What is the appropriate management for a patient with a urine culture showing mixed flora?

From the Guidelines

When a urine culture shows mixed flora, the most appropriate management is to repeat the urine culture with a properly collected specimen rather than initiating antibiotic treatment, as mixed flora usually indicates specimen contamination from the skin or perineal area during collection, not a true urinary tract infection (UTI) 1.

Key Considerations

• The method of collecting, storing, and preserving urine specimens has a critical influence on culture results, and poorly collected or preserved specimens can become easily contaminated with perineal, vaginal, and periurethral flora 1.
• Midstream urine collection may be the preferred choice for collection for most patients, but there are patient populations and clinical scenarios where a more invasive method of collection is preferred 1.
• If the patient has symptoms of a UTI (dysuria, frequency, urgency, suprapubic pain), empiric antibiotic therapy may be considered while awaiting repeat culture results, with common options including nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin 1.

Management Approach

• Instruct the patient to perform proper cleansing of the genital area and collect a midstream sample, with specific techniques for women (spreading the labia and cleansing front to back) and men (retracting the foreskin if uncircumcised and cleansing the glans).
• If the patient is asymptomatic, antibiotics should be withheld until a clean-catch specimen confirms infection, to prevent unnecessary antibiotic use and potential resistance 1.
• In catheterized patients, a new catheter should be placed before collecting the repeat specimen to avoid contamination from biofilm in the existing catheter.

Antibiotic Selection

• Consider using nitrofurantoin as a first-line agent for re-treatment, as resistance is low and, if present, decays quickly 1.
• Take into account patient allergies, side effects, and cost, as well as local antibiograms, when selecting an antibiotic regimen 1.

From the FDA Drug Label

When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. Appropriate culture and susceptibility tests should be performed before treatment in order to isolate and identify organisms causing infection and to determine their susceptibility to ciprofloxacin If anaerobic organisms are suspected of contributing to the infection, appropriate therapy should be administered.

The presence of mixed flora in a urine culture may indicate contamination. Re-culture is recommended to confirm the presence of a urinary tract infection. If a urinary tract infection is confirmed, antibiotic therapy should be guided by culture and susceptibility results 2. In the absence of susceptibility data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy 3.

• Key considerations:
  • Confirm the diagnosis of urinary tract infection with a repeat culture.
  • Use culture and susceptibility results to guide antibiotic selection.
  • Consider local epidemiology and susceptibility patterns when selecting empiric therapy.

From the Research

Urine Culture Mixed Flora Management

• A urine culture showing mixed flora is often considered contaminated, but it can also represent a true mixed infection, particularly in certain clinical settings such as long-term catheterization 4.
• The clinical significance of mixed bacterial cultures of urine is not always clear, and the frequency with which it signifies treatable mixed infection versus contamination or colonization is unknown 5.
• Studies have shown that mixed flora in urine cultures can be associated with female sex and older age, and patient education may not impact the rate of mixed flora 6.
• In cases of suspected urinary tract infection (UTI), empiric antibiotic therapy may be initiated, but it is essential to use the new antimicrobials wisely to avoid resistance development 7.
• Treatment options for UTIs due to various organisms, including ESBL-producing Enterobacteriales, carbapenem-resistant Enterobacteriales, and multidrug-resistant Pseudomonas spp., are available, and the choice of antibiotic should be guided by local susceptibility patterns and the patient's clinical condition 7.

Treatment Options

• For acute uncomplicated bacterial cystitis, first-line empiric antibiotic therapy options include nitrofurantoin, fosfomycin tromethamine, and pivmecillinam 7.
• Second-line options include oral cephalosporins, fluoroquinolones, and β-lactams, such as amoxicillin-clavulanate 7.
• For UTIs due to ESBL-producing Enterobacteriales, treatment options include nitrofurantoin, fosfomycin, pivmecillinam, and carbapenems 7.
• For UTIs caused by carbapenem-resistant Enterobacteriales, treatment options include ceftazidime-avibactam, meropenem/vaborbactam, and colistin 7.

Diagnostic Considerations

• Early species identification and antimicrobial susceptibility testing of each urinary isolate may be beneficial in the care of patients with mixed flora in their urine culture 4.
• A second urine specimen should be collected within 48 hours to compare the results and determine the clinical significance of the mixed culture 5.
• Patient education and proper collection of urine samples are crucial to minimize contamination and ensure accurate diagnosis 6.