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Landon Center on Aging

Landon Center on Aging  :  Geriatric Education & Training

Infectious Disease in Older Adults

Instructor: Mary McDonald, MD

 

Prevalence

Infectious disease accounts for 40% of deaths in older adults.  Additionally, infection often exacerbates underlying illness and leads to hospitalization.

Infectious Disease Pie Chart

Outline:

  1. Predisposing Factors
  2. Atypical Presentation of Infection in Older Adults
  3. Antibiotic Management in Older Adults
  4. Common Infections in Older Adults
  5. Summary

Learning Objectives:

After completing this web module, each medical student should be able to……..

    1. Recognize the infectious diseases that are most common in older adults
    2. List 3 contributing factors that can make older adults more susceptible to infectious disease
    3. Describe how infection may present differently in older adults than in younger individuals
    4. Recall the different causative pathogens for urinary tract infection in older adults compared to younger counterparts.
    5. Identify a positive TB tine test
    6. Recognize the most effective treatment for prosthetic device infection
    7. Identify the predominant bacterial pathogen in septic arthritis and osteomyelitis
    8. Recall the primary route of exposure of HIV in older adults
    9. Identify the most disabling complication of reactivated herpes zoster infection
    10. Define fever of unknown origin

 

1. PREDISPOSING FACTORS

  1. Immune Senescence
    The immune response to infection declines with age, a phenomenon known as immune senescence. 
  • The main features are depressed T-cell responses and depressed T-cell/macrophage interactions
  • The most marked deficits of immunity in the elderly:
    • Drying and thinning of the skin and mucous membranes
    • Poor antibody production
    • Decreased production of IL-2 and T-cell “help"
  1. Comorbid Illness
  • The impact of comorbid illnesses on innate immune function and host resistance is greater than the impact of age itself
  • Comorbid diseases also indirectly complicate infections (eg, community-acquired pneumonia in an elderly person with multiple comorbidities often requires hospitalization)
  1. Nutritional Compromise
  • On hospital admission, global undernutrition is present in 30%–60% of patients ³65 years
  • 11% of older outpatients suffer from undernutrition, mostly due to reversible conditions such as depression, poorly controlled diabetes mellitus, and medication side effects
  • Some nutritional interventions may boost immune function in older adults, but results vary depending on the population studied and the supplements used.

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2. ATYPICAL PRESENTATION OF INFECTION IN OLDER ADULTS

  • Older adults may present without typical signs and symptoms, even if the infection is severe
  • Fever may be absent in 30%–50% of frail older adults with serious infections
  • Fever in elderly nursing-home residents can be redefined as:
    • Temperature > 2°F (1.1°C) over baseline, or
    • Oral temperature > 99°F (37.2°C) on repeated measures, or
    • Rectal temperature > 99.5°F (37.5°C) on repeated measures
  • Elderly patients with bacteremia are less likely than younger adults to have chills or sweating, and fever is commonly absent
  • GI and genitourinary sources of bacteremia are more common than in younger adults
  • Mortality rate with nosocomial gram-negative bacteremia: 5%–35% in younger adults, 37%–50% in elderly patients

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3. ANTIBIOTIC MANAGEMENT IN OLDER ADULTS

  • Drug distribution, metabolism, excretion, and interactions can be altered with age
  • Even in the absence of disease, aging is associated with a reduction in renal function
  • Antibiotic interactions occur with many medications commonly prescribed for elderly persons
  • Risk factors for poor adherence include poor cognitive function, impaired hearing or vision, multiple medications, and financial constraints

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4. COMMON INFECTIONS IN OLDER ADULTS

  1. Pneumonia
  • Patients ≥65 account for over 50% of cases
  • Cumulative 2-year risk for long-term-care residents is about 30%
  • Mortality in elderly patients is 3x to 5x times that of younger adults
  • Comorbidity is the strongest independent predictor of mortalityPneumonia graph 
  • Prevention strategies for pneumonia in older adults include:
    • Immunization
    • Smoking cessation
    • Aggressive treatment of comorbidities (eg, minimizing aspiration risk in post-stroke patients, limited use of sedative hypnotics)
    • System changes with attention to infection control may be particularly effective in the nursing home
  1. Influenza
  • Annual influenza vaccination is recommended for all adults over 50
  • Treatment with M2 inhibitors or neuraminidase inhibitors is most effective if initiated within 24 hours of symptom onset
  1. Urinary Tract Infection
  • One of the most common illnesses in older adults
  • As in younger adults, gram-negative bacilli are most common
  • Older adults are more likely to have resistant isolates, such as Pseudomonas aeruginosa, and gram-positive organisms, including enterococci, coagulase-negative staphylococci, and Streptococcus agalactiae
  • Additional organisms in patients with indwelling catheters include enterococci, S. aureus, and fungi, particularly Candida spp.
  • Less common in men.  Usually due to obstructive prostatic disease or functional disability; ≥14 days of therapy needed
  1. Tuberculosis
  • Demographics
    • Patients ≥65 account for 25% of active cases in US
    • In long-term-care residents, prevalence of skin-test reactivity is 30%–50%, due to high rates of exposure in the early 1900s
    • Thus, most active cases in older adults are due to reactivation
    • Primary infection is of particular concern in nursing-home outbreaks
  • Presentation
    • Older adults may present with fatigue, anorexia, decreased functional status, or low-grade fever instead of classic symptoms
    • Lung involvement common (75%); pneumonic processes in older adults should raise suspicion
    • Elderly patients are more likely than younger adults to have extrapulmonary disease
    • Virtually any body structure can be involved, and that organ system can account for the major presenting symptom
  • Skin Testing
    • Induration ≥15 mm 48 to 72 hours after placement of a 5-tuberculin-unit PPD indicates a positive test in all situationsTB-tine test
    • Induration ≥10 mm is considered positive in nursing-home residents, recent converters (previous PPD <5 mm), immigrants from countries with high endemicity of TB, underserved US populations, and persons with specific risk factors
    • Induration ≥5 mm is considered positive in HIV-infected patients, those with a history of close contact with persons with active TB, and those with chest radiographs consistent with TB
  • Management
    • Treatment of active TB is similar to that in younger adults
    • Regardless of age, provide 9 months of prophylactic isoniazid for asymptomatic patients:
    • Who have a positive PPD and are recent converters (defined in persons over 35 as a PPD that has gone from <10 mm to ³15 mm within 2 yrs)
    • Regardless of PPD positivity if the patient has a specific risk factor for TB
  1. Prosthetic Device Infection
  • Device removal usually required for cure
  • Early and prolonged (months) antibiotic intervention, combined with aggressive surgical drainage, may be successful if symptoms have been present only for a brief duration
  • When full functionality is the goal, the best course is device removal and administration of antibiotics for 6–8 weeks, followed by reimplantation
  • Administration of prophylactic antibiotics other than for heart valves remains controversial
  1. Septic Arthritis
  • More likely in joints with underlying pathology
  • Early arthrocentesis is indicated in any mono- or oligoarticular syndrome, to exclude infection
  • S. aureus is the most likely pathogen
  • Aggressive antibiotic therapy should be combined with serial arthrocentesis in uncomplicated cases
  • Surgical drainage required when conservative strategy fails
  1. Osteomyelitis
  • S. aureus is the predominant organism
  • GI and genitourinary flora are more common than in younger adults, so a specific microbiologic diagnosis is useful
  • Infections of pressure ulcers and diabetic foot infections commonly require surgical consultation plus aggressive antimicrobial therapy aimed at mixed aerobic and anaerobic bacteria
  • Surface swab cultures of pressure ulcers are not useful
  1. HIV Infection and AIDS
  • Heterosexual activity is the primary mode of infection in older adults
  • Untreated older adults progress to AIDS more rapidly than young adults, but response to HAART is similar
  • Management is similar to that used for younger adults, except that a more aggressive approach to CVD prevention is warranted
  • HIV is probably the most treatable infectious cause of dementia and much more likely to reverse with therapy than syphilis (which is more commonly tested)
  1. Neurosyphilis
  • Possible underlying process in stroke or dementia; also consider in unilateral deafness, gait disturbances, uveitis, and optic neuritis
  • Positive CSF serology (VDRL test) may be diagnostic, but the sensitivity is only 75% in most series
  • Optimal treatment is penicillin G 
  1. Reactivated Varicella Zoster Virus (Herpes Zoster, Shingles)
  • Advancing age is the major risk factor
  • The most disabling complication, post-herpetic neuralgia, is common in elderly persons
  • A recently reported vaccine can reduce the risk of zoster and post-herpetic neuralgia by >50%
  1. Facial Nerve Palsy (Bell’s Palsy)
  • Associated with at least three infectious causes: herpes simplex virus, varicella zoster virus, and Borrelia burgdorferi (which causes Lyme disease)
  • If facial nerve palsy occurs as part of an episode of varicella zoster virus, antiviral treatment is indicated and corticosteroids should be administered as well
  • If Lyme disease is suspected on a clinical basis, antibiotic for two weeks is recommended
  1. Gastrointestinal Infections
  • Can present diagnostic dilemmas in the absence of fever or elevated WBC counts; a high index of suspicion is necessary
  • Diagnostic aids:
  • Intra-abdominal infection—CT or labeled WBC study
  • Cholecystitis, appendicitis, abscess—ultrasound
  • Ischemic bowel—often requires angiography or flexible sigmoidoscopy
  • Treat infectious diarrhea as in younger adults
  1. Fever of Unknown Origin
  • Defined as temperature > 38.3°C (101°F) for at least 3 weeks, undiagnosed after 1 week of medical evaluation
  • About 35% of cases are due to treatable infections, especially intra-abdominal abscess, bacterial endocarditis, and tuberculosis
  • Collagen vascular diseases are more common causes than in younger patients (about 30% of cases)
  • Neoplastic disease accounts for another 20% of cases

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5. SUMMARY

  • Immune function and host resistance are compromised in elderly persons as a consequence of both immune senescence and comorbid disease
  • A redefinition of fever should be considered in the frail older patient
  • There are suggested criteria for initiating antibiotic therapy in residents of long-term-care facilities
  • Careful selection of first-line therapy is warranted in older patients with pneumonia
 

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