Diagnosis is based on clinical signs or symptoms of pneumonia in a person with a history or risk factors for aspiration.
Sputum or tracheal Gram stain reveals mixed flora.
Infection usually involves the dependent lung lobe.
Complications of disease include lung abscess and empyema.
Aspiration pneumonia results from inhalation of oropharyngeal contents into the lower airways that leads to lung injury and resultant bacterial infection. It commonly occurs in patients with altered mental status who have an impaired gag or swallowing reflex.
The bacteriology and presentation of aspiration pneumonia have changed over the past five decades. Older studies characterised an anaerobic pleuropulmonary syndrome, with necrotising pneumonia, putrid sputum, and abscess formation as a result of the presence of anaerobic bacteria.  More recent literature suggests that aspiration pneumonia resulting from anaerobic bacteria is less common than previously thought, and often is not distinct from pneumonia caused by aerobic bacteria.   There is debate on whether aspiration pneumonia represents a distinct entity from typical pneumonia, or whether it is one end of the spectrum of pneumonia syndromes.   Typical pneumonia can also occur from microaspiration of oronasopharyngeal contents, and can present with similar microbiology and clinical course as aspiration pneumonia, as well as needing similar treatment.
Adjunct Assistant Professor
Division of Pulmonary and Critical Care Medicine
Intermountain Medical Center
University of Utah
Salt Lake City
MJL declares that he has no competing interests.
Dr Michael J. Lanspa would like to gratefully acknowledge Dr Richard Kanner and Dr Krishna Sundar, previous contributors to this monograph. DK and KS declares that they have no competing interests.
Consultant Respiratory Physician
Department of Respiratory Medicine
Royal Brompton Hospital
TM has received research funding from the Wellcome Trust and GlaxoSmithKline. He has acted as a paid consultant to GSK, Actelion, and Respironies.
Chief of Pulmonary and Critical Care
King Hussein Cancer Center
FH declares that he has no competing interests.
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