To determine whether a statistical association exists between low-count bacteriuria (>10² to 10⁴ colony-forming units/mL) and acute urinary symptoms in young women.

Prospective, case–control study.

Gynecology clinic at a student health center.

Women with or without urinary or vaginal symptoms.

History of urinary infections and sexual activity. Quantitative determination of bacteriuria and pyuria and bacterial species; urine leukocyte esterase test; specific gravity; creatinine levels; vaginal leukocytes; and in vitro culture of urine.

The frequency of recent sexual activity, pregnancies, and contraceptive practices was not statistically different between women with acute urinary symptoms and asymptomatic controls. Escherichia coli and Staphylococcus saprophyticus were the only microorganisms statistically associated with urinary symptoms and pyuria (P < 0.001). Low counts of these organisms were found in 10.2% of asymptomatic women. As the bacterial count increased, the association between these organisms and symptoms increased, and a step-wise increase occurred in the frequency and magnitude of pyuria, but the specific gravity and urine creatinine levels remained unchanged. Escherichia coli, even at low counts, grew well in the patients' own urine. Pyuria (>20 leukocytes/mm³) was present in 19.6% of asymptomatic women and was associated with vaginal leukorrhea.

Low-count bacteriuria was statistically more frequent among young women with urinary symptoms than among asymptomatic controls. The low counts could not be explained by dilution of the urine or failure of the bacteria to grow well in the patients' urine. These findings suggest that the infection was not established in the bladder urine and that low-count bacteriuria might be an early phase of urinary tract infection.