A urinary tract infection (UTI) in a newborn (infant less than 28 days old) is a serious medical event requiring immediate attention. Unlike UTIs in older children, this condition often indicates a systemic illness, or urosepsis, where the infection has spread to the bloodstream. Prompt diagnosis and treatment are necessary to prevent severe outcomes, including long-term kidney damage. UTIs are one of the most frequent serious bacterial infections in young infants.
Recognizing the Signs of UTI in Newborns
Identifying a UTI in a newborn is challenging because the signs are frequently non-specific and subtle. The most common sign is an unexplained fever, which may be the only indication of infection in up to 85% of cases. Some newborns may instead present with hypothermia, an abnormally low body temperature.
Behavioral changes are common, including lethargy, excessive irritability, or a general appearance of being unwell. Feeding difficulties are another strong indicator, manifesting as poor feeding or a failure to gain weight (failure to thrive). Gastrointestinal symptoms, such as vomiting or diarrhea, can also occur, further complicating the diagnosis.
Other associated signs include prolonged or worsening jaundice after the first week of life. Respiratory symptoms like a rapid breathing rate (tachypnea) or temporary cessation of breathing (apnea) may also be present, especially in premature infants. Due to the high risk of serious bacterial illness, any newborn with a fever and no clear source of infection should be evaluated for a UTI.
Primary Causes and Vulnerability Factors
The primary cause of a neonatal UTI is the entry and multiplication of bacteria from the gastrointestinal tract, most commonly Escherichia coli. This bacteria accounts for the majority of infections. Fecal contamination in the diaper area facilitates the bacteria ascending the urethra into the bladder. In newborns, the infection often travels up to the kidneys, causing pyelonephritis, a more serious kidney infection.
Anatomical differences make newborns susceptible to these infections. Uncircumcised male infants have a higher risk because bacteria can accumulate under the foreskin. A UTI in this age group can also signal an underlying structural issue known as congenital anomalies of the kidney and urinary tract (CAKUT).
CAKUT includes conditions like vesicoureteral reflux (VUR), where urine flows backward toward the kidneys, and obstructions like pelvi-ureteral junction obstruction (PUJO). These structural issues compromise the normal flow of urine, creating stasis that allows bacteria to multiply easily. Premature infants are also at an increased risk, with UTIs occurring in up to 3% of preterm babies compared to 0.7% of full-term infants.
Medical Confirmation and Testing Methods
Confirming a UTI requires obtaining a sterile and reliable urine sample for laboratory analysis, which is challenging since the infant cannot voluntarily urinate on command. Collecting urine using a bag attached to the perineum is highly discouraged for culture due to the high contamination rate and unreliable results. A definitive diagnosis requires a sample collected directly from the bladder.
The two most reliable methods are urinary catheterization (UC) and suprapubic aspiration (SPA). Catheterization involves inserting a small, sterile tube through the urethra into the bladder to withdraw a sample. SPA, considered the gold standard for uncontaminated samples, involves inserting a fine needle through the lower abdominal wall directly into the full bladder.
SPA is often preferred because it bypasses the urethra, minimizing the risk of a false-positive culture. Using a bladder ultrasound to confirm the bladder is full improves the success rate of SPA. A urine culture is performed to confirm the presence and type of bacteria, with a positive catheterized specimen typically requiring at least 50,000 colony-forming units per milliliter for diagnosis.
Therapeutic Approaches and Hospitalization
The standard treatment protocol for a neonatal UTI involves immediate hospitalization and the administration of broad-spectrum antibiotics. This aggressive approach is necessary because UTIs in this age group are frequently associated with urosepsis, the spread of infection to the bloodstream. Intravenous (IV) antibiotics, such as a combination of ampicillin and gentamicin, are typically started immediately before culture results are available.
The initial course of IV antibiotics is generally maintained until the infant shows clinical improvement, such as the resolution of fever, and the specific bacteria’s antibiotic sensitivities are known. Clinical practice has moved toward shorter IV courses, sometimes reducing the duration to three days before transitioning to oral medication. The total duration of antibiotic treatment for a neonatal UTI typically ranges from 10 to 14 days.
Transitioning to an oral antibiotic regimen is possible once the infant is clinically stable, tolerating oral feeding, and blood cultures are negative. The choice of oral antibiotic is then narrowed based on the laboratory’s sensitivity report to target the specific pathogen. Close monitoring in the hospital setting ensures that the infection is rapidly controlled and complications are avoided.
Potential Long-Term Health Consequences
The most significant long-term consequence of a complicated neonatal UTI is renal scarring, which is permanent damage to the kidney tissue. When the infection causes pyelonephritis, the resulting inflammation can lead to scar formation, potentially occurring in up to 15% of children after a first febrile UTI. This scarring can impair the kidney’s function over time.
Renal scarring is associated with a higher risk of long-term health issues, including hypertension and chronic kidney disease later in life. Although the risk is low in children without underlying anatomical problems, a UTI can indicate a pre-existing condition that increases vulnerability to kidney damage, such as vesicoureteral reflux (VUR).
Follow-up imaging is necessary after an initial UTI to assess the urinary tract for underlying abnormalities. A renal and bladder ultrasound (RBUS) is commonly performed to check for structural issues or signs of damage. In some cases, a voiding cystourethrogram (VCUG) may be performed, using X-rays and contrast dye to visualize the bladder and check for VUR.