Bacteriology and clinical outcomes of urine mixed bacterial growth in pregnancy

The objective was to analyse the risk of significant bacteriuria in repeat urine cultures from pregnant women, following initial mixed bacterial results.

This retrospective study examined maternal characteristics and clinical features of women who repeated urine cultures due to previous mixed cultures results.

Of 262 women included, 80 (30.5%) had negative cultures and 125 (47.7%) had mixed bacterial growth in their repeat cultures. Positive results (≥10⁴ CFU/ml of a urinary pathogen) were obtained for 57 women (21.8% [95% CI 17.1-27.0]). For 37 (14.1%), the repeat specimen grew 10⁴-10⁵ CFU/ml of microorganisms; whereas for 20 women (7.6% [95% CI 4.9-11.3]), it grew ≥10⁵ CFU/ml. Among women with positive (>10⁴ CFU/ml) compared with those with negative or mixed growth, rates of urinary symptoms were higher (38.6% vs 23.4%, p=0.028), abnormal dipstick results (49.1% vs 21.0%, p<0.001) and hydronephrosis, as demonstrated by renal ultrasound (12.3% vs 2.0, p=0.003). In a multivariate logistic regression analysis, hydronephrosis was associated with the occurrence of a positive repeat culture (aOR = 10.65, 95% CI 2.07-54.90). The sensitivity and specificity for predicting a repeat urine culture with ≥10⁵ CFU/ml were 12.9% and 94.3% respectively, for urinary symptoms; and 19.7% and 97.4% respectively, for abnormal dipstick results.

Mixed bacterial growth might represent a true urinary tract infection in a considerable proportion of women who are symptomatic and have an abnormal dipstick urinalysis.