What is the cause of urinary tract infection after kidney transplantation?

Kidney transplantation is a method of kidney transplantation performed through surgery. Urinary tract infection is likely to occur after kidney transplantation. There are many reasons for urinary tract infection after kidney transplantation. This may be caused by not paying attention to hygiene. Infection will occur after kidney transplantation, which can easily lead to urinary tract infection, causing patients to have hematuria or kidney pain.

Causes

The causes of UTI after renal transplantation mainly include factors such as the host (kidney transplant recipient), the donor kidney, the anatomical structure of the transplant recipient, and susceptible microorganisms. These causes may occur singly, or they may overlap and interact with each other.

Host factors were divided into preoperative, intraoperative and postoperative factors according to the time of surgery.

Preoperative factors include: female, diabetic nephropathy, long-term use of glucocorticoids and immunosuppressants (such as patients with SLE and rheumatoid arthritis), urinary tract malformations, and excessive dehydration before surgery.

Intraoperative factors included: cadaveric kidney, contaminated kidney, double "J" tube placed in the renal pelvis, double renal pelvis, secondary transplantation and prolonged urinary catheter retention; urinary catheter was routinely placed during surgery. Even with strict aseptic techniques, UTI can occur. In the general population, the incidence of bacteriuria increases with in situ catheterization (one day increase in indwelling time increases the incidence of UTI by 5%), excessive postoperative immunosuppression, transplant renal insufficiency and rejection, primary urinary tract infection, and intraurethral instrumentation. Therefore, the urinary catheter should be routinely removed on the fifth day after renal transplantation.

Clinical manifestations

Symptomatic UTI after renal transplantation may present as acute cystitis or allograft pyelonephritis (with or without primary pyelonephritis). Its typical clinical manifestations can be divided into lower and upper urinary tract symptoms. The former have frequent urination, urgency, pyuria, hematuria and suprapubic pain; the latter have chills, fever, hematuria, pain in the autologous kidney and transplanted kidney areas. Valer et al. analyzed 161 renal transplant patients and found that acute bacterial cystitis accounted for 77% of UTI, while in a group of 172 renal transplant recipients, acute pyelonephritis accounted for 19% of UTI. Pelle et al. also found that pyelonephritis was more common in women than in men, and the frequency of recurrent UTI (referring to patients with recurrent UTI ≥ 3 times or infection with different strains within 12 months, without any symptoms) was related to the number of rejection reactions.

Often, immunosuppressants mask the clinical manifestations of infection. At the same time, due to the denervation of the transplanted kidney, the localization of transplanted kidney pain is inaccurate. However, the clinical manifestations of patients are different when infected with special pathogens. For example, BK virus infection can cause BK virus nephropathy and lead to transplanted renal failure. In addition, tuberculosis often presents with low-grade fever and granulomatous renal damage.

Diagnosis

Once a post-transplant UTI is suspected, a thorough workup is warranted. Several initial examinations and their possible abnormal findings are briefly described below. Clinical manifestations of UTI include pyuria, fever, tachycardia and hypotension (rare); urine test shows positive leukocyte esterase, increased nitrite with hematuria or proteinuria; abdominal examination may reveal tenderness in the lumbar region or above the pubic bone; urogenital rectal examination may reveal prostatic hypertrophy, tenderness of the prostate, testicles, epididymis, and atrophic vaginitis; urine test, urine culture and drug sensitivity may reveal microorganisms and pyuria as well as drug-resistant strains; laboratory tests may reveal elevated creatinine and C-reactive protein (if above 100 mg/L, indicating pyelonephritis); tracking of the patient's medication history may reveal excessive immunosuppressants or improper use of antibiotics; and urinary system ultrasound examination may reveal calyceal dilatation, stones, and incomplete bladder emptying.

Many host, microbial, and anatomical factors may contribute to UTI after renal transplantation. Generally, it is not a routine examination of the patient's urinary system (including the kidneys) before kidney transplantation, but relevant examinations must be performed after the acute infection period. Patients with recurrent UTI and recurrent UTI must undergo additional examinations, but secondary infection through instrumental examinations should be avoided. Excessive use of immunosuppressants can also lead to recurrent UTI and drug resistance.

Once early post-renal transplant UTI is suspected, infection due to contamination of the storage fluid should be excluded first, and a sample of the storage fluid from the transplanted organ should be cultured for bacteria. When necessary, PCR (polymerase chain reaction) was used to detect cytomegalovirus (CMV) and BK virus infection in the recipient's peripheral blood and urine samples.

Kidney transplant rejection can coexist with UTI. Currently, only transplanted kidney biopsy can be used to differentiate between transplanted kidney pyelonephritis and rejection, but kidney biopsy carries the risk of bleeding and infection.