Aspiration pneumonia

Aspiration pneumonia is diagnosed based on clinical signs or symptoms of pneumonia in a person with a history of, or risk factors for, aspiration.

Chest x-ray will show a new infiltrate; infection usually involves the dependent lung lobe. Sputum culture and Gram stain are usually inconclusive but may identify the infecting organism.

Complications of disease include lung abscess and empyema.

Aspiration pneumonia results from inhalation of oropharyngeal contents into the lower airways that leads to a chemical pneumonitis, lung injury, and resultant bacterial infection. It commonly occurs in patients with risk factors such as impaired conscious level, swallowing dysfunction, and gastrointestinal disease.

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.[1]Bartlett JG, Gorbach SL, Finegold SM. The bacteriology of aspiration pneumonia. Am J Med. 1974 Feb;56(2):202-7. http://www.ncbi.nlm.nih.gov/pubmed/4812076?tool=bestpractice.com 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.[2]El-Solh AA, Pietrantoni C, Bhat A, et al. Microbiology of severe aspiration pneumonia in institutionalized elderly. Am J Respir Crit Care Med. 2003 Jun 15;167(12):1650-4. https://www.atsjournals.org/doi/10.1164/rccm.200212-1543OC http://www.ncbi.nlm.nih.gov/pubmed/12689848?tool=bestpractice.com [3]Marik PE. Pulmonary aspiration syndromes. Curr Opin Pulm Med. 2011 May;17(3):148-54. http://www.ncbi.nlm.nih.gov/pubmed/21311332?tool=bestpractice.com 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.[4]Lanspa MJ, Peyrani P, Wiemken T, et al. Characteristics associated with clinician diagnosis of aspiration pneumonia: a descriptive study of afflicted patients and their outcomes. J Hosp Med. 2015 Feb;10(2):90-6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310822 http://www.ncbi.nlm.nih.gov/pubmed/25363892?tool=bestpractice.com [5]Taylor JK, Fleming GB, Singanayagam A, et al. Risk factors for aspiration in community-acquired pneumonia: analysis of a hospitalized UK cohort. Am J Med. 2013 Nov;126(11):995-1001. http://www.ncbi.nlm.nih.gov/pubmed/24054176?tool=bestpractice.com [6]Mandell LA, Niederman MS. Aspiration pneumonia. N Engl J Med. 2019 Feb 14;380(7):651-63. http://www.ncbi.nlm.nih.gov/pubmed/30763196?tool=bestpractice.com There is also debate on whether aspiration pneumonia is not associated with infection in some patients and instead may represent a chemical pneumonitis.[7]Daoud E, Guzman J. Q: Are antibiotics indicated for the treatment of aspiration pneumonia? Cleve Clin J Med. 2010 Sep;77(9):573-6. http://www.ncbi.nlm.nih.gov/pubmed/20810867?tool=bestpractice.com

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.