eMedicine Specialties > Emergency Medicine > Pulmonary

Pneumonia, Viral: Differential Diagnoses & Workup

Author: Gloria J Kuhn, DO, PhD, FACEP, Professor, Vice-Chair of Academic Affairs, Dept of Emergency Medicine, Wayne State University School of Medicine; Professor, Department of Internal Medicine, Section of Emergency Medicine, Michigan State University College of Osteopathic Medicine
Contributor Information and Disclosures

Updated: Jun 11, 2009

Differential Diagnoses

Acute Respiratory Distress Syndrome
Pneumonia, Immunocompromised
Asthma
Pneumonia, Mycoplasma
Bronchitis
Chronic Obstructive Pulmonary Disease and Emphysema
Pneumonia, Bacterial

Other Problems to Be Considered

Bronchiolitis
Acute exacerbation of asthma or bronchitis

Workup

Laboratory Studies

  • Because of the difficulty in distinguishing between the various etiologic agents, both viral and bacterial, causing pneumonia, the workup for symptomatic patients with an infiltrate on chest radiograph should include laboratory studies.
  • Viral testing: Rapid antigen detection using RT-PRC can provide results rapidly enough for ED use. Test kits can detect influenza, RSV, rhinoviruses, parainfluenza, and other viruses. Sensitivity for influenza in adults ranges between 50% and 60%, and specificity is greater than 90%. Nasal swabs or washings are easy to obtain. SARS can be diagnosed by RT-PCR or by enzyme-linked immunosorbent assays (ELISAs) specific for SARS. A call to the hospital laboratory is suggested to determine what test is being used and whether a specific viral identification should be requested or whether a general request for viral detection will result in testing for a panel of pathogens. If rapid test results are negative but clinical suspicion is high, cultures can be obtained and the patient treated until results are known. Positive viral identification cannot rule out bacterial co-infection.
  • If Ad 14 is suspected, because of severity of illness and negative bacterial and viral cultures, clinicians should contact their state public health department for aid in testing.10
  • Sputum Gram stains and cultures: Sputum Gram stains are often contaminated with oral pathogens and are difficult to obtain. They are not recommended by the American Thoracic Society or the American College of Emergency Physicians. The Infectious Diseases Society of America recommends obtaining a sputum sample, particularly in hospitalized patients.
  • The utility of blood cultures in patients with pneumonia remains controversial. Local hospital protocols should be consulted to determine which patients with pneumonia and who are candidates for hospitalization should have blood cultures drawn prior to administration of medications. Leukopenia occasionally is present. Patients with SARS can have multiple laboratory abnormalities including lymphopenia (73%), thrombocytopenia (50%), hyponatremia (60%), and elevated levels of lactate dehydrogenase (47%) and C-reactive protein (75%). Elevated lactate dehydrogenase level in patients with SARS is a predictor of mortality.23
  • ABGs may be of great value in identifying hypoxemia in severe disease but are unnecessary in mild or moderate disease. Pulse oximetry should be obtained in all patients.

Imaging Studies

  • No firm guidelines exist for when to obtain a chest radiograph in patients to aid in diagnosing lower respiratory tract infection. Chest pain, dyspnea, and productive cough are some of the indications used by clinicians. The Infectious Diseases Society of America recommends chest radiography to confirm infiltrates when pneumonia is suspected for the following reasons: the severity of disease may be revealed, detection of pneumonia may not be possible on purely clinical grounds, and antibiotics are not useful for treatment of bronchitis. It is recommended that a chest radiograph be obtained in patients with suspected pneumonia, both to find complications, such as pleural effusions, and to discourage the use of antibiotics in healthy patients with bronchitis rather than pneumonia.
    • Antibiotics are recommended for pneumonia, and a chest radiograph is necessary to make this diagnosis.
    • Antibiotics have not been shown to be efficacious in bronchitis.
    • The widespread use of antibiotics in inappropriate situations is leading to drug resistance and may explain the increases in death rates since 1979.
    • Antibiotics can cause adverse drug reactions; thus, they should be avoided when they are not needed. However, if an infiltrate is seen on a chest radiograph, it may be due to viral or bacterial disease or both. In the ED, differentiating the etiology may be impossible.
  • None of the viral etiologies of pneumonia result in pathognomonic findings on chest radiographs, and bacterial pneumonia can not be differentiated from viral pneumonia based on radiographic findings. Of concern was the fact that some patients with SARS had negative findings on chest radiographs but infiltrates were seen on chest CT. Chest radiography may reveal the following findings:
    • Patchy interstitial or alveolar infiltrate, which may be bilateral or involve 2 or more lobes
    • Peribronchial thickening
    • Consolidation
    • Pleural effusion

Procedures

  • Patients with respiratory failure require endotracheal intubation and ventilator support.

More on Pneumonia, Viral

Overview: Pneumonia, Viral
Differential Diagnoses & Workup: Pneumonia, Viral
Treatment & Medication: Pneumonia, Viral
Follow-up: Pneumonia, Viral
References
Further Reading
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References

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Further Reading

Clinical guidelines

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 consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007 Mar 1;44 Suppl 2:S27-72. [335 references] PubMed

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Keywords

viral pneumonia, pneumonia influenza, severe acute respiratory syndrome, SARS, coronavirus, CoV, RSV, respiratory syncytial virus, influenza virus, influenza A, parainfluenza 1, parainfluenza 2, parainfluenza 3, adenovirus, parainfluenza virus, rhinovirus, Hantavirus, cytomegalovirus, CMV, Paramyxovirus species, measles, varicella-zoster virus, Epstein-Barr virus, herpes simplex virus, community-acquired pneumonia, Sin Nombre virus, respiratory illness, pneumococcal vaccines

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Contributor Information and Disclosures

Author

Gloria J Kuhn, DO, PhD, FACEP, Professor, Vice-Chair of Academic Affairs, Dept of Emergency Medicine, Wayne State University School of Medicine; Professor, Department of Internal Medicine, Section of Emergency Medicine, Michigan State University College of Osteopathic Medicine
Gloria J Kuhn, DO, PhD, FACEP is a member of the following medical societies: American College of Emergency Physicians and American Osteopathic Association
Disclosure: Nothing to disclose.

Medical Editor

Michael S Beeson, MD, MBA, FACEP, Professor of Emergency Medicine, Northeastern Ohio Universities College of Medicine and Pharmacy; Attending Faculty, Summa Health System
Michael S Beeson, MD, MBA, FACEP is a member of the following medical societies: American College of Emergency Physicians, Council of Emergency Medicine Residency Directors, National Association of EMS Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Paul Blackburn, DO, FACOEP, FACEP, Program Director, Department of Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of Surgery, University of Arizona
Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Robert E O'Connor, MD, MPH, Professor and Chair, Department of Emergency Medicine, University of Virginia Health System
Robert E O'Connor, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Heart Association, American Medical Association, Medical Society of Delaware, National Association of EMS Physicians, Society for Academic Emergency Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

 
 
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