Urinary tract infections (UTIs) are infectious diseases caused by the invasion of various pathogens into the urinary tract; the pathogens of UTIs are mainly bacteria, but can also be fungi, viruses, mycoplasma and parasites, etc. UTIs are common and frequent clinical diseases that can occur in all populations, mostly in women, especially women of childbearing age. About 20% to 30% of women have had UTI in their lifetime, while men have less incidence. Infants, the elderly, kidney transplant patients, and those with abnormal urethral structure or function are prone to the disease, so if you feel abnormal, please seek medical attention as soon as possible. There are various causes of urinary tract infections, which are summarized below, so we should pay attention to prevention. 1, upstream infection Usually urinary tract infection is caused by upstream infection, that is, bacteria along the urethra up to the bladder, ureter and even the kidneys caused by infection. Healthy people have bacteria residing around the urethral opening, these bacteria come from fecal contamination. In women, because of the shorter urethra, the final urine after rapid urination is contaminated by bacteria around the urethral orifice, and the contaminated urine is sucked back into the bladder at the end of bladder contraction; bacteria around the female urethral orifice can be squeezed into the bladder during sexual intercourse; in the state of urinary incontinence, there is continuous fluid between the bladder and the urethral orifice, and bacteria are more likely to travel up to the bladder; retrograde manipulation of medical origin brings bacteria directly into the bladder. Pyelonephritis, on the other hand, occurs when infected bacterial urine then ascends retrogradely from the bladder to the renal pelvis. The mechanism may be related to ureteral reflux. However, even in the absence of reflux, there is a urinary connection between the bladder and the kidney, and it can travel up to the kidney due to the attachment of cilia of the pathogenic bacteria to the mucosa of the urinary tract. 2. Bloodstream infection Less common. Bacteria in foci of infection in various parts of the body, such as tonsillitis, skin boils, carbuncles, etc., otitis media, dental caries, etc., can be transmitted directly from the bloodstream to the genitourinary organs, commonly as renal cortical infection. The causative organism is mostly Staphylococcus aureus. Most of them occur in people with severe urinary tract obstruction or those with very poor immunity. Lymphatic infection The lymphatic vessels of the bladder, ureter and kidney are connected, and there are lymphatic vessels between the ascending colon and the right kidney, so the pathogenic bacteria spread from the foci of the neighboring organs to the genitourinary organs through the lymphatic vessels, such as serious infection of the intestine or retroperitoneal abscess, which is a more rare route of infection. 4, direct spread of infection Due to direct spread of infection from neighboring organs, such as appendiceal abscess, pelvic suppurative inflammation, or foreign infection. Urinary tract infections caused by trauma leading to the connection of the urinary tract with the skin are rare.