Nocardiosis is an infectious disease affecting either the lungs (pulmonary nocardiosis) or the whole body (systemic nocardiosis). It is due to infection by bacterium of the genus Nocardia, most commonly Nocardia asteroides or Nocardia brasiliensis.

It is most common in men, especially those with a compromised immune system. In patients with brain infection, mortality exceeds 80%; in other forms, mortality is 50%, even with appropriate therapy. It is one of several conditions that have been called the great imitator.^[1]Cutaneous nocardiosis commonly occurs in immunocompetent hosts.^[2]

Diagnosis may be difficult.Nocardiae are weakly acid-fast organisms and can be visualized by modified Ziehl Neelsen stains like Fite-Faraco method. In the clinical laboratory, routine cultures may be held for insufficient time to grow nocardiae, and referral to a reference laboratory may be needed for species identification.

Infiltration and pleural effusion are usually seen via x-ray.