A lung abscess happens often in patients who are older, where the immune system is weak and where the normal cough reflexes are modified or suppressed. A common mechanism is aspiration of stomach contents by vomiting and aspiration of part of the vomitus with all the bacteria from the pharynx, or gastrointestinal tract.
Often the first step is that aspiration pneumonia develops and out of this a lung abscess can develop. High risk persons are alcoholics at the height of a drinking bout, patients with severe neurological diseases such as MS, stroke, Alzheimers in stage 3, patients with a coma or patients during major surgery when the patient is paralyzed from a general anesthetic. The bacteria that cause a lung abscess are usually anaerobes that stem from the gastrointestinal tract or from the oral cavity or the pharynx.
The feared bacteria are Staphylococcus aureus, a pus bacterium that is devastating to lung tissue due to a lytic enzyme it produces. Intravenous drug users who work with contaminated needles may end up with this bacterium in the lung tissue causing a lung abscess as well.
Signs and symptoms:
The patient usually is sick for several weeks or months with a lack of appetite and the resulting weight loss. A chronic cough is usually present, but may not be so in a debilitated elderly person.
With a smaller abscess that drains well there might be only a low grade fever of 101.5°F (38.5°C). However, in a patient where the abscess is larger and some of the toxins get into the bood stream there would be a much more acute clinical picture with high temperatures of 103°F (39.5°C) or higher. Most of the time the phlegm production is copius and has a foul smell. The physician would detect certain signs such as dullness to percussion in one area of the lung with diminished breath sounds over this area using the stethoscope. In a chronic case where a lung abscess is not diagnosed for several months a thickening of the fingers, called clubbed fingers, can develop as a result of the chronic shortage of oxygen in the tissues.
Treatment consists mainly in giving the appropriate antibiotic therapy. Initially this is given by the intravenous route. Later when the patient is afebrile this can be switched to oral antibiotics. However, it is important that the lung abscess is followed along with repeat imaging studies until it is resolved completely.
This requires often a prolonged antibiotic therapy for 2 to 4 months! This should be done under proper supervision by a physician, preferably by a lung specialist. The choice of the antibiotic is dictated by the culture results. Often the clinician might start the patient on intravenous clindamycin intitally or a combination of penicillin G (or erythromycin) with Flagyl until the culture report is back. At that point a switch to an antibiotic that fits the culture report would be done, if necessary. The death rate of an anaerobic lung abscess is about 15%, if Staphylococcus aureus or Klebsiellae pneumoniae are involved, can be 30 to 50%. Occasionally there might be a case where the antibiotic therapy does not resolve the lung abscess because of underlying lung diseases such as a bronchictasis or an area of atelectasis that gets repeatedly infected. In this case a referral to a thoracic surgeon night be necessary to get an opinion whether surgery would help solve this problem. These cases are rare, but when done in the appropriate patient, can be helpful.