Infectious Diseases

Donald A. Jurivich, D.O. & James R. Webster Jr., M.S., M.D.

Infections are a major cause of morbidity and mortality in the elderly due primarily to changes of chronic illness and decreased nutrition, not to age. There is some "normal" decrease in T-lymphocyte function, however, B-cells, macrophages, and neutrophils generally function as well in healthy elderly as in healthy young individuals. Local (urinary, respiratory, gastrointestinal tract, and skin) resistance is also normal in healthy, well-nourished elderly patients, but may be impaired, e.g., reduced function of the pulmonary mucociliary elevator in ill, smoking patients.

Clinical presentations

Diagnostic problems with infections in the aged occur for several reasons, and delay in diagnosis is a major issue. These include:

• Underreporting of symptoms, because the elderly may attribute problems to aging.
  
• Multiple co-existing, chronic diseases, e.g., DM, COPD, BPH, CHF, which confuse the presentation.
  
• Atypical presentations, with non-specific complaints such as delirium and falls as first manifestations or misleading history, physical, or laboratory exams, e.g., pneumonia without cough due to COPD, acute appendicitis or cholecystitis without abdominal pain, or lower lobe tuberculosis on chest x-ray.
  
• A blunted febrile response due to reduced thermohomeostasis, IL-1, TNF and hypothalamic functions, or failure to produce or conserve body heat. The failure to mount a febrile response is a poor prognostic sign.
  
• Uncommon pathogens which are common in the elderly. For example, Moraxella catarrhalis and Strep. agalactia pneumonias occur virtually only in the elderly.
  
• Diagnostic assessment should take into account the patient's usual basal temperature. For example, if basal temperatures are usually 96.5 - 97*F, then 99 - 100*F may represent a "febrile response." Assessment of dehydration should include an orthostatic BP/HR check. "Moribund" patients can have orthostasis evaluated by dangling the patient's legs over the bedside. Nuchal rigidity due to advanced arthritis and dystonia from the dementias often can be confused with that seen in meningitis. A previous history of sustained head flexion in the supine position will help clarify the etiology of nuchal rigidity. Conjunctival and soft palate petechiae should be sought as indicators of SBE, an often overlooked disease of the aged. Fundi should also be examined, and sluggish, sausage-shaped retinal veins ought to raise concern for hyperviscosity syndromes which may predispose to infections. A general rule of physical examination of the elderly is that the signs of infection may be blunted if not masked.

Immune system, laboratory, and other parameters

Immunosenescence (decreasing host defenses with aging) contributes to the increased prevalence of infections, cancer and autoimmune disorders in the elderly population.

Extrinsic (e.g., nutrition) and intrinsic (e.g., cell dysfunction) causes of immunosenescence should be considered.

Mechanical factors related to aging, lifestyle or diseases predispose to infections, e.g., paralysis of mucociliary elevator due to smoking, * cough due to * muscle mass.

Clinical implications of T-cell failure include diminished skin reactivity to common antigens (anergy) and suboptimal antibody responses to pathogens and vaccines. Demargination of PMNs with infection may be less pronounced in the elderly; however, WBC function does not change with age. Lymphopenia occurs in preterminal settings, due to malnutrition, ETOH, and from medications. It is not normal aging.

Immunoglobulins do not change with age. Calculation of a globulin fraction of 3.5 gm/dl or greater from the chemistry profile should raise concern of gammopathies. Monoclonal gammopathies occur in 2% of 70 year olds and 19% of 90 year olds. Ten percent may progress to multiple myeloma each year, not necessarily linked to age.

Old age does not preclude acquisition of new allergies, so age does not diminish the importance of a past history of PCN allergy or other potential anaphylactic sources.

Treatment

Empirical antibiotic therapy should be considered earlier and more often in older patients who appear to have an infectious process, started after all cultures have been obtained. Initiation with a broad spectrum, antimicrobial agent against the most likely pathogens should be chosen. Cephalosporins are a good choice because of their proven efficacy, broad spectrum, safety and favorable dosing regimes. If parenteral therapy is initiated, it should be continued until the patient has clinically improved cultures evaluated and then the patient should be changed to oral antibiotics as soon as possible (3-10 days). Aminoglycoside antibiotics should be reserved for select circumstances.

Withholding treatment for infections while providing comfort measures is a seldom considered option, but one that may be advocated when patients with advanced, progressive terminal diseases have directives that warrant this approach.

Respiratory infections

Respiratory infections are the 4th leading cause of death in the elderly, and 90% of pneumonia-related deaths occur in patients > 65 years old.

Treating community-acquired pneumonias in the elderly is confounded by the increased colonization of the oropharynx with gram negative (GN) organisms seen in chronically sick elderly. In healthy elderly, community-acquired pneumonias most often involve Pneumococcus or H. Influenza, although up to 15% of the cases involve other pathogens such as mycoplasma, staph, or Legionella. Risks for GN-pneumonia include being bedridden, having chronic pulmonary disease, diabetes, ETOH abuse and recent institutionalization. 45% of elderly exhibit microaspiration and this rises to 70% when the level of consciousness is decreased. Sputum samples yield only a 33% diagnostic rate, thus blood cultures are important even in the absence of fever since up to 10% of afebrile patients with pneumonia have positive blood cultures.

Urinary tract infections (UTI's)

UTI's are the most common bacterial infections, the most frequent source of bacteremia and most common causes of nursing home to hospital transfers in the geriatric population. Useful observations for UTI's in the elderly include:

• While E. coli is the most common organism in both men and women, it probably accounts overall for less than half of the episodes in institutionalized patients.
  
• Septic syndromes and irritative symptoms are common but not universally present. Pathogenic polyuria is a sensitive indicator (clean voided specimen) for men and women, but truly asymptomatic bacteria need not routinely be treated.
  
• Ultrasonography is indicated with fever > 72 hours, persistent bacteriuria or likely obstruction. CT is used only when technical problems limit ultrasonography.
  
• Therapy depends on gram stains (Cytospin®), cultures, known prior (or current) susceptibility patterns and host and drug factors such as history of allergy, presence of a Foley catheter, previous therapy, renal function status, costs and so forth.
  
• Long-term, even closed or suprapubic catheterization is inevitably associated with bacteriuria and complications (e.g., stones, bacteremia, and death) and should be avoided if possible by using such strategies as condom catheters and intermittent catheterization.

Meningitis

Streptococcus (55%), Neisseria (15%), and GN's (8%) are the commonly found pathogens in elderly with meningitis.

GI infections

Colon: C. difficile pseudomembranous colitis occurs frequently in the elderly after antibiotic therapy. Diverticulitis can lead to perforation, peritonitis or abscess. Periappendiceal abscesses may present with weight loss and/or abdominal mass, but little pain.

Liver: A disproportionate number of elderly have cholelithiasis, thus predisposing them to cholangitis with enteric bacteria.

Skin infections

Herpes Zoster primarily affects elderly. Although usually self-limited, complications to consider are: encephalitis, Gillian-Barre syndrome, atonic bladder, and post-herpetic neuralgia. Decubitus ulcers are refractory to most interventions (only 12% actually heal in the setting of limited mobility and malnutrition), so prevention is essential (see Pressure Sores).

Vaccinations

Influenza vaccine has been proven to significantly reduce both morbidity and mortality in the elderly and is covered under Medicare. Pneumococcal is recommended as a routine at age 55 and according to the CDC can be repeated at seven-year intervals.