Pneumonia

An inflammatory reaction to microbes or to microbial products involving the pulmonary parenchyma.

Pneumonia is one of the most common and significant health problems in the elderly. It is the 4th leading cause of death and the leading infectious cause of death in this age group. Pneumonia is often the terminal event after prolonged serious illness; it has been called the "old man's friend."

The annual incidence in the elderly varies from 20 to 40/1000 for community-acquired pneumonia to 100 to 250/1000 for pneumonia acquired in long-term care facilities. At any given time, an estimated 2.1% of elderly residents of long-term care facilities have pneumonia. Nosocomial pneumonia is common among hospitalized elderly patients who have undergone thoracic or abdominal surgery, mechanical ventilation, or tube feeding.

The major risk factor for developing pneumonia in the elderly is the presence of other serious illness. Additionally, the likelihood of a serious outcome with pneumonia, including death, is directly related to the number of comorbid illnesses; the mortality rate increases from 9/100,000 without comorbidity to 217/100,000 with one high-risk condition and 979/100,000 with two or more high-risk conditions. Elderly patients are likely to experience more complications from pneumonia, such as bacteremia, empyema, and meningitis.

Etiology

The most common identifiable organisms causing pneumonia in the elderly are discussed below. In 30 to 50% of cases, no specific pathogen is detected. Colonization of the respiratory tract with potentially pathogenic gram-negative and gram-positive bacteria occurs more often in the elderly than in younger persons, owing in part to such factors as repeated antibiotic therapy, endotracheal intubation, smoking, malnutrition, surgery, and therapy that lowers gastric acidity, thereby raising pH.

Streptococcus pneumoniae: S. pneumoniae (causing pneumococcal pneumonia) is the most common bacterial cause of community-acquired pneumonia in the elderly. It accounts for 15 to 50% of all culture-diagnosed pneumonias in adults. The attack rate of pneumococcal pneumonia is estimated to be 46/1000 in persons > 65. Patients > 65 years are 3 to 5 times more likely to die of pneumococcal pneumonia than their younger counterparts.

Gram-negative bacilli: These pathogens are more common in institutional settings, where Klebsiella, Pseudomonas aeruginosa, Enterobacter sp, Proteus sp, Escherichia coli, and other gram-negative bacilli account for about 40 to 60% of all culture-diagnosed pneumonias. Gram-negative bacilli may colonize the posterior pharynx in debilitated and seriously ill patients.

Anaerobic bacteria: Anaerobes cause 20% of community-acquired and 31% of nosocomial cases of pneumonia in the elderly. Pneumonia caused by anaerobes usually results from aspiration. Elderly patients tend to aspirate because of conditions associated with aging that alter consciousness, such as sedative use and medical conditions (eg, neurologic disorders, weakness). Anaerobes frequently implicated include Fusobacterium nucleatum, black-pigmented anaerobes (formerly called Bacteroides melaninogenicus), peptostreptococci, peptococci, and, occasionally, B. fragilis.

Haemophilus influenzae: Strains of H. influenzae account for 8 to 20% of pneumonias in the elderly. These organisms are more frequent causes of pneumonia in patients with chronic bronchitis.

Legionella sp: Susceptibility to Legionella infections (5% of all culture-diagnosed pneumonias) increases with age. L. pneumophila accounts for about 85% of all Legionella pneumonias among the elderly, and L. micdadei for about 15%. Although legionnaires' disease occurs sporadically, outbreaks have been reported in hotels and hospitals.

Viruses: Viral causes of pneumonia in elderly patients include influenza and parainfluenza viruses, respiratory syncytial virus, and possibly adenoviruses. Parainfluenza viruses infrequently invade healthy adults; their relatively frequent occurrence among the elderly may reflect waning immunity.

Influenza is the most important cause of pneumonia in the elderly. Its incidence in persons >= 70 is about 4 times that in persons < 40. About 90% of influenza-associated deaths in the USA occur in persons >= 65. Secondary bacterial pneumonia may complicate a course of influenza.

Pathogenesis

Two major factors predisposing the elderly to pneumonia are oropharyngeal colonization and silent aspiration. Colonization of the oropharynx with various gram-negative bacilli is especially common among hospitalized and critically ill patients. Predisposing factors include poor oral hygiene; abnormal swallowing; increased adherence of gram-negative bacilli to mucosal cells; debility from cardiac, respiratory, or neoplastic diseases; decreased ambulation; and exposure to broad-spectrum antibiotics. Silent aspiration of oropharyngeal secretions is often related to alcoholism, use of sedatives or narcotics, cerebrovascular disease, esophageal disorders, and nasogastric intubation.

Microorganisms reach the tracheobronchial tree via four routes: inhalation, aspiration, direct inoculation from contiguous sites, and hematogenous spread. Inhalation and aspiration are the most common routes.

Inhalation pneumonia: Aerosolized pathogens inhaled into the lower airways as microparticles include Mycobacterium tuberculosis, Legionella sp, and the influenza virus. M. tuberculosis and the influenza virus are transmitted via aerosolized secretions produced by coughing. Although most cases of pneumococcal pneumonia are acquired by aspiration, in rare cases, especially in an epidemic, the organism is inhaled. Legionella infection is not transmitted from person to person, but rather, is acquired by inhaling infected aerosols from a waterborne source (eg, from air conditioners or shower heads). Waterborne organisms may also be introduced into the lower airways by instrumentation or delivered by small-particle aerosols from a contaminated reservoir nebulizer used with ventilation equipment.

Aspiration pneumonia: In community-acquired aspiration pneumonia, the usual pathogens are the anaerobic bacteria that normally reside in the gingival crevices (eg, peptostreptococci, fusobacteria, black-pigmented anaerobes). In nosocomial aspiration pneumonia, the usual pathogens are gram-negative bacilli, sometimes in association with anaerobes. Most cases of pneumococcal and gram-negative bacillary pneumonia presumably follow microaspiration, in which a fairly small inoculum of bacteria travels from the posterior pharynx into the lungs. Large-volume aspiration results in a relatively large inoculum of oropharyngeal bacteria into the lower airways and occurs with conditions that compromise consciousness or that cause dysphagia.

Symptoms, Signs, and Diagnosis

The characteristic clinical features of pneumonia--fever, cough, and sputum production--are often subtle and incompletely expressed in elderly patients. Only 33 to 60% of elderly patients present with a high fever. Instead, elderly patients with pneumonia commonly present with acute confusion or delirium and deterioration of baseline function. Tachypnea and tachycardia may be presenting signs.

Chest x-ray is usually diagnostic but does not indicate cause. Progression and multilobe involvement are seen more often in elderly patients. Leukocytosis with immature white blood cells develops less often in elderly patients. Blood cultures should routinely be performed.

The diagnosis should not be made based on expectorated sputum, because expectorated sputum does not distinguish colonization from true pulmonary infection. However, expectorated sputum is useful for culturing M. tuberculosis, pathogenic fungi (Histoplasma, Blastomyces, and Coccidioides), and Legionella sp. A gram stain of expectorated specimens may be useful if a predominance of one organism is seen along with a large number of neutrophils. Transtracheal aspiration (sputum sample removal through a cannula passed to the lower airways through a percutaneous puncture at the cricothyroid membrane), transthoracic aspiration, and fiberoptic bronchoscopy using a protected brush may produce reliable results but are rarely used in elderly patients for routine diagnostic evaluation. Obtaining a specimen for anaerobic culture and etiologic identification is often problematic because of contamination of the expectorated sputum specimens by the normal flora of the upper airways.

Prevention

Two types of pneumonia can be prevented--influenza and pneumococcal. A yearly influenza vaccine is highly protective. Even when the vaccine fails to prevent infection, the severity of disease and the frequency of complications are reduced. Pneumococcal vaccine is recommended for all persons >= 65. There is a 60% protection rate in immunocompetent adults. In healthy elderly persons, protection is presumed to be lifelong; thus, reimmunization is unnecessary. In high-risk elderly patients, however, including those with chronic renal failure, diabetes mellitus, heart failure, chronic obstructive pulmonary disease (COPD), or an underlying malignancy, reimmunization with pneumococcal vaccine is recommended every 6 to 10 years.

Treatment

Treatment includes antimicrobial drug therapy, respiratory and other forms of supportive care, and drainage of empyemas and large pleural collections.

Recommendations for antimicrobial drug use depend on the specific organism (see Table 76-1). They are similar across age groups, although the elderly require closer therapeutic monitoring. Potentially nephrotoxic drugs, primarily aminoglycosides, require close serum monitoring and frequent measurements of renal function and should be avoided unless a non-nephrotoxic drug cannot be used. Because elderly persons have reduced cardiac reserve, IV fluids and electrolytes and other forms of osmotic loading must be given cautiously. With age, the risk of antibiotic-associated diarrhea or colitis increases with ampicillin, cephalosporin, or clindamycin use. Antimicrobials may interact with other drugs (eg, warfarin) commonly used to treat the elderly. Sedatives that decrease deep inspiration and cough should be avoided.

Chest percussion and pulmonary hygiene measures are often useful in frail elderly patients with a diminished cough reflex. Such measures aid in clearing thick, inspissated secretions, thereby reducing the risk of mucous plugs, which often lead to lung collapse.

Patient and Caregiver Issues

Stable elderly patients with pneumonia who have no comorbid diseases can often be treated as outpatients. The caregiver's role is to ensure compliance with and completion of the treatment regimen. Frail and bedridden elderly patients for whom outpatient treatment is being considered may require home health care services. Elderly persons often have an increased risk of delirium associated with infection, poor adherence with drugs, and polypharmacy, which can result in drug-drug interactions. Regular communication between the physician and the patient and caregiver should be emphasized.

End-of-Life Issues

Pneumonia in the elderly is often the terminal event of comorbid diseases such as diabetes mellitus, COPD, heart failure, malignancy, and dementia. Elderly patients with comorbidity are more likely to develop complications, eg, adult respiratory distress syndrome, empyema, and septic shock. In some cases, comfort measures may be more appropriate than antibiotics. Advance directives in such severe cases can often assist the physician in making appropriate decisions regarding resuscitative measures. When palliative care is the goal, opioids often help patients with dyspnea.