Urine culture becomes negative extremely fast after an antibiotic treatment (few hours). It is therefore absolutely necessary to perform this exam before any antibiotic treatment.
- Urine culture results are interpreted using leukocyturia and bacteriuria
- The presence of significant leukocyturia and/or bacteriuria in the absence of clinical signs of UTI should lead to reconsideration of the diagnosis of UTI
- The positivity threshold for leukocyturia is 10.4 leukocytes/mL or 10 leukocytes/mm3, without indwelling catheter, and in an immunocompetent host
The only exceptions to this rule are active pregnancy and before urological surgery
Immunocompetent host, without indwelling catheter
The significant thresholds for bacteriuria are as follows, and vary according to the germ isolated and patient’s gender:
| Germ | Men | Woman |
|---|---|---|
| E. coli, S. saprophyticus | ≥10.3 CFU | ≥10.3 CFU |
| Other bacteria: enterobacteria other than E. coli, enterococc | ≥10.3 CFU | ≥10.4 CFU |
If there is a discrepancy between clear symptoms of urinary tract infection and a non-significant bacteriuria and/or leukocyturia, the clinical diagnosis should take priority.
Modalities and duration must be adapted to patient’s condition and severity, gender and type of suspected infection (cystitis, pyelonephritis or prostatitis, and complicated or uncomplicated).
This is a situation of bacterial urinary colonization. This situation should not lead to the prescription of antibiotics, except:
- Pregnancy: any bacteriuria ≥ 10.5/mL in a pregnant woman must be treated, even if the patient is asymptomatic. Leukocyturia is non interpretable during pregnancy (physiological leukocyturia during
pregnancy). - Scheduled urological surgery: a significant but asymptomatic bacteriuria should be treated before any urological surgery. Antibiotic treatment should start 48 hours before surgery and continue until 48 hours after surgery (5 days of
antibiotics).
This situation corresponds to aseptic leukocyturia (leukocyturia ≥ 10.4/mL and bacteriuria below the expected threshold).
The main causes are:
- Urine culture performed after initiation of antibiotic therapy
- Urethritis
- Non-bacterial cystitis (tumor, foreign body in urinary tract, medication, urinary tract radiotherapy, etc.)
- Vaginitis
In the presence of a urinary catheter, leukocyturia is uninterpretable (will always be positive due to the presence of material in the urinary tract). Bacteriuria is also difficult to interpret, due to the very high frequency of urinary colonization on urinary material (presence of biofilm).
The diagnosis of catheter-associated urinary tract infection may be assessed if:
- Presence of bacteriuria ≥ at 10.5/mL
- AND presence of infection clinical signs (abdominal or back pain, behavioural changes such as confusion in the elderly, or patient clinical worsening)
The presence of ≥ 10.5/mL bacteriuria on urinary catheter and the absence of clinical signs of infection should not lead to antibiotic therapy, but rather to the diagnosis of bacterial colonization of the catheter.
If urinary tract infection is suspected, the recommended approach is to replace the urinary catheter and collect a urine sample for culture from the new catheter before prescribing antibiotics