Why this matters:
Let me briefly tell you a story that was published in JAMA: A patient was admitted to the hospital for seizures and intubated for airway protection. CXR showed infiltrates so patient was started on antibiotics and despite rapid improvement in 24 hours, received a 7 day course of antibiotics ‘just in case’. He was re-admitted to the hospital a week later with severe C.diff infection that did not improve despite adequate treatment and died in the hospital.
Antibiotics can cause harm. Sometimes they can be life-saving but risks and benefits need to be weighed each time.
Did that patient have aspiration pneumonia or aspiration pneumonitis?
Aspiration pneumonia = clinical evidence of pneumonia due to a bacterial infection
Aspiration pneumonitis = chemical lung injury due to gastric acid in the lower airways
– 13-26% can progress to develop bacterial pulmonary superinfections
|Aspiration pneumonitis||Aspiration pneumonia|
|Fever||Low grade only/-||+/-|
|CXR infiltrate||Resolves w/in 48-72 hrs||Takes weeks to resolve|
|Sputum culture||negative||Positive/negative; purulent|
|Time to sx resolution||Quick (48-72 hrs)||Slow (>72 hrs)|
|Bronchoscopy||Bronchial erythema||Bronchial purulence|
Risk factors for aspiration pneumonia:
- Risk of aspiration
- altered mental status
- esophageal disorders (inc. GERD)
- neurological disorders that promote dysphagia (i.e. ALS, stroke, etc.)
- heavy alcohol use
- recent intubation, bronchoscopy, upper endoscopy, or NG tube (any mechanical disruption of the natural mechanisms that prevent aspiration)
- Risk of aspirating increased inoculum of bacteria
- poor dental hygiene
- acid-suppressive medications (H2-blockers, PPIs) – loss of gastric acidity allows more pathogens to survive in the stomach ⇒ higher inoculum is present when aspiration occurs
Prevention of aspiration:
- aspiration is pretty common in small amounts
- it becomes pathogenic when a patient has chronic, recurrent aspiration or when the inoculum of bacteria in the aspirate increases to reach the threshold for causing chemical lung injury +/- bacterial infection.
- there are not enough data to suggest that any interventions help to prevent recurrent aspiration
- Flora – oral cavity and stomach (strep spp., H.flu, anaerobes, aerobic GNR)
- Community: strep spp., haemophilus influenza > anaerobes
- Hospital/long term care facilities:
staphylococcus aureus, aerobic gram-neg bacilli >> anaerobes
– these pathogens colonize the oral cavity
– Staph and aerobic GNR are more likely to be the infectious cause in these patients due to their intrinsic higher pathogenicity
- Anaerobes – peptostreptococcus, fusobacterium nucleatum, Prevotella, Bacteroides spp.
- Most of these infections are polymicrobial
– usually a clinical diagnosis
– sputum culture may help to isolate aerobic gram-neg bacilli or staph aureus to alter antimicrobial therapy
– “anaerobic bacteria are virtually never detected in pulmonary infections due to lack of access to specimens that are uncontaminated with the normal flora of the upper airways” (UpToDate) and we also do not culture sputum anaerobically so obligate anaerobes would not be able to grow in a typical sputum culture.
– CXR should be ordered to assess for evidence of an infiltrate
- Imaging: does location of infiltrate matter? YES.
- aspiration in sitting position: lower lobes
- aspiration in lying position: lower lobes OR posterior segment of upper lobes
- consider repeat CXR to evaluate for resolution of pulmonary infiltrate if patient has clinically improved within 48 hours ⇒ if CXR infiltrate resolved and symptoms resolved, likely pneumonitis and can discontinue the antibiotics.
So far, no trials looking at the utility of pro-calcitonin in differentiating aspiration pneumonitis vs. pneumonia that I know of, although would be a great study to do!
When to suspect anaerobic involvement
- indolent course
- risk factors for aspiration
- absence of rigors
- no main isolated pathogen on sputum cultures
- putrid odor sputum
- evidence of periodontal disease
- imaging shows cavitation/necrosis or empyema
1. To treat or not to treat
- It seems difficult to imagine coming into a patient’s room who is in respiratory distress with a leukocytosis and possible fever, and deciding to withhold antibiotics. At that time, everyone will likely start antibiotics.
- Consider clinically re-evaluation at 48 hours – if CXR infiltrates and symptoms have resolved, it’s likely aspiration pneumonitis and you can probably stop antibiotics
2. Anaerobes: to treat or not to treat
- community-acquired: always treat for anaerobes in addition to other common pathogens (see above)
- hospital-acquired: consider treating if patient has poor dentition (that predisposes them to pathogenic anaerobic infections)
3. Antibiotic regimens (with anaerobic coverage)
a) Amoxicillin-clavulanate or Ampicillin-sulbactam
b) Ceftriaxone + metronidazole
c) Clindamycin (if penicillin/cephalosporin allergic, not ideal regimen due to high resistance rates to certain pathogens)
- Hospital-acquired or recent history of antibiotics – cover for drug-resistant pathogens as well
a) Vancomycin + Piperacillin-tazobactam
b) Vancomycin + Carbapenem (if history of MDR pathogens)
- Duration – 7 days for uncomplicated pneumonia
*For complicated pneumonia, duration of antibiotics will depend on the complication as well as patient’s clinical status and rate of recovery
- ARDS (can happen both in pneumonitis and pneumonia)
- Lung abscess
- Aspiration pneumonitis ≠ Aspiration pneumonia
- Re-evaluate patient in 48 hours and decide whether patient needs to continue antibiotics
- Anaerobes are less likely to play a pathogenic role in hospital-acquired pneumonia (consider treatment for anaerobes if patient has poor dentition)
1. Bartlett, J. G. 2017. Aspiration pneumonia in adults. Uptodate.
2. Finegold, S.M. 1991. Aspiration Pneumonia. CID. 13(9), S737-S742. DOI: 10.1093/clinids/13.Supplement_9.S737
3. Mandell, L. A. et al. 2007. IDSA guidelines for CAP. Section on aspiration pneumonia. 2007. CID. 44(S2): S27-72. DOI: 10.1086/511159
4. Dragan, V. et al. 2018. Prophylactic antimicrobial therapy for acute aspiration pneumonitis. CID. DOI: 10.1093/cid/ciy120
5. Loeb, M.B. et al. 2003. Interventions to prevent aspiration pneumonia in older adults: a systematic review. Journal of American Geriatric Society. 51(7):1018.
DOI: Joundi, R.A. et al. 2015. Antibiotics “Just-In-Case” in a Patient with aspiration pneumonitis. JAMA Internal Medicine: Teachable moment – Less is more. 175(4); 489-490. DOI:10.1001/jamainternmed.2014.8030