Recurrent bacterial UTIs that occur following withdrawal of therapy may be classified as relapses or reinfections.
Table 3 Potential sequela to untreated or improperly treated bacterial urinary tract infections
Relapses are defined as recurrences of clinical signs caused by the same species of microbe. In this situation, remission of clinical
signs and eradication of bacteria from the urine is not associated with eradication of pathogenic bacteria from tissues of
the urinary tract. Relapses usually emerge within several days to a few weeks after remission of clinical manifestations of
UTI; the bacteria may have become more resistant to antimicrobial agents than prior to therapy. The pathogenesis of relapsing
UTI likely involves failure to completely eliminate pathogenic bacteria before antimicrobic therapy is withdrawn. Relapses
represent antimicrobial treatment failures associated with one or more causes (Table 4). Relapses have the potential to cause
significant morbidity if mismanaged (Table 3).
Table 4 Checklist of potential causes of recurrent UTIs due to relapses
Reinfections are defined as recurrent infections caused by a different pathogen(s). In this situation, bacteria have been eradicated from
urine and surrounding tissue, but persistent dysfunction of one or more host defense mechanisms predisposes to infection with
different uropathogens (Table 2 and 5). If superficial damage to tissues of the urinary tract induced by bacteria during the
initial infection have time to heal, recurrence of clinical manifestations of reinfections often occur at a longer interval
following cessation of therapy than relapses.
Table 5 Checklist of potential causes of recurrent UTIs due to reinfections
Caveat: The therapeutic plan for relapses often differs from the therapeutic plan for reinfections. Therefore it is important to
compare results of bacterial culture of urine obtained prior to initiation of therapy to bacterial cultures of urine obtained
during and/or after withdrawal of therapy.
Diagnostic and therapy vary
What is the gold standard of diagnosis of bacterial UTI?
Because UTI encompasses a spectrum of underlying abnormalities in host defense mechanisms in addition to bacterial pathogens,
diagnostic and therapeutic requirements vary from case to case. There are no pathognomonic history, physical examination,
radiographic or ultrasonographic findings associated with bacterial UTI.
In addition to bacterial infection, many diverse noninfectious disease processes, including neoplasia and urolithiasis, result
in inflammatory lesions of the urinary tract characterized by exudation of RBC, WBC and protein into urine.
The resultant hematuria, pyuria and proteinuria suggest inflammatory urinary tract disease, but do not indicate its cause
or location within the urinary tract. Diagnosis of bacterial UTI solely on the basis of urinalysis and detection of inflammatory
cells in urine sediment will result in over-diagnosis. Therefore, it is essential to distinguish between inflammation and
infection related to urinary tract disease. Although detection of bacteria in fresh urine sediment should prompt consideration
of UTI, it should be verified by urine culture. Non-bacterial "look-alikes" in urine sediment are often confused with bacteria.
Quantitative urine culture is considered the gold standard for diagnosis of bacterial UTIs. In addition to facilitating differentiation of bacterial contaminants from bacterial pathogens,
accurate identification of specific bacterial species aids in selection of antimicrobial drugs. Also recall that recurrent
UTIs due to relapses can not be distinguished from recurrent UTIs due to reinfections without comparison of pretreatment bacterial
culture results to follow-up culture results.