Treatment of urinary tract infections offer an example of the hazards and difficulties encountered when initial response is
insufficient. Treatment of bacterial UTI offers a good example of how treatment of bacterial infections might be approaches.
The goal of drug therapy has been to eliminate bactiuria, but this goal should be modified to include eradication of infection
while minimizing the advent of resistance. Further, the goal may need to be modified in the presence of asymptomatic bacteria
(see Flow Chart).
Confirming the need for infection.
The lack of perceived toxicity to antimicrobials has contributed to our willingness to use antibiotics in the absence of convincing
data supporting infection. Failure for infection to progress has been interpreted as therapeutic success...even if infection
was not present in the first place. There is good reason to avoid indiscriminant antimicrobial use. Therapy can be successful
in that an infection is eradicated, but resistance may still develop. However, lack of infection does not preclude the development
of resistance when antimicrobials are used. Antimicrobial therapy should be used only when reasonable evidence of infection
exists. Generally, a quantitative culture yielding less than 103 CFU/ml can be considered for no treatment unless mitigating circumstances indicate otherwise (ie, clinical signs consistent
with UTI, immunesuppression that can lead to worsening of infection etc). In humans, the presence of bacturia is not necessarily
an indication of the need for therapy. In order to avoid resistance, treatment generally is not indicated in asymptomatic
bacturia except under certain conditions in which the patient is at risk, such as pregnancy, or invasive surgical procedures.
On the other hand, bacterial UTI occurs much less frequently in cats than in dogs, and clinical signs indicative of cystitis
in cats should not be interpreted as a need for antimicrobial therapy. Finally, culture may fail to identify infecting microbes,
particularly if slow growing organisms or those requiring special media are present (eg, Mycoplasma or Ureaplasma).Likewise, for our veterinary medical patients, the risk of emerging resistance must be weighed against the risk of failing
to treat. Clearly, if the decision is made to treat a UTI, then therapy must be aggressive, designed to kill invading pathogens
as well as emerging mutants as rapidly as possible. In all but simple UTI, culture is indicated.