Urinary tract infection in children

　　Any pathogenic bacteria can cause urinary tract infections in children, but the vast majority are gram-negative bacilli, such as Escherichia coli, Paracoccus, Proteus, Klebsiella, Pseudomonas aeruginosa, with a few being Enterococcus and Staphylococcus. Escherichia coli is the most common pathogen in urinary tract infections in children, accounting for 60% to 80%. For newborns who are first diagnosed with urinary tract infections, girls of all ages and boys under 1 year old, the main pathogen is still Escherichia coli, while for boys over 1 year old, the main pathogen is often Proteus. For girls aged 10 to 16, Staphylococcus albus is also common, and Klebsiella and Enterococcus are more common in newborn urinary tract infections.

　　Urinary tract infections in children can cause high fever, convulsions, sepsis, and recurrent infections can lead to chronic hypertension and chronic renal failure, among other complications, and can also cause renal papillary necrosis, perinephritis, and perinephric abscess, infectious renal calculi, and gram-negative bacillary sepsis.

　　1. Renal papillary necrosis: Renal papillary necrosis can affect the entire pyramid, with large pieces of necrotic tissue falling off from the tip of the papilla to the junction of the renal cortex and medulla. Small pieces of tissue can be excreted in urine, while large pieces can block the urinary tract, leading to symptoms of pyelonephritis complicated with renal papillary necrosis, in addition to the exacerbation of symptoms of pyelonephritis, including renal colic, hematuria, high fever, rapid deterioration of renal function, and possible concurrent gram-negative bacillary sepsis. If both kidneys are affected by acute renal papillary necrosis, the patient may experience oliguria or anuria, leading to acute renal failure. The diagnosis of this disease mainly relies on the inciting factors and clinical manifestations, with two main diagnostic criteria: ① Finding necrotic renal papillary tissue in urine, confirmed by pathological examination; ② Discovering annular signs in intravenous pyelography, and/or worm-eaten-like changes at the edge of the renal calyces, both of which are helpful for diagnosis. Treatment should include the use of effective antibiotics to control systemic and urinary tract infections; various supportive therapies to improve the patient's condition; and active treatment of the underlying diseases such as diabetes and urinary tract obstruction.

　　2. Perinephritis and perinephric abscess: Infection of the fatty tissue between the renal capsule and perirenal fascia is called perinephritis. If an abscess occurs, it is called a perinephric abscess. This disease is often caused by direct extension from pyelonephritis (90%), with a small part (10%) being hemogenous infection. The onset of the disease is insidious, and obvious clinical symptoms appear after several weeks. Patients, in addition to the worsening symptoms of pyelonephritis, often experience unilateral, pronounced back pain and tenderness. Some patients may feel a mass in the abdomen. When the inflammation involves the diaphragm, respiration and diaphragmatic movement are restricted, and there is often a pulling pain during respiration. Chest X-ray fluoroscopy shows local diaphragmatic bulging. If the lesion is caused by an intrarenal lesion, there may be a large number of pus cells and pathogenic bacteria in the urine. If the lesion is only in the perirenal area, there are only a few white blood cells. The diagnosis of this disease mainly relies on clinical manifestations, X-ray examination, renal cystography, ultrasound, and CT, which are helpful in confirming the diagnosis. Treatment should be the early use of antimicrobial drugs to promote the regression of inflammation, and if an abscess forms, incision and drainage should be performed.

　　3. Infection-related renal calculi: Infection-related renal calculi are formed by infection and are a special type of calculus, accounting for 15% to 20% of renal calculi. Their main components are magnesium ammonium phosphate and calcium phosphate. The treatment of infection-related renal calculi is difficult, with a high recurrence rate. If not properly treated, it may lead to chronic pyelonephritis and even renal failure. Clinical manifestations, in addition to those commonly seen in renal calculi, also have their own characteristics. Infection-related calculi grow quickly and often appear in large, antler-like shapes. They are visible on X-ray films and are often accompanied by a history of persistent or recurrent infections with pathogenic bacteria such as Proteus. The diagnosis of this disease can be made based on medical history, physical examination, urine analysis, and X-ray examination. Patients often have a history of Proteus urinary tract infection, with urine pH greater than 7 and positive urine bacterial culture. Treatment includes medical treatment, surgical treatment, and other treatment methods. For renal calculi less than 0.7 to 1 cm in diameter with smooth surfaces, medical treatment can be used. At present, there are no satisfactory drugs for dissolving calculi, and it is usually necessary to use drugs sensitive to bacteria. Secondly, acidifying urine can be achieved with ammonium chloride, etc. Surgical treatment is an important treatment measure, and patients should be advised to undergo surgery as soon as possible. Other treatments include increased fluid intake, acidifying urine, diuresis, and antispasmodics.

　　4. Gram-negative bacillary sepsis: In Gram-negative bacillary sepsis, 55% is caused by urinary tract infection. The main symptoms include chills, high fever, and generalized sweating upon onset. Some patients may only experience mild general discomfort and moderate fever. Later, the disease can become severe, with a rapid drop in blood pressure, which may lead to obvious shock. Clinical manifestations of ischemia in the heart, brain, and kidneys, such as oliguria, azotemia, acidosis, and circulatory failure, may occur. Shock usually lasts for 3 to 6 days, and severe cases may result in death. The diagnosis of this disease relies on positive blood bacterial culture, so it is advisable to perform blood bacterial culture and drug sensitivity test before applying antimicrobial drugs, and to carry out repeated cultures during the course of the disease. The mortality rate of Gram-negative bacillary sepsis is 20% to 40%. Eliminating the source of infection is an important measure for the treatment of septic shock, and common measures include antimicrobial therapy, correcting water and electrolyte and acid-base imbalances, using large amounts of corticosteroid hormones to alleviate toxic symptoms; trying heparin to prevent and treat DIC, and ensuring a通畅 urinary tract.

　　Due to different ages and infection sites, pediatric urinary tract infection mainly has three forms: namely, pyelonephritis, cystitis, and asymptomatic bacteriuria.

　　1. Pyelonephritis: Infants and young children are most affected, with systemic infection and poisoning symptoms as the main manifestation. There is often a fever above 38.5℃, with convulsions or chills during high fever, accompanied by general discomfort, fatigue, yellowish complexion, vomiting, nausea, diarrhea, and in older children, pain in the costal or lumbar region, renal area percussion pain. Newborns may present like sepsis, with weight loss, feeding difficulties, jaundice, irritability, fever, or body temperature not rising.

　　1. Cystitis: Most common in older girls, with symptoms such as frequent urination, urgency, difficulty in urination, incomplete urination, discomfort in the lower abdomen, suprapubic pain, urinary incontinence, sometimes with foul-smelling urine, vulvar eczema, and cystitis usually does not cause fever.

　　2. Asymptomatic bacteriuria: Asymptomatic bacteriuria refers to positive urine culture in children without any clinical symptoms of infection, almost all are girls. However, if not treated, it may develop into symptomatic urinary tract infection. Patients often have symptoms of infection or urinary tract irritation, and a diagnosis can be made by combining urinalysis and urine culture colony count.

　　The importance of urine screening in the prevention of pediatric urinary tract infection should be emphasized. Detect patients in a timely manner and treat them promptly; develop good habits of drinking plenty of water, not holding urine, and keeping the perineum clean; strictly control the indications for catheterization and try to avoid urinary tract instrumental examination; for patients with frequent recurrence of urinary tract infection, a comprehensive examination should be conducted, a diagnosis and evaluation should be made, and urinary tract obstruction and vesicoureteral reflux should be ruled out.

　　In clinical practice, urinalysis and radionuclide examination are mainly used to diagnose pediatric urinary tract infection. The main methods are as follows:

　　1. Blood test

　　Acute pyelonephritis often has significantly increased total blood leukocytes and neutrophil percentage, rapid blood sedimentation, and C-reactive protein >20mg/L. These above-mentioned test indicators are mostly normal during cystitis.

　　2. Urinalysis

　　Cleaned midstream urine centrifugal examination with white blood cells ≥5 per high power (Hp) suggests urinary tract infection. If there are white blood cell casts, it indicates pyelonephritis, and the renal papilla or bladder inflammation may have significant hematuria. In severe urinary tract inflammation, there may be transient and obvious proteinuria, and some children may have hematuria or terminal hematuria.

　　3. Bacteriological examination

　　Urine culture is an important evidence for diagnosis, and it should be done before the use of antibiotics. Do not drink a lot of water before urination, and strictly follow the routine operation during urine collection to avoid urine contamination. Urine culture may be contaminated by bacteria from the anterior urethra and the surrounding urethra, so it is necessary to do a clean midstream urine culture and colony count before treatment. If the colony count is ≥100,000/ml, it has diagnostic significance; 10,000 to 100,000/ml is suspicious. However, for patients with cystitis and urinary tract irritation symptoms, if the urine culture colony count is 1,000 to 10,000/ml, it should also be considered for the diagnosis of urinary tract infection. In addition, certain Gram-positive cocci such as enterococcus, which have slow division, can also be diagnosed as urinary tract infection if the count is 1,000/ml. For infants and newborns, and children who have difficulty urinating and are suspected of having urinary tract infection, suprapubic bladder puncture culture can be performed, and a positive culture has diagnostic significance. If the urine for bacterial culture cannot be sent for testing in a timely manner, it should be temporarily stored in a 4℃ refrigerator, otherwise it may affect the results. Urinary tract infections with fever should be accompanied by blood culture. Large diuresis or the use of antibacterial treatment may affect the results of urine culture. If the urine culture is positive, a drug sensitivity test should be performed to guide treatment.

　　4. Urine direct smear for bacteria

　　Place a drop of uniform fresh urine on a glass slide, dry it, and stain it with methylene blue or Gram stain. Under a high-power or oil immersion lens, if bacteria are seen ≥1 per field, it indicates that the urine colony count is >100,000/ml. The Gram stain and bacterial morphology of the urine sediment smear can be used as a reference for drug treatment selection.

　　5. Bacterialuria auxiliary examination

　　Urine nitrite reduction test can be used as a screening examination, with a positive rate of up to 80%.

　　6. Other examinations

　　Other laboratory indicators of renal tubular injury, such as increased urine β2-mG, urine N-acetyl-β-D-glucosaminidase (NAG), and decreased urine osmolality, suggest pyelonephritis.

　　7. Ultrasound examination

　　It can explore whether there are any abnormalities in the structure of the urinary system and the excretion function of the bladder, such as stones, obstruction, residual urine, etc., which may cause infection.

　　8. X-ray examination

　　Intravenous pyelography can show whether there are congenital malformations in the urinary system (such as horseshoe kidney, polycystic kidney, etc.), hydronephrosis and its degree, understand the size of the kidney, whether there are deformations of the renal pelvis and calyces due to chronic inflammation and renal scarring, and for

　　9. Radioisotope examination

　　The renal static imaging of 99mTc-Dimercaptosuccinic acid (DMSA) can be a reliable indicator for the diagnosis of upper urinary tract infection. It has sensitivity and specificity over 90% for detecting pyelonephritis. When acute pyelonephritis occurs, the renal outline is normal. Due to inflammatory cell infiltration in the renal parenchyma, interstitial edema, and tubular cell necrosis, the DMSA level decreases, resulting in a sparse area of isotope distribution in the lesion site. After the inflammation subsides, this sparse area can disappear. In chronic pyelonephritis, when renal scarring occurs, the DMSA uptake in the lesion site is even less, and the renal shape may shrink due to scar contraction or there may be wedge-shaped defects.

　　The diet should be avoided for pediatric urinary tract infection patients, and more清热利湿 foods such as winter melon, Job's tears, Poria cocos, and raw licorice root can be eaten to clear heat. It can be combined with eating. Strengthen physical exercise in daily life, prevent colds, and reduce the chance of infection. Maintain a cheerful spirit and smooth Qi and blood flow, and all diseases will be far away from you.

　　The treatment methods for pediatric urinary tract infection differ according to the etiology and clinical manifestations.

　　First, treatment

　　1. General treatment:During the acute stage, bed rest, increased fluid intake, easily digestible diet, containing sufficient calories and protein.

　　2. Anti-infection treatment:

　　(1) Drug selection: For bacterial urinary tract infections, drug selection is based on the localization diagnosis of the infection and the pathogen: ① For upper urinary tract infection, drugs with high blood and renal concentrations are selected, and for lower urinary tract infection, drugs with high urinary concentrations are selected. ② Drugs are selected based on the identified pathogen and its drug sensitivity test. ③ Low-toxic drugs should be used as much as possible. Active and effective treatment should be adopted for infants and young children, and intravenous medication is recommended for those with vomiting and apathy. Cephalosporin antibiotics, especially second and third-generation cephalosporins, have good effects. Due to the increasing trend of resistance to ampicillin (ampicillin), there is a trend to be replaced by amoxicillin/clavulanate potassium (Anmyting). Aminoglycosides should be used with caution by intravenous infusion, and the duration should not be long. Quinolone drugs have strong antibacterial effects, but they should be used with caution in children under 7 years old. Sulfamethoxazole (SMZ) and nitrofurantoin (furazolidone) are suitable for the treatment of lower urinary tract infections, generally for 5 to 7 days. Antifungal drugs can be used for urinary tract infections caused by fungi.

　　(2) Course of treatment: Due to the difficulty in distinguishing between clinical symptoms of pediatric cystitis and pyelonephritis, a higher proportion of neonates and infants with urinary tract infections and malformations have been observed. Short-term therapy, including single-dose therapy and 3-day therapy, is not suitable for children. Children with acute urinary tract infections treated with short-term therapy have a higher recurrence rate and the chance of re-infection than conventional therapy of about 2 weeks. Short-term therapy should only be considered for children over 5 years old with no urinary tract malformations. Acute primary upper urinary tract infection responds well to effective antibacterial treatment, with fever subsiding more than 2 to 3 days, and urine routine quickly returning to normal. The conventional course of treatment is 2 weeks. For those who do not respond well to treatment, timely replacement of antibiotics should be made based on urine culture and drug sensitivity testing, with a course lasting 4 to 6 weeks. Follow-up of midstream urine culture and colony count should be conducted at the 1st, 2nd, 3rd, 6th, and 12th months after the initial cure of urinary tract infection, for at least 1 year.

　　(3) Treatment for recurrence and reinfection: Acute urinary tract infection can be cured within a few days after reasonable antibacterial treatment, with symptoms usually disappearing, but 50% of children may experience recurrence, which often occurs within one month after treatment. Common causes include: ①Inappropriate selection of antibacterial drugs: This includes not choosing drugs that are sensitive to the pathogenic bacteria and only using drugs with low concentrations in renal tissue, thus failing to achieve effective杀菌目的. ②Development of drug-resistant strains: This is rare in patients with primary infection. If symptoms and bacteriuria have not disappeared within 72 hours after initial treatment, it is necessary to change antibiotics according to the results of drug sensitivity tests. ③L-form bacteria: They account for 20% of recurrent pyelonephritis. Since they can only survive in the hypertonic environment of the renal medulla, their survival environment can be destroyed by increasing fluid intake to reduce the osmotic pressure of the renal medulla. At the same time, re-treatment should be carried out with drugs that inhibit protein synthesis, such as erythromycin and chloramphenicol. ④Urolithiasis: The presence of urinary tract stones can provide a protective shelter for bacteria, allowing them to survive by escaping the killing effect of antibacterial drugs. They often become the cause of recurrence after the cessation of treatment. ⑤Pathogenic bacteria: In addition to Escherichia coli, Proteus is the most common pathogen. In boys over 1 year of age, the primary pathogen of initial infection is also Proteus. For these patients, antibiotics should be selected according to drug sensitivity tests, with high doses and long courses, at least 6 weeks. If bacteriuria persists or if frequent recurrence occurs after two treatments of more than 6 weeks, long-term low-dose antibacterial therapy should be considered, preferably taken once a day before bedtime, with a dose of 1/3 to 1/4 of the conventional treatment dose. Drugs can include sulfamethoxazole (SMZ) + trimethoprim (TMP), amoxicillin, cefalexin, or nitrofurantoin (furazolidone), or a combination of two drugs to prevent the development of drug-resistant strains. This should be continued for at least one year. Reinfection often occurs more than one month after the initial treatment and is common in girls, accounting for 80% of recurrent urinary tract infections. Reinfection is usually caused by different strains or different serotypes of Escherichia coli, often accompanied by urinary tract obstruction and vesicoureteral reflux, among other urinary tract abnormalities. For patients with reinfection, the first line of treatment should be a 10-14-day conventional treatment. If symptoms and bacteriuria disappear, follow-up with a low-dose antibiotic to prevent recurrence. The drugs available include sulfamethoxazole (SMZ) + trimethoprim (TMP), nitrofurantoin, amoxicillin, or cefalexin, with a dose of 1/4 to 1/5 of the conventional treatment dose. If the 10-14-day conventional treatment is ineffective, the course should be extended to 6 weeks. Effective patients should continue with low-dose antibiotic prophylaxis, while ineffective patients or those who initially respond but then have frequent recurrences should consider long-term low-dose antibacterial therapy, with a course of at least one year. If urinary tract abnormalities are confirmed, treatment should continue until the abnormalities are corrected or vesicoureteral reflux stops spontaneously, for at least one year after that.

　　(4) Treatment of asymptomatic bacteriuria: Asymptomatic bacteriuria usually does not require treatment because antibiotic treatment cannot reduce the incidence of reinfection. However, if the child has urinary tract obstruction, vesicoureteral reflux, or other urinary tract anomalies, or has left old renal scars from past infections, active treatment should be given. Otherwise, bacteriuria and coexisting anomalies can promote the development of old scars and the formation of new scars, leading to kidney function damage, renal hypertension formation, and eventually end-stage renal failure. The treatment of asymptomatic bacteriuria first adopts a 10-14 day routine therapy, followed by a low-dose long-term prevention after the bacteriuria becomes negative. The drug selection, dosage, and duration of treatment are the same as those for the prevention of recurrent infection patients.

　　(5) Treatment of chronic pyelonephritis: Chronic pyelonephritis often has renal cortex scarring, accompanied by deformation and expansion of renal papillae and renal pelvis calyces, or persistent renal function damage and kidney atrophy. Chronic pyelonephritis is often accompanied by vesicoureteral reflux, a few have urinary tract obstruction, and it is very rare without anomalies. The treatment of chronic pyelonephritis includes medical conservative treatment and surgical treatment. For patients with urinary tract anomalies or urinary tract obstruction, surgery should be performed as soon as possible.

　　(6) Treatment of urinary tract anomalies: For renal pelvis hydronephrosis caused by narrowing at the ureteropelvic junction or kidney stones, posterior urethral valves and bladder ureteral reflux grade III or above, surgical treatment should be performed.

　　II. Prognosis

　　For most children with chronic urinary tract infections, the frequency of acute attacks can be significantly reduced and the risk of renal scarring formation decreased with the correction of urinary tract anomalies and active anti-infection treatment. Only a few children with early onset of disease and extensive renal scarring at the time of visit will develop hypertension, progressive renal damage, and eventually chronic renal failure. Therefore, sufficient attention should be paid to urinary tract infections in children, especially infants and young children.