Table 1.

Etiologic agents of pediatric urinary tract infections.

Gram-negative organisms	Features
Escherichia coli	Most common organism. Causative agent in >80% of first UTIs.
Klebsiella species	Second most common organism. Seen more in young infants. Sixteen percent of bacteremic children have underlying urinary tract anomalies.
Proteus species	May be more common in males. Three of nosocomial UTIs.
Enterobacter species	Cause <2% of UTIs. Mostly nosocomial.
Pseudomonas species	Cause <2% of UTIs. Most prevalent non-enteric gram-negative pathogen.
Gram-positive organisms
Enterococus species	Uncommon >30 days of age. Commonest gram-positive pathogen. Up to 5% of UTIs.
Coagulase-negative Staphylocccus	Uncommon in childhood. If suspicion is high for UTI, adjust antibiotic therapy to cover; otherwise, a repeat culture is prudent.
Equivalent Staphlococcus saprophyticus	Rare prior to puberty. Up to 15% of adolescent female UTI.
Staphylococcus aureus	Uncommon >30 days of age.
Group B streptococci	Uncommon in childhood.