Bacterial infections cause over 80 percent of urinary tract infections. Usually, the source of the bacteria is the stool or the vagina. Bacteria enter the urethra, and then spread to the bladder of kidneys. E. coli bacteria are the most common cause of urinary tract infection.

Less common bacterial causes of urinary tract infections in children include:

• Staphylococcus saprophyticus
• Staphylococcus aureus
• Klebsiella pneumoniae
• Proteus mirabilis
• Enterococci
• Pseudomonas aeruginosa
• Enterobacter species

Rare causes of urinary tract infections in children include:

• Fungi
• Parasites
• Viruses