Quantitative definition of bacteriuria.

Quantitative criteria distinguish bacterial infection (or colonization) of the urine from contamination. These criteria depend on the fact that the density of bacteria in infected urine is usually several orders of magnitude higher than the density of bacteria in contaminated urine. Most research on quantitative definitions of infection has concerned Gram-negative rod infections in women. For asymptomatic bacteriuria, the most prevalent urinary tract infection, and for pyelonephritis, a criterion of 1 X 10(5) cfu/ml provides optimal separation of infection from contamination of voided urine. For acute dysuria and frequency, recent evidence supports the use of a colony count of 1 X 10(2) cfu/ml bacteria as the most useful criterion. For the diagnosis of catheter-associated urinary tract infection, the criterion of 1 X 10(5) cfu/ml has been used most commonly, although a lower threshold may be appropriate. Additional investigation is required to determine the most appropriate quantitative definition of infection in this and several other circumstances.