Nocardia: Difference between revisions

Latest revision as of 22:05, 12 March 2023

Background

Microbiology

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
Ubiquitous environmental saprophyte found in soil and water

Pathophysiology

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
Forms difficult-to-treat biofilms when involved in CLABSIs

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
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
Also diabetes and alcohol use

Clinical Manifestations

Primary Cutaneous

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

Pulmonary

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

Disseminated

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

CNS Disease

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

Other

Mycetoma
Bacteremia
Ocular infection, either from direct inoculation or hematogenous spread
Bone and joint infection, primarily from dissemination

Management

Further Evaluation

Consider screening MRI brain in all patients with disseminated or pulmonary disease regardless of neurologic symptoms
Consider CT chest in all patients
Consider assessment for immunodeficiency; at the very least, HIV testing and a good history

Antimicrobial Selection

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

Duration

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

Monitoring

Serial CT scans to assess response to therapy
Monitoring for antibiotic toxicity

@@ Line 3: / Line 3: @@
 ===Microbiology===
-*Beaded [[Stain::Gram-positive]] [[Stain::partially acid-fast]] [[Shape::bacillus]]
+*Beaded [[Stain::Gram-positive]] [[Stain::partially acid-fast]] [[Shape::bacillus]] within the class [[Class::Actinobacteria]] and order [[Order::Corynebacteriales]]
+*Catalase [[Catalase::positive]] and lyzozyme resistant
-*Appearance similar to [[Actinomyces]], differentiated by acid fast staining ([[Actinomyces]] is ''not'' acid fast)
+*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
+*Ubiquitous environmental saprophyte found in soil and water
+=== Pathophysiology ===
+* 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
+* Forms difficult-to-treat biofilms when involved in [[CLABSI|CLABSIs]]
+=== 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]]
+* 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
+* Also diabetes and alcohol use
+== Clinical Manifestations ==
+=== Primary Cutaneous ===
+* 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]]
+=== Pulmonary ===
+* 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
+=== Disseminated ===
+* Usually starts with a focal infection (skin or lung), which then disseminates hematogenously
+* Most commonly involves skin, lungs, and CNS, but can also disseminate to kidney, joint, retina, and heart
+* Much more common in immunosuppressed patients
+=== CNS Disease ===
+* Most common site of hematogenous dissemination
+* Presents with typical symptoms of fever, headache, meningismus, seizure, and focal neurologic deficits
+* Can also be asymptomatic, so immunocompromised patients should get imaging and possibly LP
+=== Other ===
+* [[Mycetoma]]
+* [[Bacteremia]]
+* Ocular infection, either from direct inoculation or hematogenous spread
+* Bone and joint infection, primarily from dissemination
 ==Management==
+=== Further Evaluation ===
+* Consider screening MRI brain in all patients with disseminated or pulmonary disease regardless of neurologic symptoms
+* Consider CT chest in all patients
+* Consider assessment for immunodeficiency; at the very least, HIV testing and a good history
+=== Antimicrobial Selection ===
 *Mild to moderate: [[Is treated by::TMP-SMX]]
 **Immunocompetent: 5-10 mg/kg split tid to qid
@@ Line 21: / Line 83: @@
 * Any non-cutaneous disease in immunocompromised host: at least 12 months, and possibly lifelong suppression
+=== Monitoring ===
-{{DISPLAYTITLE:''Nocardia''}}
+* Serial CT scans to assess response to therapy
+* Monitoring for antibiotic toxicity{{DISPLAYTITLE:''Nocardia''}}
 [[Category:Gram-positive bacilli]]