Urinary tract infection (UTI) refers to the invasion of pathogenic microorganisms into the urinary tract, leading to pyelonephritis, cystitis, or urethritis. When the exact location is difficult to determine, it is collectively referred to as a urinary tract infection. This condition is relatively common in pediatrics and ranks third among hospitalized children with urinary system diseases. In infants and young children, urinary tract symptoms may be inconspicuous, easily leading to misdiagnosis as fistula disease. In children under 4 years old, especially those with vesicoureteral reflux, kidney scarring may occur. Among those with reflux nephropathy, 5–10% may develop hypertension, warranting clinical attention. During the neonatal period, the incidence is higher in boys than in girls, but after 1 year of age, girls are more commonly affected. Common pathogens include Escherichia coli (accounting for about 80%), Proteus, and Enterococcus faecalis, with fewer cases caused by Staphylococcus aureus, Pseudomonas aeruginosa, hemolytic streptococci, and Staphylococcus epidermidis. In neonates, infections often result from hematogenous spread, whereas in older children, ascending infections are more common. Congenital urinary tract abnormalities (especially obstructive anomalies such as ureteropelvic junction stenosis or posterior urethral valves), vesicoureteral reflux, urinary tract instrumentation, indwelling catheters, systemic immunodeficiency, urinary tract foreign bodies, and stones can predispose to this condition. Such children often experience recurrent or persistent infections. If the condition lasts for more than 6 months, it is termed chronic urinary tract infection, with common pathogens including Pseudomonas aeruginosa, Clostridium perfringens, Proteus, Enterococcus faecalis, or occasionally mixed infections.

1. Urinalysis: Clean-catch midstream urine, centrifuged and examined under a microscope, shows >5 white blood cells per high-power field in the sediment, occasionally seen in clusters. However, it should be noted that urine pH affects the white blood cell count in urine. White blood cells in alkaline urine may be destroyed. In Proteus infections, urea is decomposed to produce ammonia, making the urine alkaline, resulting in fewer white blood cells in the urine. Additionally, there may be a small amount of urinary protein, and occasional hematuria.
2. Urine culture and colony count: Since the anterior urethra of healthy individuals harbors a small number of bacteria, a clean-catch midstream urine culture with bacterial counts >10⁵/ml indicates significant bacteriuria, confirming a urinary tract infection. When the count is <10< 10³/ml, it suggests bacterial contamination of the urine sample. Low bacterial counts may still have diagnostic value if the same bacterial species is repeatedly cultured. A positive suprapubic bladder puncture culture in infants and young children, especially with bacterial counts >10³/ml, is more diagnostically significant. Note that prior or current use of antibiotics, urine dilution, or excessively acidic or alkaline urine can affect culture results. Drug sensitivity testing should be performed simultaneously with urine culture.
3. Urine smear for bacteria: A fresh drop of urine is placed on a slide, dried, and Gram-stained. The presence of at least 1 bacterium per oil-immersion field suggests a culture count >10⁵/ml, which is also diagnostically significant.
4. Although urinary tract infection can be diagnosed based on clinical manifestations and urine culture, further differentiation between upper urinary tract infection (pyelonephritis) and lower urinary tract infection (cystitis, urethritis) is sometimes necessary to determine treatment and prognosis. The following methods may be helpful:
   1. Urine antibody-coated bacteria (ACB) test: Fluorescent-labeled anti-IgG is used to detect antibody-coated bacteria in the urine sediment. This simple method has considerable sensitivity and specificity for distinguishing upper (positive) from lower (negative) urinary tract infections.
   2. Urine β2-microglobulin measurement: Elevated in upper urinary tract infections but usually within the normal range in lower urinary tract infections.
   3. Urine lysozyme measurement: Elevated in upper urinary tract infections, but note that the number of white blood cells in the urine may sometimes interfere with the results.
5. Renal function tests: Pyelonephritis often involves impaired urine concentration. In advanced-stage chronic pyelonephritis, renal function (including glomerular function) is generally affected, but tubular dysfunction is more prominent.
6. X-ray examination: Should be performed for recurrent or persistent cases. Plain films and intravenous pyelography can detect stones, congenital anomalies, and hydronephrosis. Voiding cystourethrography examines vesicoureteral reflux and bladder/urethral abnormalities.
7. Ultrasound examination: Safe and simple, it can assess kidney size, bladder capacity, residual urine, and the presence of hydronephrosis or stones.
8. Renogram: A screening method for split renal function, helpful in detecting urinary obstruction and reflux. Generally, X-ray and nuclear studies are reserved for recurrent cases or those unresponsive to 2–4 weeks of treatment.

bubble_chart Diagnosis

The symptoms and signs of pediatric patients vary depending on the site of infection (upper or lower urinary tract), age, and whether the infection is acute or chronic. Neonates and infants primarily exhibit systemic symptoms, while local urinary symptoms may be inconspicuous.

In the neonatal period, most cases result from hematogenous infection, often accompanied by sepsis or as part of sepsis. The manifestations include severe systemic symptoms such as fever, refusal to feed, pallor, vomiting, diarrhea, and failure to gain weight, sometimes with abdominal distension and fullness, and jaundice. Some infants may present with convulsions, drowsiness, or irritability.

Infants and young children show prominent systemic symptoms, including fever, vomiting, diarrhea, abdominal pain, abdominal distension and fullness, and lethargy. Urinary symptoms often manifest as frequent urination, persistent diaper rash, or crying during urination.

Older children exhibit both systemic and distinct local symptoms, such as frequent urination, urgency, dysuria, and sometimes enuresis. Those with pyelonephritis may experience fever, chills, lumbago, and costovertebral angle tenderness, occasionally with transient hematuria.

Chronic cases are often associated with urinary tract obstruction, with a病程 typically exceeding six months. Symptoms vary in severity and generally include recurrent fever, lumbar soreness, lack of strength, emaciation, growth retardation, and anemia. A少数 may develop hypertension or even renal impairment. During physical examination, special attention should be paid to abdominal palpation to check for masses in the renal, ureteral, or bladder regions, changes in mass size before and after urination, and the presence of phimosis. The urethral orifice and surrounding areas should be inspected for inflammation. In boys,排尿情况 (e.g., straining, interrupted stream, or dribbling) should be noted. Blood pressure should be measured in chronic cases.

(1) General Treatment

Rest, drinking plenty of water, and timely urination can reduce the retention of bacteria in the bladder. Pay attention to the cleanliness of the external genitalia. Severe bladder irritation symptoms may be appropriately treated with sedatives such as Luminal or Valium. Anticholinergic antispasmodics like atropine can also be administered orally. There are also reports of using oxybutynin chloride, which can inhibit the detrusor muscle, relieve perineal muscle spasms, and alleviate urethral pain.

(2) Antibacterial Therapy

Before administering medication, urine samples should be collected for bacterial culture and drug sensitivity testing. If clinical symptoms do not improve within 48 hours, a second culture should be sent to assess whether the initial drug choice was appropriate. Since most pathogens are Escherichia coli or paracolon bacilli, drugs sensitive to E. coli should be used first before culture results are obtained.

1. Sulfonamides: Commonly used compound sulfamethoxazole (SMZ, TMP tablets): SMZ 50mg/kg daily, divided into two oral doses.
2. Nitrofurantoin: 5–10mg/kg daily, divided into three doses. It has a broad antibacterial spectrum, being effective against E. coli and staphylococci, less effective against Proteus and Aerobacter, and ineffective against Pseudomonas aeruginosa. It may cause local gastric irritation, such as nausea and vomiting, and should be taken after meals if necessary. Long-term use may lead to peripheral neuritis.
3. Nalidixic acid: Adults 500mg, three times daily; dosage should be reduced for children and generally not used for infants. Side effects include gastrointestinal reactions, urticaria, eosinophilia, leukopenia, and overdose may cause convulsions. It should not be used concurrently with nitrofurantoin due to antagonistic effects.
4. Quinolone antibiotics: Include pipemidic acid (20–30mg/kg daily), norfloxacin (10–15mg/kg daily, rarely used in children), and ofloxacin (300–600mg daily for adults), divided into 2–3 oral doses. This class Yaodui is effective against Gram-negative bacilli such as E. coli, Proteus, Pseudomonas aeruginosa, and Klebsiella. Ofloxacin has a broader spectrum, being effective against Staphylococcus aureus and Enterococcus. It is well absorbed orally and primarily excreted unchanged in urine. Side effects include gastrointestinal reactions, leukopenia, occasional elevated transaminases, and accumulation in patients with renal insufficiency.
5. Semi-synthetic broad-spectrum penicillins: Commonly used ampicillin (50–100mg/(kg·d)) orally or intravenously. However, bacterial production of β-lactamase may reduce efficacy. Recently, sulbactam (an inhibitor of β-lactamase produced by penicillin-resistant bacteria) combined with ampicillin (brand name Unasyn) (dose 150mg/(kg·d), equivalent to 50mg/kg sulbactam and 100mg/kg ampicillin) has been used intramuscularly or intravenously. A skin test is required before use. Another option in this class is amoxicillin (20mg/(kg·d)) divided into three oral doses.
6. Cephalosporins: Semi-synthetic broad-spectrum antibiotics with a core structure similar to penicillin, leading to cross-allergenicity but no cross-resistance. They have strong bactericidal and bacteriostatic effects against both Gram-negative and Gram-positive cocci or bacilli. Commonly used for urinary tract infections include cephalexin (25–50mg/kg daily in divided oral doses) and cefazolin (25–50mg/kg daily intramuscularly or intravenously).
7. Aminoglycosides: These have stronger antibacterial effects against Gram-negative bacilli than against Gram-positive bacteria. However, they are toxic to the eighth cranial nerve and can cause permanent sensorineural deafness. They should also be used with caution in patients with renal insufficiency. Examples include gentamicin (30,000–50,000 U/kg per day, divided into two doses for intramuscular injection or intravenous infusion) and amikacin (15 mg/kg per day, divided into 2–3 doses for intramuscular injection). There is still no consensus on the duration of treatment. For acute infections without complications, some authors advocate a single high-dose treatment for efficacy, but most still use a 7–10 day course. For upper urinary tract infections with systemic symptoms, treatment is given for 10–14 days. Severe infections in newborns are managed as sepsis. For recurrent cases, after acute symptoms are controlled, a small dose (usually one-third of the standard dose) is given once daily at bedtime for 3–6 months.

(4) Strengthening Follow-up

Urinary tract infections are prone to recurrence. For acute cases, follow-up should be conducted once a month for a total of 3 times. For recurrent cases, re-examination should be performed every 3 to 6 months for a total of 2 years. In addition to monitoring general symptoms and routine urine tests, follow-up examinations should include bacteriological urine tests. For children with pyelonephritis who already show X-ray changes, renal function tests and renal X-ray plain films or ultrasound examinations should be performed every 1 to 2 years to assess kidney parenchymal thickness, kidney development, and the presence of scarring, among other conditions.