Epidemiology and Prevention of Infections in Residents of Long-Term Care Facilities
Jennie Johnstone
Mark Loeb
Infectious diseases pose an important threat to the health of residents of long-term care facilities (LTCFs) (1) who are at increased risk of infection due to advanced age and multiple comorbidities. Environmental factors such as close living conditions facilitate outbreaks of infection by increasing the likelihood of exposure among the often frail residents of LTCFs. Given demographic trends in aging, it is anticipated that this burden of infection will continue to increase. Infection prevention and control programs therefore play a paramount role in preserving the health and quality of life of residents of LTCFs. In this chapter, we outline the most common infections that place residents of LTCFs at risk and discuss both the reasons why the burden of disease is so high in this population and strategies that can be implemented for prevention. The role and structure of an LTCF infection control program are outlined, and the current scientific evidence for prevention of infectious disease in LTCFs is reviewed.
DEFINITION
Although LTCFs are often thought to be synonymous with nursing homes, the term in fact encompasses a heterogeneous group of institutions including nursing homes, psychiatric facilities, stroke rehabilitation facilities, facilities for the developmentally challenged, and group homes. The risk of infection in these facilities varies greatly but is highest in skilled nursing homes. Nursing homes, which may be freestanding or affiliated with acute care hospitals, are inpatient facilities for persons who require nursing care and related medical or psychosocial services. This chapter focuses primarily on infections that occur in the nursing home setting, because they account for the majority of LTCFs. The vast majority of LTCF studies about infection and its prevention are set in nursing homes. Wherever possible, this chapter includes observations and data from other types of LTCFs, but the description of infections in these other settings is unfortunately sparse.
As a prime example, an important recent infection control challenge comes from long-term acute care hospitals (LTACHs) (2). These facilities combine the acuity of acute care with long-term placement. Patients often have severe respiratory and other medical problems that include need for chronic ventilation and reside in these facilities for a prolonged period of time (2). Residents of LTACHs typically have had long lengths of stays at their acute care hospitals including stays in intensive care; hence, the burden of infection with antimicrobial-resistant microorganisms is high. Surveillance data from these facilities are relatively limited; however, one surveillance study performed in the Unites States found that 64% of patients were colonized or infected with methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), or both (3). Clearly, further defining the burden of infectious disease in LTACHs and its prevention requires further study and is an important area of future research (2).
DEMOGRAPHICS
Demographic trends in the United States and Canada suggest that older adults are the fastest growing sector. In fact, it is estimated that in 2030, 30% of the population will be 65 years and older (4). As a consequence, rates of admission to LTCFs are increasing. It has been estimated that the lifetime risk of a 65-year-old entering a nursing home is approximately 50% (5). In terms of infection control, these figures raise challenges with respect to the burden of illness in this population.
INCIDENCE AND PREVALENCE OF INFECTION IN LONG-TERM CARE
The overall incidence of infection in various types of Canadian and US LTCFs is estimated to range from 1.8 to 9.4 infections per 1,000 resident care days. One well-designed inception cohort study estimated the incidence of infection to be 7.2 per 1,000 resident care days (6). This rate did not include cases of asymptomatic bacteriuria and used standardized definitions and involved intensive surveillance by a nurse practitioner who visited all residents 2 to 4 times per month. One limitation of the study is the fact that it was conducted prior to the development of LTCF surveillance definitions. Other study designs were limited by not including patients with upper respiratory tract infections or bronchitis, thereby underestimating the true frequency of infection (7). Studies using the Centers for Disease Control and Prevention (CDC) definitions for healthcareassociated infection may have underestimated their rates, because some LTCFs lack routine access to laboratory and radiologic investigations.
A number of 1-day prevalence studies have been conducted in LTCFs in an attempt to capture the burden of illness due to infection in this population. Most have focused on nursing homes or other specific units for the elderly. The prevalence of infection on the day of study in all surveys ranged from 2.4% to 18.4%. This broad range likely reflects differing definition of infection (8,9,10,11,12 and 13). For example, some studies counted asymptomatic bacteriuria, whereas others used CDC definitions of healthcare-associated infection that may have underestimated the prevalence of infection (9,12,13).
WHY THE BURDEN OF INFECTION IN LTCFs IS HIGH
The reason for the high burden of infectious disease in LTCFs is multifactorial. Residents of LTCFs have multiple comorbidities and functional impairments and can be malnourished, all of which contribute to risk of infection. Furthermore, most residents of LTCFs are elderly and are at increased risk of infection due to immunosenescence, the waning of protective immunity with age. Outbreaks of infection in LTCFs are facilitated by environmental factors. Last, recognition of an outbreak may be missed due to unique challenges in diagnosis of infection in this population.
Comorbidities
Many residents of LTCFs have comorbidities. The most commonly reported diagnoses are circulatory system disease (26%), mental disorders including Alzheimer’s disease (26%), and diseases of the respiratory system (11%) (14). Diabetes mellitus is also common, affecting 20% to 30% of nursing home residents, and is known to affect immune dysfunction (15). Underlying comorbidities predispose nursing home residents to infection including lower respiratory tract illness, skin and soft-tissue infection, and urinary tract infections through a variety of mechanisms.
At any point in time, nursing home residents are on an average of six to eight different medications (16). Frequently prescribed drugs include sedatives, neuroleptics, and narcotic analgesics, which may depress the level of consciousness and increase the risk for lower respiratory tract infections (17). Medication such as tricyclic antidepressants can precipitate urinary retention predisposing residents to subsequent urinary tract infections. Other commonly used medications in the long-term care setting include H2 blockers and proton pump inhibitor therapy, which may increase the risk of lower respiratory tract infection (18,19); corticosteroids, which reduce immune function; and antibiotics, which encourage colonization with resistant microorganisms.
Invasive medical devices such as urinary catheters, feeding tubes, tracheostomies, and intravenous catheters further increase risk of infection by breeching the already compromised host defenses of nursing home residents. Urinary catheters are particularly common and are used in 5% to 10% of nursing home residents (20).
Functional Impairment
Functional impairments such as immobility, incontinence, and dysphagia have been reported to increase the risk of infections (21,22). In one study, 95% of nursing home residents needed assistance with at least one self-care activity, and three quarters were dependent in three to five such activities (14). Approximately 60% of all nursing home residents use a walker and almost half are incontinent of urine (14). Decreased mobility and incontinence predispose residents to respiratory tract infections, skin and soft-tissue infections, and urinary tract infections.
Malnutrition
Protein calorie malnutrition is common in nursing home residents affecting between 52% and 85% of residents in one study (23). Malnutrition is associated with impaired immune function manifested by a decrease in cell-mediated immunity. The consequences of malnutrition such as delayed wound healing, decreased level of consciousness, and decline in functional status all increase the risk of infection.
Effect of Aging on Immunity
There are a number of changes that occur to the immune system with age and are collectively called immunosenescence (24). Although all components of the immune system appear affected by aging, changes in T-cell parameters are by far the most pronounced (25). Changes include a reduction in the number of naive T cells and a corresponding
increase in memory T-cell subsets. Notably, aging is associated with accumulation of terminally differentiated memory T cells (26). The lack of naive T cells is thought to impair the ability of the host to respond against novel pathogens (24,27). The terminally differentiated memory T cells are considered to have poor functionality, resulting in impaired responses to recall antigens and is the mechanism thought to be responsible for increased risk of infection and poor response to vaccines seen in the elderly (24).
increase in memory T-cell subsets. Notably, aging is associated with accumulation of terminally differentiated memory T cells (26). The lack of naive T cells is thought to impair the ability of the host to respond against novel pathogens (24,27). The terminally differentiated memory T cells are considered to have poor functionality, resulting in impaired responses to recall antigens and is the mechanism thought to be responsible for increased risk of infection and poor response to vaccines seen in the elderly (24).
Environmental Reasons
In addition to the risk factors for infection described above, residents of LTCFs are at increased risk of infection simply by living in an LTCF (28). Outbreaks of infectious diseases are extremely common due to environmental factors including sharing sources of air, water, the close proximity of residents to other residents, and shared medical care and caregivers (28).
Diagnosis of Infectious Disease in LTCFs
The diagnosis of infectious diseases in LTCFs can be a challenge as the classic presenting signs and symptoms of infection are often blunted, altered, or absent in elderly nursing home residents. Reasons for this include cognitive impairment or reluctance to complain (29,30). In addition, comorbid conditions can mask the symptoms of infection or make them difficult to interpret. Declines in functional status in the frail elderly may be the chief herald of serious infection (31). Thus, urinary tract infections may present with confusion rather than dysuria and pneumonia with a fall not a cough (32). Compared with younger patients, older persons with bacteremia are less likely to develop chills, diaphoresis, altered mental state, physical complaints, or lymphopenia (33). The signs of infection are often subtle and appreciated only by staff members who know the resident well.
In general, the principals and criteria used for the diagnosis of infection in LTCF residents are comparable to those used for healthcare-associated infections. It should be noted, however, that LTCFs often lack ready access to laboratory and radiologic services, and physicians may not be present to diagnose infections as they occur. McGeer et al. (34) offered a comprehensive set of definitions for surveillance in LTCFs that account for the unique circumstances of these institutions (Table 98-1).
LONG-TERM CARE AND INFECTION CONTROL: CURRENT CHALLENGES
The main infection control challenges in LTCFs include managing antimicrobial resistance (e.g., MRSA, VRE, and Enterobacteriaceae-producing extended spectrum beta-lactamases [ESBLs] among others); reducing the burden of endemic infections such as respiratory, urinary, skin, and soft-tissue infections; providing surveillance and early recognition of outbreaks; and recognizing emerging infectious diseases.
Antimicrobial Resistance
Nursing homes play an important role in the problem of antimicrobial resistance. The most common and worrisome resistant pathogens in LTCFs are MRSA, VRE, and ESBLs (35,36 and 37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53 and 54). Also concerning but less common antibiotic-resistant pathogens include aminoglycoside-resistant gram-negative bacilli (38,47), high-level aminoglycosideresistant enterococci (38,53), multidrug-resistant pneumococci (46,55,56), and fluoroquinolone-resistant gram-negative bacilli (46,51,57).
The frequency of antimicrobial-resistant pathogens in LTCFs varies by location, stressing the importance of knowledge of local resistance patterns (10,35,38,44,52,53 and 54). For example, Scheckler and Peterson (10) found antimicrobial resistance to be rare in their survey of eight small rural nursing homes in Wisconsin. Likewise, Mylotte et al. (54) found antimicrobial-resistant pathogens uncommonly (in <20% of admissions) in residents of community nursing homes admitted to an inpatient geriatric service in Buffalo. In contrast, a number of large urban facilities have reported high frequencies of resistant pathogens. Trick et al. (44) found at least one antimicrobial-resistant bacterial isolate in 43% of 117 LTCF residents screened in one urban facility in Illinois. Of the 50 culture-positive residents, 24% harbored MRSA, 18% ESBL-producing Klebsiella pneumoniae, 15% ESBL-producing Escherichia coli, and 3.5% VRE.
Eradication of antibiotic resistance in LTCFs is particularly challenging due to high frequencies of antibiotic use and difficulties in eradication due to serious underlying disease, poor functional status, open wounds such as decubiti, presence of invasive devices, and prior antimicrobial therapy (35,36,38,43,44,52,53). As a result, residents of LTCFs can remain colonized for months to years. Resistant microorganisms can also be reintroduced from hospitals following a transfer for management of acute illnesses (35,38,49,50).
Endemic Infections
Common endemic infections in LTCFs include lower respiratory tract infections, symptomatic urinary tract infections, and skin and soft-tissue infections (58).
Lower Respiratory Tract Infections Pneumonia in nursing home residents (nursing home-associated pneumonia [NHAP]) is associated with significant morbidity and mortality in this population (59,60 and 61). NHAP occurs approximately once per 1,000 resident days of care, which is 10 times more frequent than in community dwelling elderly (62,63). Residents are at increased risk of pneumonia due to decreased ability to clear the airways, altered oropharyngeal flora, poor functional status, and swallowing difficulties leading to aspiration (1). Although there are over 100 etiologies that can cause NHAP, Streptococcus pneumoniae is the most common (64). Influenza is also an important cause of lower respiratory tract infection in residents of LTCFs and is discussed in the “Outbreak” section.
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