| disease | Pediatric Urinary Tract Infection |
| alias | Urinary Tract Infection, Feeling of Urination, Urinary Tract Infection, Urinary 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 affect both the upper and lower urinary tracts and is collectively termed UTI due to the difficulty in precise localization. Symptoms are categorized into acute and chronic types. The acute type has a sudden onset with more typical symptoms, making it easier to diagnose. Chronic and recurrent infections can lead to kidney damage. In children, recurrent infections are often associated with structural abnormalities in the urinary tract. It is essential to thoroughly investigate the underlying causes, address congenital obstructions, and prevent kidney damage and scar formation.
bubble_chart Etiology
1. Reasons why children are prone to urinary tract infections (UTIs)
(1) Physiological characteristics: Infants use diapers, and the urethral opening is often contaminated by feces. Combined with weak local defense mechanisms, this makes them susceptible to ascending infections, especially in girls due to their shorter urethra. Young infants also 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 stenosis at the ureteropelvic junction, hydronephrosis, posterior urethral valves, and polycystic kidneys can obstruct urine flow and lead to secondary infections. Additionally, obstruction may be caused by neurogenic bladder, stones, or tumors. In specialized medical centers, urinary tract abnormalities account for 25–50% of all UTIs.
(3) Vesicoureteral reflux (VUR): This is common in infants and young children. Internationally, 35–60% of children under 10 with UTIs 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, preventing reflux. In infants, however, the intravesical ureter is shorter, leading to incomplete closure during urination and subsequent 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, but Grade III often requires surgical correction. Therefore, identifying reflux in children with UTIs is crucial for accurate diagnosis and treatment.2. Pathogens: 80–90% of cases are caused by enteric bacteria. In primary UTIs, Escherichia coli is the most common pathogen, followed by Proteus, Klebsiella, and Enterobacter. Less frequently, infections are caused by Streptococcus faecalis, Staphylococcus aureus, or occasionally viruses, mycoplasma, or fungi. Over 90% of E. coli strains isolated from children with acute pyelonephritis are P-fimbriated, and the adhesiveness of P-fimbriae is believed to facilitate bacterial ascent. Incomplete treatment or underlying urinary tract abnormalities can lead to bacterial resistance, resulting in recurrent or chronic infections. Sometimes, under antibiotic pressure, bacteria may undergo morphological changes, with ruptured cell membranes, yet survive in the hypertonic renal medulla. If antibiotics are stopped prematurely, the bacteria can revert and cause relapse. These altered bacteria may not grow in standard culture media but require hypertonic, nutrient-rich conditions. Thus, for chronic pyelonephritis cases with persistent symptoms but negative urine cultures, hypertonic culture should be performed to identify the pathogen.
bubble_chart Clinical Manifestations
1. Acute urinary tract infection refers to cases with a disease course of less than 6 months. Symptoms vary depending on age and the affected site. Older children present similarly to adults, while younger children exhibit more systemic symptoms, with local urinary irritation symptoms often being milder or easily overlooked.
(1) Neonatal period: Mostly caused by hematogenous infection. Symptoms range in severity, primarily manifesting as systemic symptoms such as fever, poor feeding, pallor, vomiting, diarrhea, abdominal distension and fullness, and other nonspecific manifestations. Most infants may experience growth stagnation or slow weight gain. Some may have convulsions, drowsiness, or 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 diagnosis.
(2) Infancy and toddler stage: Systemic symptoms remain predominant, such as fever, mild cough, or recurrent diarrhea. Urinary symptoms like frequency, urgency, and dysuria become more apparent with age. Crying during urination, frequent urination, or stubborn diaper rash should raise suspicion. Jaundice may occasionally occur.
(3) Childhood: Lower urinary tract infections mainly present with irritative symptoms like frequency, urgency, and dysuria, sometimes with terminal hematuria or enuresis, while systemic symptoms are often mild. However, upper urinary tract infections typically feature more pronounced systemic symptoms, including fever, chills, malaise, possibly accompanied by lumbago and kidney tenderness, alongside urinary irritation symptoms. Some patients may have hematuria, but proteinuria and edema are usually mild. Renal function is generally unaffected. Incomplete treatment, recurrent episodes, or complicating factors like urinary obstruction or malformation may lead to chronicity.
bubble_chart Auxiliary Examination
1. Urine Sample Collection After cleaning the vulva, rinse with a 1:1000 solution of benzalkonium bromide, and collect the midstream urine for testing. Due to its simplicity and convenience, this is currently the most common method of urine collection. For infants, a sterilized plastic bag can be fixed to the vulva to collect urine, but if no urine is obtained within 30 minutes, disinfection must be repeated. Catheterization carries the risk of introducing bacteria and is generally avoided whenever possible. Suprapubic bladder puncture, performed under completely sterile conditions, yields reliable results and can be used when midstream urine or catheterization results are questionable. This method is simple and safe, with only 0.6% of cases showing hematuria within 24 hours post-procedure.
2. Routine Urine Test If the sediment of a clean midstream urine sample shows more than 5 white blood cells per high-power field (HPF), urinary tract infection should be considered. The presence of clumped white blood cells, white blood cell casts, or proteinuria increases diagnostic value, with the latter two indicating kidney involvement. However, the detection of white blood cells alone is insufficient to diagnose upper urinary tract infection.
3. Urine Culture and Colony Count These are critical for diagnosing the condition. Although the bladder is normally sterile, urine may be contaminated by 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%, though colony counts are lower. Therefore, relying solely on the presence of bacteria for diagnosis can lead to errors, and colony counts must also be performed. A colony count of ≥100,000/ml confirms a urinary tract infection, while 10,000–100,000/ml is suspicious, and <10,000/ml is likely contamination. For girls, if two consecutive urine cultures show ≥100,000/ml of the same bacterial species, the diagnosis is further supported. For boys, if the urine sample is uncontaminated and the colony count is ≥10,000/ml, a diagnosis of bacteriuria should be considered. Using fresh urine is crucial for culture; if immediate culturing is not possible, the sample should be stored at 4°C.
4. Direct Microscopic Examination of Urine for Bacteria A drop of well-mixed fresh urine is placed on a slide, dried, and stained with methylene blue or Gram stain. If more than one bacterium is observed per oil-immersion field, it indicates a bacterial count of ≥100,000/ml. This method is simple, rapid, and reasonably reliable, providing valuable diagnostic information.
5. Supplementary Tests for Bacteriuria Common tests include the nitrite reduction test, which serves as a screening tool with a positive rate of 80–90%. This method is simple, reliable, and free of false positives. However, it may yield false negatives if the urine lacks nitrates, if diuresis is excessive, or if antibiotics are being used. {|104|}
The diagnosis of typical cases can be confirmed based on symptoms and laboratory tests. Older children exhibit symptoms similar to adults, with obvious localized urinary symptoms, making diagnosis relatively easy. However, in infants and young children, urinary symptoms are often not apparent, leading to a high risk of misdiagnosis. For children with unexplained fever, 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 involves the upper or lower urinary tract, and whether there are any structural abnormalities in the urinary tract. Localizing urinary tract infections in children is often challenging, but clinical symptoms, renal function, and routine urine tests can be referenced for differentiation.
bubble_chart Treatment 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 the time bacteria remain in the bladder. Girls should pay attention to the cleanliness of the external genitalia and actively treat pinworms.
2. Antibacterial therapy: Early and aggressive use of antibacterial drugs is essential. 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 are preferred; ② Results of urine culture and drug sensitivity tests; ③ Drugs with minimal renal toxicity. Acute initial infections treated with the following drugs often show symptom improvement within 2–3 days, with disappearance of bacteriuria. If symptoms do not improve or bacteriuria persists after 2–3 days of treatment, it usually indicates bacterial resistance to the drug, and an early adjustment is necessary. In some cases, 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 developing resistance, and affordability, they are often the first choice for initial infections. The commonly used preparation is sulfamethoxazole (SMZ), often combined with the potentiator trimethoprim (TMP) (i.e., the compound formula co-trimoxazole, SMZco). The dose is 50 mg/(kg·d), divided into two doses. The usual course of treatment 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 Escherichia coli, due to its high urinary excretion rate, it is highly effective. It is suitable for various types of urinary tract infections. The dosage is 30–50 mg/(kg·d), divided into 3–4 oral doses. Side effects are minimal, with occasional grade I gastric discomfort. Use with caution in young children.
(3) Nitrofurantoin: It has a broad bacteriostatic spectrum and is highly effective against Escherichia coli, with a low likelihood of developing resistance. The dose is 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 stubborn infections requiring continuous treatment for 3–4 months.
(4) Norfloxacin: A fully synthetic broad-spectrum antibacterial drug of the quinolone class, it has strong antibacterial effects against both Gram-negative and Gram-positive bacteria. The dose is 5–10 mg/(kg·d), divided into 3–4 oral doses. Due to its potent antibacterial effects, long-term use may lead to microbial imbalance, so caution is advised. It is 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 tract infections. Although kanamycin and gentamicin have good 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 be adequate. After recovery, regular follow-ups should be conducted 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 each recurrence as an acute case; ② For patients with frequent recurrences, after acute symptoms are controlled, a small dose (1/3–1/4 of the therapeutic dose) of one of the following drugs—SMZco, nitrofurantoin, pipemidic acid, or norfloxacin—can be taken once daily at bedtime for 3–6 months. For patients with multiple recurrent infections or varying degrees of renal parenchymal damage, the treatment duration can be extended to 1–2 years. To prevent the emergence of resistant strains, combination therapy or rotating therapy can be employed, where each drug is used for 2–3 weeks before switching to another, 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.
Proper care of an infant's external genitalia is crucial. The buttocks should be cleaned after each bowel movement, and diapers should be washed frequently. Towels and basins used for the baby should be kept separate from those of adults, and open-crotch pants should be avoided 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 rapidly with appropriate antibiotic treatment, but half of the patients may experience recurrence or reinfection. Chronic sexually transmitted disease can be cured in 1/4 of cases, but some patients may progress to renal insufficiency over many years, especially those with congenital urinary tract malformations or obstructions. If not corrected in time, the prognosis is poor.
Follow-up: Due to the high likelihood of recurrence and the fact that 50% of cases are asymptomatic, regular follow-up for pediatric patients 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 patients with recurrent episodes, follow-up every 3 to 6 months should continue for 2 years or longer.
1. Pyonephrosis Pyonephrosis, also known as pyonephrosis (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 a cystic mass. After improving the general condition with antibiotics, blood transfusions, and other treatments, nephrectomy can be performed. Due to severe adhesions and scarring of the perirenal tissues, conventional nephrectomy may sometimes encounter significant difficulties, requiring subcapsular nephrectomy.
2. Perinephritis 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 parenchymal 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 condition irritates the psoas muscle, causing spasms and hip flexion, making it difficult to straighten the leg. Blood leukocytes are elevated, while routine urine tests are often normal. When coexisting with pyelitis, symptoms such as frequent urination and pyuria may also occur.
B-mode ultrasound is highly helpful for diagnosis, while X-ray examinations, though not definitive, provide significant assistance. The kidney and psoas muscle images appear blurred, and the spine curves toward the affected side. During respiration, pyelography shows the kidney remains immobile. Treatment primarily involves antibiotics combined with local heat or medicated compresses and fluid supplementation. 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. Routine urine tests show increased red blood cells, a few white blood cells, but mostly casts and proteinuria, often accompanied by edema and hypertension. A negative urine culture helps 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, and intravenous pyelography may reveal destructive sexually transmitted disease changes in the renal pelvis and calyces.
