UTI in children BY DR VIJITHA

1. UTI IN CHILDREN
PRESENTER :DR VIJITHA A S
CHAIRPERSON : DR PUSHPALATHA

2. Definitions
• Infection of the urinary tract is identified by growth of a significant
number of organisms of a single species in the urine, in the presence
of symptoms.
• Recurrent UTI, defined as the recurrence of symptoms with significant
bacteriuria in patients who have recovered clinically following
treatment. common in girls.

3. DEFINITIONS
• Significant bacteriuria - Colony count of >10 5/mL of a single species in a
midstream clean catch sample
• Asymptomatic bacteriuria - Significant bacteriuria in the absence of
symptoms of urinary tract infection (UTI).
• Simple UTI- UTI with low grade fever, dysuria, frequency, and urgency; and
absence of symptoms of complicated UTI
• Complicated UTI -Presence of fever >39ºC, systemic toxicity, persistent
vomiting, dehydration, renal angle tenderness and raised creatinine

4. PREVALENCE
• UTIs are most common in children under age 1 year
• <1 year - M : F 2.8 : 5.4
• >1 year, striking female predominance, M:F - 1:10
• Higher in uncircumcised boys

5. RISK FACTORS
• Female gender
• Uncircumcised male
• Vesicoureteral reflux
• Toilet training
• Voiding dysfunction
• Obstructive uropathy
• Urethral instrumentation
• Sources of external irritation(such
as tight clothing, pinworm
infestation)
• Constipation
• Anatomic abnormality (labial
adhesion)
• Neuropathic bladder
• Sexual activity
• Pregnancy

7. ETIOLOGY
• UTIs are caused primarily by colonic bacteria.
• Escherichia coli causes 54–67% of all UTIs, followed by Klebsiella spp.
and Proteus spp, Enterococcus, and Pseudomonas
• Other bacteria known to cause UTI - Staphylococcus saprophyticus
- Group B streptococcus
• less commonly, Staphylococcus aureus, Candida spp, and Salmonella
spp.

8. • PYELONEPHRITIS
• Involvement of the renal parenchyma - acute pyelonephritis
No parenchymal involvement, the condition termed pyelitis.
• Acute pyelonephritis can result in renal injury, termed pyelonephritic scarring
• Acute lobar nephronia (acute lobar nephritis) is a localized renal parenchymal
mass caused by acute focal infection without liquefaction.
• it more commonly occurs in older children.
• It may be an early stage in the development of a renal abscess. Manifestations are
identical to those of pyelonephritis - fever and flank pain

9. CYSTITIS
• Indicates only bladder involvement;
• Symptoms include dysuria, urgency, frequency, suprapubic pain, incontinence, and possibly
malodorous urine.
• Acute hemorrhagic cystitis- uncommon in children, is often caused by E. coli; other causes adenovirus
types 11 and 21.
• Adenovirus cystitis is more common in boys; self-limiting, with hematuria lasting approximately 4
days.
• Patients receiving immunosuppressive therapy (e.g., solid-organ or bone marrow transplantation) are
at higher risk for hemorrhagic cystitis; adenoviruses and polyomaviruses (i.e., JC virus and BK virus) are
important causes in Immunocompromised populations.

10. • Other rare types of cystitis include eosinophilic cystitis or interstitial
cystitis.
• Eosinophilic cystitis present with hematuria
• interstitial cystitis present with irritative voiding symptoms but a
negative urine culture.

11. Asymptomatic Bacteriuria
• Asymptomatic bacteriuria is the presence of significant bacteriuria in the absence of symptoms
of UTI. Its frequency is 1-2% in girls and 0.2% in boys.
• Asymptomatic bacteriuria is a benign condition, which does not cause renal injury and requires
no treatment. The organism isolated in most instances is E. coli, which is of low virulence.
• Eradication of these organisms is often followed by symptomatic infection with more virulent
strains.
• Therapy of asymptomatic bacteriuria or antibiotic prophylaxis is not required.The presence of
asymptomatic bacteriuria in a patient previously treated for UTI should not be considered as
recurrent UTI.

13. VESICOURETERIC REFLUX
• VUR seen in 40-50% infants and 30-50% children with UTI, and resolves with
age.
• Its severity is graded I to V, using the International Study Classification based
on the appearance of the urinary tract on MCU .
• Secondary VUR is often related to bladder outflow obstruction, as with
posterior urethral valves, neurogenic bladder or a functional voiding disorder.
• Lower grades of reflux- (grade I-III) are more likely to resolve.

14. • The presence of moderate to severe VUR, particularly if bilateral, is an
important risk factor for pyelonephritis and renal scarring, subsequent
risk of hypertension, albuminuria and progressive kidney disease.
• The risk of scarring is highest in the first year of life.
• The presence of intrauterine VUR has been associated with renal
hypoplasia or dysplasia.

15. VESICOURETERIC REFLUX GRADING

16. Bowel bladder dysfunction
• Children presenting with recurrent UTI or persistent VUR often have an associated
voiding disorder, which are characterized by abnormal patterns of micturition in
presence of intact neuronal pathways without congenital or anatomical abnormalities.
• Abnormal bladder pressure and urinary stasis predispose these children to recurrent
UTI.
• There may be an abnormality either during the filling phase as in an overactive bladder,
or the evacuation phase as in dysfunctional voiding.
• Since constipation is often associated with a functional voiding disorder, the condition
is referred to as Bowel bladder dysfunction (BBD).

17. FEATURES SUGGESTIVE OF BOWEL BLADDER
DYSFUNCTION
• Recurrent urinary tract infections
• Persistent high grade vesicoureteric reflux
• Constipation, impacted stools
• Maneuvers to postpone voiding (holding maneuvers, e.g.,Vincent curtsy,
squatting)
• Voiding less than 3 or more than 8 times a day
• Straining or poor urinary stream
• Thickened bladder wall >2 mm
• Post void residue >20 mL
• Spinning top configuration of bladder on micturating cystourethrogram

18. Clinical Features
• Neonates- UTI is usually a part of septicemia and - presents with fever, vomiting,
lethargy, jaundice and seizures.
• children less than 2 years - UTI is an important cause for fever without a focus
• Infants and young children present with - recurrent fever, diarrhea, vomiting,
abdominal pain and poor weight gain.
• Older children - fever, dysuria, urgency, frequency and abdominal or flank pain.
• Adolescents may have symptoms restricted to the lower tract, and fever may not
be present.

19. CLINICAL FEATURES OLDER CHILDREN
• Dribbling, prolonged voiding, straining, crying during micturition and poor urinary stream -
abnormality of the distal urinary tract.
• Diurnal incontinence, urgency, frequency and squatting suggest - voiding dysfunction.
• Patients with urinary stasis (mechanical or neurogenic) having UTI from urea splitting
organisms, usually Proteus but also Klebsiella, are at risk of developing hyper ammonemia
and encephalopathy.
• Venous drainage of the bladder enters directly into the systemic circulation and thus
ammonia bypasses liver without being detoxified

20. SYMPTOMS
UPPER UTI
High grade fever, toxic look
Vomiting, nausea
Abdominal pain flanks
Diarrhea
CYSTITIS
Dysuria
Urgency
Frequency
Supra pubic pain
+/-Hematuria
Usually no fever

21. Severe or Complicated UTI
• fever > 39°C,
• marked toxicity
• persistent vomiting
• dehydration
• and renal angle tenderness
• Raised creatinine
• hospitalized and treated with
parenteral antibiotics
• Patients with features of systemic
toxicity are considered as having
complicated UTI
Simple UTI
• Low grade fever
• Dysuria, frequency and urgency
• Absence of symptoms of
complicated UTI

22. INITIAL EVALUATION
• The patient is examined for the degree of toxicity, dehydration and ability
to retain oral intake.
• The blood pressure should be recorded and history regarding bowel and
bladder habits elicited. The child is examined for features that suggest an
underlying functional or urological abnormality.
• Complete blood counts, serum creatinine and a blood culture should be
done in infants and children with complicated UTI.

23. FEATURES SUGGESTING UNDERLYING
STRUCTURAL ABNORMALITY
• Distended bladder
• Palpable, enlarged kidneys
• Tight phimosis; vulval synechiae
• Palpable fecal mass in the colon
• Patulous anus
• neurological deficit in lower limbs
• Urinary incontinence
• Previous surgery of the urinary tract,
• anorectal malformation or
meningomyelocele

24. INVESTIGATIONS
• Urine
• Blood
• Imaging

25. URINE
•Dipstick
•Microscopy
•Culture & sensitivity

26. DIAGNOSIS
• The diagnosis of UTI is based on positive culture of a properly
collected specimen of urine.
• urinalysis enables a provisional diagnosis of UTI,
• A specimen must be obtained for culture prior to therapy with
antibiotics

27. COLLECTION OF SPECIMEN FOR CULTURE
• A clean-catch midstream specimen is used to minimize contamination by periurethral
flora. Contamination can be minimized by washing the genitalia with soap and water.
• Antiseptic washes and forced retraction of the prepuce are not advised.
• In neonates and infants, urine sample is obtained by either suprapubic aspiration or
transurethral bladder catheterization. Both techniques are safe and easy to perform.
• suprapubic aspiration performed safely using a 21 gauge needle, 1-2 cm above the
pubic symphysis.

28. • The urine specimen should be promptly plated within one hour of collection.
If delay is anticipated, the sample can be stored in a refrigerator at 4ºC for
up to 12-24 hours.
• Cultures of specimens collected from urine bags have high false positive
rates, and are not recommended.
• A urine culture should be repeated in case contamination is suspected, e.g.,
mixed growth of two or more pathogens, or growth of organisms that
normally constitute the periurethral flora (lactobacilli in healthy girls;
enterococci in infants and toddlers).

29. • The culture should also be repeated in situations where UTI is strongly
suspected but colony counts are equivocal. The number of bacteria
required for defining UTI depends on the method of urine collection.

30. • Significant pyuria is defined as >10 leukocytes per mm3 in a fresh
uncentrifuged sample, or >5 leukocytes per high power field in a
centrifuged sample.
• The detection of leukocyturia in absence of significant bacteriuria is not
sufficient to diagnose a UTI.
• Rapid dipstick tests- which detect leukocyte esterase and nitrite, are useful
in screening for UTI.
• A combination of these tests has moderate sensitivity and specificity for
detecting UTI, and is diagnostically as useful as microscopy.

31. Sterile pyuria (positive leukocytes, negative
culture)
• Occur in partially treated bacterial UTIs
• viral infections
• urolithiasis
• Renal tuberculosis
• renal abscess
• UTI in the presence of urinary obstruction
• Urethritis as a consequence of a sexually
transmitted infection
• Inflammation near the ureter or bladder
(appendicitis, Crohn disease), Kawasaki disease
• schistosomiasis,
• neoplasm
• renal transplant rejection
• interstitial nephritis (eosinophils).

32. CRITERIA FOR THE DIAGNOSIS OF UTI
Method of collection Colony count Probability of infection
Suprapubic aspiration Any number of pathogens 99%
Urethral catheterization >5 × 104 CFU/mL 95%
Midstream clean catch >105 CFU/Ml+ pyuria 90-95%

33. Renal Ultrasonography
• Ultrasound is the first-line type of imaging for screening, It is routinely
performed after the diagnosis of first UTI.
• It is a noninvasive test, demonstrate, information on kidney size, number
and location, presence of hydronephrosis, urinary bladder anomalies and
post-void residual urine.
• shape of the kidneys such - as solitary or dysplastic kidney, horseshoe kidney
and the presence of ureterocele
• Posterior urethral valves are commonly detected in male infants with UTI.

34. • It is reliable for diagnosing urinary tract obstruction, which may be present
in children with first UTI.
• Ultrasound (US) is not sensitive enough to detect presence of
hydronephrosis or hydroureter secondary to VUR because of the dynamic
nature of reflux.
• It is also poorly sensitive test for acute pyelonephritis and renal scarring.
• demonstrate an enlarged kidney with a possible mass in the case of acute
lobar nephronia or renal abscess.

35. MICTURATING CYSTOURETHROGRAM (MCU)
• MCU is performed, with strict aseptic precautions, after the urine has been sterile for 3 to 4
weeks.
• Radiocontrast medium into the bladder through a thin catheter, or directly through suprapubic
puncture.
• MCU detects VUR and provides anatomical details regarding the bladder and the urethra
• Detect distal urinary tract -posterior urethral valve.
• It gives useful information on bladder dynamics as assessed by filling and emptying of bladder
and the amount of residual urine.
• The child’s cooperation is necessary; an infant may be scared and unable to empty the bladder
fully

36. • Catheterization of the urinary tract, during MCU, carries the risk of
introducing bacteria into the urinary tract.
• Antibiotic prophylaxis (oral cotrimoxazole: first dose 12 hr before the
procedure and 3 doses thereafter; oral amoxicillin: one dose 1 hr
before MCU, followed by a dose 6 hour later; or parenteral gentamicin
30 minutes before the procedure) reduces the risk of iatrogenic
infections.

37. Intrarenal reflux. VCUG in an infant boy with a history of
a UTI. Note the right VUR with ureteral dilation, with
opacification of the renal parenchyma representing intrarenal
reflux.

39. RADIONUCLIDE IMAGING
• DMSA SCAN: DMSA scintigraphy is a sensitive technique for detecting renal parenchymal
infection and cortical scarring.
• It is superior to ultrasonography and IVP in detecting renal parenchymal scarring.
• Acute pyelonephritis - decreased areas of tracer uptake are seen without distortion of
normal renal outline.
• Direct radionuclide cystourethrogram (DRCG): Instead of the radiocontrast agent, a
radionuclide is introduced into the bladder.
• This procedure is more sensitive in detecting VUR, but the grading of VUR cannot be done.
• As it exposes the child to less radiation, it can be employed for follow-up studies.

40. multiple focal cortical defects in the upper and lower
poles of the left kidney (posterior view) or at least Grade II
99m Tc-DMSA scan (posterior view) in
patient with recurrent urinary tract infection.
Cortical defects (arrows) at upper pole and
lateral margin of left kidney indicate scarring

41. INTRAVENOUS PYELOGRAPHY (IVP, EXCRETORY
UROGRAM)
• This study provides sharper details and is a good indicator of kidney
function.
• Hazards of radiocontrast agent and the high dose of radiation, the
IVP is not performed provided a good ultrasonographic examination
can be done.

42. MANAGEMENT OF UTI

43. IMMEDIATE TREATMENT
• Therapy should be prompt to reduce the morbidity of infection, minimize
renal damage and subsequent complications.
• Children less than 3 months of age and those with complicated UTI should
be hospitalized and treated with parenteral antibiotics.
• The choice of antibiotic should be guided by local sensitivity patterns. A
third generation cephalosporin is preferred.
• Therapy with a single daily dose of an aminoglycoside may be used in
children with normal renal function.

44. • Once the result of antimicrobial sensitivity is available, the treatment may be
modified.
• Intravenous therapy is given for the first 2- 3 days followed by oral antibiotics once
the clinical condition improves.
• Children with simple UTI and those above 3 months of age are treated with oral
antibiotics.
• With adequate therapy, there is resolution of fever and reduction of symptoms by
48-72 hours.
• Failure to respond may be due to presence of resistant pathogens, complicating
factors or noncompliance; these patients require re-evaluation

45. ANTIMICROBIALS FOR TREATMENT OF UTI
Medication Dose, mg/kg/day
Parenteral
• Ceftriaxone 75-100, in 1-2 divided doses IV
• Cefotaxime 100-150, in 2-3 divided doses IV
• Amikacin 10-15, single dose IV or IM
• Gentamicin 5-6, single dose IV or IM
• Coamoxiclav 30-35 of amoxicillin, in 2
divided doses IV
Oral
• Cefixime 8-10, in 2 divided doses
• Coamoxiclav 30-35 of amoxicillin, in 2
divided doses
• Ciprofloxacin 10-20, in 2 divided doses
• Ofloxacin 15-20, in 2 divided doses
• Cephalexin 50-70, in 2-3 divided doses

46. DURATION OF TREATMENT
• The duration of therapy is 10-14 days for infants and children with
complicated UTI, and 7-10 days for uncomplicated UTI.
• Adolescents with cystitis-treated with shorter duration of antibiotics,
lasting 3 days.
• Following the treatment of the UTI, prophylactic antibiotic therapy is
initiated in children below 1 year of age, until appropriate imaging of
the urinary tract is completed.

47. Supportive Therapy
• During an episode of UTI, it is important to maintain adequate hydration. A
sick, febrile child with inadequate oral intake or dehydration may require
parenteral fluids.
• Routine alkalization of the urine is not necessary.
• Paracetamol is used to relieve fever; therapy with non steroidal anti-
inflammatory agents should be avoided.
• A repeat urine culture is not necessary, unless there is persistence of fever
and toxicity despite 72 hours of adequate antibiotic therapy.

48. Therapy for Primary VUR
• Over the last decade it has been increasingly recognized that not all
children with VUR benefit from diagnosis or treatment.
• In some patients the reflux is innocuous and self limiting.
• In others, VUR is accompanied with renal damage that has an onset
during the intrauterine period with dysplastic kidneys at birth, where
the treatment of VUR will not change the long term outcome.

49. • Conventional therapy for VUR includes -antibiotic prophylaxis and surgical
intervention.
• A recent systematic review on patients with dilating reflux concluded that
the outcomes following surgical repair versus prophylaxis were similar in
terms of the number of breakthrough UTI and risk of renal scarring.
• Experts recommend that the management of patients with VUR should
depend on the patient age, grade of reflux and whether there are any
breakthrough infections.

50. MANAGEMENT OF VESICOURETERIC REFLUX
• VUR grade Management
• Grades I and II - Antibiotic prophylaxis until 1 yr old.
• Restart antibiotic prophylaxis if breakthrough febrile UTI.
• Grades III to V - Antibiotic prophylaxis up to 5 yr of age. Consider surgery
if breakthrough febrile UTI.
• Beyond 5 yr: Prophylaxis continued if there is bowel bladder dysfunction

51. • It is recommended that patients should initially receive antibiotic prophylaxis
while awaiting spontaneous resolution of VUR.
• A close follow up is required for occurrence of breakthrough UTI, Repeat
imaging is required after 18-36 months in patients with grade III-V VUR.
• Radionuclide cystogram, with lower radiation exposure, has higher sensitivity
for detecting reflux and is therefore preferred for follow-up evaluation.
• Risk of recurrent UTI and renal scarring is low after 4-5 years of age, it is
advised that prophylaxis be discontinued in children older than 5 years with
normal bowel and voiding habits, even if mild to moderate reflux persists.

52. • Patients with grade III to V reflux may be offered surgical repair if they
have breakthrough febrile UTI, if parents prefer surgical intervention to
prophylaxis, or in patients who show deterioration of renal function.
• An evaluation for voiding dysfunction (based on history, voiding diary)
should be done before surgery.
• Antibiotic prophylaxis is continued for 6 months after surgical repair.

53. • Dextranomer/hyaluronic acid copolymer (Deflux) endoscopic
treatment has been proposed as an alternative to surgical repair for
patients with VUR. results are satisfactory.

54. Evaluation after the first UTI
• The aim of investigations is to identify - patients at high risk of renal
damage(<1 year), and those with VUR or urinary tract obstruction.
• Evaluation includes - Ultrasonography
Dimercaptosuccinic acid (DMSA)
Renal scan
Micturating cystourethrography (MCU).

55. • Ultrasonography should be done soon after the diagnosis of UTI.
• The MCU is recommended 2-3 weeks later
• DMSA scan is carried out 2-3 months after treatment.
• Patients showing hydronephrosis in the absence of VUR should be
evaluated by diuretic renography using 99mTc-labeled diethylene
triamine- pentaacetic acid (DTPA) or mercaptoacetylglycine (MAG-3).
• These techniques provide quantitative assessment of renal function
and drainage of the dilated collecting system.

56. The Urological Society of India Guidelines 2021
First Urinary Tract Infection
All patients with recurrent UTI need detailed evaluation with ultrasonography,
DMSA scan and MCU
AGE <1 YR
ULTRASOUND
MCU
DMSA RENAL SCAN
AGE 1-5 YR
ULTRASOUND
DMSA & MCU IF ULTRASOUND
SCAN IS ABNORMAL
AGE >5 YR
ULTRASOUND
MCU AND DMSA SCAN TO
BE DONE SELECTIVELY
FIRST URINARY TRACT INFECTION*

58. PREVENTION OF RECURRENT UTI
• General
• Adequate fluid intake and frequent voiding is advised
• constipation should be avoided.
• In children with VUR who are toilet trained, regular and volitional low
pressure voiding with complete bladder emptying is encouraged.
• Double voiding ensures emptying of the bladder of post void residual
urine.
• Circumcision reduces the risk of recurrent UTI in infant boys, and
benefits in patients with high grade reflux.

59. management of voiding disorders
• Evaluation for a voiding disorder includes a record of frequency and voided
volume and fluid intake for two to three days. It is useful to watch the
urinary stream, and for post void dribbling in boys.
• Urodynamic studies are done in selected cases.
• The should be carried out in collaboration with an expert. This includes the
exclusion of neurological causes, institution of structured voiding patterns
and management of constipation.
• In patients with an overactive bladder, therapy with anticholinergic
medications (e.g.,oxybutinin) is effective.
• Patients with bowel bladder Long-term, low dose, antibacterial prophylaxis
is used to prevent recurrent, febrile UTI (Table VII). The antibiotic used
should be effective, non-toxic with few side effects and should not alter the
growth of commensals or induce bacterial resistance

60. ANTIBIOTIC PROPHYLAXIS
1. The antibiotics used should be effective, nontoxic with few side effects
and should not alter the growth of commensals or induce bacterial
resistance.
2. Antibiotic prophylaxis should not be routinely recommended in infants
and children following the first-time UTI.
3. The indications and duration of prophylaxis depend on patient’s age
and presence or absence of VUR.

61. 4. Antibiotic prophylaxis is recommended for patients with
a. UTI below 1 year of age, while awaiting imaging studies
b. VUR - all grades in infants <2 years
dilating VUR
Grade III–V in 2–5 years
c. Recurrent febrile UTI (3 or more episodes in a year) even if the
urinary tract is normal

62. ANTIMICROBIALS FOR PROPHYLAXIS OF URINARY
TRACT INFECTIONS
Medication Dose - mg/kg/day Remarks
Cotrimoxazole 1-2* Avoid in infants <3 mo, glucose-6-phosphate
dehydrogenase deficiency
Nitrofurantoin 1-2 May cause vomiting and nausea; avoid in infants <3
mo, G6PD deficiency, renal insufficiency
Cephalexin 10 Drug of choice in first 3-6 mo of life
Cefadroxil 5 An alternative agent in early infancy

63. 5. Antibiotic prophylaxis is not advised in patients with urinary tract obstruction (e.g.,
posterior urethral valves), urolithiasis, and neurogenic bladder and in patients on clean
intermittent catheterization. In these cases, the primary cause needs to be addressed first.
6. Asymptomatic bacteriuria in infants and children should not be treated with prophylactic
antibiotics.
7. Breakthrough UTI usually results either from poor compliance or associated voiding
dysfunction. The UTI should be treated with appropriate antibiotics.
8. A change of medication being used for prophylaxis is usually not necessary.
9. There is no role for cyclic therapy, where the antibiotic used for prophylaxis is changed
every 6–8 weeks.

64. Follow-up
1. When results are satisfactory, a follow-up outpatient appointment is not
routinely required
2. Parents or caregivers should be informed of the results of all the
investigations in writing
3. Infants and children who have recurrent UTI or abnormal imaging results
should be assessed by a paediatric urologist
4. Assessment of infants and children with renal parenchymal defects should
include height, weight, blood pressure, and routine testing for proteinuria

65. Follow-up
5. Infants and children with a minor, unilateral renal parenchymal defect
do not need long-term follow-up unless they have recurrent UTI or family
history or lifestyle risk factors for hypertension
6. Infants and children who have bilateral renal abnormalities, impaired
kidney function, raised blood pressure, and/or proteinuria (random spot
protein creatinine ratio >0.2 suggesting significant proteinuria) should
receive monitoring and appropriate management by a pediatric
nephrologist to slow the progression of chronic kidney disease

66. Follow-up
7.Infants and children who are asymptomatic following an episode of
UTI need not routinely have their urine re-tested for infection (no
screening urinalysis or culture)
8. Asymptomatic bacteriuria is not an indication for follow-up.

67. INDICATION FOR REFERRAL TO A PEDIATRIC
NEPHROLOGIST
• Recurrent urinary tract infections
• Urinary tract infections in association with bowel bladder dysfunction
• Patients with vesicoureteric reflux
• Underlying urologic or renal abnormalities
• Children with renal scar, deranged renal functions, hypertension

68. THANK YOU

69. REFERENCES
• Bagga 6th edition
• 21st edition of nelson textbook of pediatrics
• Indian society of pediatric nephrology 2011
• The urological society of india guidelines 2021

70. • Nearly all UTIs are ascending infections. The bacteria arise from the fecal
flora, colonize the perineum, and enter the bladder via the urethra. In
uncircumcised males, the bacterial pathogens arise from the flora beneath
the prepuce. In some cases, the bacteria causing cystitis ascend to the
kidney to cause pyelonephritis. Rarely, renal infection occurs by
hematogenous spread, as in endocarditis or in some bacteremic neonates.
If bacteria ascend from the bladder to the kidney, acute pyelonephritis can
occur. Normally, the simple and compound papillae in the kidney have an
antireflux mechanism that prevents urine in the renal pelvis from entering
the collecting tubules. However, some compound papillae, typically in the
upper and lower poles of the kidney, allow intrarenal reflux. Infected urine
stimulates an immunologic and inflammatory response, causing renal
injury and scarring (Figs. 553.5 and 553.6). Children of any age with a
febrile UTI can have acute pyelonephritis and subsequent renal scarring,
but the risk is highest in those younger than 2 yr of age

72. DIAGNOSIS OF URINARY TRACT INFECTION
1. The diagnosis should be based on the presence of both pyuria and
>105 CFU/ml in a clean-catch midstream voided urine sample
2. If urine is obtained by catheterization, 1000–50,000 CFU/ml is
considered positive in symptomatic patient
3. Any counts obtained after suprapubic aspiration should be
considered significant.