The most common routes of infection for urinary tract infections are upstream infection and bloodstream infection, as follows: 1. Upstream infection: pathogenic bacteria enter the bladder via the urethra and can also spread along the ureteral lumen to the kidneys, and about half of the cases of lower urinary tract infections lead to upper urinary tract infections; 2. Bloodstream infection: in the case of low immune function of the body, bacteria in infected lesions in other parts of the body, such as boils on the skin, tonsillitis, otitis media, caries and other infected lesions, can enter the blood circulation directly and spread to the urinary system via bloodstream, thus leading to urinary tract infections, commonly in the renal cortex.