Which patients are commonly susceptible to Nocardia species infections, particularly those with compromised immune systems, chronic lung diseases, or taking immunosuppressive medications like prednisone (corticosteroid) or cyclosporine (immunosuppressant)?

Patients Commonly Susceptible to Nocardia Infections

Patients receiving corticosteroids (particularly ≥20 mg prednisone daily for ≥2 weeks) represent the single most important risk group for Nocardia infections, followed by solid organ transplant recipients, patients with HIV/AIDS (especially CD4 <50 cells/μL), and those with chronic lung diseases. 1, 2

Primary High-Risk Populations

Immunosuppressed Patients on Medications

• Corticosteroid users are at highest risk, particularly those receiving doses equivalent to ≥20 mg prednisolone daily for ≥2 weeks or longer, which is associated with increased infection risk and represents the most common risk factor present in over 60% of nocardiosis cases 1, 2, 3

• Solid organ transplant recipients (kidney, heart, liver) on immunosuppressive regimens including cyclosporine, tacrolimus, or combination therapy are at substantially elevated risk, with disseminated infection being highest in this population 1, 4, 3, 5

• Patients on anti-TNF therapy (infliximab, adalimumab, etanercept) for inflammatory bowel disease or rheumatoid arthritis face increased risk of systemic and cutaneous Nocardia infections 1

• Patients receiving calcineurin inhibitors (cyclosporine, tacrolimus) are susceptible to opportunistic infections including Nocardia, particularly when combined with corticosteroids 1, 4

• Patients on thiopurines (azathioprine, mercaptopurine), methotrexate, or combination immunosuppressive therapy have elevated infection risk 1

Patients with Underlying Immunodeficiency States

• HIV/AIDS patients with CD4 counts <50 cells/μL are at risk for disseminated Nocardia infection, with HIV infection representing the most common underlying condition (27% of cases) in recent series 1, 3

• Hematopoietic cell transplant recipients, particularly allogeneic transplant patients, have significantly increased risk of pulmonary and disseminated nocardiosis 1, 5

• Patients with hematologic malignancies (leukemia, lymphoma) receiving chemotherapy, especially those with neutropenia, are susceptible 1, 6

• CAR T-cell therapy recipients face increased infection risk due to neutropenia, lymphopenia, and hypogammaglobulinemia 1

Patients with Chronic Lung Diseases

• Chronic obstructive pulmonary disease (COPD) patients represent 21.6% of nocardiosis cases, particularly those on chronic corticosteroid therapy 3, 5

• Bronchiectasis patients are at increased risk for pulmonary nocardiosis, especially when combined with cigarette smoking 5, 7

• Patients with other structural lung diseases including cystic fibrosis or prior tuberculosis with residual lung damage are susceptible 3, 7

Patients with Autoimmune/Inflammatory Disorders

• Systemic lupus erythematosus patients on immunosuppressive therapy including corticosteroids are at risk 1, 3

• Inflammatory bowel disease patients (Crohn's disease, ulcerative colitis) on immunomodulators or biologics, though overall risk remains low 1

• Rheumatoid arthritis patients receiving immunosuppressive therapy including corticosteroids, methotrexate, or anti-TNF agents 1, 3

Secondary Risk Populations

Immunocompetent Patients with Specific Risk Factors

• Chronic lung disease patients not on systemic corticosteroids still account for approximately 40% of nocardiosis cases, particularly those with bronchiectasis or COPD 5, 7

• Cigarette smokers with underlying lung pathology have increased susceptibility to pulmonary nocardiosis 5

• Patients with direct inoculation exposure through trauma, surgery, or occupational exposure (farmers, gardeners) may develop primary cutaneous nocardiosis 8

Important Clinical Considerations

Combination Risk Factors

• Multiple immunosuppressive agents used concurrently (e.g., corticosteroids plus anti-TNF therapy, or triple immunosuppression in transplant recipients) substantially increase infection risk beyond single-agent therapy 1

• Malnutrition combined with immunosuppression represents an additive risk factor for opportunistic infections including Nocardia 1

Age-Related Risk

• Advanced age is an independent risk factor for opportunistic infections in IBD and other immunosuppressed populations, with mean age of nocardiosis patients being 55-56 years 1, 3, 5

Geographic and Exposure Considerations

• Patients in endemic areas or with specific environmental exposures (soil, decaying vegetation) face higher risk, though Nocardia is ubiquitous worldwide 1, 3

Prophylaxis Limitations

• Cotrimoxazole prophylaxis is not universally protective, with 21.6% of nocardiosis cases occurring despite prophylaxis, and 10.8% of isolates showing resistance to trimethoprim-sulfamethoxazole 3

• Breakthrough infections can occur even with appropriate prophylaxis, particularly with resistant Nocardia species such as N. farcinica 3, 7