Complicated Urinary Tract Infections

Diagnosis and Interpretation

The presence of S. aureus at significant colony counts with concurrent Klebsiella suggests a complicated UTI, as S. aureus is an uncommon uropathogen and typically indicates either hematogenous seeding, instrumentation, or structural abnormality 1
The lower colony count of Klebsiella may represent contamination or colonization rather than true infection, though Klebsiella is a recognized pathogen in complicated UTIs 1

Fluoroquinolones like levofloxacin should be reserved for important uses other than routine UTI treatment and are not first-line agents, due to their significant propensity for collateral damage 2
The European Urology guidelines recommend that fluoroquinolones should only be used for complicated UTI when local resistance rates are <10%, when the entire treatment can be given orally, when the patient doesn't require hospitalization, or when there is anaphylaxis to β-lactam antimicrobials 1
For complicated UTI with systemic symptoms, the preferred empirical regimen is a combination therapy, such as amoxicillin plus an aminoglycoside, or a second-generation cephalosporin plus an aminoglycoside, or an intravenous third-generation cephalosporin 1
If the patient is hemodynamically stable without systemic symptoms, consider a β-lactam agent targeting both organisms based on susceptibilities, and treatment duration of 7-14 days 1

The Infectious Diseases Society of America and the European Urology guidelines recommend that antimicrobial stewardship principles and guideline recommendations supersede susceptibility testing alone, and levofloxacin should not be assumed appropriate simply because both organisms test susceptible in vitro 1, 2
The presence of S. aureus in urine warrants investigation for underlying urological abnormalities, recent instrumentation, or bacteremia 1
Fluoroquinolones should not be used as first-line therapy when guideline-recommended alternatives are available, to avoid contributing to resistance development 1, 2

Levofloxacin could be appropriate in specific scenarios, such as documented anaphylaxis to β-lactam antibiotics, local fluoroquinolone resistance rates <10%, patient does not require hospitalization, and no fluoroquinolone use in the preceding 6 months 1