| disease | Pediatric Urinary Tract Infection |
| alias | Ruinary Tract Infection |
Urinary tract infection (UTI), commonly referred to as urinary infection, is an inflammation caused by the direct invasion of bacteria into the urinary tract. The infection can involve both the upper and lower urinary tracts, and due to the difficulty in localization, it is collectively termed as UTI. Symptoms are categorized into acute and chronic types. The former has a sudden onset with more typical symptoms, making it easier to diagnose. Chronic and recurrent infections can lead to kidney damage. In children with recurrent infections, structural abnormalities of the urinary tract are often present, necessitating a thorough investigation to identify the cause, relieve congenital obstructions, and prevent kidney damage and scar formation.
bubble_chart Etiology
Disease Causes
1. Reasons Why Children Are Prone to Urinary Tract Infections
(1) Physiological Characteristics: Infants often use diapers, leading to frequent contamination of the urethral opening by feces. Combined with weak local defense mechanisms, this makes them susceptible to ascending infections, especially in girls due to their shorter urethra. Additionally, infants have poor antibacterial capabilities, making them prone to bacteremia, which can lead to descending infections.
(2) Congenital Malformations and Urinary Tract Obstruction: These are more common in children than adults. Conditions such as ureteropelvic junction stenosis, hydronephrosis, posterior urethral valves, and polycystic kidneys can obstruct drainage and lead to secondary infections. Other causes include neurogenic bladder, stones, and tumors. In specialized medical centers, urinary tract malformations account for 25–50% of all urinary tract infections.
(3) Vesicoureteral Reflux (VUR): Common in infants and young children. Internationally, 35–60% of children under 10 with urinary tract infections have VUR, though domestic reports are limited and require further observation. Normally, a segment of the ureter runs within the bladder wall. When the bladder fills with urine or during urination, the bladder wall compresses this segment to prevent reflux. In infants, the intravesical ureter is shorter, often leading to incomplete closure during urination and reflux. Bacteria can ascend with the reflux, causing infection. The danger of VUR lies in its potential to cause reflux nephropathy and renal scarring, particularly in children under 5. The severity of reflux correlates with the extent of renal scarring. Grade I reflux may resolve with age, while Grade III often requires surgical correction. Therefore, identifying reflux in children with urinary tract infections is crucial for diagnosis and treatment.2. Pathogens: 80–90% of cases are caused by enteric bacteria. In primary cases, Escherichia coli is the most common, followed by Proteus, Klebsiella, and Citrobacter. Less common pathogens include Enterococcus faecalis and Staphylococcus aureus. Occasionally, viruses, mycoplasma, or fungi may be responsible. Over 90% of E. coli strains isolated from children with acute pyelonephritis are P-fimbriated, with P-fimbriae adhesion being a key factor in ascending infections. Incomplete treatment or structural abnormalities can lead to bacterial resistance, resulting in recurrent or chronic infections. Sometimes, antibiotics cause bacterial mutations, rupturing cell membranes, but the bacteria survive in the hypertonic renal medulla. If antibiotics are stopped prematurely, the bacteria can revert and cause relapse. These bacteria may not grow in standard culture media, requiring hypertonic, nutrient-rich media. Thus, for chronic pyelonephritis with persistent symptoms and negative cultures, hypertonic cultures should be performed to identify the pathogen.
3. Routes of Infection: (1) Ascending infection, more common in girls; (2) Hematogenous infection, often seen in newborns and infants with conditions like impetigo, pneumonia, or sepsis; (3) Rarely, infection may spread via lymphatic pathways or from adjacent organs/tissues; (4) Instrumental urinary tract examinations can also introduce infection.bubble_chart Clinical Manifestations
1. Acute urinary tract infection refers to cases with a disease course within 6 months. Symptoms vary depending on age and the site of infection. Older children present similarly to adults, while younger children exhibit more pronounced systemic symptoms, with local urinary irritation symptoms often being milder or easily overlooked.
(1) Neonatal period: Mostly caused by hematogenous infection. Symptoms vary in severity, primarily manifesting as systemic symptoms such as fever, poor feeding, pallor, vomiting, diarrhea, abdominal distension and fullness, and other nonspecific presentations. Most infants may experience growth stagnation and slow weight gain. Some may have convulsions, drowsiness, and occasionally jaundice. However, local urinary symptoms are generally not obvious, so vigilance is required. For unexplained fever, early urine routine tests and urine/blood cultures should be performed for definitive diagnosis.
(2) Infancy: Systemic symptoms remain predominant, such as fever, mild cough, and recurrent diarrhea. Urinary symptoms like frequency, urgency, and dysuria become more apparent with age. Crying during urination, frequent urination, or persistent diaper rash should raise suspicion of this condition. Jaundice may occasionally occur.
(3) Childhood: Lower urinary tract infections mostly present with irritative symptoms like urinary frequency, urgency, and dysuria, sometimes with terminal hematuria and enuresis, while systemic symptoms are often minimal. Upper urinary tract infections, however, typically feature more pronounced systemic symptoms such as fever, shivering, malaise, possibly accompanied by lumbago and kidney tenderness. Irritative urinary symptoms may also coexist. Some patients may have hematuria, but proteinuria and edema are usually mild. Renal function is generally unaffected. In cases of incomplete treatment, recurrent episodes, or complicating factors like urinary obstruction or malformations, the condition may become chronic.
2. Chronic urinary tract infection refers to cases with a disease course exceeding 6 months and prolonged symptoms. Severity varies, ranging from asymptomatic to renal failure (initially manifesting as impaired concentrating ability). Recurrent episodes may present as intermittent fever, lumbar soreness, lack of strength, emaciation, and progressive anemia. Local lower urinary tract irritation symptoms may be absent or intermittent. Pyuria and cellular urine may be present or inconspicuous. Most affected children have concurrent urinary reflux or congenital urinary tract abnormalities. B-ultrasound or intravenous pyelography may reveal renal scarring, which can be mitigated with early intervention.[Auxiliary examinations]
1. Urine specimen collection: After cleaning the perineum, rinse with 1:1000 benzalkonium bromide solution, then collect midstream urine for testing. This simple and practical method is currently the most commonly used. For young infants, a sterilized plastic bag may be affixed to the perineum for urine collection, but if no urine is obtained within 30 minutes, repeat disinfection is necessary. Catheterization carries a risk of introducing bacteria and should generally be avoided. Suprapubic bladder puncture, performed under complete aseptic conditions, yields reliable results and may be used when midstream urine or catheterized urine results are questionable. This method is simple and safe, with only 0.6% of cases showing hematuria within 24 hours post-procedure.
2. Urine routine: In clean midstream urine sediment, white blood cells (WBC) >5/HP suggest possible urinary tract infection. Clustered WBCs, WBC casts, or proteinuria enhance diagnostic value, with the latter two indicating renal involvement. However, detecting WBC casts alone is insufficient for diagnosing upper urinary tract infection.
3. Urine culture and colony count are important bases for the diagnosis of this disease. Although the normal bladder is sterile, urine may be contaminated by miscellaneous bacteria during voiding. Midstream urine cultures from healthy children show bacterial growth in 60–70% of cases, while catheterized urine cultures show growth in 38%, but with fewer colonies. Therefore, relying solely on the presence or absence of bacterial growth as a diagnostic criterion often leads to errors, and colony counts must also be performed. A colony count of 100,000/ml or higher confirms a urinary tract infection, 10,000–100,000/ml is suspicious, and less than 10,000/ml is mostly contamination. If a girl's two urine cultures both show colony counts of 100,000/ml or higher with the same bacterial species, the diagnosis is further confirmed. For boys, if the urine sample is uncontaminated and the colony count is 10,000/ml or higher, a diagnosis of bacteriuria should be considered. Collecting fresh urine is crucial for culture; if immediate culturing is not possible, the sample should be stored at 4°C in a refrigerator.
4. Direct urine smear for bacteria: Take a drop of well-mixed fresh urine, spread it on a glass slide, and dry it. Stain with methylene blue or Gram stain. If more than one bacterial cell is observed per field under oil immersion, it indicates a bacterial count exceeding 100,000/ml in the urine. This method is simple, rapid, and reasonably reliable, providing meaningful diagnostic value.
5. Supplementary tests for bacteriuria: Commonly used methods include the nitrite reduction test, which serves as a screening test for this condition, with a positive rate of 80–90%. This method is simple, reliable, and free from false positives. However, it may yield negative results if the urine lacks nitrates, during vigorous diuresis, or when antibiotics are being used.
The diagnosis of typical cases can be confirmed based on symptoms and laboratory tests. In older children, the symptoms are similar to those in adults, with obvious local urinary symptoms, making diagnosis relatively easy. However, in infants and young children, urinary symptoms are often not obvious, leading to a high risk of misdiagnosis. For children with fever of unknown origin, urine should be repeatedly examined, and urine culture, bacterial count, and drug sensitivity tests should be performed before initiating antibiotic treatment.
For those confirmed to have the disease, further determination should be made regarding whether it is a primary infection or a recurrence, whether it is an upper or lower urinary tract infection, and whether there are any structural abnormalities in the urinary tract. Localizing urinary tract infections in children is often challenging, and differentiation can be based on clinical symptoms, renal function, and routine urine tests.
bubble_chart Treatment Measures
Therapeutic Measures:
The key to treating this disease lies in actively controlling infections, preventing recurrence, eliminating predisposing factors, correcting congenital or acquired urinary tract structural abnormalities, and preventing renal function damage.
1. General Treatment During acute infection, patients should rest in bed, drink plenty of fluids, and urinate frequently to reduce bacterial retention in the bladder. Girls should pay attention to vulvar hygiene and actively treat pinworms.
2. Antibiotic Therapy Early and aggressive antibiotic treatment should be applied. Drug selection is generally based on: (1) Site of infection: For pyelonephritis, drugs with high blood concentration should be chosen, while for lower urinary tract infections, drugs with high urinary concentration such as nitrofurans or sulfonamides should be selected; (2) Urine culture and drug sensitivity results; (3) Drugs with minimal renal toxicity. In acute initial infections, symptoms often improve and bacteriuria disappears within 2–3 days of treatment. If symptoms do not improve or bacteriuria persists after 2–3 days, it usually indicates bacterial resistance, and the drug should be adjusted early. If necessary, a combination of two drugs may be used.
(1) Sulfonamides: Due to their strong bacteriostatic effect against most Escherichia coli, high solubility in urine, low likelihood of resistance, and affordability, they are often the first choice for initial infections. The commonly used preparation is sulfamethoxazole (SMZ), often combined with the synergist trimethoprim (TMP) (i.e., the compound formula co-trimoxazole, SMZco). The dosage is 50 mg/(kg·d), divided into two doses. The usual course is 1–2 weeks. To prevent crystal formation in urine, patients should drink plenty of fluids. Use with caution in cases of renal insufficiency.
(2) Pipemidic acid (PPA): For urinary tract infections caused by E. coli, due to its high urinary excretion rate, it is highly effective. Suitable for various types of urinary infections. Dosage: 30–50 mg/(kg·d), divided into 3–4 oral doses. Side effects are rare, with occasional grade I gastric discomfort. Use with caution in young children.
(3) Nitrofurantoin: It has a broad bacteriostatic spectrum, is highly effective against E. coli, and rarely induces resistance. Dosage: 8–10 mg/(kg·d), divided into three oral doses. It may cause gastrointestinal reactions and is best taken after meals. It can also be used in combination with TMP. Nitrofurantoin is particularly suitable for persistent infections requiring 3–4 months of continuous treatment.
(4) Norfloxacin: A fully synthetic broad-spectrum quinolone antibiotic with strong antibacterial effects against both Gram-negative and Gram-positive bacteria. Dosage: 5–10 mg/(kg·d), divided into 3–4 oral doses. Due to its potent antibacterial action, long-term use may lead to microbial imbalance, so caution is advised. Generally not used in young children.
(5) Ampicillin and cephalosporins: Both are broad-spectrum antibiotics with good bacteriostatic effects and are commonly used to treat urinary infections. Although kanamycin and gentamicin have strong bacteriostatic effects, their significant nephrotoxicity and adverse effects on hearing warrant cautious use.
3. Treatment Duration For acute infections, if the chosen antibiotic is effective against the bacteria, a 10-day course is usually sufficient to control the infection in most patients. For cases without fever, a 5-day course may suffice. After recovery, patients should be followed up regularly for a year or longer. Since most recurrences are due to reinfection, long-term therapy is not recommended for all patients. Specific recommendations are as follows: (1) For patients with infrequent recurrences, treat as acute cases upon recurrence; (2) For patients with frequent recurrences, after acute symptoms are controlled, a small dose (1/3–1/4 of the therapeutic dose) of SMZco, nitrofurantoin, pipemidic acid, or norfloxacin may be taken once nightly before bedtime for 3–6 months. For patients with multiple recurrent infections or existing renal parenchymal damage, the course may extend to 1–2 years. To prevent resistant strains, combination therapy or alternating drugs may be used, switching every 2–3 weeks to enhance efficacy.
4. Active treatment of urinary tract structural abnormalities About half of pediatric urinary tract infections may be accompanied by various predisposing factors, especially in chronic or recurrent cases, which are often associated with urinary tract structural abnormalities. It is essential to actively identify and treat these abnormalities as early as possible to prevent kidney parenchymal damage.
It is important to carefully care for the baby's external genitalia. Clean the buttocks after each bowel movement, wash diapers frequently, and ensure the baby's towels and basins are separate from those used by adults. Avoid open-crotch pants as early as possible. During childhood, education on perineal hygiene should be emphasized, such as washing the buttocks daily, changing underwear frequently, and avoiding using foot-washing water to clean the buttocks.
Acute urinary tract infections can often recover quickly with appropriate antibiotic treatment, but half of the patients may experience recurrence or reinfection. Chronic sexually transmitted diseases can be cured in 1/4 of cases, but some patients may develop renal insufficiency over many years, especially those with congenital urinary tract abnormalities or obstruction, and the prognosis is poor if not corrected in time.
Follow-up: Due to the high likelihood of recurrence and the fact that 50% of cases are asymptomatic, regular follow-up for affected children is crucial. After completing the acute treatment course, monthly follow-ups should be conducted for 3 months. If no recurrence occurs, the condition can be considered cured. For those with recurrent episodes, follow-up every 3 to 6 months should continue for 2 years or longer.
1. Pyonephrosis Pyonephrosis, also known as pyonephrosis, refers to the extensive destruction of the kidney parenchyma caused by purulent infection, forming a pus-filled cavity. It often complicates infectious hydronephrosis, kidney stones, and pyelonephritis, especially when accompanied by urinary tract obstruction or sexually transmitted diseases. The clinical manifestations mainly include chronic pyuria and systemic wasting symptoms, such as fatigue, weakness, weight loss, malnutrition, anemia, and fever. Sometimes, due to extreme narrowing or complete occlusion of the ureteropelvic junction, there may be no urinary symptoms in the late stage [third stage], with the main manifestation being a lumbar mass. However, careful questioning may reveal a history of past urinary tract infections. Intravenous pyelography shows loss of kidney function on the affected side, and ultrasound can detect cystic masses. After improving the general condition with antibiotics and blood transfusions, a nephrectomy can be performed. Due to severe adhesions and scarring of the perirenal tissues, a standard nephrectomy may sometimes encounter significant difficulties, necessitating a subcapsular nephrectomy.
2. Perinephritis Perinephritis, also known as perinephric abscess, is rare in pediatrics but can occur at any age. The infection is located in the perirenal fat tissue and is usually unilateral. The pathogen is often Staphylococcus aureus, which spreads to the perirenal area via the bloodstream or lymph from other foci, particularly skin infections, which are often the primary source. It can also spread directly from kidney parenchyma infections to the perirenal tissues. Symptoms vary in severity, with severe cases presenting with high fever, shivering, nausea, vomiting, lumbago, and upper abdominal pain. Sometimes, the pain may radiate to the abdominal wall or lower limbs. The lesion irritates the psoas muscle, causing spasms and resulting in hip flexion, making it difficult to straighten the leg. Blood leukocyte counts are elevated, but urine tests are often normal. When perinephritis coexists with pyelitis, symptoms such as frequent urination and pyuria may also occur.
B-mode ultrasound is highly helpful for diagnosis. Although X-ray examination cannot confirm the diagnosis, it provides significant assistance. The kidney and psoas muscle images appear unclear, and the spine curves toward the affected side. During respiration, pyelography shows the kidney remains immobile. Treatment primarily involves antibiotics combined with local hot or medicated compresses and fluid replacement. If pus forms, incision and drainage can be performed after confirmation by puncture.
1. Glomerulonephritis Acute nephritis initial stage [first stage] may present with mild urinary tract irritation symptoms. Urinalysis shows increased red blood cells, a few white blood cells, but mostly casts and proteinuria, often accompanied by edema and hypertension. A negative urine culture aids in differentiation.
2. Renal tuberculosis More common in older children. There is a history of tuberculosis contact and symptoms of subcutaneous node infection and toxicity, with a positive subcutaneous node bacillus test. If the lesion involves the bladder, hematuria, pyuria, and urinary tract irritation symptoms may occur. Subcutaneous node bacilli can be detected in the urine. Intravenous pyelography may reveal destructive sexually transmitted disease changes in the renal pelvis and calyces.
