Are antibiotics indicated for the treatment of aspiration pneumonia?

PRIMARY BACTERIAL ASPIRATION PNEUMONIA

Primary bacterial aspiration pneumonia—ie, caused by bacteria residing in the upper airways and stomach gaining access to lower airways through aspiration in small or large amounts—is the most common form of aspiration pneumonia, although the actual episode of aspiration is seldom observed.

Signs of bacterial pneumonia

Primary bacterial aspiration pneumonia bears the hallmarks of bacterial pneumonia.¹² The clinical picture is more indolent than chemical pneumonitis and includes cough, fever, and putrid sputum, mainly in patients who have clinical conditions predisposing to aspiration (eg, coma, stroke, alcoholism, poor dentition, tube feedings).^1,12,20

The characteristic signs on chest radiography are infiltrates involving mainly the lung bases (the right more then the left). If untreated or inadequately treated, complications such as lung abscess, empyema, bronchiectasis, and broncopleural fistula are common.²³

Are aerobic organisms replacing anaerobic ones in the community?

The causative organisms in community-acquired aspiration pneumonia are still debated despite abundant research. Older studies^1,24,25 found mostly anaerobic organisms (pepto-streptococci, peptococci, Fusobacterium, Prevotela, Bacteroides) as the underlying pathogens, whereas more recent studies^16,26,27 found mostly aerobic organisms (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Enterobacteriaceae) and failed to recover anaerobic organisms. These discrepancies may be the result of different techniques used to isolate organisms: older studies used transtracheal sampling, and transtracheal aspirates may be easily contaminated or colonized by oropharyngeal flora; more recent studies used protected specimen brushes to collect lower-airway specimens.²

In addition, the pathogenic organisms that predominate in community-acquired aspiration pneumonia, as listed above, are different from those most often found in nosocomial cases; gram-negative bacilli (Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli) are most often isolated in patients with aspiration pneumonia acquired in hospitals and nursing homes.^16,27,28S aureus also is an important causative organism in nosocomial cases.^16,28

Knowing the causative organisms in bacterial aspiration pneumonia is important for guiding antimicrobial therapy.

Antibiotics are required for bacterial aspiration pneumonia

A course of antibiotics is required for bacterial aspiration pneumonia. While there are no definitive recommendations for the duration of treatment, 7 to 8 days is probably appropriate in uncomplicated cases (ie, no lung abscess, empyema, bronchopleural fistula).^22,29 Patients who have complications may need drainage of abscesses or empyema along with a longer duration of antibiotic therapy until clinical and radiographic signs improve.

For community-acquired cases of aspiration pneumonia, a number of antibiotics have proven effective:

• Clindamycin (Cleocin) is still the agent most commonly used, although it lacks gram-negative bacterial coverage.
• Beta-lactam penicillins and newer quinolones have been used successfully.^2,29–31 In addition to covering the previously mentioned bacteria, these antibiotics have the added benefit of covering anaerobic bacteria.
• Metronidazole (Flagyl) should not be used alone because it has a higher clinical failure rate.^32,33

For nosocomial aspiration pneumonia, giving a broad-spectrum antibiotic empirically is warranted. Beta-lactam penicillins with extended gram-negative coverage, carbapenems, or monobactams in combination with an anti-staphylococcal drug have been advocated for nosocomial aspiration.^2,22 A strategy of broad-spectrum coverage followed by narrowing or de-escalating coverage according to lower respiratory tract cultures is encouraged.^21,22,34

SECONDARY BACTERIAL INFECTION OF CHEMICAL PNEUMONITIS

Nearly 25% of patients with chemical pneumonitis improve initially, then show clinical deterioration secondary to superimposed bacterial infection.¹³ Chest radiographs show worsening of initial infiltrates or the development of new ones. The causative organisms and treatment depend on whether the superimposed infection is community-acquired or nosocomial, as is the case in primary bacterial aspiration pneumonia.

PREVENTING ASPIRATION

Measures should be taken to prevent aspiration pneumonia and chemical pneumonitis, especially in institutionalized patients at high risk.¹²

Elevation of the head of the bed while feeding, dental prophylaxis, and good oral hygiene are known to reduce the incidence of these problems.^35–37

A swallowing evaluation for patients with dysphagia can identify those at higher risk of aspiration. These patients may be candidates for postural adjustments, diet modification, strengthening, and other measures offered by the speech and language pathology teams to improve swallowing physiology, biomechanics, safety, and endurance.^2,35

Although percutaneous endoscopic gastrostomy tubes are often placed in patients who have aspirated or who are at high risk of aspiration, they do not protect against aspiration, nor do orogastric or nasogastric tubes.³⁸

To date, we have no evidence that prophylactic antibiotic therapy prevents bacterial aspiration pneumonia. In addition, this practice encourages the development of resistant organisms.^19,39,40