eMedicine Specialties > Infectious Diseases > Lower Respiratory Tract Infections

Nosocomial Pneumonia: Differential Diagnoses & Workup

Author: Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Contributor Information and Disclosures

Updated: May 28, 2009

Differential Diagnoses

Acute Respiratory Distress Syndrome
Pulmonary Edema, Cardiogenic
Pulmonary Embolism

Workup

Laboratory Studies

All patients with presumed nosocomial pneumonia (NP; also known as hospital-acquired pneumonia [HAP] or health care–associated pneumonia [HCAP]) should undergo testing to rule out conditions that mimic nosocomial pneumonia. The presumptive diagnosis of nosocomial pneumonia is difficult because the diagnosis does not depend on the presence of fever, and leukocytosis is unhelpful. A summary of management strategies is available through a practice guideline provided by the ATS.2

  • White blood cell count
    • A white blood cell (WBC) count is usually suggested but does not yield a specific finding.
    • The WBC count may be normal or elevated in cases of nosocomial pneumonia or conditions that mimic nosocomial pneumonia. A left shift reflects the stress that the patient is being subjected to and neither rules out nor confirms infection. The degree of left shift indicates the degree of stress in the host.
    • Neither leukocytosis nor a normal WBC count favors the diagnosis of nosocomial pneumonia over the diseases that mimic nosocomial pneumonia, as these can produce a similar elevation.
  • Obtain blood cultures as early as possible to retrospectively diagnose infection with hematogenous pathogens.

Imaging Studies

  • Obtain serial chest radiographs to assist in evaluating the progress of the pneumonia and the efficacy of appropriate antimicrobial therapy.
  • Radiographs may also be useful in distinguishing various mimics from actual nosocomial pneumonia. In these patients, CT scanning or spiral CT scanning may be useful.

Other Tests

  • ECGs and ventilation-perfusion scans should eliminate pneumonia mimics. ECGs, cardiac enzymes, and Swan-Ganz readings may rule out left ventricular failure caused by exacerbation of heart failure or new myocardial infarction.
  • Obtain other tests that are related to the possible underlying causes of the pulmonary infiltrates; for example, if lupus pneumonitis is suspected, ask the patient about a history of SLE pneumonitis. Afterward, serologic tests should be performed to assess for SLE.
  • Tests such as arterial blood gas (ABG) studies are merely used to assess the degree of severity of lung dysfunction but are not useful in diagnosing nosocomial pneumonia. Obtain ABGs to help diagnose a diffusion defect related to interstitial lung diseases.

Procedures

  • Bronchoscopic techniques
    • These techniques yield variable sensitivities and specificities, although there are accepted criteria for semiquantitative cultures to improve the diagnostic reliability of bronchoscopically derived cultures.
    • A bronchoscopic bacteriologic strategy has been shown to reduce the short-term mortality risk in one study.

Histologic Findings

Histologic study of lung tissue reveals either necrotizing pneumonia or nonnecrotizing pneumonia, depending on the pathogen. P aeruginosa produces a necrotizing pneumonia with vessel invasion, local hemorrhage, and microabscess formation. Other aerobic gram-negative bacilli produce a polymorphonuclear response at the site of invasion, but microabscess formation and vessel invasion are absent.

More on Nosocomial Pneumonia

Overview: Nosocomial Pneumonia
Differential Diagnoses & Workup: Nosocomial Pneumonia
Treatment & Medication: Nosocomial Pneumonia
Follow-up: Nosocomial Pneumonia
Multimedia: Nosocomial Pneumonia
References
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Further Reading

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Keywords

nosocomial pneumonia, NP, hospital-acquired pneumonia, HAP, healthcare-associated pneumonia, health care–associated pneumonia, HCAP, ventilator-associated pneumonia, VAP

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Contributor Information and Disclosures

Author

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

Wesley W Emmons, MD, FACP, Assistant Professor, Department of Medicine, Thomas Jefferson University; Consulting Staff, Infectious Diseases Section, Department of Internal Medicine, Christiana Care, Newark, DE
Wesley W Emmons, MD, FACP is a member of the following medical societies: American College of Physicians, American Medical Association, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, and International AIDS Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Ronald A Greenfield, MD, Professor, Department of Internal Medicine, Section of Infectious Diseases, University of Oklahoma College of Medicine
Ronald A Greenfield, MD is a member of the following medical societies: American College of Physicians, American Federation for Medical Research, American Society for Microbiology, Central Society for Clinical Research, Infectious Diseases Society of America, Medical Mycology Society of the Americas, Phi Beta Kappa, Southern Society for Clinical Investigation, and Southwestern Association of Clinical Microbiology
Disclosure: Pfizer Honoraria Speaking and teaching; Gilead Honoraria Speaking and teaching; Ortho McNeil Honoraria Speaking and teaching; Wyeth Honoraria Speaking and teaching; Abbott Honoraria Speaking and teaching; Astellas Honoraria Speaking and teaching; Cubist  Speaking and teaching

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD, Professor, Stewart G Wolf Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center
Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physician Executives, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Federation for Clinical Research, American Medical Association, American Society for Microbiology, Association of Professors of Medicine, Association of Program Directors in Internal Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

 
 
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