Abstract

Aspiration pneumonia is a type of lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complications may include lung abscess. Some include chemical pneumonitis as a subtype, which occurs from acidic but non-infectious stomach contents entering the lungs, while other do not.

Infection can be due to a variety of bacteria. Risk factors include decreased level of consciousness, problems with swallowing, alcoholism, tube feeding, and poor oral health. Diagnosis is typically based on the presenting history, symptoms, chest X-ray, and sputum culture. Differentiating from other types of pneumonia may be difficult.

Treatment is typically with antibiotics such as clindamycin, meropenem, ampicillin/sulbactam, or moxifloxacin. For those with only chemical pneumonitis antibiotics are not typically required. Among people hospitalized with pneumonia, about 10% are due to aspiration. It occurs more often in older people, especially those in nursing homes. Both sexes are equally affected.

Causes

Aspiration pneumonia is often caused by a defective swallowing mechanism, often due to a neurological disease or as the result of an injury that directly impairs swallowing or interferes with consciousness. Examples of the former are stroke, Parkinson's disease, and multiple sclerosis, and examples of the latter are some types of dementia, seizures, intoxication, and general anaesthesia. For many types of surgical operations, patients are therefore instructed to take nothing by mouth (nil per os, abbreviated as NPO) for at least four hours before surgery.

Causes | Risk factors

Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy. Both causes may be present with similar symptoms.

Causes | Implicated bacteria

When bacteria are implicated, they are usually aerobic:

- "Streptococcus pneumoniae"

- "Staphylococcus aureus"

- "Haemophilus influenzae"

- "Pseudomonas aeruginosa"

They may also be admixed with anaerobic bacteria oral flora:

- "Bacteroides"

- "Prevotella"

- "Fusobacterium"

- "Peptostreptococcus"

Location

The location is often gravity dependent, and depends on the patient position. Generally, the right middle and lower lung lobes are the most common sites affected, due to the larger caliber and more vertical orientation of the right mainstem bronchus. Patients who aspirate while standing can have bilateral lower lung lobe infiltrates. The right upper lobe is a common area of consolidation in alcoholics who aspirate in the prone position.

Diagnosis

Aspiration pneumonia is typically diagnosed by a combination of clinical circumstances (a debilitated or neurologically impaired person), radiologic findings (an infiltrate in the proper location), and sometimes with the help of microbiologic cultures. Some cases of aspiration pneumonia are caused by aspiration of food particles or other particulate substances like pill fragments; these can be diagnosed by pathologists on lung biopsy specimens.