Why Should the Infectious Diseases Community Focus on Aging and Care of the Older Adult?
- Sections of Infectious Diseases and Hematology/Oncology, Wake Forest University School of Medicine, Winston Salem, North Carolina
- Reprints or correspondence: Dr. Kevin P. High, Sections of Infectious Diseases and Hematology/Oncology, Wake Forest University School of Medicine, Winston Salem, NC 27157-1042 (khigh{at}wfubmc.edu).
In this editorial commentary, I have several tasks I wish to accomplish: to review the evidence on why aging should be an important part of the practice paradigms and research agenda for infectious diseases specialists, to introduce the reader to a 5-part series entitled “What's Different about Infection in Older Adults?” that will appear in the Aging and Infectious Diseases section of Clinical Infectious Diseases (CID) during the next few months, to indicate how a career that blends study of infection and aging is a viable pathway for academic physicians over the coming decades, and finally, but perhaps most importantly, to recognize the accomplishments of those persons who have blazed this trail and raised our understanding of both aging and infection.
How will Demographics Change the Infectious Diseases Practice in the Coming Decades?
Many leading clinicians and academics have continued to question whether there is truly a need for geriatrics and gerontology within the field of internal medicine and its constituent subspecialities. Indeed, when I was making calls in the late 1990s to invite prominent infectious diseases faculty to participate in a conference to integrate the study of geriatrics and gerontology into the study of infectious diseases, I was frequently greeted with the retort, “Aren't we all geriatricians? All I do is take care of older people.” The overwhelming evidence of the “demographic imperative” clearly supports this contention and suggests that it will be even truer in the future. Four of the top 20 diagnosis-relate groups paid by Medicare in fiscal year 2001 were for infectious diseases (Centers for Medicare and Medical Services/Office of Information Services). In the United States, by the year 2030, the population of persons aged ⩾65 years will double, and the population of persons aged >85 years will triple; this cohort constitutes the fastest growing segment of the US population [1]. The same trends are occurring worldwide (figure 1). During the period from 1998 to 2025, the world's population of persons aged ⩾65 years will more than double. Despite the continuing high birth rates in many developing countries, the population of persons aged <15 years will increase by only 6% during this same period [1]. The age wave seen in developed countries will occur much more rapidly in developing countries. For example, it took 85 years (from 1890 to 1975) for the population of persons aged ⩾65 years to double, from 7% to 14%, in Sweden. This same doubling (from 7% to 14%) will occur during the next 20–30 years in China (from 2000 to 2027), Thailand (from 2003 to 2025), and Brazil (2011 to 2032) [1].
Figure 1
Percentage of the population aged ⩾65 years in the year 2000 in the indicated countries. Adapted from High [2], with permission.
Although the sheer numbers paint a daunting picture, when one considers disabilities and the burden on health care, as well as the size of the “productive” labor force supporting this vulnerable population, the numbers become staggering. The US Census Bureau estimates the number of “dependents,” which is defined as persons who are supported by the adult (age, 18–64 years) labor force [3]. Currently, that number is 70 dependents per 100 adults aged 18–64 years. The proportion of dependents aged <18 years is ∼65%, with persons aged ⩾65 years constituting only ∼25% of dependents, a ratio of ∼2.5 : 1 (disabled adults aged 18–64 years constitute the remainder). By 2030, the number of dependent persons per 100 adults aged 18–64 years will increase to 80 (an increase of ∼14%), and the ratio of dependents aged <18 years to those aged ⩾65 years will nearly equalize, to 1.1 : 1 (figure 2).
Figure 2
Number of dependents per 100 adults aged 18–64 years in the United States. Adapted from Guyer et al. [3], with permission.
So why would these trends matter to the specialty of infectious diseases? Certainly, drug-drug interactions and changes in pharmacology that occur with age have been well publicized and are part of training in both internal medicine and infectious diseases. Furthermore, we all trained with mentors who made us acutely aware of the changing microbiology in older adults and the need to alter our antimicrobial selections to match these changes. Indeed, for years, the American Board of Internal Medicine (ABIM) certifying examination has contained questions and explored issues related to the “cross-content” focus of geriatrics. These efforts are to be applauded for their foresight. However, the typical ABIM examination question starts with, for example, “An 85-year-old man is admitted with fever ...” From that point on, the case history could be the same regardless of whether the patient was 85 years old or 25 years old. The only factor typically communicated to our fellows in training and tested in such questions is the changes in microbiology that occur with age. However, there are many other factors that underscore the need to integrate geriatrics into our subspecialty. Elderly individuals are the largest group of immunocompromised patients we treat, and yet the immunology of aging is rarely emphasized or even discussed in infectious diseases training. Furthermore, the rates of acquisition of disease; the efficacy and acceptance of preventive measures; the sensitivity, specificity, and predictive value of diagnostic tests; the differential diagnosis of noninfectious diseases; and, perhaps most importantly, the desired functional outcome of treatments for infection all change with advancing age.
Aged Populations tn Infectious Diseases Research
Research into the epidemiology of infectious agents and the prevention and treatment of infections in older adults is starting to address some of these issues. Occasionally, prospective data are collected and emphasized by regulatory agencies. For example, the US Food and Drug Administration now mandates that pharmacokinetic and drug interaction studies for new antibiotics include a number of older adults sufficient to make it possible to draw conclusions about safety and efficacy in this population, a mandate that recognizes the changing physiology (particularly with regard to renal clearance and common drug interactions) associated with advanced age. However, this also highlights the fact that much of our knowledge base for the care and prevention of infection in aged populations comes from subgroup analyses of older adults in other studies. This strategy is inherently limiting, because important end points for older adults are rarely included in such a design.
This limitation is well illustrated by the study presented in this issue of CID by Ely et al. [4]. Their study is extremely well done, and the authors should be commended for their efforts to focus on vulnerable elderly individuals as a specific population of interest. The authors demonstrate the efficacy of activated protein C for the treatment of sepsis in older adults (defined in their study as age of ⩾75 years) using the hardest of end points, mortality. This is an extremely important issue to examine in older adults, because the major side effect of activated protein C that could lead to morbidity or mortality is bleeding—particularly intracranial bleeding, a factor more commonly seen in older than in younger adults in other studies of anticoagulant or thrombolytic therapies. Of importance, Ely et al. [4] determined prehospitalization functional status (assessed by Activities of Daily Living score) and adjusted for this variable in their analysis. However, as the authors suggest in the discussion, an important end point for this study would have been to examine the functional outcomes for these older adults, not just whether they lived or died. These data were not collected prospectively in the Protein C Worldwide Evaluation of Severe Sepsis (PROWESS) study. Although this is a valid question for both young and old adults, the probability of debilitating functional outcomes in older adults is likely much higher, given the frequent comorbidities and limited physiologic reserves of this group of patients.
Functional outcome becomes a paramount parameter in the older adult and may markedly influence our decision-making and recommendations as infectious diseases consultants. One technique for examining this issue was addressed in a modeling study of alternate strategies for the treatment of prosthetic hip infection, in which Fisman et al. [5] compared debridement and retention with 2-stage arthroplasty. Two-stage arthroplasty can tremendously increase the function and independence of an older adult who has been hobbled by an infected prosthesis. However, the long period of immobility necessitated by this procedure and the resultant delay in rehabilitation can be crippling for some older adults, often leading to longer stays in the hospital and/or long-term care facility, pressure ulcers, and spiraling disability. Therefore, few people would argue that, in very debilitated elderly persons, debridement and retention is a reasonable strategy. However, in their modeling, which used functional outcomes and duration of life expectancy, Fisman et al. [5] suggested that, given a relapse rate of ∼30%, this strategy may be most effective in older adults aged ⩾79 years, even among those who are quite functional at baseline. Many more studies that emphasize functional outcomes, that recognize the importance of expected life span at the ages of 75, 80, and 85 years, and that specifically address clinical evaluation and treatment paradigms in older adults are needed.
An Upcoming Series in CID
During the next few months, in the Aging and Infectious Diseases section of CID, prominent clinicians and researchers in the field of aging and infection will address the question, “what's different about infection in older adults?” An article by Mark Loeb and Shelly McNeill will focus on the multiple-determinant model of infection acquisition in older adults. Older adults differ from their younger counterparts in modes of acquisition, acceptance of preventive care, nutritional status, and physiologic, economic, and social differences that determine exposure risk and host susceptibility. This means that the “web of causation”—risk factors that may be necessary but not necessarily sufficient to cause disease—is vastly different for older adults and requires different research strategies for investigation and different clinical approaches for prevention [6]. An excellent example of this concept involves HIV infection. Measures for prevention of HIV infection have focused on abstinence and barrier contraception, primarily in young adults. However, in 1996, 11% of patients with AIDS were aged >50 years, and 1 of every 11 new diagnoses of HIV infection occurred in this age group [7]. With the marked decrease in the rate of death due to HIV infection, adults in this age group are sure to continue increasing during the coming decades. Older adults are the least likely of all sexually active groups in the United States to practice safe sex [8]. This group did not grow up dating in an era in which HIV infection was a concern, nor is preventing pregnancy usually an issue for these persons. Thus, sexual acquisition of HIV is a real risk that requires markedly different prevention efforts in older adult populations. This fact has even been recognized in the lay literature [9], but it is often not considered by physicians, leading to delays in the diagnosis of HIV infection.
Once an infection is acquired, prognostic scoring systems are often used to indicate the level of care and the breadth and mode of treatment required. This is particularly true in this era, when care pathways are a major focus of our health care systems. However, many prognostic scoring systems use age as an overriding factor in tallying a score. For example, the pneumonia severity index most widely used is that described by Fine et al. [10]. This scoring system correctly recognizes the contribution of age to the attributable mortality associated with pneumonia. However, age is an overwhelming factor in this scoring system; nearly any senior with a fever, regardless of his or her functional status, will reach severity level III, which is often used as a cutoff for hospital admission. Several authors have shown that, for the elderly population, alternate scoring systems may be more appropriate [11]; the utility of prognostic scoring systems for infectious syndromes in older adults will be reviewed by Vincent Quagliarello.
Other articles in the series will explore the impact of an aging population on infectious diseases in the developing world, explore the role of older adults as a reservoir for antibiotic resistance in the community, and provide a blueprint for conducting research on infection in older adults, highlighting topics of importance, variables of interest, and techniques to recruit older adults in studies on prevention and treatment. Evaluation and treatment paradigms also differ markedly for specific infectious syndromes in older adults. This final point has been the focus of the Aging and Infectious Diseases section of CID during the past 4 years, and we will continue to bring you these important reviews.
Is a Focus on Aging a Viable Career Path for Infectious Diseases Academics?
A recent issue of Science (28 February 2003; volume 299) devoted to aging includes several research articles and editorials recognizing the need for fundamental research on aging, as well as the return on investment this research can provide. If we are to advance our knowledge and understanding of infection in older adults, there must be infectious diseases clinician/scientists who emphasize aging throughout their careers to translate this knowledge to clinical practice. The difficulties associated with attracting clinicians to research careers have been widely explored in many journals in recent years. One such review focused on the translational blocks that prevent basic knowledge from becoming part of bedside care (figure 3) and emphasized the lack of qualified investigators [12]. For junior faculty making career decisions, all of these factors essentially boil down to a specific question: “Is clinical research in this field a viable career pathway for me?” For research in aging and infectious diseases, I believe, the answer to that question is a resounding “Yes!” The need to understand the immunology, preventive strategies, treatment paradigms, and functional outcomes of care for older adults is and will remain a focus of the National Institutes of Health (NIH) and funding foundations for the foreseeable future. The baby boomers who are creating the age wave described above are going to shape all public policy, including health care and health care research, in the coming decades. Already, the NIH and, specifically, the National Institute of Allergy and Infectious Diseases have recognized the importance of this area of investigation. Aging and older adults are routinely mentioned as priority areas in program announcements and requests for proposals. Even in recent bioterrorism-related initiatives, older adults are recognized as a vulnerable group requiring specific study, and, therefore, they are recognized as a priority for research funding.
Figure 3
Blocks in translating biomedical discoveries into clinical advances for improved health. Reprinted from Sung et al. [12], with permission.
The most vulnerable time and the point at which the focus of one's career is typically made, however, is that critical juncture between fellowship and faculty appointment. At that stage, one typically moves toward a specific research focus. The Infectious Diseases Society of America (IDSA) has taken a pioneering stance in recognizing the importance of research on aging and infection, and, in particular, addressing the vulnerability of faculty making the transition from fellow to faculty. The Association of Subspecialty Professors/IDSA Faculty Development Awards were initiated in 2002. These awards fund junior investigators within 3 years after their first faculty appointments. These 2-year, $150,000 grants were awarded to Dr. Keith Kaye at Duke University in 2002 and to Dr. Albert Shaw at Yale University in 2003. The overall goal of the program is to develop a cadre of young investigators who will be the researchers, educators, and mentors of infectious diseases fellows in the areas of aging and infection. A parallel program is ongoing in most other subspecialities of internal medicine, including allergy and immunology, cardiology, endocrinology, nephrology, oncology, pulmonary and critical care, and rheumatology [13].
Additional or subsequent support for faculty at the instructor/assistant professor level is available through several foundations that emphasize faculty development in research on aging. These include both federal (e.g., K awards) and private (e.g., awards from the John A. Hartford Foundation or the Brookdale Foundation) programs. One program focusing on research on aging that supports junior faculty should be of great interest to those in the field of infectious diseases because of its ties to one of the founders of infectious diseases as a specialty, Dr. Paul Beeson (see below). The Beeson awards (http://www.afar.org/beeson.html), which are sponsored by a consortium of funding agencies and administered by the American Federation for Aging Research and the Alliance for Aging Research, support junior faculty within 12 years after graduation from medical school for 3 years at $150,000 per year. The project must focus on research on aging, but the applicant need not be a geriatrician. Of importance, this is extremely flexible funding that does not have many of the limitations of K awards from the NIH. An exhaustive list of funding agencies that support research in aging and databases of value to clinician-researchers in the field of aging can be found at http://iucar.iu.edu/links/fundlinks.php3.
Aging and Infectious Diseases: a Rich History
Recognition of the importance of research on aging and the clinical care of the older adult has a rich history in the infectious diseases community. It is impossible to list all of the persons who have laid the foundation for the integration of aging and infectious diseases research, and if one tried to produce such a list, it would inevitably be incomplete. I would be remiss, however, if I did not mention 2 leaders in academic medicine who have spurred much of this interest and contributed mightily to this effort, Dr. Paul Beeson and Dr. Tom Yoshikawa.
One of the foremost mentors of our time, and former Chair of Medicine at the Emory University and Yale University schools of medicine, Dr. Paul Beeson is a renowned figure in infectious diseases. Perhaps best known as senior author of the classic 1961 treatise on fever of unknown origin written with Dr. Robert Petersdorf [14], many infectious diseases clinicians may not realize the hand that Beeson had in the rise of geriatrics as a subspecialty within internal medicine. Beeson chaired the first Institute of Medicine committee that eventually issued The Beeson Report in 1978, which recommended that geriatrics and gerontology be recognized within medicine as a means of enhancing the care of older adults, a sentinel event in the creation of geriatrics as a discipline. First and foremost, Dr. Beeson has always focused on the individual patient and the patient's specific circumstance. In no way did this ever diminish his enthusiasm for new scientific knowledge and the application of the scientific method. But his emphasis steadfastly remained on how those data applied to the patient sitting before him—a lesson for all clinicians. The study of aging and the care of elderly individuals, our most vulnerable patients and members of society, was a natural extension of this compassion.
Although I am sure he would rapidly dismiss any comparison in usual modest fashion, my predecessor as editor of this section, Dr. Tom Yoshikawa, has followed closely in Dr. Beeson's footsteps. Dr. Yoshikawa's career, like Dr. Beeson's did in a previous era, grew out of an infectious diseases background to focus on the care of older adults. He spent many years in the Veterans Administration, and he is currently Chair of Medicine at the Charles R. Drew University of Medicine and Science in Los Angeles. Dr. Yoshikawa came out of the infectious diseases community to gain such prominence in the world of geriatrics that he has assumed the editorship of the premier clinical journal in geriatric medicine, The Journal of the American Geriatrics Society, which Dr. Beeson formerly edited. However, Dr. Yoshikawa's roots have always remained in infectious diseases, and he has contributed heavily to our specialty, most recently having served a distinguished term as chair of the IDSA's Practice Guidelines Committee. He has edited multiple textbooks and written hundreds of articles on infection in older adults, and he has inspired and mentored many of us in the field. Furthermore, it was Dr. Yoshikawa's vision that brought the section on Aging and Infectious Diseases to CID. On behalf of the entire infectious diseases community, I would like to express our thanks.
- Received April 29, 2003.
- Accepted April 30, 2003.
- © 2003 by the Infectious Diseases Society of America
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