How should aspiration pneumonia be treated?

How should aspiration pneumonia be treated?  Is anaerobic coverage required?

The concept of aspiration pneumonia and anaerobic coverage is a complex, controversial topic.  Like most controversial topics, there is paucity of evidence, and the literature that does exist is controversial.

IDSA Guidelines

The 2007 IDSA community-acquired pneumonia guidelines offer the following (unreferenced and poorly substantiated) comments regarding aspiration pneumonia:1

Anaerobic coverage is clearly indicated only in the classic aspiration pleuropulmonary syndrome […] or after seizures in patients with concomitant gingival disease or esophogeal motility disorders

Antibiotic trials have not demonstrated a need to specifically treat [anaerobic] organisms in the majority of CAP cases.

The guidelines later describe the most common pathogens for aspiration pneumonia as gram-negative enteric pathogens and oral anaerobes.  For these pathogens, the guidelines recommend the following antimicrobial coverage:

  • ß-lactam/ß-lactamase inhibitor (with clindamycin?).  These include piperacillin/tazobactam (Zosyn), ticarcillin/clavulanate (Timentin), ampicillin/sulbactam (Unasyn), or amoxicillin/clavulanate (Augmentin)
  • Alternative antimicrobials: carbapenem

While guidelines can be incredibly helpful, these IDSA guidelines offer little in supported, referenced literature for these recommendations.  In fairness, however, these are community-acquired pneumonia, not aspiration pneumonia, guidelines.

Evidence for Anaerobes – El-Solh et al (2003)

The IDSA CAP guidelines have a single reference for their aspiration pneumonia recommendations.2  In this manuscript by El-Solh et al, 95 long-term care facility patients admitted to an ICU for suspected severe pneumonia were prospectively studied.  The study only required risk factors for oropharyngeal aspiration (eg, dysphagia) — witnessed or strongly suspected aspiration was not required. Because of the inclusion criteria, the study inclusion may have been a hybrid between aspiration pneumonia and healthcare-associated pneumonia (HCAP).

Bacteroides fragilis isolated from a blood culture obtained from a patient with an abdominal abscess. Isolate was sensitive to Metronidazole.The study collected bronchoalveolar lavage (BAL) samples on all patients.  Of the 95 patients, 54 (57%) had a positive BAL result.  Gram-negative enteric bacilli were most common (49%), followed by anaerobes (16%) and S. aureus (12%).  22% of positive cultures were polymicrobial.

On the surface, the study implicates anaerobes as an important pathogen in aspiration pneumonia.  It is important to remember, however, that the study had no method of distinguishing aspiration-risk pneumonia and HCAP.  Furthermore, a positive anaerobic culture may not necessarily indicate a pathogenic organism.  This idea is supported by the fact that seven patients with anaerobic pathogens received inappropriate anaerobic therapy, but six of the seven showed clinical improvement.

An Alternative View to the IDSA Guidelines

A “1-minute consult” review paper, published by Daoud et al, provides a more detailed examination of aspiration pneumonia than the IDSA CAP guidelines.3  I love that the paper distinguishes three different forms of “aspiration pneumonia” that are commonly lumped together: chemical pneumonitis, primary bacterial aspiration, and secondary bacterial infection of pneumonitis.

Chemical Pneumonitis

Includes cases in which aspiration of sterile stomach contents causes inflammation and pneumonitis.  In most cases (60%), the symptoms of dyspnea, cough, hypoxia, and low-grade fever resolve over 2-4 days.  About 15% of cases will have rapid progression to hypoxic respiratory failure, and about 25% will initially improve but worsen due to secondary bacterial infection.  Because chemical pneumonitis can be difficult to distinguish from bacterial pneumonia, antibiotics are commonly used, although the practice is very controversial.  In general, there is no evidence to support the use of antibiotics for chemical pneumonitis to improve clinical outcomes.

Primary Bacterial Aspiration

As described in the El-Solh paper, small aspiration of oropharyngeal contents is another term under the “aspiration pneumonia” umbrella.  Usually this form of aspiration is unwitnessed, but is highly suspected in patients with risk factors for microaspiration (eg, stroke, dysphagia).  The clinical presentation is similar to a classic community-acquired pneumonia.  It is unclear whether the antibiotic regimen should deviate from the traditional CAP or HCAP regimens.

Secondary Bacterial Infection of Chemical Pneumonitis

There is even less evidence supporting the optimal antimicrobial regimen for patients with chemical pneumonitis and initial improvement, but clinical deterioration days later.  Antibiotics are required, and the regimen likely mirrors that of primary bacterial aspiration, but there is little/no evidence for this subset of aspiration pneumonia.

Which antibiotics should be used for aspiration pneumonia?

As with most great questions, there is no clear answer to the optimal antibiotic regimen for aspiration pneumonia.  In patients with primary or secondary bacterial aspiration pneumonia (not chemical pneumonitis), the following recommendations may be considered:1,3,4

  • The risks of anaerobic infection in aspiration pneumonia are largely overstated.  The data are very weak implicating anaerobes as pathogenic bacteria in aspiration pneumonia, and there is even less data supporting improvement in clinical outcomes with anaerobic coverage.
  • Most data describing anaerobes for aspiration pneumonia was done decades ago in patients with abscesses, necrotizing pneumonia, or empyema.  The addition of anaerobic coverage with clindamycin or metronidazole may be appropriate in these patients.
  • In general, the same antibiotics for community-acquired or nosocomial/HCAP (depending on onset and risk factors) are likely appropriate for patients with aspiration pneumonia.  The addition of anaerobic coverage is unlikely to be necessary in most patients.


  1. Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44 Suppl 2:S27-72. PMID 17278083.
  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;167(12):1650-4. PMID 12689848.
  3. Daoud E, Guzman J. Q: Are antibiotics indicated for the treatment of aspiration pneumonia? Cleve Clin J Med. 2010;77(9):573-6. PMID 20810867.
  4. Marik PE. Aspiration pneumonitis and aspiration pneumonia. N Engl J Med. 2001;344(9):665-71. PMID 11228282.  Excellent editorial and response available at 11407356.

Photos by isafmedia and nathanreading

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