What is the most likely source of Mycobacterium chelonae infection in an immunocompetent patient, who developed infection in the inguinal and iliac lymph nodes 2 months after a podiatrist session, and also had a history of an infected blister on the foot 3 years ago?

Source of Mycobacterium Chelonae Infection in Inguinal and Iliac Lymph Nodes

The podiatrist session 2 months prior to diagnosis is the most likely source of the Mycobacterium chelonae infection affecting the inguinal and iliac lymph nodes. 1

Epidemiology and Transmission of M. chelonae

• M. chelonae is a rapidly growing nontuberculous mycobacterium (NTM) that is ubiquitous in natural resources including soil and water, and can proliferate in drinking water systems 1
• The primary route of M. chelonae infection is through skin-breaching trauma, which includes traumatic injury, surgery, or cosmetic procedures 1
• The time from exposure to diagnosis of NTM infections is typically 2-10 months, which aligns with the 2-month timeline between the podiatrist visit and diagnosis in this case 1

Analysis of Potential Sources

Podiatrist Session (2 months prior)

• The temporal relationship between the podiatrist session and diagnosis (2 months) falls within the typical incubation period for M. chelonae infections 1
• The anatomical progression from foot (site of podiatry intervention) to inguinal and iliac lymph nodes follows the expected lymphatic drainage pattern 1
• NTM infections, including M. chelonae, have been documented following podiatric and other medical procedures due to contaminated instruments or solutions 1

Infected Blister (3 years prior)

• The 3-year time gap between the infected blister and current lymph node infection is significantly longer than the typical incubation period for M. chelonae 1
• While swimming pools can harbor NTM, the extended timeframe makes this exposure less likely to be the causative event 1
• M. chelonae infections typically present within months of exposure, not years 1

Diagnostic Considerations

• M. chelonae infections often present with nonspecific clinical features, including abscesses, cellulitis, nodules, ulcers, and draining sinus tracts 1
• Diagnosis requires tissue samples specifically cultured for mycobacteria, as swab cultures have limited diagnostic value 1
• The lymph node involvement suggests lymphatic spread from a distal site of inoculation, consistent with the podiatrist session as the source 1

Clinical Implications

• M. chelonae infections can occur in both immunocompromised and immunocompetent patients, though historically considered opportunistic pathogens 1
• Treatment typically requires:
  • Thorough surgical debridement of affected tissues 1
  • Culture-directed antibiotic therapy, usually with two oral antibiotics for 4-6 months for limited infections 1
  • Consultation with an infectious disease specialist 1

Common Pitfalls and Caveats

• Delays in diagnosis are common with NTM infections due to their indolent nature and nonspecific presentation 1
• Standard bacterial cultures may be negative, requiring specific mycobacterial cultures that should be held for up to 6 weeks 1
• Initial laboratory values including ESR and CRP may be normal despite active infection 1
• New skin lesions during treatment may represent immunologic response rather than treatment failure 1

In conclusion, the recent podiatrist session represents the most likely source of infection based on the established timeline of M. chelonae infections and the anatomical progression of disease from the foot to inguinal and iliac lymph nodes through lymphatic spread.