Nocardia infection or nocardiosis is a rare, opportunistic bacterial infection caused by genus Nocardia primarily affecting immunosuppressed patients. Nocardiosis presents in a diverse manner based upon the site of infection. A distribution of three types is available and includes pulmonary, extrapulmonary nocardiosis, and primary cutaneous lesions including mycetoma.
The course of Nocardia infection may range in severity (from asymptomatic to acute and chronic) and presentation of patients may vary widely, correlating to the affected organs.
It is important to obtain history data about any chronic rheumatologic diseases that could require immunosuppressive therapy and data about any immunosuppressive disease. It is important because nocardiosis is opportunistic and infects mostly immunocompromised patients .
Pulmonary nocardiosis is the most common type of nocardiosis  and is characterized by non-specific manifestations such as fever, fatigue and weight loss. Specific findings include productive or a non-productive cough, abscess in lungs, empyema, cavitations, bronchiectasis, pleural effusion, and pneumonia . Symptoms like chest pain, shortness of breath can indicate a chronic condition. An infectious mass in the lungs is prone to dissemination. Dissemination occurs locally to the pericardium, pleura, vena cava, and mediastinum. Systematic dissemination could be the cause of abscess formation in other organs, usually extremities .
Extrapulmonary nocardiosis most commonly affects cerebral tissue by forming multiple or solitary deep abscesses. These lesions compress the lobes and are held accountable for neurologic manifestations such as headaches, seizures, and altered mental state  . Meningitis and non-specific symptoms such as nausea and vomiting can also be present. These signs and symptoms may evolve gradually or acutely, depending on size and location of the abscess. Extrapulmonary manifestations, although mostly involve the cerebrum (44%) , can manifest in any organ, especially in the extremities. Infection in such locations arises due to hematogenous dissemination .
Primary cutaneous infection occurs from direct inoculation of Nocardia spp. spores and is prevalent in patients who are not immunocompromised. Patients present with purulent inflammation of dermis that is able to ascend to regional lymph nodes (lymphocutaneous infection) or form local abscesses. These masses are typically in lower extremities in adults and on the face in children .
Mycetoma is a characteristic chronic state of primary cutaneous infection. It is characterized by purulent fistulas of many colors and sizes as well as granulomas and nodules that are painless and affect subcutis as well as other soft tissues and bone . Superficial cutaneous infection, on the other hand, manifests with all signs of inflammation like pain, warmth, swelling and erythema. Lymphocutanious lesions originate from primary purulent ulcerations allowing the noxious organism to penetrate deeply in affected areas .
The most important workup findings in nocardiosis infection are those of microbiology and radiology.
If pulmonary nocardiosis is suspected, a chest X-ray or computed tomography (CT) is usually performed. Discovery of solitary or multifocal lesions is typically made. The lesions can be either nodular or of an infiltrative kind, cavitations and pleural effusions can also be identified  . Nevertheless, radiography is non-specific and no radiologic signs point specifically to nocardiosis.
An imaging study of central nervous system (CNS) should be performed for patients suffering from severe nocardiosis. Particularly pulmonary nocardiosis and suspected systemic infection or if neurologic symptoms are present, imaging is of vital significance. Magnetic resonance imaging (MRI) is the investigation of choice for such cases . Abscesses either solitary or multiple can be found in different lobes of the cerebrum, perifocal edema usually is also present. The radiologic picture is frequently misdiagnosed as malignancies, vasculitis, or stroke . To avoid misdiagnosis it is necessary to confirm nocardiosis with a microbiologic evaluation.
Depending on the affected site different types of specimens should be collected. A specimen of sputum or bronchial washing in pulmonary nocardiosis, cerebrospinal fluid (CSF) in suspected meningitis, skin biopsy or aspiration from abscess masses in cutaneous nocardiosis. It is necessary to inform laboratories about possible Nocardia infection as haste and slow growth of Nocardia may be the cause of altered results. Nocardia spp. stains with modified acid-fast and Gram stain with cultures being generally isolated in 3-5 days .