C4A and hepatitis A virus infection: Comprehensive admission immunological evaluations – including lymphocyte subset analysis (normal CD3+, CD4+, and CD8+ counts), quantitative immunoglobulins (normal IgG, IgA, IgM), complement levels (normal C3, C4), and negative serology for HIV, hepatitis, syphilis, and autoimmunity – confirmed her immunocompetent status.