The presentations of bronchitis and pneumonia are similar. Cough may be productive or nonproductive of sputum, and associated symptoms, including fever, chest discomfort, and fatigue, may be present in both entities. Pleurisy or dyspnea tends to suggest more extensive involvement, as seen in pneumonia. “Classic” community-acquired pneumonia presents with a sudden chill followed by fever, pleuritic pain, and productive cough. The atypical pneumonia syndrome, associated with Mycoplasma or Chlamydophila infection, often begins with a sore throat and headache, followed by a nonproductive cough and dyspnea. Physical examination findings may be misleading, especially in the patient with underlying lung disease. Evidence of consolidation on the lung examination (bronchial breath sounds, egophony) is indicative of pneumonia but is present in few outpatients. The chest x-ray film in acute bronchitis usually reveals no infiltrate or signs of consolidation, in contrast to the x-ray film in pneumonia. However, even this most clear-cut distinction between bronchitis and pneumonia can be misleading because changes of chronic lung disease can simulate new infiltrates in some patients with bronchitis, whereas dehydration can minimize radiographic abnormalities in patients with pneumonia. The clinical presentations are, in part, a function of the causative organism (see discussion of specific organisms).

Traditionally, most cases of pneumonia that develop in the outpatient setting have been designated as “community acquired.” They can range in severity from mild to severe and may require hospitalization (see Indications for Admission). Prognosis is usually good for cases deemed safe for outpatient management.

Less appreciated is pneumonia acquired in the community setting that is health care associated, defined in guidelines established by the American Thoracic Society and the Infectious Disease Society of America as pneumonia occurring in outpatients in contact with the health care system, typically by virtue of living in a nursing home, attending a dialysis clinic, or having had a recent hospitalization. In a large prospective observational study, health care pneumonia accounted for a quarter of pneumonia admissions. Patients required longer hospital stays, had more severe disease, and had higher mortality rates. They were more likely to have bilateral or multilobar involvement. Recent receipt of empirical antibiotic therapy was a risk factor for poor outcome.

Streptococcus pneumoniae is the most common cause of pneumonia, accounting for 30% to 50% of all cases of bacterial pneumonia. It is especially likely to be the agent infecting healthy young ambulatory patients, but it may affect all age groups. It is also responsible for acute exacerbations in patients with chronic bronchitis, but its role in acute bronchitis in healthy persons is unclear. Classic clinical features of pneumococcal pneumonia include abrupt onset of fever with a single rigor, cough with rusty sputum, and pleuritic chest pain. Radiologic evidence of lobar consolidation is typical, but infiltrates can be patchy, especially in patients with chronic lung disease. The sputum gram stain reveals abundant polymorphonuclear leukocytes and Gram-positive diplococci (classically lancet shaped) in pairs or short chains.

The most common complication of pneumococcal pneumonia is bacteremia, which occurs in about one third of patients. Blood-borne distant sepsis (e.g., septic arthritis, peritonitis, meningitis) is much less common. Sterile pleural effusions are common, whereas empyema is less frequent.

Staphylococcus aureus is the etiologic agent in up to 10% of cases of bacterial pneumonia. Except in infancy, when it can be a primary infection, staphylococcal pneumonia most commonly follows a viral respiratory tract infection, particularly influenza. It may also occur as a nosocomial infection or as a result of bacteremic seeding of the lungs, especially in patients who have staphylococcal endocarditis or are intravenous drug users. Patients with staphylococcal pneumonia of respiratory or bloodstream origin are usually extremely ill. Staphylococcus aureus produces tissue necrosis, and the distinctive feature of staphylococcal pneumonia is the tendency to produce multiple small lung abscesses. Healing usually leaves some degree of residual fibrosis. Abundant polymorphonuclear leukocytes and grampositive cocci in pairs, clumps, and clusters are found on the sputum Gram stain. Local suppurative complications, including lung abscess, empyema, and pneumothorax, are relatively common. Bacteremia with metastatic seeding of distant sites, such as endocardium, bone, joints, liver, and meninges, may occur.

Group A streptococci are a rather uncommon cause of infection, but this type of pneumonia has occurred in epidemics, especially in closed groups such as military units. Occasionally, streptococcal pneumonia can occur after primary influenza pneumonia. Streptococcal pneumonia usually begins abruptly with fever, cough, and severe debility. Chest pain is prominent in most patients. The distinctive clinical and radiologic feature is rapid spread in the lung, with resultant early empyema formation. Initially, the empyema fluid may be thin, possibly because of the many enzymes elaborated by group A streptococci, but later, frank purulence occurs. Other complications, such as lung abscess, bacteremia, metastatic infection, and poststreptococcal glomerulonephritis, are uncommon. In patients with streptococcal pneumonia, the sputum Gram stain reveals numerous polymorphonuclear leukocytes and gram-positive cocci in pairs and short to long chains.

Haemophilus influenzae has long been recognized as a common cause of bronchitis in adults with chronic lung disease; however, recognition of this organism as a cause of frank pneumonias, sometimes with bacteremia, is increasing. Most cases of bronchitis are caused by untypeable strains of H. influenzae, but pneumonias are often caused by the more invasive encapsulated strains, especially type b. Radiographically, a bronchopneumonia pattern is typical. Abundant polymorphonuclear leukocytes and small, pleomorphic, gram-negative coccobacillary organisms are the characteristic findings in the sputum of patients with pneumonia or bronchitis cased by H. influenzae. Complications of H. influenzae pneumonia in adults are uncommon, but in patients with underlying chronic lung disease, the illness may be particularly severe, with development of hypoxia and respiratory failure.

Klebsiella pneumoniae typically produces pulmonary infection in debilitated patients, especially alcoholics, and Klebsiella pneumonia is one of the few gram-negative bacillary pneumonias seen commonly in ambulatory patients. It usually presents as an acute illness; rarely, it may cause chronic pneumonitis. The organism has a high propensity to produce tissue necrosis, which accounts for the hemoptysis, dense lobar consolidation, and high incidence of abscess formation seen in this illness. Sputum may appear dark red and mucoid (“currant jelly” sputum). Abundant polymorphonuclear leukocytes and large gram-negative bacilli, occasionally with thick capsules, are characteristically seen on sputum Gram stain. Lung abscess and empyema may occur.

Other gram-negative bacillary pneumonias were once rare but have increased during the last 15 years and now account for up to 15% of cases of bacterial pneumonia. They are principally hospital-acquired infections and remain rare in the ambulatory population. Patients with gram-negative bacillary pneumonia are typically debilitated from other illnesses or elderly and frequently have received antibiotic therapy during which their normal respiratory flora is replaced with these otherwise unusual pathogens. Abundant polymorphonuclear leukocytes and gram-negative bacilli are seen on sputum Gram stain. Complications, including lung abscess, empyema, and bacteremia with metastatic spread of infection, may occur.

Moraxella (Branhamella) catarrhalis is a gram-negative coccus that morphologically resembles organisms of the Neisseria family but differs in biochemical and DNA characteristics. It is found in the oropharynx of normal hosts and was not considered pathogenic until the 1980s, when it was established as the cause of lower respiratory tract infection in some patients with chronic obstructive pulmonary disease (COPD). In more than 80% of M. catarrhalis infections, an underlying pulmonary disease is present. Diabetes, alcoholism, malignancy, and steroid use are other known risk factors. Cases appear to be concentrated in the winter months, perhaps indicating a relation to preceding viral infection. The typical lower respiratory tract infection that ensues is mild and sometimes even self-limited. The organism is readily identified by Gram stain, and almost all sputum cultures are positive for organisms. Chest radiography shows an interstitial or interstitial-airspace infiltrate. Bacteremia is rare, and full recovery with prompt response to antibiotics is the rule, although almost all isolates are positive for β-lactamase.

Bordetella pertussis, a gram-negative pleomorphic bacillus, is a frequently overlooked cause of acute bronchitis. Acquired immunity from childhood wanes after 15 to 20 years, so young adults are rendered susceptible to pertussis. Several studies have shown that pertussis accounts for up to 25% of patients with acute bronchitis lasting 2 or more weeks. The disease typically has three phases. The catarrhal phase is indistinguishable from an upper respiratory infection, with rhinorrhea, low-grade fever, and mild congestion lasting 1 to 2 weeks. Patients are contagious in this stage and early into the next stage, the paroxysmal phase, which lasts for at least 2 to 4 weeks and may persist for up 8 weeks, characterized by severe paroxysms of nonproductive coughing, with 10 to 30 coughs in a row. Hallmark symptoms of posttussive syncope and vomiting are not uncommon; the characteristic whoop in children (due to a forceful inhalation after prolonged coughing in the presence of a narrowed airway in children) is absent in adults because of their larger airways. Finally, the symptoms gradually resolve during the next 1 to 3 months in the convalescent phase. Untreated patients are infectious up to 4 weeks from onset of symptoms.

Mycoplasma pneumoniae is a cell wall-deficient organism that accounts for 10% to 20% of cases of community-acquired pneumonia. It is a leading cause of the atypical pneumonia syndrome (fever, dry cough, nonspecific infiltrate on chest film) and also a cause of acute bronchitis in otherwise healthy adults. The organism spreads by way of respiratory droplets and appears to have a long incubation period; onset of illness tends to be insidious. The disease often begins with headache, sore throat, and malaise and then progresses to a nonproductive cough. The physical examination findings are usually unimpressive in comparison with the patchy peribronchial infiltrates seen on chest x-ray films. Bullous myringitis has been reported in Mycoplasma pneumonia, but it is actually uncommon in clinical practice. Skin examination may show erythema multiforme, which is highly correlated with Mycoplasma infection in the patient with pneumonia. Laboratory studies reveal a normal white blood cell count and differential in most cases. The sputum is scant, with a predominance of mononuclear cells and no organisms. Sputum culture is not practical because a special medium is required and results do not become available for 2 weeks. Testing for the organism by polymerase chain reaction (PCR) is a new technique with high sensitivity and specificity, although it is not widely available. Cold agglutinins are present in approximately 50% of cases. Mycoplasma pneumonia is usually a mild, self-limited illness, but it can produce severe pneumonia in children with sickle cell anemia, in immunosuppressed hosts, and in the elderly. Uncommon complications include hemolytic anemia, aseptic meningitis, Guillain-Barré syndrome, and myopericarditis.

Chlamydophila pneumoniae (formerly known as Chlamydia pneumoniae or TWAR) is an obligate intracellular organism that causes an atypical pneumonia or acute bronchitis. It appears to account for 5% to 15% of cases of community-acquired pneumonia, with higher rates in young adults. Chlamydophila pneumoniae appears to spread from person to person by respiratory droplets. The prodrome resembles that of Mycoplasma pneumonia, with headache and sore throat followed by a dry cough, but the chest radiograph shows less extensive involvement. The diagnosis is difficult because culture requires tissue culture techniques that are not routinely performed. Serology (acute and convalescent titers) has been used to establish the diagnosis, and, as in Mycoplasma pneumonia, PCR is an upcoming technology. The infection is usually self-limited; rare fatalities have been reported in debilitated patients.

Psittacosis is caused by a member of the Chlamydia group of obligate intracellular parasitic bacteria, which are also responsible for lymphogranuloma venereum and trachoma. The disease is transmitted from parrots or other birds (including pigeons and turkeys) to humans. The clinical features of psittacosis are indistinguishable from those of other atypical pneumonias, with prominent headache, nonproductive cough, and fever. Occasionally, a faint macular rash or splenomegaly develops.

Q fever is caused by the rickettsial-like organism Coxiella burnetii, but differs from rickettsial infections with a prominent pneumonia, no associated rash, and airborne instead of insect vector transmission. The organisms reside principally in animals; human contact with cattle, sheep, goats, or infected animal hides or hide products is the most important epidemiologic factor and is often the only clue to diagnosis. The clinical features of Q fever are similar to those of the other atypical pneumonias, except that hepatitis occurs in up to one third of patients.

Aspiration pneumonias are usually mixed infections caused by aerobic and anaerobic streptococci, Bacteroides, and Fusobacterium. These organisms are normal flora of the upper airway that cause pneumonia if they attain a foothold in the lung parenchyma. Predisposing factors include alteration of consciousness (drugs, anesthesia, alcohol, head trauma) and diminution of the gag reflex, which permits aspiration to occur. Patients usually are mildly to moderately ill but can be toxic, especially if lung abscess or empyema occurs. Hospitalized patients, ambulatory patients receiving antibiotics, and edentulous patients have altered respiratory flora and fewer anaerobic organisms, if any. Aspiration of mouth organisms in such persons may result in staphylococcal or gram-negative bacillary pneumonia, as discussed previously, rather than the mixed aerobic-anaerobic infection considered here. The sputum from patients with aspiration pneumonia may be malodorous and characteristically shows abundant polymorphonuclear leukocytes and mixed flora, including gram-positive cocci in pairs and chains and pleomorphic gram-negative rods on Gram stain. Lung abscess and empyema are fairly common complications of aspiration pneumonia, especially if therapy is delayed.

Viruses are the most common cause of acute bronchitis, accounting for more than 80% of all cases. Viral pneumonia resembles an atypical pneumonia and is clinically indistinguishable except when it is part of a distinctive systemic viral illness, such as rubeola in children or varicella in adults. Many viruses are capable of producing lower respiratory tract infections, including influenza virus, adenoviruses, respiratory syncytial virus, and parainfluenza virus. Cytomegalovirus is a common cause of viral pneumonia in transplant recipients.

Immunosuppressed patients (e.g., those taking corticosteroids or HIV-positive patients) are at heightened risk for a community-acquired opportunistic infection (e.g., Aspergillus, Candida, or Pneumocystis; see Chapter 13). HIV-positive patients are also at increased risk for primary tuberculosis (see Chapter 49). However, some fungal infections may occur in immunocompetent hosts. For example, exposure to sporecontaining dusts may lead to histoplasmosis (in the Midwest) or coccidioidomycosis (in the Southwest), characterized in the initial phases by a nonproductive cough, flulike illness, liver or splenic enlargement, alveolar infiltrates, and sometimes hilar adenopathy; however, most often, the chest radiographic findings are normal.