What is a Febrile UTI?
A febrile UTI is a urinary tract infection accompanied by fever (temperature ≥38.0°C or 100.4°F), representing tissue invasion beyond the bladder and indicating upper urinary tract involvement (pyelonephritis) or systemic infection. 1
Clinical Significance
Febrile UTIs represent serious bacterial infections that require prompt recognition and treatment because delays in appropriate antimicrobial therapy increase the risk of permanent renal damage and scarring. 1
The urinary tract has become the most frequent site of occult serious bacterial infections in young children, particularly since the introduction of effective vaccines against Haemophilus influenzae type b and Streptococcus pneumoniae dramatically reduced rates of bacteremia and meningitis 1
Renal scarring occurs in approximately 15% of children after their first febrile UTI episode, representing the most severe long-term sequela 2
Distinction from Uncomplicated UTI
Febrile UTIs are classified as complicated UTIs because they indicate systemic symptoms and tissue invasion, distinguishing them from simple cystitis (bladder infection without fever). 3
Uncomplicated UTIs are defined as cystitis in patients without fever, tissue invasion, or systemic infection 3
The presence of fever indicates the infection has progressed beyond the bladder to involve the kidneys (pyelonephritis) or has caused systemic infection (urosepsis) 3
Diagnostic Criteria in Pediatric Populations
In febrile infants and children aged 2-24 months, diagnosis requires both urinalysis showing pyuria and/or bacteriuria AND urine culture with ≥50,000 CFUs/mL of a uropathogen from a properly collected specimen (catheterization or suprapubic aspiration). 1
The clinical presentation in young infants is typically nonspecific, with fever being the most common symptom, though vomiting, diarrhea, irritability, or poor feeding may also occur 2
Fever is defined as temperature ≥38.0°C (100.4°F) in the pediatric guidelines 1
Risk Stratification
The prevalence of UTI among febrile infants without an apparent source is approximately 5%, but varies significantly based on age, sex, and circumcision status. 1
Uncircumcised boys have 4-20 times higher risk than circumcised boys 1
Girls have more than twice the prevalence of febrile UTI compared to boys overall 1
Infants younger than 2-3 months with fever and suspected UTI are considered high-risk patients 2
Clinical Implications
Prompt treatment is essential because experimental and clinical data demonstrate that delays in appropriate antimicrobial therapy for pyelonephritis increase the risk of permanent renal damage. 1