Infectious Disease – Atypical Mycobacteria  

FUNDAMENTALS AND DESCRIPTION  
Infection by a species of nontuberculous mycobacteria (NTM). Pediatric Considerations Atypical mycobacteria must be contemplated in patients exhibiting unilateral cervical lymphadenitis. • This virus predominantly affects youngsters between the ages of 1 and 5 years. • Edema frequently manifests around the impacted nodes, typically in the anterior cervical chain. Adenitis may develop swiftly, and the creation of fistulas through the skin is prevalent. Enlarged lymph nodes are frequently asymptomatic. • Systemic symptoms are seldom. • The majority of symptoms are attributed to MAC; however, Mycobacterium scrofulaceum and Mycobacterium tuberculosis are also observed, but less commonly.  

 

Epidemiology  
Annually, there are 300 cases of MAC lymphadenitis in the United States. Prevalence: 1–7.2 cases per 100,000 in the United States. • Significantly changeable, contingent upon location. Approximately 50% of non-tuberculous mycobacteria isolates are pathogenic.  

 

RISK FACTORS
• Age • Immunosuppression • HIV with diminished CD4 cell counts or other opportunistic infections • Interferon (IFN)-gamma deficiency • Preexisting structural pulmonary disease Genetics: Deficiency of IFNγR1 or IL-12βR1  

 

COMPREHENSIVE PREVENTION 

 In individuals with AIDS (CD4 count <100 cells/mm3), weekly administration of 1200 mg azithromycin is recommended as primary prophylaxis. Alternative preventative regimens are clarithromycin 500 mg three times day or rifabutin 300 mg daily.  

 

PATHOPHYSIOLOGY • Environmental exposures such as soil, water, hot tubs, and tap water are frequently implicated. • Human-to-human transmission has not been recorded. • Initial infection occurs through ingesting or inhalation; reactivation is not a risk. • Granuloma formation arises from the interaction among macrophages, lymphocytes, and natural killer cells. • Disseminated disease stems from a localized infection.  

 

ETIOLOGY • Aerobic, non-spore-forming bacilli characterized by cell walls containing mycolic acid (2). • Rapidly growing organisms encompass the following rapid-growing mycobacteria (RGM) (growth within 7 days): – Mycobacterium fortuitum complex – Mycobacterium chelonae/abscessus – Mycobacterium smegmatis • Organisms with intermediate growth rates encompass the following: – Mycobacterium marinum – Mycobacterium gordonae • Organisms with a slow growth rate (10–21 days) encompass the following: – Mycobacterium avium complex (MAC) – Mycobacterium kansasii – Mycobacterium xenopi – Mycobacterium scrofulaceum – Mycobacterium haemophilum – Mycobacterium ulcerans  

 

FREQUENTLY CO-OCCURRING CONDITIONS • Immunosuppression, such as AIDS or transplant recipients • Utilization of TNF inhibitors • Cystic fibrosis • Pre-existing pulmonary disorders: silicosis, resolved tuberculosis, bronchiectasis, or chronic obstructive pulmonary disease  

 

DIAGNOSIS CLINICAL SYNDROMES • Pulmonary • Lymphadenitis • Cutaneous and soft tissue • Osteoarticular • Catheter-associated • Disseminated • Pulmonary: Persistent cough typically yielding sputum. Advanced disease correlates with constitutional symptoms (e.g., weight loss, fatigue) and may encompass dyspnea, hemoptysis, and chest discomfort (2). • Soft tissue: Frequently linked to inoculation or recent surgical procedures or instrumentation. • Osteoarticular. • Disseminated: Characterized by fevers, tiredness, and anorexia. • Exposures: Water (cutaneous/soft tissue), catheters (bacteremia) • Suppression of the immune system  

 

PHYSICAL EXAM • Pulmonary: Rales, wheezes, rhonchi. Pectus excavatum (27%) and scoliosis (52%) are prevalent among patients with pulmonary MAC. • Soft tissue: Minor, papular lesions typically located on the extremities; may become ulcerated and disseminate locally or via lymphatics. Lymphadenitis: An swollen lymph node, typically located in the submandibular or jugular area, that is either painless or mildly uncomfortable, but not fluctuant.  

 

DIAGNOSTIC TESTS AND INTERPRETATION LAB Pancytopenia may arise due to marrow suppression in disseminated illness. • Increased alkaline phosphatase may be observed in 5% of disseminated MAC (20–40 times the normal level). • Mycobacterial blood cultures yield positive results in 90% of dispersed cases. Imaging: Preliminary Strategy Chest X-ray (CXR) or chest CT (pulmonary): Upper lobe cavitary illness, nodular or reticulonodular disease, or adenopathy. Pleural effusions are infrequent. Subsequent Actions & Unique Considerations • Serial imaging will be conducted to monitor for progression (if asymptomatic) or improvement (during therapy). Cavitary illness occurs in 60–90% of Mycobacterium avium complex lung infections. Cavitations may range from 2 to 4 centimeters in size and are generally characterized by thin walls. Diagnostic Procedures and Additional Methods • Tissue for acid-fast bacillus (AFB) smear, mycobacterial culture, and pathology is crucial, as these organisms may behave as colonizers (2). In cases of pulmonary disease, it is advisable to obtain three or more sputum samples (or perform bronchoalveolar lavage) for culture analysis. RNA probes can facilitate the first identification of M. tuberculosis, MAC, and M. kansasii from positive cultures. • Upon isolation, mycobacterial cultures must be dispatched to a specialized facility for confirming identification and antibiotic susceptibility assessment. Pathological Observations • Granuloma containing large cells and acid-fast bacilli observed in localized infection. In widespread illness, the presence of well-formed granulomas is less probable.  


DIFFERENTIAL DIAGNOSIS
• Mycobacterium tuberculosis (MTb) • Other non-tuberculous mycobacteria (NTM) • Endemic fungi (histoplasmosis, cryptococcosis, blastomycosis, nocardiosis) • Pre-existing structural lung disease  


TREATMENT MEDICATION  
Initial Line • MAC (pulmonary): Rifampin 600 mg daily, ethambutol 15 or 25 mg/kg daily based on radiographic pattern, azithromycin or clarithromycin 500 mg, with the addition of an aminoglycoside as necessary (2). • Kansasii (pulmonary): Isoniazid 300 mg daily, rifampin 600 mg daily, ethambutol 15 mg/kg daily. • RGM (soft tissue): Two of the following agents to which the isolate is susceptible: Trimethoprim-sulfamethoxazole (TMP-SMX), doxycycline, levofloxacin, clarithromycin. • Severe abscess: Amikacin + clarithromycin + cefoxitin or imipenem • Fortuitum or chelonae (severe): Amikacin or tobramycin combined with cefoxitin, with the option of adding imipenem or levofloxacin. • MAC (disseminated/HIV): Administer clarithromycin 500 mg orally twice daily or azithromycin 500–600 mg orally twice daily, along with ethambutol 15 mg/kg orally daily; consider adding rifampin with input from infectious disease specialists. • M. marinum (soft tissue): Administer clarithromycin 500 mg orally twice daily and ethambutol 15 mg/kg, with the inclusion of rifampin for osteomyelitis and the potential for surgical debridement. Mild illness may be managed alone with clarithromycin. Second Line • Moxifloxacin 400 mg daily • Amikacin • M. abscessus: Linezolid, doxycycline, TMP–SMX ADDITIONAL THERAPY Comprehensive Strategies • Susceptibility testing is required for MAC (clarithromycin), kansasii (rifampin), and RGM (eight medicines on the susceptibility panel) (2). Treatment duration is extended; for pulmonary MAC, administer therapy for 12 months following negative cultures (totaling 12–24 months), and for disseminated MAC, treat for 12 months or 6 months beyond when CD4 counts exceed 100 cells/mm³. Skin and soft tissue infections may require three months or more of treatment. Catheter-associated infections necessitate 6 to 12 weeks of therapy following catheter removal. Referral Issues Due of the drug resistance of these indolent organisms, doctors with expertise in these illnesses are required for therapy. Occasionally, people necessitate years of treatment.  


OPERATIVE INTERVENTIONS/ADDITIONAL PROCEDURES  
• MAC: Lung resection is advisable for patients with upper lobe disease, particularly if they are intolerant to medical therapy or exhibit culture positivity after six months of antibiotic treatment. • MAC lymphadenitis: Resection yields a 90% cure rate without the use of antimicrobials. • Incision and drainage for soft tissue infections or tenosynovitis, particularly for rapidly growing mycobacteria.  


INPATIENT CONSIDERATIONS 
Criteria for Admission • For diagnostic evaluation. • For the commencement of parenteral antibiotics. CONTINUING CARE FOLLOW-UP SUGGESTIONS Monthly follow-up during the initial phases of treatment is frequently advised due to antimicrobial toxicity. • Following patient tolerance of drugs, follow-up intervals may be extended. Patient Surveillance • Laboratories for assessing medication toxicity. • Assessment for pharmacological interactions. • Monitoring therapeutic medication levels for antibacterial peaks and troughs.  

PROGNOSIS 
 It is contingent upon the disease's location, the detection of non-tuberculous mycobacteria (NTM), and the particular host.  

COMPLICATIONS  
• Laboratories for assessing medication toxicity. • Evaluation of pharmacological interactions between drugs. • Disseminated MAC: Intussusception, gastrointestinal hemorrhage, and bowel blockage may develop, however these are few. • MAC lymphadenitis: Ulceration and the development of fistulas.