CHAPTER 38 INFECTIONS
Practice of Geriatrics
CHAPTER 38 INFECTIONS
Mira Cantrell, M.D., and Dean C. Norman, M.D.
Pathogenesis of Infection in the Elderly
Factors Peculiar to Infections in the Elderly
General Approach to the Management of Infection in the Elderly
Infections have a major impact on the elderly, particularly those who are more disabled and institutionalized. Many infections occur more frequently in the elderly, and most of these have greater morbidity and mortality rates in the old than in the young (Table 38-1 and Table 38-2).1,2 and 3 Since many of these illnesses are preventable or curable, it is imperative that geriatricians have a good understanding of the diagnosis, treatment, and prevention of infection in aging adults.
TABLE 38-1 MORTALITY RATE OF INFECTIONS IN ELDERLY COMPARED TO YOUNG
TABLE 38-2 EXCESS MORBIDITY OF INFECTIONS IN ELDERLY
PATHOGENESIS OF INFECTION IN THE ELDERLY
The risk and severity of infection are directly related to the virulence and inoculum of the pathogen and inversely related to the integrity of the host defenses.
Approximately 40% of acute care hospital beds are occupied by patients in the geriatric age category, and 5% of elderly patients reside in long-term care institutions. Thus, the risk of exposure to nosocomial pathogens such as gram-negative bacilli is increased in this population. In the acute care setting it has been established that the risk per day of hospitalization among older acute care patients for developing a nosocomial infection is 1.5 times that of the young.4 Similarly, the risks of developing a nosocomial urinary tract infection (threefold increase), bacteremia (fivefold increase), pneumonia (threefold increase), or wound infection (twofold increase) increase with age.5 The risk of colonization and infection with gram-negative bacilli is also high in the nursing home population.6,7 Moreover, the widespread and in some cases inappropriate use of antimicrobial agents, along with often inadequate infection control procedures has had a dramatic impact on the microbial flora. For example, studies demonstrate that patients treated with antibiotics in a nursing home may become colonized by Clostridium difficile (the pathogen most often associated with antibiotic-associated colitis).8,9 Methicillin-resistant Staphylococcus aureus (MRSA) infections also occur in long-term care facilities, and vancomycin-resistant Enterococcus (VRE) poses a new threat.
Older adults are more likely to be exposed to higher inocula (quantity) of pathogens for a variety of reasons. For example, in the case of bacterial pneumonia the elderly are more likely to aspirate oropharyngeal flora secondary to central nervous system disorders, oversedation, or placement of feeding nasogastric tubes; pressure sores remove skin, which is an important physical barrier against bacterial colonization; and the use of chronic indwelling bladder catheters allows colonization of the lower urinary tract with potential pathogens.
As alluded to earlier, the skin and mucosal epithelial lining are important physical barriers to infection. The epidermis thins with age, and this thinning is exacerbated by chronic diseases and malnutrition. Other important changes in the skin include decreases in Langerhans cells, interleukin-1 production, and production and response to epidermal thymocyte-activating factor. These changes, coupled with poor perfusion, further increase the risk of damage to the skin and the subsequent development of soft tissue infection such as cellulitis and infected decubitus ulcers. Mucosal surfaces are also adversely affected by age, disease, and lifestyle (e.g., cigarette smoking with loss of the ciliary action of the epithelial cells of the upper respiratory tract and possibly reduction of secretory immunoglobulins).
Primary immunity (also called natural immunity) consists of phagocytosis, complement, and natural killer cells. Age in itself may have little effect on this form of immunity, which does not depend on prior exposure to pathogens (antigens) to be effective (hence the term primary). However, acute and chronic diseases, especially malnutrition, may compromise these defense mechanisms.
Secondary immunity (also called acquired immunity) refers to immune function that is activated only after prior exposure to a pathogen (antigen). This arm of the immune system requires a complex interaction between thymus-derived cells (T lymphocytes or T cells), bursa-derived cells (B lymphocytes or B cells), and antigen-presenting macrophages. T cells are most adversely affected by aging, during which there is a qualitative loss of function that parallels the involution of the thymus and the reduction of thymic hormones, which occurs by middle age. Two subsets of T cells, the CD45RO+ and the CD45RA, change most dramatically with age. The first is a predominantly naive subset, while the second consists predominantly of memory cells. With advancing age, the percentage of memory cells increases in relation to naive cells as the naive cells undergo a transition to memory cells. This altered ratio contributes to age-related changes in T-cell function including a decreased proliferative response to mitogens, production of and response to interleukin-2 and anti-CD-3 monoclonal antibody. T cells are necessary to enhance B-cell function. Although B cells are the cells responsible for antibody production, the diminished antibody response to vaccines that is observed with aging is due to defects in helper T-cell function and possibly B-cell function. Secondary immunity is also compromised by chronic diseases, malnutrition, and immunosuppressive agents.10
Other factors leading to increased morbidity and mortality for infectious diseases in the elderly include low physiologic reserve, presence of chronic underlying diseases, delays in diagnosis due to atypical clinical presentations leading to therapeutic delays, higher rates of adverse antibiotic and other drug interactions, and complications resulting from invasive diagnostic procedures.
FACTORS PECULIAR TO INFECTIONS IN THE ELDERLY
Pathogens infecting older persons are different and more diverse than those infecting younger adults. Community-acquired pneumonia in young persons is most often due to Mycoplasma pneumoniae and Streptococcus pneumoniae. However, in aging adults, Mycoplasma is uncommon, and although S. pneumoniae causes 40% to 60% of cases of pneumonia, a variety of bacterial organisms including Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Branhamella catarrhalis, and Haemophilus sp as well as mixed flora (including anaerobes) account for many cases of lower respiratory infection in this population. A variety of Legionella sp cause a variable number of cases of pneumonia in the elderly depending on geographic location and immune status; Chlamydia pneumoniae causes a still undefined number of pneumonias in the elderly.
Urinary tract infections (UTIs) in the general population occur almost exclusively in sexually active women and are caused by Escherichia coli in over 85% of cases. In contrast, UTIs occur frequently in both elderly women and men, and the cause is frequently uropathogens other than E. coli (e.g., Klebsiella sp, Proteus sp, and Enterococcus sp). Moreover, polymicrobial bacteriuria is common in patients with indwelling bladder catheters.
The elderly are more likely to be in institutions and account for an increasing percentage of acute care hospital inpatients. They are therefore more likely to be exposed to nosocomial pathogens such as aerobic gram-negative bacilli and S. aureus as well as to multidrug-resistant pathogens including MRSA and VRE.
Viral illnesses also have a major impact on the elderly. Although rhinovirus infection (the “common cold”) decreases with age, respiratory viruses such as influenza virus cause very high morbidity and mortality in older adults, and there is a risk of hospitalization of about 1 per 300 and a risk of death of 1 per 1500 during influenza outbreaks.11 Respiratory syncytial virus12,13 as well as influenza virus may cause outbreaks of respiratory illness in nursing homes. Varicella-zoster virus is another important pathogen that is manifest in the elderly in the form of herpes zoster. This infection carries with it the dreaded potential complication of postherpetic neuralgia, which also occurs almost exclusively in the geriatric age group (see later)
The diagnosis and therapy of infections in the elderly present unique problems that are reviewed here briefly. Aside from prevention, early diagnosis with rapid institution of antimicrobial therapy is the mainstay of treatment for reducing the appallingly high morbidity and mortality of infection in the aged. Unfortunately, infection may present in an atypical manner in a significant number of cases (e.g., blunted or absent fever response in 20% to 30% of patients). This is particularly true in the old-old (i.e., persons 75 years old or older) and in long-term care institutions, in which residents are typically frail, suffer from multiple diseases, and are cognitively impaired.
There are basically four factors that contribute to the atypical presentation of infection in the elderly compared to the young. These include underreporting of illness, which may cause delay in bringing an elderly patient to medical attention, and different pathogens (which was discussed earlier). Underreporting of illness is an important problem in the cognitively impaired elderly patient, who may not complain or may be unable to communicate information about symptoms. Furthermore, even noncentral nervous system infections may result in compromising cognition in elderly patients. The presence of coexisting diseases such as chronic bronchitis, which may mask acute pneumonia, or rheumatoid arthritis, which can confound the presence of septic arthritis, may compound difficulties in making the diagnosis of infection. Finally, altere physiologic responses to infection, or for the manner to any acute illness, are due to man factors including the decremental biologic changes of normal aging, which may be exacerbated by lifestyle. For example, age-related changes in chest wall expansion and lung tissue elasticity, which may be made worse by smoking, contribute to a diminished cough reflex. A weakened cough has the double negative effect of contributing to a decline in pulmonary host defenses and making the diagnosis of respiratory infection more difficult.
Another example of an altered physiologic response to infection in older persons that deserves special mention is the often-observed blunted fever response.14,15 Although fever is the cardinal sign of infection, the traditional definition of fever (oral temperature of 100.4° to 101°F or 38° to 38.3°C) may not be sensitive enough to diagnose infection in elderly patients. We have found in a nursing home population that baseline body temperatures are approximately 1°F below those of a normal young person and that with infection, despite a rise in temperature comparable to that seen in the young, the maximum temperature may be below the traditional definition of fever. However, we also found that a temperature of 100°F (37.8°C) coupled with a decline in functional status is highly indicative of infection in this population.16,17
The presence or absence of fever—aside from facilitating or inhibiting the diagnosis of infection—has other implications. The presence of fever (as defined by an oral temperature of 101°F) is highly specific for the presence of a serious, usually bacterial, infection.18,19 Moreover, when the syndrome of fever of unknown origin (FUO) occurs in elderly persons, it typically signifies a treatable condition such as intra-abdominal infection, infective endocarditis, temporal arteritis, or other rheumatologic condition.20,21 A blunted fever response to infection frequently portends a poor prognosis.22 This may be relevant to the mounting evidence that fever may play an important role in host defenses.15,23
In summary, an acute infection in the elderly may present with either typical clinical manifestations or subtle findings. Signs and symptoms pointing to a specific organ system infection may be lacking. Thus, an infection should be sought in any elderly person with an unexplained acute to subacute (days to weeks) decline in functional status.
It is more difficult and hazardous to perform invasive diagnostic tests in the elderly, particularly if they are frail and unable to cooperate. Furthermore, waning cellular immunity with age makes skin testing less reliable (e.g., for tuberculosis), whereas increased nonspecific immunoglobulin production may give false-positive serologic test results (e.g., positive rheumatoid factor). Also, radiologic procedures may be difficult to interpret in older adults because of biologic changes with age and age-related disorders (e.g., changes secondary to chronic congestive heart failure or obstructive pulmonary disease may confound the diagnosis of pneumonia). Finally, colonization of normally sterile sites by bacteria such as the age-related gastric colonization by Helicobacter pylori may make it difficult to assess the role of this pathogen in gastrointestinal disease in the elderly.24 Similarly, colonization of the bladder in elderly persons who are often completely asymptomatic may make it difficult to assess the clinical significance of a positive urine culture.
Still, basic laboratory studies such as a white blood cell (WBC) count with a differential remain the cornerstone of laboratory diagnosis. A high WBC count with a left shift, regardless of a patient’s hydration status, is highly suggestive of a developing infectious process.
A detailed description of the pharmacology of antibiotics is beyond the scope of this chapter, and the reader is referred to a more comprehensive review.25 Briefly, oral absorption, tissue penetration, hepatic metabolism, and volume of distribution are either minimally or variably affected by age. In the pharmacology of antibiotics age affects mainly renal clearance. This is not a trivial effect because the majority of antibiotics are cleared predominantly by this mechanism. Therefore, drugs that are cleared predominantly by the kidneys, such as the aminoglycosides and vancomycin, require serial monitoring of the patient’s clinical status, renal function, and serum drug levels because they are associated with low therapeutic indices and potential serious adverse side effects (i.e., nephrotoxicity and ototoxicity). It has been demonstrated that reliance on simple serum creatinine measurements or formulas predicting creatinine clearance based on serum creatinine levels are inadequate in seriously ill elderly patients with an infection.25,26
Table 38-3 lists some of the antibiotics more frequently used for treating infection in the elderly as well as their spectrum of action and potential indications. The list is not exhaustive and summarizes only some of the antibiotics believed by the authors to be particularly relevant for use in the elderly.
TABLE 38-3 SOME IMPORTANT ANTIBIOTICS FOR INFECTION IN THE ELDERLY
GENERAL APPROACH TO THE MANAGEMENT OF INFECTION IN THE ELDERLY
The diagnostic approach should take into consideration the setting in which the infection occurs. Community-acquired infections are more likely to be found in the respiratory tract, urinary tract, or abdomen. More than 80% of infections in nursing homes are pneumonias, urinary tract infections, and soft tissue infections (acronym, PUS). Hospital-acquired infections commonly comprise aspiration pneumonia involving nosocomial flora, catheter-associated urinary tract infections, and intravenous catheter-associated septic thrombophlebitis.
Empirical therapy with broad-spectrum antibiotics is often indicated pending culture results in seriously ill frail elderly patients with an infection. In general, this therapy should include a broad-spectrum beta-lactam antibiotic. The more toxic aminoglycosides should be avoided in the elderly unless the risk of death from sepsis outweighs the risk of ototoxicity and nephrotoxicity. Therapy should be altered to more narrow-spectrum agents based on the culture data.27,28 Because of cost considerations, patients should be switched to oral antibiotics as soon as possible.
Home intravenous antimicrobial therapy may be given to selected elderly patients who have stable infections if they and their caregivers are motivated to participate in this form of therapy.29
Despite some questions about cost-effectiveness and reimbursement for this kind of treatment, a significant number of infected elderly patients may benefit from this therapeutic option. Broad-spectrum cephalosporins with long half-lives and limited toxicity such as ceftriaxone are the antibiotics most frequently used in home intravenous therapy.
Pneumonia or influenza is the leading infectious cause of mortality in the elderly and the fourth leading cause of mortality in those over age 75. Moreover, compared with younger adults, the elderly have a five- to tenfold increased risk of developing pneumonia. One study showed that the risk was highest in those with coexisting alcoholism, followed in order by chronic obstructive pulmonary disease, immunosuppressive therapy, cardiovascular disease, and institutionalization.30
The majority of pneumonias are secondary to micro- or macroaspiration of oral pharyngeal flora in patients with compromised host defenses (e.g., diminished cough reflex, waning cellular immunity). The causes of pneumonia differ significantly from those in the young depending on the clinical setting (see earlier section on etiology). Data on the etiology of pneumonia in long-term care facilities are limited, and the available information is based primarily on sputum culture results, which are not definitive in establishing the actual etiologic pathogen.31 Nevertheless, it is estimated that, compared to community-acquired pneumonia, of which 40% to 60% of cases are caused by S. pneumoniae, pneumonia occurring in the nursing home frequently results from mixed causes. Moreover, in nursing homes there is an increased likelihood of isolating aerobic gram-negative bacilli such as Klebsiella sp and E. coli from the sputum. Fortunately, multiple drug-resistant pathogens such as Pseudomonas aeruginosa are infrequently found as respiratory pathogens unless the patient has recently been in an acute care facility or has been taking broad-spectrum antibiotics. Hospital-acquired pneumonia in the elderly is more likely to be caused by mixed flora, usually oral aerobic and anaerobic flora. In people over the age of 65, the risk of oropharyngeal colonization by staphylococci and aerobic gram-negative bacilli increases with decreasing functional status and increasing level of care.32 Therefore, it is not surprising that a significant proportion of cases involve these pathogens, again usually in mixed infections.
The diagnosis of pneumonia in debilitated elderly patients may be difficult.28 Cough and fever may be diminished or absent. Tachypnea and tachycardia are sensitive but not specific findings. Older patients may present simply with altered mental status or a decline in functional status. Physical examination usually does not reveal signs of consolidation and may be confusing in aging patients with coexisting congestive heart failure or chronic obstructive pulmonary disease. The chest radiograph along with the history and physical examination are important in establishing a diagnosis of pneumonia in the elderly patient. The chest radiograph typically shows a patchy pattern of bronchopneumonia but may be initially negative or difficult to interpret in patients with coexisting pulmonary disease. Following hospitalization, the pulmonary infiltrates may become worse in approximately half the patients. Moreover, resolution of the infiltrates typically takes longer in elderly patients than in younger ones.
Higher mortality rates for pneumonia in the elderly should not discourage aggressive therapy given that in one large study of community-acquired pneumonia (excluding nursing home cases) 2-year mortality rates for pneumonia patients discharged from the hospital were similar in both old and young.33 Management of pneumonia in the elderly requires hospitalization in most cases because of the higher mortality and more frequent complications, difficulties in establishing both the diagnosis and the precise cause, severity of the illness (which may be masked by the clinical presentation), and the need to monitor therapy. Pneumonia in nursing home patients with mild to moderate illness may be managed in the nursing home only if sufficient resources are available (e.g., staff, laboratory support, administration of intravenous fluids and antibiotics).
In all cases, an effort should be made to obtain sputum for a Gram’s stain smear and bacterial culture, and for a smear and culture for mycobacteria if tuberculosis is suspected. Older patients may be unable to provide an optimal sputum specimen (less than 10 epithelial cells and more than 25 polymorphonuclear cells per low-power field), but more invasive procedures such as transtracheal aspiration, shielded bronchoscopy, and transbronchial biopsy should be reserved for patients who are at high risk of unusual or opportunistic infections (e.g., those with immunosuppressed status) or who fail to respond to initial antimicrobial therapy and show clinically deteriorating signs. Other routine laboratory tests, including blood cultures (positive in about 5% to 10% of cases), serum electrolytes, complete blood count, and renal function tests, should also be performed. Monitoring of arterial blood gases is important for assessing adequate gas exchange and acid-base balance. At a minimum, measurement of oxygen saturation with a pulse oximeter should be performed, and an electrocardiogram should be obtained initially to evaluate any potential cardiac complications of pneumonia. Additionally, skin testing for tuberculosis and, in certain geographic areas, assessment for fungal infection (e.g., coccidioidomycosis) should be performed in elderly patients with pneumonia. Finally, diagnostic thoracocentesis for pleural fluid smear, culture, pH, leukocytes, glucose, protein, and cytologic examination as well as pleural biopsy should be considered in patients who have no coagulopathy and who can cooperate with the procedure. This is especially appropriate for patients who have large pleural effusions or in whom the effusion does not improve with therapy.
Antimicrobial therapy for pneumonia in the elderly should be based on the results of the tests just mentioned. In view of the severity of the illness, early empirical therapy with broad-spectrum antibiotics is advised for most older patients with pneumonia; adjustments are made when the culture data become available.28 It is the authors’ recommendation that for clinically stable elderly patients with community-acquired pneumonia, treatment should be started according to the Gram’s stain results. If the sputum specimen is of “poor” quality, empirical therapy with any one of the following antibiotics should be considered: parenteral second- or third-generation cephalosporin, ampicillin-sulbactam, or ticarcillin-clavulanate. In mildly ill patients, oral ciprofloxacin, with or without ampicillin to ensure adequate coverage of S. pneumoniae, may be considered. Clinically unstable patients—those with nosocomial-acquired pneumonia, who have recently begun taking antibiotics or who are immunosup pressed—should receive empirical therapy consisting of a parenteral third-generation cephalosporin plus either aztreonam, quinolone, or an aminoglycoside. Aminoglycosides should be avoided if possible. Erythromycin should be part of the therapeutic regimen if Legionnaire’s disease is suspected.
The prevention of pneumonia is best accomplished by reducing the risk of aspiration whenever possible (e.g., avoiding sedating medications, alcohol, and nasogastric tubes [Table 38-4]). Vaccination with the current pneumococcal vaccine is now strongly recommended despite some past questions about its efficacy. Influenza vaccination is very important in preventing influenza pneumonia as well as secondary bacterial pneumonia (see next paragraph).
TABLE 38-4 PREVENTION OF PNEUMONIA
Although other respiratory viruses such as respiratory syncytial virus are capable of infecting older persons, influenza has had the greatest impact by far, and much of the excess morbidity and mortality ascribed to influenza outbreaks has occurred in people at the extreme ends of the age scale.11 It should be kept in mind that in addition to damaging respiratory epithelial cells, decreasing the effectiveness of cell-mediated immunity, and causing upper and lower viral respiratory infection and secondary bacterial bronchitis and pneumonia, influenza may exacerbate and worsen chronic underlying medical conditions. This activity accounts in part for the high hospitalization rates of the elderly observed during influenza outbreaks in the community.
The virus undergoes antigenic changes (usually “drift,” although an actual “shift” occurs about every 10 years), and manufacturers of vaccines must take these changes into account annually. Thus, vaccinations must be given yearly. The precise efficacy of the influenza vaccine has not been established in the elderly, but it appears to be at least 60% effective in reducing the incidence of influenza infection. In addition to patients with special health problems and health care professionals who interact regularly with patients at high risk for influenza, the vaccine is recommended for all persons aged 65 and older. Amantadine and presumably rimantadine are effective for the early treatment of influenza (within 48 hours of exposure) and for prophylaxis against influenza A (not influenza B). The efficacy of amantadine is better established in the literature than that of rimantadine. Both are usually given in a reduced dosage of 100 mg orally per day in elderly persons. However, in the case of amantadine, which is cleared by the kidneys, even this dose may be too high for some debilitated elderly persons, and the dose must be adjusted downward based on creatinine clearance.7,34
Mycobacterium tuberculosis infection occurs disproportionately in the older population and is associated with higher mortality rates in this population. Among all cases of tuberculosis in the United States, 26% occur in people over the age of 65, in whom the morbidity rate is 60%. Although the majority (80%) of all cases are diagnosed in community dwellers, the incidence rate is three to four times higher in those residing in nursing homes. The association between the tuberculous pathogen and the aged may exist in part because the majority of elderly people have been exposed to tuberculosis at an earlier age (when tuberculosis infection was quite common in the general population) but were able to eliminate or control the infection at that time. However, the waning of cell-mediated immunity with age as well as the presence of coexisting chronic illnesses, which may further compromise host defenses, may allow for “reactivation” of this infection in the geriatric age group. Although reactivation of preexisting infection is the usual pathogenesis of tuberculosis in the elderly, it should be emphasized that outbreaks of primary infection with active pulmonary tuberculosis have been well described in long-term care institutions.7,35
The diagnosis of tuberculosis should be considered in any elderly individual who has a cough, chronic fatigue, night sweats, unexplained fever, weight loss, or gradual or subacute decline in functional status. Unfortunately, a proper diagnosis may be difficult to ascertain because of subtle or unusual clinical features and atypical chest x-ray findings are common. Moreover, skin testing for tuberculosis is often unreliable in the elderly because reactivity to the tuberculin antigen (purified protein derivative [PPD]) wanes with age. Nevertheless, elderly patients with unexplained pulmonary infiltrates should undergo skin testing with PPD as well as with control antigens to exclude cutaneous anergy, and multiple sputum specimens for acid-fast bacteria smears and mycobacterial culture should be collected. In patients with significant pleural effusion, a pleural biopsy and culture should be attempted, and in patients with suspected miliary tuberculosis, a transbronchial biopsy and culture may be indicated.
Uncomplicated (drug-susceptible) pulmonary tuberculosis can be treated with 6 months of isoniazid 300 mg/day and rifampin 600 mg/day plus pyrazinamide 30 mg/kg/day for the first 2 months (intensive phase) of treatment, or, alternatively, 9 months of daily isoniazid (300 mg) and rifampin (600 mg) can be given. If the sputum smear and culture remain negative and drug resistance is unlikely, therapy can be shortened from 9 to 4 months. Elderly patients should also receive 25 mg/day of pyridoxine to reduce the risk of peripheral neuropathy associated with isoniazid.35
Due to a substantial increase in the incidence of multidrug-resistant tuberculosis (MDR-TB), the Centers for Disease Control recently published new recommendations for treatment of tuberculosis. In persons with a high likelihood of acquiring multidrug-resistant tuberculosis, the recommendations for treatment include three treatment options with four drug regimens consisting of isoniazid, rifampin, pyrazinamide, and ethambutol or streptomycin. However, most elderly patients do not require this type of treatment because of the low risk of drug resistance in this population group.
Pressure sores develop from the interaction of external factors with the patient’s own internal factors. Major external factors are pressure, shearing forces, friction, and moisture. Major internal factors include the patient’s overall skin condition, mobility, nutritional state, and underlying medical or surgical condition. Most patients with pressure sores are in the geriatric age group, and those over the age of 70 account for two thirds of all patients with bed sores. Although the prevalence of pressure sores is highest in patients residing in long-term care facilities, the incidence is highest in patients in acute care hospitals. More than 60% of patients with pressure sores develop them in hospitals, 18% in nursing homes, and another 18% at home. It is significant that the majority of pressure sores develop during the first 2 weeks of hospitalization.
Since pressure sores are wounds that are chronically contaminated, lowering the bacterial count may facilitate healing. Healing wounds typically show no anaerobic bacteria, whereas nonhealing wounds show the highest counts of both aerobic and anaerobic organisms.36
A local bactericidal effect can be achieved by using conservative measures consisting of cleansing, disinfection, and debridement. The use of topical antibiotics for this purpose remains controversial. Although they may lower bacterial counts, they penetrate poorly through devitalized tissue. Topical antibiotics can cause localized tissue sensitivity and promote the relatively rapid emergence of resistant organisms (especially the Pseudomonas species).
When cellulitis, osteomyelitis, or sepsis is present, treatment with systemic antibiotics directed against a mixed population of aerobic and anaerobic bacteria is mandatory. The most commonly found bacteria are S. aureus, gram-negative rods, and Bacteroides fragilis. A combination of clindamycin or metronidazole (for anaerobic coverage) with a quinolone, an aminoglycoside, a third-generation cephalosporin, or aztreonam (for coverage of gram-negative bacilli) provides an effective treatment. Ticarcillin-clavulanic acid and ampicillin-sulbactam also provide good coverage for the variety of organisms found in pressure sores. A decision about the use of antibiotics for infections associated with pressure sores frequently must be made empirically pending the results of meaningful cultures (blood cultures, tissue biopsy). Swab cultures of the necrotic debris are of little value. If the exact wound microbiology is sought, a biopsy of the viable tissue interface should be performed.
Sepsis associated with pressure sores carries a mortality rate of approximately 50%. It is even higher in patients over the age of 60 and in those who have multiple ulcer sites. Wound debridement may be associated with transient bacteremia but appears to have no serious consequences. Osteomyelitis occurs in 26% of patients with nonhealing pressure sores; the diagnosis should be confirmed by radionuclide scintigraphy of the bone and bone biopsy.37 Septic arthritis may also be seen and is frequently associated with a sinus tract leading from an ulcerous lesion.
The possibility of tetanus infection should be considered in patients with deep necrotic lesions that are becoming progressively larger and are resistant to local and systemic treatment. Because many elderly patients have not received adequate tetanus immunization, administration of tetanus toxoid should be considered.
URINARY TRACT INFECTIONS
Urinary tract infections (UTIs) are the most common type of infection and the most frequent cause of gram-negative bacillary sepsis in the elderly.
The frequency of bacteriuria in ambulatory patients over the age of 65 is 10% to 30% in women and 5% to 10% in men. These figures increase to 15% to 20% in elderly men and 25% to 50% in elderly women residing in long-term care facilities. Bacteriuria in the elderly is typically caused by a variety of gram-negative organisms. E. coli is responsible for the majority of episodes, but organisms such as Proteus, Klebsiella, Pseudomonas species, and, less frequently, Citrobacter and Providentia species are increasing in importance. Bacteriuria, especially when it is associated with chronic indwelling catheter use, is polymicrobial and often includes group D streptococcus (Enterococcus sp).38
Asymptomatic bacteriuria in the elderly is a well-described phenomenon. It is defined by a finding of 105 or more colony-forming units (CFU)/mL bacteria in urine, is not associated with clinical signs and symptoms of infection, and is frequently transient or intermittent. Often pyuria is lacking as well. The available data on the long-term sequelae of asymptomatic bacteriuria are conflicting. However, there is general agreement among clinicians that in the absence of chronic urinary obstruction, asymptomatic bacteriuria in aging adults should not be treated with antibiotics.39,40
An uncomplicated, symptomatic community-acquired UTI can present with fever, dysuria, frequency, and urgency, or, less typically, as weakness and fatigue, anorexia, or change in mental status. Once the diagnosis has been made, the choice of antimicrobial agent will depend on the urine bacteriology, clinical status of the patient, and pharmacokinetic properties of the agent chosen as well as patient tolerance of the drug. The antimicrobials most commonly used today are as follows: trimethoprim-sulfa-methoxazole (TMP/SMZ); first-generation cephalosporins such as cephradine, cefazolin, cefadroxil, and cephalexin; quinolones; and clavulanic acid combinations with amoxicillin or ticarcillin. Ampicillin and amoxicillin provide good coverage for enterococcal infections. Treatment is usually given for 7 to 14 days with the goal of alleviating the symptoms and sterilizing the urine. Single-dose treatment of uncomplicated urinary tract infections in the elderly is not recommended because it carries an unacceptably high relapse rate.
Complicated UTIs are associated with structural or functional abnormalities of the urinary tract. These infections are frequently caused by organisms that are resistant to different antibiotics. Hence, culture and sensitivity data are essential for the appropriate management of a complicated UTI. Empirical therapy requiring parenteral antibiotics for these infections should include third-generation cephalosporins, aztreonam, quinolones, or aminoglycosides. Complicated UTIs may be recurrent because of either relapse or reinfection and may require prolonged treatment of 4 to 6 weeks, usually with an oral agent such as quinolone, TMP-SMZ, or a cephalosporin.41,42 and 43
Patients with chronic indwelling urinary catheters invariably have infected urine and often present with polymicrobial bacteriuria. The rate of acquisition of bacteria after the catheter has been inserted is 7% to 8% per day. After a period of 3 to 4 weeks, virtually 100% of patients become bacteriuric. Characteristically, the microbial flora changes during the period of catheterization, averaging 2.0 species changes per month. However, antimicrobial treatment is reserved only for patients who develop clinical signs of infection. About 20% of these patients develop symptomatic urinary tract infection within 1 year. Routine surveillance of urine cultures in patients with indwelling urinary catheters is not necessary or cost-effective. Urine cultures should be obtained in all patients with indwelling catheters who show clinical signs of infection or changes in mentation or functional status. When a urine sample is to be obtained from a patient with an indwelling catheter, it should be done by using a needle and syringe, aspirating the specimen through the aspiration port after the port has been thoroughly cleaned with an iodophor agent. Treatment of catheter-associated infections in patients who are clinically stable can be accomplished by using oral quinolones, TMP/SMZ, or amoxicillin-clavulanic acid. In unstable patients who have a septic presentation, a combination of parenteral ampicillin with either aztreonam, a third-generation cephalosporin, quinolone, or an aminoglycoside, or imipenem plus cilastatin provides good coverage for most polymicrobial flora.44,45
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