013 and 2018 demonstrated methicillin resistance in 56% of S. aureus isolates, as well as carbapenem resistance in 49% of Klebsiella species isolates and 92% of Acinetobacter species isolates.

One example of the emergence and rapid dissemination of multidrug-resistant gram-negative bacilli is carbapenem-resistant Enterobacteriaceae, particularly K. pneumoniae ( Chapter 281 ). In the United States, carbapenem resistance among the Enterobacterales is usually, but not always, due to the production of K. pneumoniae carbapenemase (KPC), a class A serine β-lactamase enzyme that hydrolyzes all β-lactam antibiotics. The K. pneumonia carbapenemase enzyme, which was first described in 2001, is encoded by the bla _KPC gene carried on a transmissible plasmid that also carries additional genes that confer resistance to several other classes of antimicrobial agents. Thus, in addition to carbapenem resistance, these organisms demonstrate resistance to other β-lactam antibiotics and to several other classes of antibiotics.

Asymptomatic carriage of multidrug-resistant organisms is relatively common among persons exposed to health care. In fact, patients with clinically apparent multidrug-resistant organism infections represent a relatively small proportion of the total burden of these pathogens. Reported rates of MRSA carriage have ranged from 4.6 to 13.6% among hospital patients, 2 to 22% among U.S. ambulatory dialysis patients, and 10 to 100% among residents of long-term care facilities. The prevalence of carriage of vancomycin-resistant enterococci among hospital patients and ambulatory dialysis patients has been reported to range from 6.3 to 67% and 0 to 16%, respectively. Studies that have included a variety of multidrug-resistant gram-negative bacilli have reported carriage rates of 19 to 32% in ICU patients and hospital patients with diarrhea, 25% among residents of long-term care facilities, and 16% among chronic hemodialysis patients. Studies that have focused specifically on carbapenem-resistant Enterobacterales have demonstrated prevalence rates ranging from 2 to 5.4% among high-risk hospital patients in the United States and 2 to 49% among post–acute care facility patients in Israel. These asymptomatic carriers play an important role in the epidemiology of multidrug-resistant organism infections. First, they represent a substantial risk of subsequent infection, with up to one third of carriers of MRSA, vancomycin-resistant enterococci, and multidrug-resistant gram-negative bacilli developing symptomatic infection within 12 months. Second, carriers of asymptomatic multidrug-resistant organisms can contribute to widespread transmission within the health care system through contamination of their surrounding environment. Several studies have demonstrated that the risk of acquiring a multidrug-resistant organism during hospitalization is related to the prevalence, or colonization pressure, of that multidrug-resistant organism among other patients. Finally, admission to a hospital room in which the prior patient was colonized or infected with MRSA, vancomycin-resistant enterococci, or multidrug-resistant gram-negative bacilli has been associated with an increased risk of acquisition of those organisms.

Over the past 15 to 20 years, encouraging data have shown a decline in the incidence of some multidrug-resistant organisms, particularly MRSA. In the United States, for example, the incidence of hospital-onset MRSA blood stream infections decreased by 74% between 2005 and 2016. These changes occurred despite the emergence of community-associated MRSA among persons without typical health care–associated risk factors and the introduction of community-associated MRSA as a health care–acquired pathogen. In the United Kingdom, a 97% reduction in the number of cases of ICU-associated MRSA blood stream infection was reported through a mandatory reporting system between 2007 and 2016. In more recent years, however, the incidence of MRSA infections in hospitalized patients appears to have plateaued. The specific cause of these observed decreases in MRSA health care–associated infections is uncertain and may be the result of improvements in basic infection control practices, introduction of specific MRSA prevention practices, or other changes in the epidemiology of this pathogen.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here