In this episode, I’ll discuss why the CAP guidelines do not recommend treating most cases of suspected aspiration pneumonia with broadening antibiotic therapy.
Broadening therapy in community-acquired pneumonia to cover potential anaerobes in the case of suspected aspiration pneumonia is a common occurrence. This results in the use of clindamycin or piperacillin-tazobactam when more narrow therapy might otherwise have been chosen.
Examples of patients with CAP that might be suspected of aspiration pneumonia are those from nursing homes, with dementia, or those with a seizure disorder.
While aspiration was not previously addressed head-on in CAP guidelines, new data prompted the 2019 IDSA CAP guideline authors to include the following question:
Question 10: In the Inpatient Setting, Should Patients with Suspected Aspiration Pneumonia Receive Additional Anaerobic Coverage beyond Standard Empiric Treatment for CAP?
The recommendation given, although conditional and based on low-quality evidence is:
We suggest not routinely adding anaerobic coverage for suspected aspiration pneumonia unless lung abscess or empyema is suspected.
One issue with aspiration pneumonia is that aspiration is a very common event, occurring in up to half of the population yet “aspiration pneumonia” lacks a specific definition that separates it from other pneumonia diagnoses.
Simply aspirating GI contents into the lungs does not result in bacterial pneumonia. Instead, gastric acid causes a pneumonitis reaction where symptoms resolve within 1 or 2 days.
While studies from over 40 years ago suggested that anaerobes are present in pneumonia from aspiration, methodological flaws leave the validity of these conclusions in doubt. Much of the basis for the concern for the presence of anaerobes in patients with pneumonia and aspiration histories is a study of 34 patients from 1975. This study split patients into two groups based on whether or not the authors considered them “aspiration-prone”. Anaerobes were isolated in all 17 of the patients who were aspiration-prone as contrasted with only 20% of those who were not.
Flaws in this study that have since been pointed out are the use of trans-tracheal sampling and waiting to evaluate patients late in their disease course may explain why anaerobic pathogens were isolated rather than other patient risk factors regarding aspiration.
Newer studies of acute aspiration events in hospitalized patients have suggested that anaerobic bacteria do not play a major role in the etiology of CAP.
One of these studies was in 1999 by Paul Marik. 143 pneumonia patients were thoroughly cultured using bronchial-alveolar lavage. The authors were able to isolate only one anaerobic organism (nonpathogenic) from this entire group of patients.
Another study from 2003 looked at 95 institutionalized elderly patients with severe aspiration pneumonia. Out of the 67 pathogens identified, anaerobic bacteria comprised only 16%. The authors of this study concluded:
In view of the rising resistance to antimicrobial agents, the importance of adding anaerobic coverage for aspiration pneumonia in institutionalized elders needs to be reexamined.
Both of these studies had been published for several years when the 2007 CAP guidelines were authored, but aspiration pneumonia was not addressed specifically in the old guidelines.
Now in the current iteration in addition to a recommendation against broadening therapy unless lung abscess or empyema is suspected, the guideline authors state:
Increasing prevalence of antibiotic-resistant pathogens and complications of antibiotic use highlight the need for a treatment approach that avoids unnecessary use of antibiotics.
Because of the long-standing belief of many clinicians that patients with aspiration risk factors should receive broader antibiotic therapy, it is likely that these new guideline recommendations will take time and effort to be translated into clinical practice. Pharmacists can assist in this process by providing education and influencing stewardship teams to focus on narrowing anaerobic coverage for patients with CAP when it is not likely to be helpful.
Members of my Hospital Pharmacy Academy have access to my complete breakdown of the CAP guidelines and the treatment of aspiration pneumonia from a pharmacist’s point of view as well as many other resources to help in your practice. To sign up go to pharmacyjoe.com/academy.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.