Diabetes Mellitus with Influenza Virus and Subsequent Bacterial Infection: Triple Pathological Interactions and Challenges

Diabetes mellitus (DM), characterized by persistent hyperglycemia, not only induces chronic damage and dysfunction across multiple tissues and organs but also increases susceptibility to a broad spectrum of pathogens. Diabetes serves as a significant risk factor for influenza virus infection and associated secondary bacterial pneumonia. This review mainly focuses on the complex pathological and physiological interactions among type 2 diabetes mellitus, influenza and bacterial infections. Chronic hyperglycemia and the resulting immune–metabolic disorders lead to impaired innate and adaptive immune functions. Influenza virus infection further compromises the respiratory barrier, induces an excessive inflammatory response, and depletes immune cells, thereby creating an ideal microenvironment for bacterial colonization. The ensuing bacterial infection synergizes with the virus, forming a vicious cycle of pathogenesis. An integrated strategy combining optimized glycemic control, enhanced vaccination, and early, precise antiviral and antibacterial therapy is paramount for the prevention and treatment of secondary bacterial infections following influenza in patients with diabetes mellitus.