Urinary tract infection (UTI) is a general term that describes infection anywhere in the urinary system. UTI can be further subclassified by the exact location of the infection, presence or absence of symptoms, and complications. In everyday practice, these classifications are subject to significant overlap and cause clinical confusion.
- Bacteriuria – Presence of bacteria in the urine.
- Cystitis – Syndrome involving constellation of dysuria, frequency, urgency, and occasionally suprapubic tenderness; can be present in the setting of lower urinary tract inflammation in the absence of infection or urethritis.
- Acute pyelonephritis – Clinical syndrome characterized by flank pain, flank tenderness, and fever often associated with cystitis symptoms in the presence of significant bacteriuria. This triad of symptoms (flank pain, fever, and nausea / vomiting) can also be seen in noninfectious etiologies, including renal calculi and renal infarction.
- Uncomplicated UTI – UTI in a structurally and neurologically normal urinary tract.
- Complicated UTI – UTI in the presence of anatomical or functional abnormalities. In general, UTIs in men, pregnant individuals, children, and patients in a health care-associated setting may be considered complicated.
- Urosepsis – Sepsis caused by a UTI.
UTIs are a common infection in neonates and children, with an incidence of approximately 1%-2%. They occur more commonly in males during the first 3 months of life and otherwise are more common in females throughout infancy and childhood.
Just as in adults, UTIs present with a range of symptoms in children. Patients may present with fever, abdominal or back pain, nausea or emesis, dysuria, hematuria, and/or fatigue. Approximately 7% of undifferentiated febrile illnesses in neonates and young infants are due to UTIs.
Bacteria are the leading cause of UTIs. Escherichia coli (80% of cases) and other gram-negative bacteria are the leading culprits. Gram-positive, viral, and fungal organisms are less likely to cause UTIs.
- Age: male patients younger than 1 year and female patients older than 4 years
- Uncircumcised males younger than 1 year
- Northern European ethnicity
- First-degree relative with history of UTI
- Anatomic or functional abnormality and resultant vesicoureteral reflux: posterior urethral valves, ureteropelvic junction obstruction
- Neurogenic bladder: spinal cord injury (ie, myelomeningocele)
- Bladder or bowel dysfunction
- Sexual intercourse (increases UTI risk in females)
- Bladder catheterization
- Ascending route – In the majority of the UTIs, pathogens gain access to the urinary tract by ascending up the urethra to the bladder. Further ascent of pathogens is the cause of the majority of renal parenchymal infections. Urethral massage and sexual intercourse facilitate the first step of this process in females. Indwelling catheters facilitate ascent, and spermicides promote vaginal colonization with pathogens.
- Hematogenous route – Associated with abscess formation in the kidneys. Usually results from bacteremia with virulent pathogens such as Staphylococcus aureus, Salmonella, or possibly Candida. Infection of the kidney with gram-negative bacilli through a hematogenous route is rare in humans, although ascending pyelonephritis can lead to bacteremia in 20%-30% of cases.
Prompt treatment of UTI is paramount to minimize potential for pyelonephritis, renal abscesses, and renal scarring that can result in chronic renal injury. If an underlying behavior or anatomic condition is identified that places the patient at increased risk for recurring UTIs, treatment of the underlying disorder is strongly advised. Risk factors for renal scarring due to UTI include delay in effective treatment, recurrent febrile UTIs, anatomic variants causing obstruction, and bladder / bowel dysfunction.