Show Summary Details
Page of



Michael P. Mendez

Page of

PRINTED FROM OXFORD MEDICINE ONLINE ( © Oxford University Press, 2022. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

date: 29 June 2022

  1. A. Introduction

    1. a. Definitions. Pneumonia is defined as an acute infection of the lung parenchyma. It may be classified into four types, based on where the organism responsible might have been acquired:

      1. i. Community-acquired pneumonia (CAP). An acute infection typically acquired by healthy individuals in the community.

      2. ii. Healthcare–associated pneumonia (HCAP). Infection in individuals who have contact with health care settings. Examples include patients who may have received intravenous therapy or wound care in the past 30 days, those that reside in a nursing home or long-term facility, patients hospitalized for more than 2 days within the prior 90 days, and those who have received chronic dialysis within the past 30 days.

      3. iii. Hospital-acquired pneumonia (HAP). Infection that occurs 48 or more hours after admission to the hospital. The infection was not apparent on admission.

      4. iv. Ventilator-associated pneumonia (VAP). A type of HAP occurring 48 hours after a patient undergoes endotracheal intubation.

    2. b. Epidemiology. CAP is the eighth most common cause of death in the United States. Mortality rate of patients with HAP ranges between 25% and 50%.

  2. B. Clinical Manifestations of Pneumonia

    1. a. Symptoms commonly include fever, cough, sputum production, pleuritic chest pain, and dyspnea.

    2. b. Signs commonly include fever, tachypnea (≥20 respirations/ min), and signs of lobar consolidation (bronchial breath sounds, egophony, dullness to percussion, crackles). In the intensive care unit (ICU), a mechanically ventilated patient might have increased mucopurulent secretions, in addition to fever and tachypnea.

  3. C. Causes of Pneumonia. The most common pathogens depend on whether infection is acquired in the community or in the health care setting.

    1. a. CAP organisms.

      1. i. Streptococcus pneumoniae is detected in 10% to 15% of cases in the United States.

      2. ii. Haemophilus influenzae is an especially common cause of CAP in patients with underlying lung disease such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF).

      3. iii. Legionella species can cause severe pneumonia in sporadic outbreaks often by aerosolized bacteria. Legionella outbreaks have been identified with contaminated aerosol-producing devices (e.g., grocery store mist machines, cooling towers of air conditioners).

      4. iv. Aerobic gram-negative rods. Organisms such as Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli are uncommon causes of CAP. However, K. pneumoniae can cause pneumonia in patients with underlying diseases such as COPD, diabetes, and alcoholism.

      5. v. Staphylococcus aureus pneumonia is classically seen in patients who are immunocompromised or have recently had infection with influenza, known as postinfluenza pneumonia. The presence of community-acquired methicillin-resistant S. Aureus (caMRSA) infection has been noted in recent years and can be a pathogen in patients with CAP.

      6. vi. Influenza virus. This is an important consideration in severe presentations of pneumonia. Watch for a superimposed secondary bacterial pneumonia in these cases.

      7. vii. Other. This category includes diverse pathogens such as respiratory viruses (e.g., respiratory syncytial virus [RSV]); fungal pneumonia in immunocompetent individuals traveling to endemic areas; Histoplasma capsulatum in the midwestern United States (histoplasmosis); Coccidioides in the southwestern United States (Valley fever); and Blastomyces in the Ohio and Mississippi River Valleys (blastomycosis). Don’t forget pneumonia due to Mycobacterium tuberculosis, especially in travelers from endemic areas of the world (e.g., Pakistan, India, China).

      8. viii. Polymicrobial infections from aspiration of oropharyngeal secretions should be considered in patients with altered mental status, a history of seizures or alcohol abuse, swallowing difficulties, or patients transferred from a nursing home.

        1. 1. If aspiration occurs in the upright position, the lower lobes are affected (the right side more often than the left). The distribution follows the law of gravity because the right side is more aligned with the trachea and airways than the left.

        2. 2. It is more of a “PUSL” to remember which lobes are involved if aspiration occurs when patients are recumbent: the Posterior segment of the Upper lobe and the Superior segment of the Lower lobe.

    2. b. HCAP, HAP, and VAP organisms. These infections tend to be polymicrobial and often include gram-negative pathogens such as E. coli, K. pneumoniae, Enterobacter species, P. aeruginosa, and Acinetobacter species. Gram-positive bacteria such as methicillin-susceptible S. aureus (MSSA) and MRSA are also common. Always consider drug resistance when dealing with these organisms. Risk for resistance increases with the following clinical factors: antibiotic use in the last 90 days; hospitalization ≥5 days, high prevalence of antibiotic resistance; immunosuppressive disease and/or therapy; and severe septic shock.

  4. D. Approach to the Patient

    1. a. Diagnostic tests

      1. i. Complete blood count (CBC) with differential.

      2. ii. Electrolytes, blood urea nitrogen (BUN), and creatinine.

      3. iii. Peripheral blood cultures on samples drawn from two separate sites.

      4. iv. Arterial blood gas (depending on severity of illness).

      5. v. Urinary antigen test for streptococcal pneumonia and legionella should be ordered in alcoholic patients, patients with severe CAP, and suspicious sporadic outbreaks.

      6. vi. Chest radiograph (posterior-anterior and lateral views).

      7. vii. Sputum analysis. For outpatient treatment of pneumonia, Gram staining and culture are not necessary. However, if hospital admission is required, collection should be performed in the following circumstances:

        1. 1. Suspicion of M. tuberculosis or Pneumocystis jirovecii (special stains are required)

        2. 2. ICU admission

        3. 3. Presence of a cavitary lesion

        4. 4. Immunocompromised host

        5. 5. Severe obstructive/structural lung disease (think severe fibrosis or COPD)

        6. 6. Failure of outpatient antibiotic therapy

        7. 7. Presence of a pleural effusion

      8. viii. Thoracentesis. If a pleural effusion is seen on chest radiography, the pleural fluid must be sampled if large enough to safely introduce a needle (see Chapter 98). Send for a cell count and differential, Gram staining and culture, total protein, lactate dehydrogenase (LDH), pH, and glucose to further evaluate presence of a complicated pleural effusion requiring chest tube drainage (see Chapter 24).

    2. b. Criteria for hospital admission. Validated scoring systems can guide the initial site of treatment for adults. The Pneumonia Severity Index (PSI) and CURB-65 score (Table 21.1) are both recommended by the 2007 American Thoracic Society/Infectious Diseases Society of America guidelines to guide the decision to admit to the hospital.

      Table 21.1 CURB-65 Severity Score for Pneumonia





      0–1, outpatient treatment

      2–3, admit medical floor

      4–5, consider ICU

      Blood Urea Nitrogen (BUN)

      >20 mg/dL

      Respiratory rate

      ≥30 breaths/min

      Blood pressure

      SBP ≤90 mm Hg

      DBP ≤60 mm Hg


      >65 years

      * One point for each criterion met.

      DBP = diastolic blood pressure; ICU = intensive care unit; SBP = systolic blood pressure.

  5. E. Treatment

    1. a. Empiric therapy. The American Thoracic Society recommends stratifying patients by place of therapy (outpatient or inpatient) and the presence of significant risk factors (e.g., nursing home residence, cardiopulmonary disease, alcoholism, and immunosuppression). Inpatients should be treated empirically until a pathogen is identified by sputum or blood culture (if a pathogen is identified, appropriate specific therapy for the organism should be used). In general, antimicrobial therapy should be given for 5–7 days depending on the pathogen and type of infection. The most important treatment strategy is to administer appropriate empiric antibiotics as soon as possible.

      1. i. Outpatient. Previously healthy patients with no comorbidities and no antibiotic exposure in the past 3 months should be treated with a macrolide. If comorbidities are present (chronic heart/lung disease, diabetes, alcoholism, malignancy, asplenia, immunosuppression, antibiotics in the past 3 months), use a respiratory fluoroquinolone (not ciprofloxacin because it lacks adequate S. pneumoniae coverage) or a β‎-lactam plus a macrolide.

      2. ii. Inpatient, non-ICU. Hospitalized patients should be treated with (1) intravenous β‎-lactam plus a macrolide or (2) intravenous respiratory fluoroquinolone alone.

      3. iii. Inpatient, ICU. If risk factors for Pseudomonas infection are absent (e.g., bronchiectasis, immunosuppression, recent antibiotics, or malnourished), treat with an intravenous β‎-lactam plus either a macrolide or intravenous respiratory fluoroquinolone (preferred).

      4. iv. Inpatient with risk factors for Pseudomonas. If risk factors for Pseudomonas infection are present, treat with an antipneumococcal, antipseudomonal β‎-lactam plus an antipseudomonal fluoroquinolone (or an intravenous aminoglycoside and azithromycin); or, the above β‎-lactam plus aminoglycoside and antipneumococcal fluoroquinolone.

      5. v. In patients at risk for community-acquired MRSA (caMRSA) or those with postinfluenza infection, initiate empiric intravenous vancomycin or linezolid until cultures to guide treatment become available.

    2. b. Response to therapy. Most patients will improve over 3–4 days. However, cough and crackles usually take longer to respond (1 week and 3 weeks, respectively) and should not be used alone to guide duration of therapy. The chest radiograph can take even longer to return to normal (4–12 weeks depending on patient age and if there is underlying lung disease). In patients not responding to therapy (i.e., persistent fever, hemodynamic instability, tachypnea, or tachycardia), consider the following possibilities:

      1. i. Bacterial resistance to antimicrobial agents

      2. ii. Unusual pathogen (e.g., M. tuberculosis, P. jirovecii, viral infection)

      3. iii. Complication of the infection (e.g., empyema, lung abscess)

      4. iv. Underlying malignancy leading to postobstructive pneumonia

      5. v. Additional noninfectious causes (e.g., congestive heart failure, acute interstitial lung disease process, bronchoalveolar cell carcinoma)

    3. c. In patients who fail to respond to what appears to be appropriate therapy, consider obtaining a pulmonary consultation (for possible bronchoscopy) and further imaging (e.g., chest computed tomography) to rule out complications (e.g., abscess, empyema).

    4. d. Vaccination. Influenza and/or pneumococcal vaccines should be administered in all patients who have not been vaccinated and develop pneumonia. It is usually not necessary to wait for recovery to vaccinate.

Suggested Further Readings

American Thoracic Society; Infectious Diseases Society of America. Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia. Am J Respir Crit Care Med 2005;171:388–416.Find this resource:

Chastre J, Wolff M, Fagon JY, et al. Comparison of 8 vs 15 days of antibiotic therapy for ventilator-associated pneumonia in adults: a randomized trial. JAMA 2003;290:2588–98.Find this resource:

Jain S, Self WH, Wunderink RG, et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. N Engl J Med 2015;373:415–27.Find this resource:

Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44 Suppl 2:S27–72.Find this resource:

Musher DM, Thorner AR. Community-acquired pneumonia. N Engl J Med 2014;371:1619–28.Find this resource: