Can a Silent Kidney Infection or Genetic Predisposition Underlie Recurrent UTIs?

, University of Calgary and Alberta Children's Hospital


Medscape General Medicine. 1996;1(1) 

In This Article

Recognizing Relapse vs Reinfection

Recurrence of UTI occurs because of either a relapse or a reinfection. Women who have relapsing infection have recurrent bacteriuria with the same infecting microorganism that was present before initial treatment, and urine cultures show no growth in the usual 2-week interval between the initial and successive episode(s). For a subgroup of women, the cause of repeated relapses is the presence of unrecognized clinically "silent" pyelonephritis, as shown by localization studies.[10,11,12] However, it is also believed that relapse may occur because of persistent colonization by the same organism of the vagina, periurethral area, or rectum, and that each recurrent episode is caused by repeated "reinfection" of the urinary tract by ascendance of the same bacterium.[8] Recurrence by this mechanism usually occurs within 2 weeks of stopping antibiotic therapy for a prior episode of cystitis, so that the timing does not help the investigator clinically distinguish between these 2 causes.

Women with "silent" pyelonephritis who present with symptoms of lower UTIs are initially treated as though they had cystitis. However, because the initial antibiotic treatment course does not cure the kidney infection, symptomatic relapse usually occurs shortly after the antibiotics are stopped (ie, within 2 weeks). Relapsing infections may therefore be indicative of an underlying persistent pyelonephritis. If appropriately treated with a prolonged course of antibiotics, patients should remain symptom-free until such time as they might become reinfected.

Reinfection is a new episode of bacteriuria with a microorganism that is different from the original one (eg, bacteriuria with Klebsiella species when the original infection was caused by E coli). Reinfection may also occur with the same organism that caused the original infection. In this case, the main feature differentiating reinfection from relapse is that individual episodes of reinfection are usually separated by a symptom-free interval of at least a month after antibiotics are stopped and the urine has shown no bacterial growth.

It is therefore important to clarify whether relapse or reinfection is occurring, since the management of these 2 UTI situations is different. Although ideally one would like to be able to prove that infection localized in the kidney is the source of relapse, there are currently no routinely available diagnostic tests with a high enough sensitivity that can do this. Special studies that have been utilized to try and document the location of infection in the urinary tract include direct ureteral catheterization and ureteral urine cultures; the Fairley bladder washout procedure, which also determines ureteral bacteriuria via Foley catheterization; and the detection of antibody coated bacteria (ACB) in urine, which has been used to localize infection to the kidney.[12,29,30,31] Although the sensitivity of the ACB test has been established by several studies that collectively approach 88% with a specificity of 76%, it is not routinely performed in laboratories due to discrepancies that result from a lack of standardization of criteria for reporting a positive test result.[31] Outcome of therapy is therefore often the only useful, albeit crude, way for clinicians to separate women with cystitis alone from those with pyelonephritis. Almost all patients with infection that is restricted to the bladder will be cured with a short course of antibiotic therapy as outlined below, but the relapse rate for patients with kidney infection is substantial even with a longer course of therapy (ie, 7-10 days).

In the case of reinfection, the causative factor(s) should be delineated (ie, reinfectionrelated to sexual intercourse, delayed voiding after intercourse, use of a diaphragm and/or spermicide, genetic susceptibility, etc.) so that specific measures may be implemented to minimize the number of episodes as much as possible.