Objective:

To present a case of hemophagocytic lymphohistiocytosis (HLH) secondary to Escherichia coli infection in a seronegative rheumatoid arthritis patient on low-dose methotrexate.

Approach:

• Diagnostic Evaluation: Bone marrow aspiration revealed active hemophagocytosis with phagocytosis of E. coli, confirming the diagnosis of HLH.

Key Findings:

• The patient exhibited severe pancytopenia and systemic inflammation.
• Bone marrow analysis showed 20% active hemophagocytosis with E. coli.
• HLH was suspected due to elevated cytokine levels and laboratory abnormalities.

Interpretation:

The case highlights the potential for E. coli infections to induce HLH, particularly in immunocompromised patients.

Limitations:

• The case is a single patient report, limiting generalizability.
• Further studies are needed to understand the mechanisms linking E. coli to HLH.

Conclusion:

HLH can occur in the context of E. coli infections, especially in patients with underlying immunosuppression.