Community Acquired Pneumonia

Didn't play the corresponding interactive case or want to try it again? Click here to do so.

Diagnosis and reasoning

This lady has presented acutely with a cough productive of yellowish sputum; she additionally complains of experiencing a non-productive cough and myalgia during the preceding few weeks. This history is suggestive of a lower respiratory tract infection such as acute bronchitis or community acquired pneumonia; note that fever may not occur in the elderly. Two other points in her history should be appreciated: first of all, her work in a homeless shelter may have exposed her to tuberculosis - thus, the possibility of pulmonary tuberculosis should be kept under consideration. Secondarily, note the history of prolonged smoking - this raises chronic obstructive pulmonary disease (COPD) as an additional possibility (although the absence of previous episodes makes this diagnosis less likely). The examination shows her to be acutely ill, dyspneic and tachycardic, with evidence of consolidation in the right lower zone. This is strongly suggestive of a pneumonia. The chest x-ray provides further evidence in this regard, by demonstrating a pneumonic patch corresponding to the clinical findings; in addition, the full blood count shows a neutrophil leukocytosis, suggesting at a bacterial origin. Note that tuberculosis can mimic this appearance - thus there is justification in examining her sputum for acid-fast bacilli. However, this turns out to be negative. All patients with community acquired pneumonia should undergo further risk stratification; the CRB-65, CURB-65 or PSI scores may be used in this regard. Based on the parameters observed so far, this patient appears to be at low-risk for 30-day mortality; she can probably be managed at home. Antibiotics are the mainstay of therapy - these should be commenced empirically (after obtaining blood and sputum cultures) and then targeted based on culture results. Supplemental oxygen is not immediately necessary; nebulization with salbutamol is not of benefit here. Steam inhalation is no longer recommended in these patients.


Pneumonia is defined as acute inflammation of the lung parenchyma. It is one of the most common infections, causing significant mortality and morbidity worldwide. In the United States itself, pneumonia is the sixth leading cause of death, and the number one cause of death from infectious diseases. In clinical practice, pneumonia is classified into community acquired pneumonia (CAP) and hospital acquired pneumonia (nosocomial pneumonia), based on where it was acquired. Note that in recent times, the term 'healthcare associated pneumonia' has also come into use; this is used to refer to pneumonia in patients who have been in recent contact with the healthcare system (even though they might not have been hospitalized). The remainder of this discussion focuses on CAP. Important predisposing factors for CAP include increasing age, and comorbidities such as chronic obstructive lung disease, diabetes mellitus, renal insufficiency, congestive heart failure, coronary artery disease, malignancy, chronic neurologic disease, and chronic liver disease. Streptococcus pneumoniae is the most commonly identified pathogen; other important organisms include Hemophilus influenzae, Mycoplasma pneumoniae, Chlamydia pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Neisseria meningitidis, Moraxella catarrhalis, Klebsiella pneumoniae, Legionella species and influenza virus. Strains of methicillin-resistant Staphylococcus aureus (MRSA) have also emerged as pathogens in certain communities. Note however that the responsible pathogen is not identified in as many as 50% of patients, even when extensive diagnostic testing is performed. In general, 'typical' bacterial pathogens such as S. pneumoniae, H. influenzae, and the enteric gram-negative organisms usually manifest acutely with high fever, chills, tachypnea, tachycardia, and a productive cough. Examination findings are localized to a specific lung zone and can include rales, rhonchi, bronchial breath sounds, dullness, increased fremitus, and egophony. In contrast, atypical pathogens such as Mycoplasma, Chlamydophila, and viruses often manifest in a subacute fashion with (milder) fever, a nonproductive cough, constitutional symptoms, and absent, minimal or diffuse findings upon pulmonary examination. Note that severe pneumococcal or Legionella pneumonia may rapidly progress to respiratory failure. The diagnosis of CAP is based upon clinical, laboratory, and radiologic data. Chest x-rays are important in establishing the diagnosis as well as detecting associated complications such as parapneumonic effusions, lung abscesses, and multilobar involvement. Laboratory tests for pneumonia include a full blood count, gram stain of sputum, blood cultures, serologic testing (for Mycoplasma species and Chlamydia species) and urinary antigens (for Legionella species). Two sets of blood cultures should be drawn before initiation of antibiotic therapy, and may help to identify the presence of bacteremia and of a resistant pathogen. Although patients with mild CAP may be treated as outpatients, those who are moderately to severely ill should be hospitalized. This decision can be made by using mortality prediction rules such as the CRB-65, CURB-65 or PSI scores. Antibiotics are the mainstay of therapy in these patients; the initial empirical antibiotic selection should be based upon the patient's characteristics (age, comorbidities and clinical presentation), place of acquisition, and severity of disease. Current consensus guidelines from American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) recommend macrolides, fluoroquinolones, or doxycycline for initial empiric therapy in outpatients. Inpatients can be treated with an IV beta-lactam (cefuroxime, ceftriaxone, cefotaxime) or a combination of ampicillin/sulbactam with a macrolide. Patients with severe disease requiring ICU admission usually need IV therapy with a beta-lactam combined with either a macrolide or a fluoroquinolone. Generally S. pneumoniae pneumonia, and other bacterial infections should be treated for 7 to 10 days; patients with M. pneumoniae and C. pneumoniae may need longer therapy ranging from 10 to 14 days; CAP due to Legionella species also needs a longer duration of therapy. The initial IV therapy can be switched to oral therapy once the patient is clinically stable (i.e. improvement in the cough and degree of dyspnea, afebrile on two occasions 8 h apart, white blood cell count decreasing, functioning gastrointestinal tract with adequate oral intake). The mortality rate is less than 1% for persons with CAP who do not require hospitalization; however, the mortality rate averages from 12% to 14% among hospitalized patients. Immunization against influenza and increasingly resistant pneumococci can play a critical role in preventing pneumonia, particularly in immunocompromised and older adults.

Take home messages

  1. CAP due to 'typical' pathogens tends to present in a florid fashion; that due to 'atypical' pathogens often manifests in a subacute fashion.
  2. The CRB-65, CURB-65 or PSI scores allow prediction of mortality in patients with CAP.
  3. Antibiotics are the mainstay of therapy; the route (Oral / IV) depends on the severity of infection.
  4. Two sets of blood cultures should be drawn before initiation of antibiotic therapy.
  5. Immunization against influenza and pneumococcus may help prevent pneumonia - particularly in the elderly and the immunocompromised.

Insightful, fun cases to improve your diagnostic skills

Use your detective skills, strengthen fundamentals faster, and access a wealth of knowledge.

  1. Am Fam Physician. 2011 Jun 1;83(11):1299-1306, Diagnosis and Management of Community-Acquired Pneumonia in Adults, Richard R. Watkins, MD, MS, Akron General Medical Center, Akron, Ohio, Tracy L. Lemonovich, MD, University Hospitals Case Medical Center, Cleveland, Ohio.
  2. American Journal of Respiratory and Critical Care Medicine, Vol. 163, No. 7 (2001), pp. 1730-1754, doi: 10.1164/ajrccm.163.7.at1010, Guidelines for the Management of Adults with Community-acquired Pneumonia, Diagnosis, Assessment of Severity, Antimicrobial Therapy, and Prevention, Michael S. NiedermanCo-chair M.D. , Lionel A. MandellCo-chair M.D. , Antonio Anzueto M.D. , John B. Bass M.D. , William A. Broughton M.D. , G. Douglas Campbell M.D. , Nathan Dean M.D. , Thomas File M.D. , Michael J. Fine M.D. , Peter A. Gross M.D. , Fernando Martinez M.D. , Thomas J. Marrie M. D. , Joseph F. Plouffe M.D. , Julio Ramirez M.D. , George A. Sarosi M.D. , Antonio Torres M.D. , Robert Wilson M.D. , and Victor L. Yu M.D.
  3. Clin Infect Dis. 2007 Mar 1;44 Suppl 2:S27-72, Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults, Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM Jr, Musher DM, Niederman MS, Torres A, Whitney CG; Infectious Diseases Society of America; American Thoracic Society.