Recurrent Urinary Tract Infections in a Patient with Diffuse Large B-Cell Lymphoma and Severe COVID-19: A Single Case of Suspected Immunosuppression Where Antibacterial Therapy Was Not Enough

<b>Background:</b> Non-Hodgkin lymphoma (NHL) is a malignancy of the immune system that includes several subtypes, most commonly diffuse large B-cell lymphoma and follicular lymphoma. Its etiology is multifactorial, with risk factors such as immunosuppressive therapy, infections, chemical exposure, and advanced age. A key aspect is the bidirectional relationship between lymphoma and immunodeficiency, which increases susceptibility to recurrent infections and complicates disease management. <b>Case presentation:</b> One particularly challenging case during the COVID-19 pandemic involved a patient with a personal history of diffuse B-cell non-Hodgkin lymphoma, diagnosed 5 years earlier, who had undergone eight cycles of rituximab-based chemotherapy. The patient tested positive for SARS-CoV-2 for three consecutive months and experienced repeated urinary tract infections warranting more in-depth investigations. The uniqueness of this case lies in the rare association of non-Hodgkin lymphoma, suspected post-rituximab immunodeficiency, severe COVID-19 infection, and recurrent urinary tract infections, which complicated clinical management. Despite appropriate treatment for both respiratory and urinary infections, as well as eight cycles of chemotherapy, the patient's condition continued to deteriorate significantly, ultimately requiring intravenous immunoglobulin replacement therapy. Following the treatment, the patient presented a remarkable clinical improvement, with resolution of the signs and symptoms, and an absence of further recurrent infections. The patient remained clinically stable under regular immunoglobulin replacement therapy, with sustained infection control and improved quality of life. <b>Conclusions:</b> This case highlights the importance of assessing immune status in patients with a hematological malignancy, especially when recurrent infections persist.