[Asymptomatic bacteriuria]

With the availability of methods to quantitate microbes in urine, one has come to recognize that a certain proportion of apparently healthy individuals have bacteria in their urine in the absence of any clinical symptoms. By definition, asymptomatic bacteriuria is present, if on 1, 2 or more consecutive occasions > 100,000 colony forming units/ml are found in aseptically collected midstream urine, granted that the same microorganism is isolated. Such asymptomatic bacteriuria is found in 2.7% of women aged between 15 and 24 years and increases to 20 to 50% in women above an age of 80 years. In men the prevalence of asymptomatic bacteriuria is considerably lower, but increases to 6 to 20% above the age of 80 years. The microbe most frequently involved in asymptomatic bacteriuria is Escherichia coli, which is characterized by the expression of multiple virulence factors. In this respect they differ from bacteria found in patients with lower or upper urinary tract infections. There is a consensus that in the absence of anatomical or functional abnormalities of the urinary tract asymptomatic bacteriuria per se does not lead to renal scarring, renal dysfunction, or hypertension. The overall prevalence of asymptomatic bacteriuria in pregnancy varies between 2 and 10% with the very small risk of an acute symptomatic episode of urinary tract infection in early pregnancy, but with a substantial risk (30 to 60%) during the last trimester. There is an association between asymptomatic bacteriuria and low birth weight. Asymptomatic bacteriurias are seen in 4 to 60% of immunosuppressed renal graft recipients. The incidence of asymptomatic bacteriuria is also high among patients with diabetes mellitus; the prevalence is approximately 3 fold higher in adult women (7.9 to 11.1%). In these patients asymptomatic bacteriuria does not carry a renal risk. Renal functional prognosis in uncomplicated asymptomatic bacteriuria is excellent. Therefore asymptomatic bacteriuria should be treated during pregnancy, after renal transplantation, prior to urological interventions and in patients with frequent episodes of symptomatic urinary tract infection.