Clinical Guidelines for Family Physicians

Guideline: Diagnosis and treatment of adults with community-acquired pneumonia


A new guideline has been published to update the 2007 guidelines for the management of adults with community-acquired pneumonia (CAP).

Dr. Tina Chuong (left), of Abington (Pa.) Jefferson Health, and Dr. Neil Skolnik of Jefferson Medical College, Philadelphia, and Abington Jefferson Health

Dr. Tina Chuong (left) and Dr. Neil Skolnik

The practice guideline was jointly written by an ad hoc committee of the American Thoracic Society and Infectious Diseases Society of America. CAP refers to a pneumonia infection that was acquired by a patient in his or her community. Decisions about which antibiotics to use to treat this kind of infection are based on risk factors for resistant organisms and the severity of illness.


Traditionally, CAP is caused by common bacterial pathogens that include Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Staphylococcus aureus, Legionella species, Chlamydia pneumonia, and Moraxella catarrhalis. Risk factors for multidrug resistant pathogens such as methicillin-resistant S. aureus (MRSA) and Pseudomonas aeruginosa include previous infection with MRSA or P. aeruginosa, recent hospitalization, and requiring parenteral antibiotics in the last 90 days.

Defining severe community-acquired pneumonia

The health care–associated pneumonia, or HCAP, classification should no longer be used to determine empiric treatment. The recommendations for which antibiotics to use are linked to the severity of illness. Previously the site of treatment drove antibiotic selection, but since decision about the site of care can be affected by many considerations, the guidelines recommend using the CAP severity criteria. Severe CAP includes either one major or at least three minor criteria.

Major criteria are:

  • Septic shock requiring vasopressors.
  • Respiratory failure requiring mechanical ventilation.

Minor criteria are:

  • Respiratory rate greater than or equal to 30 breaths/min.
  • Ratio of arterial O2 partial pressure to fractional inspired O2 less than or equal to 250.
  • Multilobar infiltrates.
  • Confusion/disorientation.
  • Uremia (blood urea nitrogen level greater than or equal to 20 mg/dL).
  • Leukopenia (white blood cell count less than 4,000 cells/mcL).
  • Thrombocytopenia (platelet count less than 100,000 mcL)
  • Hypothermia (core temperature less than 36º C).
  • Hypotension requiring aggressive fluid resuscitation.

Management and diagnostic testing

Clinicians should use the Pneumonia Severity Index (PSI) and clinical judgment to guide the site of treatment for patients. Gram stain, sputum, and blood culture should not be routinely obtained in an outpatient setting. Legionella antigen should not be routinely obtained unless indicated by epidemiological factors. During influenza season, a rapid influenza assay, preferably a nucleic acid amplification test, should be obtained to help guide treatment.

For patients with severe CAP or risk factors for MRSA or P. aeruginosa, gram stain and culture and Legionella antigen should be obtained to manage antibiotic choices. Also, blood cultures should be obtained for these patients.

Empiric antibiotic therapy should be initiated based on clinical judgment and radiographic confirmation of CAP. Serum procalcitonin should not be used to assess initiation of antibiotic therapy.


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