Last updated on:February 23rd, 2022
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Nocardia spp. can cause a wide variety of clinical syndromes. Nocardia is generally considered an opportunistic pathogen that causes disease in immunocompromised patients; however, immunocompetent persons may also be affected. The most common organs involved are the lungs, central nervous system, and the skin and subcutaneous tissue. Importantly, any organ can become involved; and infected individuals show a tendency to relapse or progress, even with appropriate treatment.
Nocardia are a group of slow-growing gram-positive aerobic environmental bacteria, which show hyphae-like branching on direct microscopy. They are weakly acid-fast due to the mycolic acid content of the cell wall. The taxonomy is complex, but the most clinically relevant pathogens include N. asteroides, N. farcinica, N. cyriacigeorgica, and N. brasiliensis species.
Risk factors for nocardiosis include long-term treatment with steroids or immunosuppressive drugs, hematological malignancies, depressed cell-mediated immunity (especially where CD4+ cell counts are <100/mm3), and allogenic hematopoietic stem cell, or solid organ transplantation. Patients with pulmonary nocardiosis often have chronic lung conditions such as chronic obstructive pulmonary disease, asthma or bronchiectasis.
Pulmonary nocardiosis is typically acquired via inhalation of airborne spores or fragments from environmental sources. It can then spread hematogenously from the primary site and reach extrapulmonary locations (most often the central nervous system). Cutaneous infection is generally due to direct inoculation of the organism from the soil following trauma; however, localization following disseminated infection may occur.
Sites of infection
The most common sites of infection are the lung followed by the central nervous system and the skin. The central nervous system is the most frequent extrapulmonary location involved.
Disseminated nocardiosis is defined as two noncontiguous sites of involvement that may or may not include a pulmonary focus. Nocardia can disseminate from a primary focus to virtually any organ. Dissemination is more frequent in immunocompromised than immunocompetent hosts.
Symptoms of pulmonary nocardiosis are diverse but nonspecific, including productive or nonproductive cough, shortness of breath, chest pain, hemoptysis, fever, night sweats, weight loss, and progressive fatigue. This is due to the inflammation of the lung parenchyma after the inhalation of spores.
Central nervous system symptoms
Solitary or multiple cerebral abscesses are the most common central nervous system (CNS) lesion. Affected patients may present with headaches, nausea, vomiting, seizures, altered mentation, and focal neurological deficits. Meningismus is rare and fever is not always present.
Cutaneous involvement can give rise to ulcerations, pyoderma, cellulitis, nodules and subcutaneous abscesses.