Diagnostic caveats for difficult bacterial urinary tract infections - DVM
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Diagnostic caveats for difficult bacterial urinary tract infections


DVM360 MAGAZINE



Table 3 Potential sequela to untreated or improperly treated bacterial urinary tract infections
Recurrent bacterial UTIs that occur following withdrawal of therapy may be classified as relapses or reinfections.


Table 4 Checklist of potential causes of recurrent UTIs due to relapses
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of relapsing UTI likely involves failure to completely eliminate pathogenic bacteria before antimicrobic therapy is withdrawn.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 5 Checklist of potential causes of recurrent UTIs due to reinfections
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.

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.


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Source: DVM360 MAGAZINE,
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