Nocardia: Difference between revisions

Revision as of 21:50, 23 January 2023

Beaded Gram-positive partially acid-fast bacillus within the class Actinobacteria and order Corynebacteriales
Catalase positive and lyzozyme resistant
Has a classic beaded branching cell morphology
Microscopic appearance similar to Actinomyces, differentiated by acid fast staining (Actinomyces is not acid fast)
Colonies are slow to grow and have a chalky white appearance
Saprophyte found in soil and water

Spores or mycelia are either inhaled into the lungs or directly inoculated in the skin and soft tissue
Traumatic inoculation includes during motor vehicle collisions, mild scratches or pricks, or nosocomial with dirt entering through an open wound or central line

More common in immunocompromised (cell-mediated immunodeficiency including HIV, hematologic malignancy, and transplant patients), though can also occur in immunocompetent who have COPD, bronchiectasis, and cystic fibrosis
Among transplant recipients, lung transplant appears to be highest risk
High-dose steroids and high levels of calcineurin inhibitors appear to be specific risk factors

Typically acquired by direct inoculation with soil
Nocardia brasiliensis is the most common cause in North America
May present with superficial soft tissue infection, including ulcer, abscess, cellulitis, pustules, plaques, or papules, most commonly on the arms and legs
Can progress to lymphocutaneous infection with sporotrichoid lesions

Subacute or chronic cough, dyspnea, fever, with or without pleuritic chest pain
Most common form of disease in US
Colonization also possible, particularly with patients who have structural lung changes like cystic fibrosis
Starts with inflammation followed by formation of granulomas and necrotic abscesses
Imaging typically showed lung nodules, lobar consolidation, and pleural effusion, and may show infiltrates and necrotizing granulomas
- Usually bilateral
- Cavitations more common in immunocompromised patients

Usually starts with a focal infection (skin or lung), which then disseminates hematogenously
Most commonly involves skin, lungs, and CNS, but can also dissemiante to kidney, joint, retina, and heart
Much more common in immunosuppressed patients

Most common site of hematogenous dissemination
Presents with typical symptoms of fever, headache, meningismus, seizures, and focal neurologic deficits
Can also be asymptomatic, so immunocompromised patients should get imaging and possibly LP

Mild to moderate: TMP-SMX
- Immunocompetent: 5-10 mg/kg split tid to qid
- Immunocompromised: 15 mg/kg split tid to qid
Severe: TMP-SMX plus either amikacin or imipenem
Other antimicrobials include ceftriaxone, minocycline, and linezolid

Isolated cutaneous infection in immunocompetent host: 3 to 6 months
Isolated cutaneous infection in immunocompromised host: 6 to 12 months
Serious pulmonary infection: 6 to 12 months or longer
Any non-cutaneous disease in immunocompromised host: at least 12 months, and possibly lifelong suppression

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 === Risk Factors ===
-* More common in immunocompromised (cell-mediated immunodeficiency including HIV, hematologic malignancy, and transplant patients), though can also occur in immunocompetent who have [[COPD]], [[bronchiectasis]], and [[cystic fibrosis]]
+* More common in immunocompromised (cell-mediated immunodeficiency including [[HIV]], hematologic malignancy, and transplant patients), though can also occur in immunocompetent who have [[COPD]], [[bronchiectasis]], and [[cystic fibrosis]]
-* Among transplant recipients, lung transplant appears to be highest risk
+* Among transplant recipients, [[lung transplant]] appears to be highest risk
-* High-dose steroids and high levels of celcineurin inhibitors appear to be specific risk factors
+* High-dose steroids and high levels of [[calcineurin inhibitors]] appear to be specific risk factors
 == Clinical Manifestations ==