DIFFERENTIAL URETHROVESICAL URINARY CELL-COUNT. A METHOD OF ACCURATE DIAGNOSIS OF LOWER-URINARY-TRACT INFECTIONS IN WOMEN

Contamination rates of three urine-sampling methods to assess bacteriuria in pregnant women

OBJECTIVE

To estimate and compare contamination rates of three different urine-sampling methods in pregnant women to assess bacteriuria.

METHODS

In this cross-sectional study, 113 pregnant women collected three different midstream urine samples consecutively: morning (first void); midstream (void without further instructions); and clean-catch sample (void after cleaning). The following end points were considered contaminants: epithelial cells, Gram-positive rods or mixed bacteria in the Gram stain, and mixed growth or skin flora in the urine culture. Intraindividual variability in contaminants was quantified with Fleiss-Cohen's weighted κ statistic. Differences between samples were assessed using generalized estimating equations.

RESULTS

Mainly low numbers of Gram-positive rods were more likely to be present in Gram stains of midstream samples compared with clean-catch samples (77.7% compared with 66.7%, P=.022). Morning samples showed more mixed growth compared with midstream samples (6.2% compared with 0.9%, P=.050). No consistency in quantity of contaminants was found in midstream samples compared with morning and clean-catch samples. No differences were found between the other end points in all three urine samples (P>.05). The study could detect an odds ratios of 2.0 for differences in urine-sampling methods with 80% power and 5% significance for most end points.

CONCLUSION

In pregnant women, the contamination rate of midstream samples is comparable with the contamination rates of morning and clean-catch samples. The quantity of contaminants varied among the three samples collected by one woman. These results show that more complex, unpractical, and time-consuming morning and clean-catch samples are not superior. Therefore, we recommend a midstream sample to assess bacteriuria in pregnant women.

LEVEL OF EVIDENCE

II.

Response to antibiotics of women with symptoms of urinary tract infection but negative dipstick urine test results: double blind randomised controlled trial

OBJECTIVE

To assess the effectiveness of antibiotic treatment of women with symptoms of urinary tract infection but negative urine dipstick testing.

DESIGN

Prospective, double blind, randomised, placebo controlled trial.

SETTING

Primary care, among a randomly selected group of general practitioners in Christchurch, New Zealand.

PARTICIPANTS

59 women aged 16-50 years presenting with a history of dysuria and frequency in whom a dipstick test of midstream urine was negative for both nitrites and leucocytes. Participants with complicated urinary tract infection were excluded.

INTERVENTION

Trimethoprim 300 mg daily for three days or placebo.

MAIN OUTCOME MEASURES

Self reported diary of symptoms for seven days, recording the presence or absence of individual symptoms each day, followed by a structured telephone questionnaire after seven days. The main clinical outcome was resolution of dysuria at three and seven days and median time to resolution. Secondary outcomes were resolution of other symptoms.

RESULTS

The median time for resolution of dysuria was three days for trimethoprim compared with five days for placebo (P = 0.002). At day 3, five (24%) of patients in the treatment group had ongoing dysuria compared with 20 (74%) in the placebo group (P = 0.005). This difference persisted until day 7: two patients (10%) in the treatment group v 11 (41%) in the placebo group; P = 0.02). The number needed to treat was 4. The median duration of constitutional symptoms (feverishness, shivers) was reduced by four days.

CONCLUSIONS

Although a negative dipstick test for leucocytes and nitrites accurately predicted absence of infection when standard microbiological definitions were used (negative predictive value 92%), it did not predict response to antibiotic treatment. Three days' treatment with trimethoprim significantly reduced dysuria in women whose urine dipstick test was negative. These results support the practice of empirical antibiotic use guided by symptoms. Balancing the competing interests of symptom relief and the minimisation of antibiotic use remains a dilemma-further research is needed to determine clinical predictors of response to antibiotics.

Measurement of pyuria and its relation to bacteriuria

Excluding specimen contamination, bacteriuria indicates either urinary colonization (replication of bacteria in urine without evidence of tissue invasion) or urinary tract infection (bacteriuria associated with clinical, histologic, or immunologic evidence of host injury). Practically speaking, measuring pyuria is the most readily available means of establishing the presence of host injury, thus differentiating colonization from infection. Careful studies have established the nonpathologic limits for pyuria (less than 10 leukocytes/mm3 in uncentrifuged urine) and have compared methods for its measurement. The most commonly used method, determination of cells per high power field in centrifuged urine, is not reproducible and does not correlate with either the actual leukocyte excretion rate or the cells per cubic millimeter as enumerated in a counting chamber. When clinical studies using the latter method of determining pyuria were reviewed, the following conclusions emerged: (1) 10 leukocytes/mm3 or greater occur in less than 1 percent of asymptomatic, nonbacteriuric patients but in greater than 96 percent of symptomatic men and women with significant bacteriuria; (2) most symptomatic women with pyuria but without significant bacteriuria have urinary infection either with bacterial uropathogens present in colony counts less than 10(5)/ml or with Chlamydia trachomatis; (3) women with asymptomatic bacteriuria probably should be divided into two subgroups: those with true asymptomatic infection (associated with pyuria) and those with transient, self-limited bladder colonization; and (4) most patients with catheter-associated bacteriuria also have pyuria and hence infection. In view of its potential value to both clinicians and microbiologists, pyuria should be accurately determined and expressed as cells per cubic millimeter in uncentrifuged urine.

Direct microscopy of uncentrifuged urine

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