Difficult bacterial urinary tract infections: recurrent infections

Sep 01, 2005

As discussed in last month's Diagnote, protocols designed to safely and effectively eliminate urinary tract infections (UTIs) should include:

  • Detection and treatment of host defense abnormalities that allow bacteria to colonize and invade the urinary tract,
  • Election of appropriate antimicrobial agents to eradicate microbial pathogens,
  • Monitoring response to therapy at appropriate intervals. The objective of the third part of this series is to summarize therapeutic caveats that should be considered in managing patients with recurrent bacterial UTIs.
  • Why is it important to differentiate recurrent bacterial UTIs as relapses or reinfection?

Table 1. Examples of patterns of bacteriuria detected by sequential urine cultures performed to monitor response to antimicrobial Rx of UTI
Recall that recurrent bacterial UTIs that occur following withdrawal of therapy may be classified as relapses or reinfection. Relapses are defined as recurrences of UTI caused by the same species of microbe (Table 1). 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of relapsing UTI likely involves failure to completely eliminate pathogenic bacteria before antimicrobic therapy is withdrawn.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 (see Table 2). Relapses have the potential to cause significant morbidity if mismanaged.

Table 2. Checklist of potential causes of recurrent UTIs due to relapses
Reinfection are defined as recurrent infections caused by a different pathogen (Table 1). 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 3). 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 reinfection often occur at a longer interval following cessation of therapy than relapses.

Table 3. Checklist of potential causes of recurrent UTIs due to reinfection
Caveat: The therapeutic plan for relapses often differs from the therapeutic plan for reinfection. 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.