Abstract
Background:
Infection is the greatest cause of mortality in burn patients. As our population ages, the need to care for elderly burn patients will increase, and with it our understanding of how infection affects older patients with burn injuries. This article presents a review of the available literature on the effect of aging on the physiologic response to burns, of the known effects of infection in the elder population, and of the contribution of underlying medical comorbidities to the outcomes for the elderly burn patient. The potential for more serious outcomes from multi-drug resistance in the elder population is also discussed.
Methods:
This article is a review of the available literature on infection in elderly burn patients. A literature search was performed for key words: elderly; geriatric; burn; infection; comorbidity; multi-drug resistance; central line; urinary tract infection; and burn sepsis. Relevant findings were included in each section.
Results:
Pre-existing conditions are common in the elderly and contribute to a higher rate of development of pneumonia, cellulitis, urinary tract infection, central line infections, and burn wound infections. Specific data pertaining to infections in the elderly burn population are scarce or confined to single-center reports.
Conclusions:
Because of the inherent susceptibility of the elder population to infection because of pre-existing medical conditions, immunosenescence, and potential exposure via frequent interaction with the medical system, vigilance must be maintained for preventing and treating infection in elderly burn patients. More research is needed to define the risks and extent of this increasingly important issue.
Infection is the major cause of morbidity and mortality in burn patients, causing between 42% and 65% of all deaths [1]. Burn injury caused 3,655 deaths in the United States in 2018 [2]. Although the majority of deaths occurring in the initial 24 hours are attributable to the burn injury itself, the deaths occurring after the initial 24 hours have been and continue to be attributable to sepsis and invasive infection [3]. This is of particular concern in the elderly burn patient. Infections in the elderly population tend to occur with greater frequency and severity than in the younger population while posing a diagnostic challenge by presenting differently [4]. Burn injury compromises the body's primary barrier to infection, and the potential for infection is exacerbated, particularly in major burns in which the use of indwelling devices is common and necessary. Although there are disparate conclusions in the literature about the relation between aging, infection, and outcomes, understanding the risks of infection in the elderly burn patient will augment our ability to care for this growing patient population.
Morbidity, Mortality, and the Response to Infection
Mortality in elderly patients shows an increase with both advancing age and increasing size of the burn [5], with one study reporting a mortality of 22.7% in the elderly versus 4% in other adults with burns over the same time period [6]. The impaired response to infection and sepsis in elderly burn patients may be associated with the increased mortality rate, but it is difficult to ascribe a causal relation between any specific infection and outcomes.
Immunosenescence, the gradual decline in the body's immune function that is associated with aging, is a major contributor to the challenges older patients have in overcoming infections. Both cellular and humoral immunity are diminished with age. CD8+ and CD4+ T-cells, respectively the killer cells and the helper cells involved in immune response, as well as B-cells responsible for humoral defense, decline functionally and quantitatively, resulting in an increased susceptibility of the elderly to new infection [4].
Infection in the elderly can be insidious and may be heralded only by subtle signs, thus resulting in diagnostic delay. Fever, although a common and reliable marker for infection in other populations, may be absent in 20% of infections in the elderly, and patients in fact may be normothermic or even hypothermic [7]. Other non-specific symptoms include confusion, loss of appetite, increase in falls, or incontinence, and may be difficult to distinguish from the hypoactive delirium that may occur with hospitalization in the elderly. Adding to the difficulty in diagnosis is the limited ability of some elders to communicate clinical changes, with 50% of elderly nursing home residents diagnosed with dementia being unable to describe symptoms [8].
This impaired immune response in the burns, however, is not always associated clearly with an increase in infection. Jeschke et al. [9] found that burns in the elderly were characterized by an early phase of hypoinflammation followed by a subsequent hyperinflammatory state some weeks later. They were unable, however, to confirm their hypothesis that compared with other adults, elderly burn patients would sustain an increase in sepsis, bacteremia, pneumonia, or burn wound infection; the incidence of these infections for both adults and the elderly were similar. In line with other authors, it was noted that similarly sized burns were associated with higher mortality in elderly patients versus adults [9]. The elderly burn patient was found to be more likely to develop multi-system organ failure, and it may be that the diminishment of the elderly patient's immune response has detrimental effects that are additive to that of infection.
The Role of Pre-Existing Comorbidities
The elderly often arrive at the hospital with a number of medical conditions that may affect their ability to heal. Again, there is some variability in the conclusions that have been drawn. Jeschke et al. [9] found higher rates of cardiovascular (47% vs 11%), respiratory (12% vs 8%), endocrine (16% vs 6%), and renal (3% vs 1.4%) comorbidities in the elderly versus other adults [9]. Pham et al. [10] reviewed the National Burn Repository (NBR) and found that any comorbid condition in the elderly increased the likelihood of developing pneumonia substantially (odds ratio [OR] 2.84; 95% confidence interval [CI], 2.40–3.37; p < 0.001), and that increasing numbers of comorbidities as measured by Charlson score were associated with an increasing odds ratio for pneumonia [10]. The same authors, while looking specifically at pneumonia, found that a higher number of comorbidities was associated with a higher odds ratio for mortality, although they were cautious not to ascribe a causal relation. Mahar et al. [11] reviewed their center's experience and found that comorbidities other than rheumatoid arthritis were not related to outcomes.
Of the common comorbidities seen in the elderly, the one most pressingly concerned with infectious complications is diabetes mellitus. A retrospective study of diabetes in burns demonstrated that patients 18 to 65 years of age had a higher rate of infection, aggregated in this case as cellulitis, urinary tract infection, wound infection, line infection, or osteomyelitis, than patients without diabetes (65% vs 51%). The rate of infection for the elderly cohort of this population (>65) was not discussed specifically, although it was noted that the elderly population had a higher proportion of patients with diabetes (84%). Mortality was not found to be different between the diabetic and non-diabetic populations, but morbidity (increased depth of injury, need for surgery, infection, length of stay, and graft failure) was substantially increased in the diabetic group. The authors concluded that the elderly, particularly if diabetic, constitute a high-risk group of burn patients, one that might benefit from early and aggressive targeted prevention and treatment [12].
Specific Infections
Some infectious complications of burn injury are related directly to the wound, but others, namely urinary tract infections (UTIs) or central line-associated blood stream infections (CLABSIs), are related to indwelling devices, and still others, most importantly pneumonia, are associated with comorbidities or the burn wound.
Burn wound infection
Patients with major burn wounds (>20% total body surface area [TBSA]) have a greater likelihood of developing burn wound infection and sepsis. A high index of suspicion for burn wound infection is necessary for all patients but would seem to be particularly important in the elderly.
Diagnosis of burn wound infection can be difficult in its initial stages, and the distinction between colonization and infection can be difficult to make. Colonization of the burn wound at low concentrations of <10,000 colony-forming units (CFUs) per gram of tissue is often encountered and is not accompanied by surrounding erythema or cellulitis, although some degradation of the wound may be seen. Burn wound infection is seen with higher concentrations of bacteria (>10,000 CFUs/g of tissue) and is accompanied by cellulitis with its attendant erythema, induration, pain, and warmth. Invasive burn wound infection is also characterized by high concentration of bacteria but carries concerning findings, most importantly new areas of necrosis as well as signs of sepsis. Invasive burn wound infection is a surgical emergency requiring prompt resuscitation, institution of antibiotic therapy, and surgical excision [3].
Although the potential for burn wound infection makes the surgical management of burn wounds in the elderly a primary concern, there is nonetheless some disagreement regarding surgery for burn wounds in the elderly. The decision for surgery, often made easily in a younger patient, may be rendered more challenging in the elderly patient with multiple comorbidities or generalized frailty. The need for burn surgery has been associated with a mortality rate of 19.8% in one study of elderly burns patients; although this is not a causal relation, it does point to the increased surgical risks in the elderly population [6]. Whereas some investigators have posited that the elderly patient will tolerate burn surgery better than burn sepsis [13,14], others have shown that elderly patients managed non-operatively can have fewer complications than those undergoing surgery [15]. The success of operative intervention in the elderly increasingly appears to be a function of frailty rather than chronologic age, rendering patient selection even more important in the elderly burn [16].
Urinary tract infections
Urinary tract infections (UTIs) are the most common nosocomial infections in the elderly overall and are associated with increases in mortality and morbidity as well as an increased rate of nursing home transfer upon discharge from the hospital [4]. In the elderly burn population, a mortality link to UTI has not been clearly established, although UTI is relatively common, occurring in 6% of patients. Along with other nosocomial complications, however, UTIs have been shown to have a negative impact on long-term quality of life in burn patients at 12 and 24 months after discharge [17]. As many as 40% of indwelling urinary catheters are thought to be unnecessary and are used to manage incontinence. Aggressive efforts in catheter care, early cessation and use of alternative urinary management devices have been successful in decreasing the incidence of UTIs in elderly burn patients.
Central venous catheter infection/CLABSI
Historically, burn intensive care units (ICUs) have been noted for having the highest rates of CLABSIs of all ICUs [18]. Whereas older reports found rates of CLABSI in burn patients to be >50% [3], the implementation of strict aseptic techniques in the placement and care of central venous catheters (CVCs) has greatly reduced the rate of these infections. Central line-associated blood stream infections have come under scrutiny similarly to urinary tract infections, and the vigilance with regard to infection has similarly increased. Although routine catheter change for burn patients at different intervals has been advocated [19], there is also an increasing acceptance of the need to minimize the use of CVCs altogether.
Pneumonia
Pneumonia is a particularly troubling complication of burn injury, being both the most common infection encountered in elderly burn and frequently associated with death. In a review of their center's experience, Wearn et al. [20] found that pneumonia occurred in 11% of their elderly burn patients and was the leading infectious cause of death in that population. Analysis of the NBR by Pham et al. [10] also demonstrated the increased risk of death from pneumonia in elderly burn patients. In this review, 8.6% of elderly burn patients developed pneumonia, which in turn was associated with an adjusted odds ratio for death of 1.91 (95% CI, 1.61–2.27; p < 0.001). Patients developing pneumonia had a higher mortality rate (30.4% vs 9.5%; p < 0.001), as well as longer length of stay (LOS) and LOS/TBSA (36.0 vs 14 days; 4.0 ± 9.5 vs 3.2 ± 6.3; both p < 0.001). Male gender, higher TBSA, presence of inhalation injury (21.2% vs 6.9%), and comorbid conditions were found to be associated with development of pneumonia. In particular, chronic pulmonary and cardiac diseases had adjusted odds ratio of 2.7 and 3.48 for development of pneumonia. However, multiplicity of comorbidities was more relevant to development of pneumonia than any single comorbidity. Chronological age was not consistently associated with a higher incidence of pneumonia, again reflecting the notion that physiological age plays an important role in development of infection and other complications of burn injury [10].
Multi-Drug Resistance and the Elderly
Multi-drug–resistant organisms (MDRO) pose a substantial danger in the burn population, and infection with MDROs is associated with an increase in burn mortality [21]. Critical illness and length of time in the burn unit are associated with development of MDROs, with one study demonstrating that 41% of respiratory cultures in the burn ICU isolated MDROs, compared with 14% of other ICUs in the same hospital [22].
Multi-drug–resistant organism infection appears in a predictable fashion, and hospital-acquired infections (HAIs) tend to originate with skin and soft tissue infections predominating in the first week (typically Staphylococcus aureus), and progressing to include Pseudomonas aeruginosa later, after 28 days, with UTIs, CLABSis, and pneumonia often appearing after more than 30 days [1]. MDROs of particular concern in burn care are Pseudomonas aeruginosa, Acinetobacter baumanii, Stenotrophomonas maltophilia, and methicillin-resistant Staphylococcus aureus (MRSA). Carbapenem-resistant Enterobateriaeae is also increasingly common.
Individual risk factors for MDR acquisition once an elderly patient is hospitalized include age, LOS, and the presence of comorbidities. Risk factors for development of MDRO include LOS of stay, previous antibiotic exposure, and invasive devices [1]. These last three are of particular relevance to elderly burn patients, who tend to have longer LOS for various reasons [23], who often have had previous antibiotic exposure, and who may have indwelling devices placed or left for convenience rather than active management [4].
Another consideration in the elderly population is colonization with MDROs even prior to burn injury. Whereas data regarding colonization of the elderly burn patients with MDROs is scant, this population overall likely has a greater risk of harboring MDROs at baseline because of their more frequent interaction with the healthcare system, whether it be in the form of increased hospitalizations, frequent office visits, or residence in a care facility.
A subset of the elderly who may be particularly prone to MDRO colonization and subsequent infection are residents of long-term care facilities. One study of 26 nursing homes found a prevalence rate of 16% for MRSA in the facilities' residents [24], although a recent study of one center found only a 3.8% prevalence [25]. A Norwegian study demonstrated that roughly 6% of elderly residents of long-term care facilities had some type of infection, either of the urinary or respiratory tract, skin, or surgical site; other studies have demonstrated a prevalence between 5% and 16% [26]. It is estimated that at least 30% of bacterial infections in nursing homes are UTIs [27]. Because of the potential for morbidity and mortality from MDRO infection, it is important to screen patients from these facilities both to determine current infection and to assess for MDRO colonization.
Conclusions
For a variety of reasons including comorbidities, immunosenescence, indolent responses to infection, colonization with MDROs, and residence in long-term facilities, the burn-injured elderly are particularly susceptible to the development of infections and associated adverse events. The current coronavirus 2019 (COVID-19) pandemic has highlighted both the vulnerability of elderly patients residing in long-term care facilities and the importance of strict infection control measures there. More detailed research into infection rates in the elderly burn patient will allow a better understanding of the extent of the risks of infection to these patients. A high index of suspicion for infection, rigorous infection screening and control practices, and a concerted effort to minimize and remove indwelling devices will be critical to controlling infection in this vulnerable patient population.
Footnotes
Funding Information
No funding was received for this article.
Author Disclosure Statement
No competing financial interests exist.