There are four causes of urinary tract infections: first, retrograde infections, which are more common in women, and the causative agent of the infection is mostly Escherichia coli. Second, infection through the blood, common are tooth decay, tonsillitis or boils on the skin. After the bacteria enter the bloodstream, they invade the urinary tract through blood circulation and cause infection; there is also tuberculosis, so that the tubercle bacillus stays in the kidney through blood circulation and causes urinary tract tuberculosis infection. Third, direct invasive infection, common are pelvic abscess, gynecological inflammation or even appendicitis, appendiceal abscess, etc., bacteria directly invade the urinary system and cause urinary tract infection. Fourthly, it is rare that transurethral instrumentation performed due to the need for clinical work brings in bacteria due to lax sterilization, resulting in urinary tract infection.