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 predominantly occurs in older adults. As such, the recommendations in this topic are principally referring to practice in adults.

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 of aspiration pneumonia has changed over the past five decades, and is a continued source of debate. 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 recently, there has been controversy around the role of anaerobes in the pathogenesis of aspiration pneumonia.[2]Bartlett JG. How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy. Infect Dis Clin North Am. 2013 Mar;27(1):149-55. http://www.ncbi.nlm.nih.gov/pubmed/23398871?tool=bestpractice.com ​ The consensus now, according to the British Thoracic Society, is that aspiration pneumonia is commonly polymicrobial, and while aerobic gram-negative bacilli are often over-represented, gram-positive organisms are also commonly isolated.[3]Simpson AJ, Allen JL, Chatwin M, et al. BTS clinical statement on aspiration pneumonia. Thorax. 2023 Feb;78(suppl 1):s3-21. https://thorax.bmj.com/content/78/Suppl_1/s3 http://www.ncbi.nlm.nih.gov/pubmed/36863772?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.