Aspiration Pneumonia in Older Adults
Aspiration pneumonia refers to an infection of the lung parenchyma in an individual that has inhaled a bolus of endogenous flora that overwhelms the natural defenses of the respiratory system. While there are not universally agreed upon criteria, the diagnosis can be made in patients with the appropriate risk factors and clinical scenario, in addition to a radiographic or an ultrasonographic image of pneumonia in the typical dependent lung segment. Treatment options for aspiration pneumonia vary based on the site of acquisition (community-acquired aspiration pneumonia [CAAP] versus healthcare-associated aspiration pneumonia [HCAAP]), the risk for multidrug-resistant (MDR) organisms, and severity of illness. Hospitalized CAAP patients without severe illness and with no risk for MDR organisms or Pseudomonas aeruginosa (PA) can be treated with standard inpatient community-acquired pneumonia therapy covering anaerobes. Patients with CAAP and either of the following—risk factors for MDR pathogens, septic shock, need for an intensive care unit (ICU) admission, or mechanical ventilation—can be considered for broader coverage against anaerobes, methicillin-resistant Staphylococcus aureus (MRSA), and PA. Severe aspiration pneumonia that originates in a long-term care facility or HCAAP with one or more risk factors for MDR organisms should be considered for similar treatment. HCAAP with one or more risk factors for MDR organisms or PA, plus septic shock, need for ICU admission or mechanical ventilation should receive double coverage for PA in addition to coverage for MRSA and anaerobes. Multiple gaps in current understanding and management of aspiration pneumonia require future research, with a particular focus on antibiotic stewardship.
© 2019 Society of Hospital Medicine
Therapeutic Strategies
The management of aspiration pneumonia has evolved significantly since it was first studied in the 1970s because of the development of antibiotic resistance patterns, newer antibiotics, and increasing information on the diversity of pathogens involved in each subset of aspiration syndromes. The antimicrobial treatment of aspiration pneumonia was classically directed against anaerobic pathogens; treatment of these infections, however, was extrapolated from studies of pulmonary abscesses and other anaerobic pulmonary infections.
A randomized controlled trial in the mid-1980s comparing penicillin and clindamycin demonstrated a significantly improved cure rate in the clindamycin group.23 A follow-up study in 1990 implicated a significant number of penicillin-resistant Bacteroides infections—the majority of these infections were subsequently reclassified as Prevotella melaninogenica—as the cause for high rates of penicillin resistance in lung abscesses and necrotizing pneumonias, further supporting clindamycin as the treatment of choice for these infections.24 Amoxicillin-clavulanic acid (IV and PO regimens), studied in the treatment of community-acquired necrotizing pneumonia/lung abscess, shows good efficacy as well.25 This study also attempted to elucidate the underlying causative organisms in these patients. Organisms associated with CAP as well as anaerobic organisms were isolated, giving more credence to the idea of broader coverage for aspiration pneumonia.
Community-Acquired Aspiration Pneumonia/Healthcare-Associated Aspiration Pneumonia
The importance of making a diagnostic distinction between CAAP versus HCAAP is critical for management strategies. A prospective population-based study demonstrated that ICU length of stay and 30-day mortality is highest for HCAAP, followed by CAAP, and lastly for those with CAP.9 Although some studies use different nomenclature for identifying aspiration pneumonia patients at risk for a wider array of microorganisms, we attempt to standardize the language by using HCAAP. The literature on nonaspiration pneumonia is changing from terms such as CAP and healthcare-associated pneumonia (HCAP) to pneumonia with the risk of MDR organisms. One study proposed a new treatment algorithm for CAP based on the presence or absence of the following six risk factors: prior hospitalization of greater than or equal to two days in the preceding 90 days, immunosuppression, previous antibiotic use within the preceding 90 days, use of gastric acid-suppressive agents, tube feeding, and nonambulatory status.26 A similar approach proposed years earlier for HCAP patients found the following to be risk factors for MDR organisms: hospitalization in the past 90 days, antibiotic therapy in the past six months, poor functional status as defined by activities of daily living score, and immune suppression.27 Other factors, such as structural lung disease, that increase the risk of organisms resistant to standard antibiotic treatment regimens28-31 should be considered in aspiration pneumonia as well. Aspiration pneumonia is following a similar trajectory where the risk of MDR organisms is taking precedence over the environment of acquisition. The final nomenclature will allow the healthcare provider to understand the organisms that need to be targeted when choosing an appropriate antibiotic treatment regimen.
There is evidence supporting the premise that CAAP and nursing home patients with no risk factors for MDR organisms can be treated with standard regimens used for patients with CAP. A prospective cohort study in 2014 did not show any statistically significant differences in clinical outcomes in nursing and healthcare-associated aspiration pneumonia patients (with no risks of MDR organisms) treated with azithromycin versus ampicillin/sulbactam. However, only 36 patients were included in the azithromycin arm, and the therapeutic choices were made by the treating physician.32
A prospective study of 95 long-term care residents reported that of those patients admitted to the ICU with severe aspiration pneumonia, the causative organisms are gram-negative enteric bacilli in 49% of isolates, anaerobes in 16%, and Staphylococcus aureus in 12%.22 This study mentioned that six of seven anaerobic pneumonia cases had inadequate anaerobic coverage yet were effectively treated; based on the organisms represented, however, the antibiotics administered did provide some coverage.22 Prevotella was one of the common anaerobic organisms that could be treated by levofloxacin or ceftriaxone/azithromycin, possibly explaining the success of azithromycin in the study quoted previously.22,32 Therefore, although anaerobic organisms still need to be considered, some may be treated by traditional CAP coverage.22
In a 2005 randomized prospective study of 100 patients aged 71 to 94 years, clindamycin was found to have clinical efficacy equivalent to ampicillin-sulbactam and panipenem in the treatment of mild-to-moderate aspiration pneumonia.33 Most patients in this study are nursing home residents, and 53% of sputum cultures in the clindamycin arm grew gram-negative rods. In contrast to the previous study, the significance of gram-negative rod infections in this population of patients, with less severe infections, is called into question, as clindamycin has no coverage against these organisms. This premise is supported by a more recent study using azithromycin in nursing and healthcare-associated aspiration pneumonia patients, mentioned previously.32 Taken together, these three studies suggest that the severity of aspiration pneumonia may be a risk factor that needs to be taken into account when considering broad-spectrum antimicrobial coverage.
While further research is needed to validate treatment approaches, based on the current literature we propose the following:
CAAP requiring hospitalization but without any of the following-risk for PA or MDR organisms, septic shock, the need for ICU admission, or mechanical ventilation-can be treated with standard CAP therapy that covers anaerobes.26,32-34 Patients with CAAP and either of the following—risk factors for MDR organisms, septic shock, need for ICU admission, or mechanical ventilation—should be considered for broader coverage with vancomycin or linezolid, antipseudomonal antibiotics, and anaerobic coverage. CAAP with specific risk for a PA infection should be considered for two antipseudomonal antibiotics (where only one can be a beta-lactam antibiotic, and one has anaerobic coverage).
Severe HCAAP without risk for MDR organisms or PA but with any of the following-septic shock, ICU admission, or mechanical ventilation-can be treated based on the 2016 Infectious Diseases Society of America guideline recommendation for hospital-acquired pneumonia, with a regimen that also provides adequate anaerobic coverage.35 If patients have HCAAP with one or more risk factors for MDR organisms, no septic shock, and no need for ICU admission or mechanical ventilation, provide coverage with a similar regimen. In contrast, HCAAP with risk factors for PA or severe HCAAP causing septic shock, requiring ICU admission, or needing mechanical ventilation, which occurs in the setting of one or more risk factors for MDR organisms, or structural lung disease, should receive two antipseudomonal antibiotics (where only one can be a beta-lactam antibiotic and one has anaerobic coverage) in addition to vancomycin or linezolid.
A recent systematic review demonstrates the paucity of studies of ideal methodologic design which complicates the ability to recommend, with confidence, one guideline-based antimicrobial regimen over another.36 Future studies may determine that despite the severity of the infection, if patients do not carry any risk for MDR pathogens or PA, they may only require CAAP coverage. When a patient presents with an acute infection, it is prudent to review previous cultures, and although it may be necessary to treat with broad-spectrum antibiotics initially, it is always important to narrow the spectrum based on reliable culture results. If future studies support the results of many studies cited in this article, we may be using fewer antibiotics with narrower spectrums in the near future.
