Age- and sex-related features and routes of transmission
The epidemiological pattern of UTIs directly depends on the child's sex and age. During the first year of life, infections are more frequently diagnosed in boys. This is due to the fact that congenital obstructive urinary tract anomalies, to which males are more predisposed, typically manifest during this age period.
In the 1-to-15-year age group, the situation changes drastically: girls are affected 6–10 times more often than boys. The reasons lie in anatomical and physiological features:
- Short and wide urethra.
- Close proximity of the external urethral meatus to the vagina and anus, which promotes high microbial contamination.
- During adolescence, hormonal changes cause transient urinary tract dilation, disrupting urodynamics.
The primary route of microbial invasion is urogenogenous (ascending). The hematogenous route of infection (associated with bacteremia) is less common and occurs predominantly in newborns and infants in their first months of life.
Etiology and defense mechanisms
The main source of infection is the patient's own intestinal microflora. In 94% of cases, inflammation is caused by gram-negative bacteria of the family Enterobacteriaceae. The absolute leader in acute uncomplicated UTIs is Escherichia coli. In complicated forms, nosocomial infection, or relapses, other pathogens come to the forefront: Proteus spp., Klebsiella spp., Pseudomonas spp., Enterococcus faecalis.
Uropathogenic strains of enterobacteria possess potent virulence factors:
- Adhesiveness: the presence of fimbriae allows bacteria to attach to the uroepithelium and retrograde migrate against the urine flow.
- Antiphagocytic activity: provided by capsular K-antigens that block phagocytosis.
- Hemolysin production: accelerates bacterial colony growth.
Normally, the urinary tract is protected from invasion by a complex of factors: the physicochemical properties of urine, adequate urine flow, and the production of anti-adhesive substances such as secretory immunoglobulin A and Tamm-Horsfall protein (uromodulin).
Classification and clinical presentation
To guide management strategy, UTIs are classified according to several criteria:
- By localization (topography): upper tract involvement (pyelonephritis) or lower tract involvement (cystitis, urethritis).
- By underlying uropathy: complicated (developing against the background of impaired urodynamics, urolithiasis, reflux) and uncomplicated (with anatomically normal tracts).
- By severity: severe (fever >39 °C, vomiting, marked dehydration) and non-severe.
- By setting of onset: community-acquired and nosocomial (iatrogenic, e.g., following catheterization).
Clinically, UTIs manifest with three main syndromes: intoxication, pain (pain localized in the abdomen or lower back), and dysuric syndromes. In young children, the equivalent of dysuria is often crying directly during urination.
Diagnostic methods
Diagnosis is based on detecting an inflammatory process (leukocyturia) and verifying the pathogen (bacteriuria).
A urinalysis in UTI typically reveals a neutrophilic type of leukocyturia (more than 10 cells per high-power field). Test strips are used for rapid assessment:
- Leukocyte esterase: an enzyme from destroyed neutrophils (the test is positive at a concentration starting from 10 cells per 1 µL).
- Nitrites: a product of gram-negative bacterial metabolism (triggered at a bacteriuria level of $\ge 10^5$ CFU/mL). The test may yield a false-negative result if the pathogen is unable to reduce nitrates.
Microbiological urine culture allows determination of the bacterial titer. A diagnostically significant threshold is considered $\ge 10^4$ CFU/mL (for free-catch urine in the presence of symptoms) or $>10^3$ CFU/mL (upon catheterization). In newborns, the diagnosis is confirmed by the mere fact of repeated isolation of the same pathogen, regardless of the titer.
Principles of treatment
The cornerstone of UTI treatment is antibiotic therapy. Urine sampling for microbiological testing must be performed strictly before treatment is initiated; however, waiting 48–72 hours for the results is unacceptable as this risks irreversible renal damage. Therefore, starting antibiotics are prescribed empirically.
- In severe cases, step-down therapy is employed: for the first 3–5 days, the drug is administered parenterally, and once acute symptoms subside, the patient is switched to oral administration of the same antibiotic class.
- For non-severe forms in children, oral agents are prescribed immediately, such as second-generation cephalosporins.
Treatment efficacy is evaluated at 72 hours. If there is no improvement, the drug must be changed based on an updated antibiogram, the urine culture repeated, and an ultrasound of the urinary system performed to rule out the formation of purulent foci or obstruction. In life-threatening conditions in an inpatient setting, the use of fluoroquinolones is permissible even in young children.
For rapid memorization of the clinical presentation of UTI, use the rule of three syndromes — the acronym BIP: Painful, Intoxication, Dysuric.
Class and exam questions
Why do girls aged 1 to 15 years contract UTIs significantly more often?
This is due to anatomical features (a short and wide urethra, proximity to the anus and vagina), and during puberty, to hormonal shifts that cause transient dilation of the urinary tract.
What does a "sterile" urine culture mean in the presence of UTI symptoms?
The absence of bacterial growth may be due to the presence of L-form bacteria, intracellular microorganisms (chlamydia, ureaplasma), or viral invasion.
What to do if the child's condition does not improve after 3 days of empirical therapy?
It is necessary to change the antibiotic taking into account culture results, submit urine for repeat microbiological testing, and perform an ultrasound to rule out purulent complications and obstruction.
What else to study on this topic
- Diagnostic criteria and management tactics for asymptomatic bacteriuria
- Differential diagnosis of acute pyelonephritis versus surgical pathology
- Reserve medications in the treatment of complicated UTIs (carbapenems, glycopeptides)
- Methods of local and physical therapy for chronic cystitis
- Lymphogenic pathway of renal infection: controversial issues
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