Clinical History
A 55-year-old female presents with severe dyspnoea, a productive cough and oral candidiasis. She is immunosuppressed with a history of rheumatoid arthritis being treated with steroids and cyclophosphamide. Sputum cultures grew Staphylococcus aureus. She was commenced on appropriate therapy but died shortly after admission.
Pathology
The right lung has been bisected. There are multiple irregular abscess cavities visible. The largest of these, in the apex of the lower lobe, measures 4 × 3 cm in diameter. At the apex of the upper lobe, there is another irregular abscess cavity which is less obvious, approximately 3 × 2 cm in diameter, surrounded by a zone of consolidation. A number of small abscesses are also seen. Patchy consolidation is present in the middle lobe. Numerous bronchi contain and are obstructed by plugs of pus. Cultures taken from the specimen grew Staph. aureus. This is an example of multiple Staphylococcal lung abscesses in an immunosuppressed patient.
Further Information
Staphylococcus aureus is a gram-positive coccus. It is part of the human microbiota, usually found on the skin or upper respiratory tract. It is generally commensal but may cause opportunistic infections such as skin infections (commonly) or, less frequently, pneumonia and endocarditis. It can cause both community- and hospital-acquired pneumonia. Hospital-acquired Staph. pneumonia is most commonly associated with intubation and prolonged hospital admissions. The prevalence of hospital-acquired pneumonia caused by Methicillin-Resistant Staph. aureus (MRSA) is increasing.
It is also an important cause of secondary bacterial pneumonia following viral respiratory infections, such as influenza. Intravenous drug users are at increased risk of developing 'metastatic' Staph. aureus pneumonia and endocarditis due to Staph. bacteraemia caused by contaminated needles. Staph. aureus pneumonia is severe and associated with a higher rate of complications, such as cavitating abscess formation and empyema.
Staph. aureus pneumonia should be suspected in any of the high-risk groups above, as well as in patients with pneumonia who present with rapid deterioration, haemoptysis, early multilobar changes on X-ray, pulmonary cavitation, or disseminated intravascular coagulation. First-line treatment for Staph. aureus pneumonia is penicillin antibiotics such as flucloxacillin. However, resistance to penicillin is very common due to penicillinase production. MRSA is treated with glycopeptide antibiotics such as vancomycin or oxazolidinones such as linezolid.
