Urinary tract infections in infants and children older than one month: Clinical features and diagnosis

INTRODUCTION — Urinary tract infections (UTIs) are a common and important problem in children. Acute pyelonephritis may lead to renal scarring, hypertension, and end-stage kidney disease.

The clinical features and diagnosis of UTI in children will be discussed here. The epidemiology, risk factors, and management of UTI in children, acute cystitis in children older than two years, and UTI in neonates (<1 month of age) are discussed separately:

●(See "Urinary tract infections in children: Epidemiology and risk factors".)

●(See "Urinary tract infections in infants older than one month and children less than two years: Acute management, imaging, and prognosis".)

●(See "Urinary tract infections in children: Long-term management and prevention".)

●(See "Acute infectious cystitis: Clinical features and diagnosis in children older than two years and adolescents" and "Acute infectious cystitis: Management and prognosis in children older than two years and adolescents".)

●(See "Urinary tract infections in neonates".)

TERMINOLOGY — UTI is best defined as significant bacteriuria of a clinically relevant uropathogen in a symptomatic patient. Most patients with UTI also have pyuria, although there are exceptions. (See 'Special circumstances' below.)

In this topic, we define UTI broadly, without attempting to distinguish cystitis from pyelonephritis. Although children with pyelonephritis tend to present with fever, it is often difficult to distinguish cystitis from pyelonephritis clinically, particularly in children younger than two years [1].

CLINICAL PRESENTATION

Younger children

●Symptoms and signs – In infants and young children, UTI usually presents with nonspecific symptoms and signs (eg, fever, irritability) [2]. Parental report of foul-smelling urine or gastrointestinal symptoms (eg, vomiting, diarrhea, poor feeding) is generally not helpful in diagnosing UTI [3-5].

Fever may be the sole manifestation of UTI in infants and children <2 years of age [6-8]. In observational studies, UTI is more common among infants and young children with maximum temperatures ≥39°C (102.2°F) than in those with lower fevers (16 versus 7 percent for infants ≤60 days and 4 versus 2 percent for children <2 years) [7-9]. (See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Prevalence'.)

Although fever >24 hours is associated with increased risk of UTI, evaluation for UTI should not be delayed in children who present with possible UTI and fever for ≤24 hours' duration [10]. The risk of renal scarring increases with increased duration of fever before initiation of antibiotics. In a retrospective cohort study of 482 children with febrile UTI, the risk of renal scarring was approximately 5 percent in children with fever duration of one to two days, 8 percent in children with fever duration of two to three days, and 14 percent in children with duration of fever of >3 days before initiation of antibiotics [11].

Having another source of fever identified (eg, upper respiratory tract infection, acute otitis media, acute gastroenteritis) decreases the risk of UTI but does not eliminate it [9]. In observational studies of young children who presented to the emergency department with fever, the prevalence of UTI ranged from 2 to 3 percent in children with and 6 to 8 percent in those without another source of fever [7,12]. This highlights the importance of obtaining urine cultures in febrile infants and young children without a definite source for fever. (See 'Decision to obtain urine sample' below.)

●Predictors of culture-confirmed UTI – Clinical and demographic factors associated with increased risk of culture-confirmed UTI were identified in a nested case-control study of febrile (>38°C [100.4°F]) children age 2 through 23 months who were evaluated for UTI in the emergency department of a tertiary care children's hospital [9]. They include:

•Age <12 months

•Maximum reported temperature ≥39°C (102.2°F)

•Female child

•Male child who is uncircumcised

•No other source of fever identified (eg, acute otitis media; upper respiratory tract infection, gastroenteritis, bronchiolitis, or other viral syndrome; pneumonia, meningitis)

Additional factors that increase the risk of UTI in young children include history of UTI and duration of fever ≥48 hours [13,14]. These factors have been used to develop a calculator to estimate the probability of UTI in children age 2 through 23 months (UTICalc, available from the University of Pittsburgh).

Older children — Symptoms and signs of UTI in older children include fever, urinary symptoms (dysuria, urgency, frequency, new-onset incontinence), abdominal pain, suprapubic tenderness, and costovertebral angle tenderness [15-17]. The constellation of fever, chills, and flank pain is suggestive of pyelonephritis in older children [2].

In a meta-analysis of the diagnostic accuracy of the clinical findings of UTI in verbal children, the following findings were the most helpful in identifying children with UTI [3]:

●Abdominal pain

●Back pain

●Dysuria, frequency, or both

●New-onset urinary incontinence

CLINICAL EVALUATION — Children with UTI symptoms should be evaluated promptly. Prompt recognition and treatment of UTI may be important in the prevention of renal scarring. (See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Risk factors for renal scarring'.)

History — The history of the acute illness should include documentation of the height and duration of fever, urinary symptoms (dysuria, frequency, urgency, incontinence), abdominal pain, suprapubic discomfort, back pain, recent illnesses, antibiotics administered, and, if applicable, sexual activity.

The past medical history should include risk factors for UTI, including:

●Chronic urinary symptoms – Incontinence, lack of proper stream, frequency, urgency, withholding maneuvers (suggestive of bladder dysfunction)

●Bowel and bladder dysfunction, including chronic constipation

●Previous UTI or previous undiagnosed febrile illnesses in which urine culture was not obtained

●Vesicoureteral reflux (VUR)

●Family history of frequent UTI, VUR, and other genitourinary abnormalities

●Antenatally diagnosed renal abnormality

●Sexually activity, particularly if barrier contraception with spermicidal agents is used (such methods predispose to UTI by altering the normal vaginal flora [18-20])

(See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Host factors'.)

Physical examination — Important aspects of the physical examination in the child with suspected UTI include [3,21,22]:

●Documentation of blood pressure and temperature

•Temperature ≥39°C (102.2°F) is associated with acute pyelonephritis that may cause renal scarring (odds ratio 2.3, 95% CI 1.6-3.3) [23]

•Elevated blood pressure may be an indication of renal scarring

●Growth parameters

•Poor weight gain may be an indication of chronic renal failure due to renal scarring

●Abdominal and flank examination [21]

•Suprapubic and costovertebral angle tenderness is associated with UTI

•Enlarged bladder or kidney may indicate urinary obstruction and palpable stool in the colon may indicate constipation, both of which predispose to UTI

●Examination of the external genitalia for anatomic abnormalities (eg, phimosis, hypospadias (picture 1), or labial adhesions (picture 2)) and signs of vulvovaginitis, vaginal foreign body, or sexually transmitted infections, which may predispose to UTI (see "Vulvovaginitis in the prepubertal child: Clinical manifestations, diagnosis, and treatment" and "Overview of vulvovaginal conditions in the prepubertal child")

●Evaluation of the lower back for signs of occult myelomeningocele (eg, midline pigmentation, lipoma, vascular lesion, sinus, tuft of hair), which may be associated with a neurogenic bladder and recurrent UTI (see "Closed spinal dysraphism: Clinical manifestations, diagnosis, and management", section on 'Clinical manifestations')

●Evaluation for other sources of fever; another source of fever decreases the risk of UTI but does not eliminate it altogether [7,12]

LABORATORY EVALUATION AND DIAGNOSIS — The laboratory evaluation for suspected UTI includes urine dipstick and microscopic analysis (table 1) and urine culture.

Decision to obtain urine sample — The decision to obtain a urine sample for urinalysis and culture is made on a case-by-case basis, considering medical history, age, sex, circumcision status, and presenting signs and symptoms (table 2) [13,14,24-26].

The indications for obtaining urine samples described below are for children without urinary tract abnormalities (table 2). Indications to obtain urine samples in children with urinary tract abnormalities vary with the type of abnormality and are discussed separately. For example, (see "Myelomeningocele (spina bifida): Urinary tract complications", section on 'Urinary tract infections' and "Management of vesicoureteral reflux", section on 'Follow-up').

In children younger than two years, UTI may present with nonspecific symptoms; fever may be the sole manifestation. UTICalc can be used to estimate the probability of UTI in febrile (temperature ≥38°C [100.4°F]) children age 2 through 23 months according to clinical characteristics [13,14,27]. We obtain a urine sample in febrile children <2 years of age with a pretest probability of UTI ≥2 percent (ie, approximately 10 children need to be tested for every UTI detected) [9,13,14]. Other considerations include the feasibility of follow-up, parental views toward catheterization (if catheterization is necessary), potential harm of not diagnosing an episode of UTI, harm of incorrectly diagnosing UTI, cost and availability of testing, and benefits of early treatment. These considerations are particularly important when the probability of UTI is close to 2 percent. (See "Urinary tract infections in infants older than one month and children less than two years: Acute management, imaging, and prognosis", section on 'Overview'.)

●Age <1 month – Indications for urine samples in infants age <1 month are provided separately. (See "Urinary tract infections in neonates", section on 'Diagnosis'.)

●Age 1 to <2 months – Fever ≥38°C (100.4°F).

●Females and uncircumcised males age 2 through 23 months

•Age 2 through 11 months – Fever ≥38°C (100.4°F)

•Age 12 through 23 months – Any of the following combinations:

-Fever ≥38°C (100.4°F) and history of UTI (documented UTI or UTI reported by caregiver)

-Fever ≥38°C (100.4°F) and no other source of fever

Other source of fever includes (but is not limited to) acute otitis media; pneumonia; meningitis; upper respiratory tract infection, gastroenteritis, bronchiolitis, or another viral syndrome.

-Maximum fever ≥39°C (102.2°F) and fever ≥48 hours

●Circumcised males age 2 through 23 months

•Age 2 through 11 months – Fever ≥38°C (100.4°F) and any of the following combinations:

-No other source of fever and history of UTI (documented or reported by caregiver)

-No other source of fever, maximum fever ≥39°C (102.2°F), and duration of fever ≥48 hours

-Other source of fever, history of UTI, maximum fever 39°C (102.2°F), and duration of fever ≥48 hours

•Age 12 through 23 months – The combination of no other source of fever, maximum fever ≥39°C (102.2°F), history of UTI, and fever ≥48 hours

●Age ≥24 months – We obtain urine samples in children ≥24 months of age with the clinical findings listed below (one or more clinical findings for females or uncircumcised males; two or more clinical findings for circumcised males):

•Dysuria

•Frequency

•New-onset incontinence

•Abdominal pain

•Back pain

•Fever ≥39°C (102.2°F) if no other cause is identified

How to obtain urine sample

●Children who are not toilet trained – Catheterization or suprapubic aspiration is the preferred method of urine collection for dipstick analysis, microscopic examination, and culture of the urine in infants and young children who are not toilet trained [28].

Urine obtained in a sterile collection bag should not be used for culture. Although we prefer not to use bag urine specimens for dipstick or microscopic analysis, others suggest that bag urine samples can be used as a first step to determine whether a catheterized urine sample should be obtained for culture in young children. This approach is discussed separately. (See "Urine collection techniques in infants and children with suspected urinary tract infection", section on 'Specimen for urine dipstick or urinalysis'.)

●Children who are toilet trained – A clean-voided specimen is the preferred method of urine collection for dipstick analysis, microscopic examination, and culture of the urine in children who are toilet trained. (See "Urine collection techniques in infants and children with suspected urinary tract infection", section on 'Selection of technique'.)

All urine specimens should be examined as soon as possible after collection. A delay of even a few hours at room temperature increases both the false-positive and false-negative rates substantially [26].

Rapidly available tests

●Use in determining probability of UTI – The results of urine dipstick and microscopic analysis are rapidly available. These results can be combined with clinical features to estimate the probability of UTI in an individual child to guide decisions about antimicrobial therapy. For children 2 through 23 months of age, UTICalc, available through the University of Pittsburgh, can be used for this estimation.

The sensitivity and specificity of the components of the urinalysis in predicting significant bacteriuria on culture has been evaluated in systematic reviews and meta-analyses (table 1) [29-31].

●Dipstick analysis – Dipstick tests are convenient, inexpensive, and require little training for proper usage; they may be the only test available in some settings. They are at best 88 percent sensitive (table 1) and will likely miss some children with UTI [30].

•Leukocyte esterase – Positive leukocyte esterase on dipstick analysis is suggestive of UTI but is nonspecific. White blood cells (WBCs) may be present in the urine in other conditions (eg, Kawasaki disease). (See 'Diagnostic criteria' below.)

•Nitrite – Positive nitrites on dipstick analysis indicate that UTI is likely [32]. The nitrite test is highly specific, with a low false-positive rate (table 1). False-negative results are common because urine must remain in the bladder for at least four hours to accumulate a detectable amount of nitrite [33]. Thus, a negative nitrite test does not exclude a UTI [34].

Although a dilute urine sample has been associated with decreased accuracy of dipstick nitrites, retrospective analysis of urinalysis and urine culture results from children <24 months who underwent bladder catheterization indicated that inclusion of urine specific gravity (SG) in the decision-making process would not have appreciably affected the care of children with UTI [35].

●Microscopic examination – Microscopic examination requires more equipment and training than dipstick tests. If available, we prefer enhanced microscopy to standard or automated microscopy, particularly for detection of bacteriuria.

•Standard microscopy – In standard microscopy, a centrifuged sample of unstained urine is examined for WBCs and bacteria.

With standard microscopy, pyuria is defined as ≥5 WBC/high-power field (hpf) and bacteriuria as any bacteria per hpf. The sensitivity, specificity, and likelihood ratios are summarized in the table (table 1).

•Enhanced microscopy – Enhanced microscopy (or enhanced urinalysis), available at some academic centers, refers to examination of an uncentrifuged urine specimen using a hemocytometer (results reported as WBC/mm³) and a Gram-stained smear [29,30,36].

With enhanced urinalysis, pyuria is defined as ≥10 WBC/mm³ and bacteriuria as any bacteria per 10 oil immersion fields of a Gram-stained smear. In young children in whom the prompt diagnosis and treatment of UTI are paramount, the enhanced urinalysis offers the best combination of sensitivity and specificity (table 1) [29,37,38]. However, enhanced urinalysis is not available in many outpatient settings.

•Automated microscopy – Many hospital laboratories have replaced manual microscopy with automated microscopy, which uses flow cytometry and microscopic analyzers to detect WBC and bacteria [39]. The definitions of pyuria and bacteriuria vary with the automated microscopy system.

Although automated microscopy appears to be comparable to manual microscopy for pyuria, Gram-stained smear of uncentrifuged urine is better for the detection of bacteriuria [38,39]. In a prospective study, automated and enhanced manual microscopy for pyuria were similarly sensitive (80 and 84 percent, respectively) and specific (90 and 94 percent, respectively) in predicting positive urine culture. However, for bacteriuria, automated microscopy was less sensitive (73 versus 84 percent) and specific (85 versus 96 percent) than enhanced manual microscopy [38].

Although SG may influence the accuracy of the WBC count with enhanced or automated microscopy [35,40,41], retrospective analysis of urinalysis and urine culture results from children <24 months who underwent bladder catheterization indicated that inclusion of urine SG in the decision-making process would not have appreciably affected the care of children with UTI [35].

Urine culture — Quantitative urine culture is required for the diagnosis of UTI.

●Children <2 years of age – We routinely perform urine culture in children <2 years in whom UTI is a diagnostic consideration and in whom a sample for urinalysis or dipstick is collected, even if the dipstick and standard and/or automated microscopic examination are negative for WBCs and bacteria because the sensitivity of these tests is <90 percent (table 1) [42,43]. (See 'Decision to obtain urine sample' above and 'How to obtain urine sample' above and 'Significant bacteriuria without pyuria' below.)

●Older children – For verbal children ≥2 years of age who are toilet trained and afebrile, the results of the dipstick or microscopic analysis can be used to decide whether to obtain a urine culture [44].

Urine obtained for culture should be processed as soon as possible after collection. A delay of even a few hours at room temperature increases both the false-positive and false-negative rates substantially [26].

Other laboratory tests — Other laboratory tests are not particularly helpful in the diagnosis of UTI and are not routinely necessary in children with suspected UTI. (See "The febrile infant (29 to 90 days of age): Outpatient evaluation" and "Fever without a source in children 3 to 36 months of age: Evaluation and management".)

●Markers of inflammation – We do not routinely obtain markers of inflammation (eg, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], or procalcitonin [PCT]) in the evaluation of children with suspected UTI.

Although markers of inflammation are associated with pyelonephritis, they do not reliably differentiate between cystitis and pyelonephritis because of their low sensitivity and/or specificity. In a meta-analysis of studies evaluating the accuracy of PCT, CRP, and ESR in predicting dimercaptosuccinic acid-confirmed pyelonephritis in children with culture-confirmed UTI, sensitivity ranged from 81 to 93 percent and specificity from 37 to 76 percent [45]. Although CRP <20 mg/L (2 mg/dL) appeared to be helpful in excluding pyelonephritis and PCT >0.5 ng/mL (0.5 mcg/L) appeared to be helpful in confirming pyelonephritis, methodologic limitations (eg, small number of studies, unexplained heterogeneity) prevented definitive conclusions.

Although elevated CRP has been associated with increased risk of renal scarring, it adds little to a prediction model that includes clinical features that do not require venipuncture (eg, temperature, pathogen, results of renal bladder ultrasonography) [23]. (See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Prediction of renal scarring after first UTI'.)

●Serum creatinine – Measurement of serum creatinine is not routinely necessary in children with suspected UTI. However, we suggest that serum creatinine be measured in children with a history of multiple UTI and suspected renal involvement or if acute kidney injury due to dehydration or sepsis is suspected.

●Blood culture – We do not routinely obtain a blood culture in children older than two months of age who have UTI and do not require blood culture for other reasons. (See "The febrile infant (29 to 90 days of age): Outpatient evaluation" and "Fever without a source in children 3 to 36 months of age: Evaluation and management".)

Bacteremia occurs in 4 to 9 percent of infants with UTI [46-52]. Fever in bacteremic infants with UTI persists, on average, one day longer than in nonbacteremic infants with UTI [53]. Nonetheless, a positive blood culture rarely alters management because the same organism usually is isolated from the blood and urine.

●Lumbar puncture – Given the low prevalence of bacterial meningitis in infants age 29 to 90 days with UTI (0.25 percent, 95% CI 0.09-0.70 percent in pooled analysis of 20 studies), lumbar puncture generally is not warranted in infants and children >1 month of age with UTI but should be assessed on a case-by-case basis [54]. (See "Bacterial meningitis in children older than one month: Clinical features and diagnosis".)

Lumbar puncture in infants younger than one month with UTI is discussed separately. (See "Urinary tract infections in neonates".)

Diagnostic criteria — UTI is best defined as significant bacteriuria of a clinically relevant uropathogen in a symptomatic patient (table 3). Pyuria is present in most cases. However, in approximately 10 to 20 percent of children with UTI, pyuria may be absent. (See 'Special circumstances' below.)

Significant bacteriuria

●Quantitative threshold – What constitutes significant bacteriuria depends upon the method of collection and the identification of the isolated organism [26].

Our thresholds for significant bacteriuria according to method of collection are as follows:

•Clean-voided sample – Growth of ≥100,000 colony forming units (CFU)/mL of a single uropathogen, or ≥100,000 CFU/mL of one uropathogen and <50,000 CFU/mL of a second uropathogen; growth of a second uropathogen with ≥50,000 CFU/mL or growth of >2 organisms is considered contamination.

This is the same as the standard definition for significant bacteriuria on clean-catch specimens in adults, which is based upon studies from the 1950s [55].

•Catheter sample – Growth of ≥10,000 CFU/mL with pyuria (see 'Pyuria' below), growth of ≥50,000 CFU/mL of a single uropathogen if no pyuria, or ≥50,000 CFU/mL of one uropathogen and <10,000 CFU/mL of a second uropathogen [26,56]; growth of a second uropathogen with ≥10,000 CFU/mL or growth of >2 organisms is considered contamination.

In a study of 341 febrile children one month to three years of age who underwent bladder catheterization for suspected UTI, a threshold of ≥10,000 CFU/mL growth from a catheterized urine culture was both sensitive (98 percent, 95% CI 93-100 percent) and specific (99 percent, 95% CI 97-100 percent) for a diagnosis of UTI [57]. A reference standard that required a threshold number of bacterial gene sequences and elevated urinary markers of inflammation was used to define UTI. The results of this study, which is the first to use an independent reference standard, support a threshold of ≥10,000 CFU/mL growth from a catheterized urine sample to diagnose UTI. These results are consistent with the conclusions from a previous prospective study of 2181 febrile children <24 months of age in which children with ≥10,000 CFU/mL of a uropathogen and evidence of inflammation were considered to be at risk for UTI [58].

•Suprapubic sample – Growth of ≥1000 CFU/mL of an uropathogen.

●Clinically relevant uropathogens – Clinically relevant uropathogens in children include Escherichia coli, Klebsiella spp, Proteus spp, Enterobacter spp, Citrobacter spp, Serratia marcescens, Staphylococcus saprophyticus, Enterococcus spp, Streptococcus agalactiae, and Pseudomonas aeruginosa.

●Clinically irrelevant uropathogens – Lactobacillus spp, coagulase-negative staphylococci, and Corynebacterium spp are not considered clinically relevant uropathogens [26].

Pyuria — For the diagnosis of UTI in children, pyuria is defined by one of the following (irrespective of urine SG):

●Positive leukocyte esterase (≥trace) on dipstick analysis

●≥5 WBC/hpf with standardized or automated microscopy

●≥10 WBC/mm³ on a hemocytometer with an enhanced urinalysis

The presence of WBC in the urine is not specific for UTI. Other causes of pyuria in children with symptoms that mimic UTI include appendicitis, group A streptococcal infection, and Kawasaki disease. (See 'Differential diagnosis' below.)

Special circumstances

Significant bacteriuria without pyuria — Pyuria is absent in approximately 10 to 20 percent of children with UTI [22,42,59,60]. The approach to diagnosis of UTI in children with significant bacteriuria without pyuria varies with the uropathogen that is isolated.

●Significant growth of Enterococcus spp, Klebsiella spp, or P. aeruginosa – UTI may be diagnosed in the absence of pyuria in children with symptoms of UTI and significant growth of Enterococcus spp, Klebsiella spp, or P. aeruginosa [42,61-63].

In a retrospective review of 1181 children (<18 years of age) with UTI who had a microscopic urinalysis for pyuria (≥5 WBC/hpf or ≥10 WBC^/mm³), 13 percent did not have pyuria [42]. UTI was defined by growth of a single uropathogen at a concentration of ≥50,000 CFU/mL from a catheterized specimen or ≥100,000 CFU/mL from a clean-voided specimen in a child with symptoms of UTI. Only 54 percent of children with Enterococcus UTI, 74 percent of children with Klebsiella UTI, and 62 percent of children with P. aeruginosa UTI had pyuria, compared with 89 percent of children with E. coli UTI. However, given that E. coli was the most frequently isolated uropathogen (85 percent), most of the children with UTI without pyuria had an E. coli UTI (107 of 150 children without pyuria).

●Significant growth of other uropathogens – Although children with growth of Enterococcus spp, Klebsiella spp, or P. aeruginosa are more likely to lack pyuria on urinalysis than children with other pathogens, given the high proportion of UTI caused by E. coli, most cases of bacteriuria without pyuria are observed in children with E. coli. It is not clear why bacteriuria occurs without pyuria in children with E. coli UTI, but it may occur [26,61]:

•Early in the course of a UTI (ie, before the local inflammatory response develops).

•If the dipstick leukocyte esterase test or microscopic analysis is falsely negative (these tests are at best 90 percent sensitive (table 1)).

•In children with colonization of the urinary tract (ie, asymptomatic bacteriuria with symptoms due to another non-specific illness).

In symptomatic children with bacteriuria without pyuria, we recommend antibiotic therapy for those with any of the following characteristics:

•Age <2 years

•Fever >38°C (100.4°F)

•History of febrile UTI or urinary tract abnormality

•Clinical worsening or lack of improvement

We recommend antibiotic therapy for these children because the prevalence of bacteriuria without pyuria far exceeds the prevalence of asymptomatic bacteriuria [64]. In preverbal febrile children in whom the urine sample was obtained by bladder catheterization, one study estimated that up to 12 children with true UTIs would be missed to protect one child with asymptomatic bacteriuria from receiving antibiotics [64].

For other children, repeating the urinalysis and urine culture can help to distinguish between early infection and colonization, particularly if the urine is obtained through catheterization or suprapubic aspiration to minimize contamination [12].

•Pyuria and bacteriuria on the second sample is suggestive of UTI.

•The absence of pyuria and bacteriuria on the second sample is suggestive of bacterial contamination of the initial sample.

•Bacteriuria without pyuria on the second sample may be due to true infection or asymptomatic bacteriuria.

Pyuria without significant bacteriuria — In children with symptoms of UTI and pyuria on dipstick or microscopic urinalysis, the absence of significant bacteriuria does not absolutely exclude a diagnosis of UTI. Failure to meet the threshold for significant bacteriuria (ie, false-negative urine culture) may occur under the following circumstances [12,58]:

●A bacteriostatic antimicrobial agent is present in the urine

●Rapid rate of urine flow with reduced incubation time

●Obstruction of the ureter that interferes with the discharge of bacteria into the bladder

When false-negative urine culture is suspected, renal scintigraphy may be helpful in establishing the diagnosis of acute pyelonephritis. (See "Urinary tract infections in infants older than one month and children less than two years: Acute management, imaging, and prognosis", section on 'Kidney scintigraphy'.)

DIFFERENTIAL DIAGNOSIS — Other considerations in the differential diagnosis in a child with suspected UTI depend upon the presenting symptoms and signs and results of the urinalysis. Quantitative urine culture results, results of cultures or other microbiologic tests from other sites, and associated clinical features distinguish UTI from these conditions.

●Fever without a source – Although occult UTI is the main consideration in the differential diagnosis of fever without a source in children age 3 to 36 months, other considerations include occult pneumonia and occult bacteremia (rare in the conjugate vaccine era). (See "Fever without a source in children 3 to 36 months of age: Evaluation and management".)

●Fever, abdominal pain, and pyuria – Considerations include:

•Group A streptococcal infection (see "Group A streptococcal tonsillopharyngitis in children and adolescents: Clinical features and diagnosis")

•Appendicitis (see "Acute appendicitis in children: Clinical manifestations and diagnosis")

•Kawasaki disease (see "Kawasaki disease: Clinical features and diagnosis")

●Urinary symptoms (eg, urgency, frequency, dysuria) with bacteriuria (with or without pyuria) – Considerations include (see "Etiology and evaluation of dysuria in children and adolescents"):

•Nonspecific vulvovaginitis, irritant or chemical urethritis (eg, due to bubble bath), and vaginal foreign body (see "Vulvovaginitis in the prepubertal child: Clinical manifestations, diagnosis, and treatment" and "Overview of vulvovaginal conditions in the prepubertal child")

•Urethritis secondary to a sexually transmitted infection, particularly chlamydia (see "Clinical manifestations and diagnosis of Chlamydia trachomatis infections")

•Urinary calculi (see "Kidney stones in children: Clinical features and diagnosis")

●Urinary symptoms without bacteriuria

•Bowel and bladder dysfunction is frequently overlooked in children with urinary symptoms and a negative urine culture, although it also contributes to the pathogenesis of UTI. (See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Bladder and bowel dysfunction'.)

●Asymptomatic bacteriuria – Asymptomatic bacteriuria in a child with nonspecific symptoms (eg, fever, abdominal pain) caused by a condition other than UTI (eg, viral gastroenteritis) is a consideration in the differential diagnosis of UTI in children.

Asymptomatic bacteriuria (ie, colonization of the urinary tract with bacteria in the absence of symptoms) is rare. The prevalence of asymptomatic bacteriuria is substantially lower than the prevalence of UTI. In a meta-analysis of 14 studies (49,806 children <19 years of age), the prevalence of asymptomatic bacteriuria was 0.47 percent in females and 0.37 percent in males [64]. The bacteria tend to be of low virulence, and spontaneous resolution is common; antibiotic treatment is not recommended [65-68]. A meta-analysis of three randomized trials found the evidence insufficient to determine the risks and benefits but concluded that antibiotic therapy is unlikely to benefit children in the long term [69].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Urinary tract infections in children".)

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SUMMARY AND RECOMMENDATIONS

●Clinical features – In infants and young children, UTI may present with nonspecific symptoms and signs (eg, fever, irritability, poor feeding, poor weight gain); fever may be the only sign. Older children may have urinary symptoms (eg, dysuria, frequency, new-onset urinary incontinence, abdominal pain, back pain, fever). (See 'Clinical presentation' above.)

●History and examination – Important aspects of the history in a child with suspected UTI include features of the acute illness (eg, fever, urinary symptoms) and risk factors for UTI (eg, previous UTI, bowel and bladder dysfunction, vesicoureteral reflux). (See 'History' above.)

The examination of the child with suspected UTI should include (see 'Physical examination' above):

•Measurement of temperature, blood pressure, and growth parameters

•Abdominal examination for tenderness or mass

•Assessment of suprapubic and costovertebral tenderness

•Examination of the external genitalia

•Evaluation of the lower back for signs of occult myelomeningocele

•Evaluation for other sources of fever

●Laboratory evaluation and diagnosis – The laboratory evaluation for suspected UTI includes urine dipstick and microscopic analysis (table 1) and urine culture. (See 'Laboratory evaluation and diagnosis' above.)

•The decision to obtain a urine sample is made on a case-by-case basis, considering age, sex, circumcision status, and presenting signs and symptoms (table 2). UTICalc can be used to estimate the probability of UTI in febrile (temperature ≥38°C [100.4°F]) children age 2 through 23 months according to clinical characteristics. (See 'Decision to obtain urine sample' above.)

•Catheterization or suprapubic aspiration is the preferred method of urine collection for infants and children who are not toilet trained. A clean-voided specimen is the preferred method for toilet-trained children. Urine obtained in a sterile bag should not be used for culture. (See 'How to obtain urine sample' above.)

•We routinely perform urine culture in children <2 years with suspected UTI if a sample for urinalysis or dipstick test is collected, even if the dipstick and microscopic examination are negative for white blood cells and bacteriuria because the sensitivity of dipstick and microscopic examination is <90 percent (table 1).

For verbal children ≥2 years of age who are toilet trained and afebrile, the results of the dipstick or microscopic analysis can be used to decide whether to obtain a urine culture. (See 'Urine culture' above.)

•UTI is best defined as significant bacteriuria of a clinically relevant uropathogen in a symptomatic patient. Although pyuria is usually present, it may be absent in 10 to 20 percent of children with UTI (table 3). (See 'Diagnostic criteria' above.)

●Differential diagnosis – Quantitative urine culture results, results of cultures or other microbiologic tests from other sites, and associated clinical features distinguish UTI from other conditions in the differential diagnosis (eg, asymptomatic bacteriuria, occult bacteremia [rare], occult pneumonia, group A streptococcal infection, appendicitis, Kawasaki disease, nonspecific vulvovaginitis, urethritis, nephrolithiasis, and bowel and bladder dysfunction). (See 'Differential diagnosis' above.)