To treat or not to treat: Anaerobes in aspiration pneumonia
Click Here to Manage Email Alerts
Aspiration pneumonia is a common diagnosis among patients seen in and out of the hospital. Aspiration pneumonia is estimated to occur in 5% to 15% of patients with community-acquired pneumonia (CAP); however, standard diagnostic criteria for aspiration pneumonia are lacking. Aspiration is the result of impaired swallowing, allowing oral or gastric contents — or both — to enter the lungs. Following an aspiration event, the pathology varies from pneumonitis to pneumonia, lung abscesses or empyema.
Pneumonitis, which is a noninfectious acute chemical lung injury, frequently occurs after patients aspirate gastric contents. However, symptoms generally abate within the first couple of days with only supportive treatment and no antibiotic use. The inflammatory conditions that ensue after aspiration can lead to favorable conditions that allow microbes to grow. Aspiration pneumonia subsequently follows in up to 25% of patients within the next week, characterized by a worsening respiratory status or fever. Unlike pneumonitis, aspiration pneumonia warrants empiric antibiotic treatment to decrease mortality. Both pneumonitis and pneumonia can present with similar symptoms, such as fever, cough, respiratory distress and infiltrates on chest radiography. The gradual onset of symptoms from infection with pneumonia can help distinguish between pneumonitis, which generally has an abrupt onset.
The long-awaited CAP guidelines were published in October 2019. Although there were several important updates, one of the changes compared with previous guidelines is the recommendation of not routinely adding anaerobic coverage for suspected aspiration pneumonia. Since the guidelines have been published, trying to override providers’ training and habits of covering anaerobes in all aspiration pneumonias has been difficult from an antimicrobial stewardship point of view.
Microbiology of aspiration
Historically, anaerobes from the oral cavity or stomach with or without aerobic organisms were the pathogens thought to cause aspiration pneumonia. This premise was based upon studies from the 1970s that showed high rates of anaerobes isolated from these patients, such as Bacteroides species, Prevotella, Fusobacterium species and peptostreptococci. It is thought that these results were probably due to the use of transtracheal aspirates and the inclusion of patients with late-onset disease. These data subsequently led to the widespread use of antianaerobic antibiotics for treatment of aspiration pneumonia.
Recent studies have demonstrated a shift away from anaerobes to organisms that are more common to community- and hospital-acquired pneumonia pathogens. In one study, patients with nursing home-acquired pneumonia who presented to an ED underwent bronchial sampling after intubation. There were 67 pathogens isolated from 55 patients. Gram-negative aerobic bacilli were the most commonly isolated pathogens (49%), followed by anaerobic organisms (16%) and Staphylococcus aureus (12%). Other studies have shown similar results. A study from Japan demonstrated that, of 111 organisms isolated from 62 patients, only 22 (20%) were anaerobes, and enteric gram-negative bacilli predominated. In another randomized trial that compared moxifloxacin with ampicillin-sulbactam for treatment of aspiration pneumonia, anaerobes were isolated in 29.6% of patients with lung abscesses, whereas no anaerobes were found in those with only aspiration pneumonia. The most frequent aerobic organisms in this study were Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Notably, the treatment response was the same in those treated with moxifloxacin or ampicillin-sulbactam.
Treatment
As stated earlier, the current guidelines recommend against adding routine anaerobic coverage in the absence of a lung abscess or empyema. The guidelines do not recommend specific antibiotics for treating community-acquired aspiration pneumonia, so using antibiotics for CAP would be recommended (Table). It should be noted, however, that the recommendations do include agents that have anaerobic coverage, such as amoxicillin/clavulanate, moxifloxacin and ampicillin/sulbactam.
If there is a history of recent hospitalization and receipt of parenteral antibiotics within the last 90 days, antipseudomonal and MRSA coverage can be considered instead of standard CAP treatment. Prior history of isolation of Pseudomonas or MRSA from respiratory cultures would also be a scenario in which coverage of these pathogens up front would be recommended. In this scenario, vancomycin or linezolid in combination with an antipseudomonal cephalosporin, carbapenem or piperacillin/tazobactam would be reasonable options.
Patients with more complicated infections after aspiration such as lung abscess or empyema should be given treatment that includes anaerobe coverage because anaerobic involvement is more common in these infections. Although not mentioned in the guidelines, covering anaerobes may also be warranted in aspiration pneumonia if patients have severe periodontal disease or a necrotizing infection. If cultures were obtained, and once culture results are known, antimicrobials should be de-escalated to provide optimal targeted therapy to help avoid unnecessary broad coverage and decrease adverse consequences of antimicrobial overuse such as Clostridioides difficile infection (CDI). Duration of therapy in aspiration pneumonia is not well studied but is derived from studies in CAP and hospital-acquired pneumonia. Short courses of 5 to 7 days of antibiotics are recommended for patients with a good clinical response. Longer durations will be necessary if empyema, lung abscess or necrotizing pneumonia is present.
Patients with aspiration pneumonia likely have multiple risk factors for developing CDI such as older age, prior hospitalization and antimicrobial use. Antimicrobial use is the only modifiable risk factor for many of our patients as a means to reduce the risk for CDI. Areas for improvement in treating aspiration pneumonia can be achieved by not using antibiotics to treat acute pneumonitis following an aspiration event, avoiding the routine empiric use of antibiotics that target anaerobes when treatment of aspiration pneumonia is necessary and limiting the duration of antimicrobial therapy to the shortest possible period (5 to 7 days) to adequately treat the infection.
- References:
- DiBardino DM, Wunderink RG. J Crit Care. 2015;doi:10.1016/j.jcrc.2014.07.011.
- El-Solh AA, et al. Am J Respir Crit Care Med. 2003;doi:10.1164/rccm.200212-1543OC.
- Mandell LA, Niederman MS. N Engl J Med. 2019;doi: 10.1056/NEJMra1714562.
- Metlay JP, et al. Am J Respir Crit Care Med. 2019;doi:10.1164/rccm.201908-1581ST.
- Ott SR, et al. Infection. 2008;doi:10.1007/s15010-007-7043-6.
- Tokuyasu H, et al. Intern Med. 2009;doi:10.2169/internalmedicine.48.1308.
- For more information:
- Jeff Brock, PharmD, MBA, BCPS-AQ ID, is an infectious disease pharmacy specialist at Mercy Medical Center in Des Moines, Iowa. He can be reached at: jbrock@mercydesmoines.org.
Disclosure: Brock reports no relevant financial disclosures.
Collapse
Click Here to Manage Email Alerts