Aspiration pneumonia and primary lung abscess: diagnosis and therapy of an aerobic or an anaerobic infection?

Pneumonia and primary lung abscesses may result from aspiration of infectious material from the oropharyngeal cavity and the upper respiratory tract. Most subjects suffer from an impaired mechanical or immunologic defense, for example alcoholism or dysphagia following stroke. The early course of the disease is uncharacteristic. Necrotizing pneumonia, pulmonary abscesses and the characteristic, foul-smelling, putrid discharge only occur 8-14 days after the initial aspiration event. Although common respiratory pathogens are frequently isolated from the lower airways of these patients, anaerobic bacteria play a pivotal role in cavitary lung disease following aspiration. Anaerobic coverage is therefore a requirement for an adequate antibiotic regimen, and antibacterial activity against common respiratory pathogens appears reasonable in most cases. Aminopenicillins/beta-lactamase inhibitors, newer fluoroquinolones with anaerobic activity (moxifloxacin) and clindamycin have demonstrated equal clinical efficacy in the treatment of aspiration pneumonia and primary lung abscess. Prolonged antibiotic therapy is required in cases with extensive damage of lung tissue. Since antibiotics can provide cure in 80-90% of cases, surgical procedures are limited to severe complications, such as pleural empyema. Cavitary lung disease has a broad differential diagnosis, including aspiration of sterile gastric content (Mendelson syndrome), staphylococcal pneumonia, tuberculosis, primary carcinoma of the lung, metastases and vasculitis.