UTI, incl questions by Dr Hwang
UTI, culture criteria for dx
Question: we traditionally think of 1st generation cephalosporins as effective against gram-positive organisms only. Why do we use it in the treatment of UTI when E.coli is the main organism we are treating? see UTI, treatment
Random note: newborns rarely present with UTI on DOL#1, so r/o sepsis on a newborn does not usually involve a urine culture. Subsequent sepsis workups should include urine culture.
Guide on imaging workup: E-medicine.com: Urinary Tract Infection
Last Updated: February 24, 2005 http://www.emedicine.com/ped/topic2366.htm
Voiding cystourethrogram (VCUG)
PEDIATRICS Vol. 103 No. 4 April 1999, pp. 843-852
AMERICAN ACADEMY OF PEDIATRICS:
Practice Parameter: The Diagnosis, Treatment, and Evaluation of the Initial Urinary Tract Infection in Febrile Infants and Young Children,
To formulate recommendations for health care professionals about the diagnosis, treatment, and evaluation of an initial urinary tract infection (UTI) in febrile infants and young children (ages 2 months to 2 years).
The presence of UTI should be considered in infants and young children 2 months to 2 years of age with unexplained fever (strength of evidence: strong).
In infants and young children 2 months to 2 years of age with unexplained fever, the degree of toxicity, dehydration, and ability to retain oral intake must be carefully assessed (strength of evidence: strong).
If the clinician determines that the degree of illness warrants antimicrobial therapy, a valid urine specimen should be obtained before antimicrobials are administered, because the antimicrobials commonly prescribed in such situations will be effective against the usual urinary pathogens; invasive means are required to obtain such a specimen. If the clinician determines that the degree of illness does not require antimicrobial therapy, a urine culture is not essential immediately. In this situation, some clinicians may choose to obtain a specimen by noninvasive means (eg, in a collection bag attached to the perineum). The false-positive rate with such specimens dictates that before diagnosing UTI, all positive results be confirmed with culture of a urine specimen unlikely to be contaminated (see below).
If an infant or young child 2 months to 2 years of age with unexplained fever is assessed as being sufficiently ill to warrant immediate antimicrobial therapy, a urine specimen should be obtained by SPA or transurethral bladder catheterization; the diagnosis of UTI cannot be established by a culture of urine collected in a bag (strength of evidence: good).
Cultures of urine specimens collected in a bag applied to the perineum have an unacceptably high false-positive rate; the combination of a 5% prevalence of UTI and a high rate of false-positive results (specificity, ~70%) results in a positive culture of urine collected in a bag to be a false-positive result 85% of the time.
Suprapubic aspiration (SPA) has been considered the "gold standard" for obtaining urine for detecting bacteria in bladder urine accurately. The technique has limited risks. However, variable success rates for obtaining urine have been reported (23% to 90%), technical expertise and experience are required, and many parents and physicians perceive the procedure as unacceptably invasive compared with catheterization. There may be no acceptable alternative in the boy with moderate or severe phimosis, however.
Urine obtained by transurethral catheterization of the urinary bladder for urine culture has a sensitivity of 95% and a specificity of 99% compared with that obtained by SPA
If an infant or young child 2 months to 2 years of age with unexplained fever is assessed as not being so ill as to require immediate antimicrobial therapy, there are two options (strength of evidence: good).
Option 1 Obtain and culture a urine specimen collected by SPA or transurethral bladder catheterization.
Option 2 Obtain a urine specimen by the most convenient means and perform a urinalysis. If the urinalysis suggests a UTI, obtain and culture a urine specimen collected by SPA or transurethral bladder catheterization; if urinalysis does not suggest a UTI, it is reasonable to follow the clinical course without initiating antimicrobial therapy, recognizing that a negative urinalysis does not rule out a UTI.
Use of bag-collected urine specimens persists because collection of urine by this method is noninvasive and requires limited personnel time and expertise. Moreover, a negative (sterile) culture of a bag-collected urine specimen effectively eliminates the diagnosis of UTI, provided that the child is not receiving antimicrobials and that the urine is not contaminated with an antibacterial skin cleansing agent. Based on their experience, many clinicians believe that this collection technique has a low contamination rate under the following circumstances: the patient's perineum is properly cleansed and rinsed before application of the collection bag; the urine bag is removed promptly after urine is voided into the bag; and the specimen is refrigerated or processed immediately. Nevertheless, even if contamination from the perineal skin is minimized, there may be significant contamination from the vagina in girls or the prepuce in uncircumcised boys. Published results demonstrate that although a negative culture of a bag-collected specimen effectively rules out UTI, a positive culture does not document UTI. Confirmation requires culture of a specimen collected by transurethral bladder catheterization or SPA. Transurethral catheterization does not eliminate completely the possibility of contamination in girls and uncircumcised boys.
Of the components of urinalysis, the three most useful in the evaluation of possible UTI are leukocyte esterase test, nitrite test, and microscopy. A positive result on a leukocyte esterase test seems to be as sensitive as the identification of WBCs microscopically, but the sensitivity of either test is so low that the risk of missing UTI by either test alone is unacceptably high The nitrite test has a very high specificity and positive predictive value when urine specimens are processed promptly after collection
|Leukocyte esterase||83 (67-94)||78 (64-92)|
|Nitrite||53 (15-82)||98 (90-100)|
|Leukocyte esterase or nitrite
|93 (90-100)||72 (58-91)|
|Microscopy: WBCs||73 (32-100)||81 (45-98)|
|Microscopy: bacteria||81 (16-99)||83 (11-100)|
|Leukocyte esterase or nitrite or
|99.8 (99-100)||70 (60-92)|
Any of the following are suggestive (although not diagnostic) of UTI: positive result of a leukocyte esterase or nitrite test, more than 5 white blood cells per high-power field of a properly spun specimen, or bacteria present on an unspun Gram-stained specimen.
In circumcised boys, whose low a priori rate of UTI (0.2% to 0.4%) does not routinely justify an invasive, potentially traumatic procedure, a normal urinalysis reduces the likelihood of UTI as the cause of the fever still further, to the order of 0.1%.
Diagnosis of UTI requires a culture of the urine (strength of evidence: strong).
All urine specimens should be processed as expediently as possible. If the specimen is not processed promptly, it should be refrigerated to prevent the growth of organisms that can occur in urine at room temperature. For the same reason, specimens requiring transportation to another site for processing should be transported on ice.
Criteria for the Diagnosis of UTI (colony count, probability of infection)
If the infant or young child 2 months to 2 years of age with suspected UTI is assessed as toxic, dehydrated, or unable to retain oral intake, initial antimicrobial therapy should be administered parenterally and hospitalization should be considered (strength of evidence: opinion/consensus).
Patients who are toxic-appearing, dehydrated, or unable to retain oral intake (including medications) should receive an antimicrobial parenterally until they are improved clinically and are able to retain oral fluids and medications. The parenteral route is recommended because it ensures optimal antimicrobial levels in these high-risk patients. The clinical conditions of most patients improve within 24 to 48 hours; the route of antimicrobial administration then can be changed to oral to complete a 7- to 14-day course of therapy.
Some Antimicrobials for Parenteral Treatment of UTI
|Ceftriaxone||75 mg/kg every 24 h|
|Cefotaxime||150 mg/kg/d divided every 6 h|
|Ceftazidime||150 mg/kg/d divided every 6 h|
|Cefazolin||50 mg/kg/d divided every 8 h|
|Gentamicin||7.5 mg/kg/d divided every 8 h|
|Tobramycin||5 mg/kg/d divided every 8 h|
|Ticarcillin||300 mg/kg/d divided every 6 h|
|Ampicillin||100 mg/kg/d divided every 6 h|
Some Antimicrobials for Oral Treatment of UTI
|Amoxicillin||20-40 mg/kg/d in 3 doses|
| - TMP in combination
|6-12 mg TMP, 30-60 mg
SMX per kg per d in 2 doses
|- Sulfisoxazole||120-150 mg/kg/d in 4 doses|
|Cefixime||8 mg/kg/d in 2 doses|
|Cefpodixime||10 mg/kg/d in 2 doses|
|Cefprozil||30 mg/kg/d in 2 doses|
|Cephalexin||50-100 mg/kg/d in 4 doses|
|Loracarbef||15-30 mg/kg/d in 2 doses|
In the infant or young child 2 months to 2 years of age who may not appear ill but who has a culture confirming the presence of UTI, antimicrobial therapy should be initiated, parenterally or orally (strength of evidence: good).
The usual choices for treatment of UTI orally include amoxicillin, a sulfonamide-containing antimicrobial (sulfisoxazole or trimethoprim-sulfamethoxazole [TMP-SMX]), or a cephalosporin. Emerging resistance of E coli to ampicillin appears to have rendered ampicillin and amoxicillin less effective than alternative agents. Studies comparing amoxicillin with TMP-SMX have demonstrated consistently higher cure rates with TMP-SMX (4% to 42%), regardless of the duration of therapy (1 dose, 3 to 4 days, or 10 days)
Agents that are excreted in the urine but do not achieve therapeutic concentrations in the bloodstream, such as nalidixic acid or nitrofurantoin, should not be used to treat UTI in febrile infants and young children in whom renal involvement is likely.
Infants and young children 2 months to 2 years of age with UTI who have not had the expected clinical response with 2 days of antimicrobial therapy should be reevaluated and another urine specimen should be cultured (strength of evidence: good).
Routine reculturing of the urine after 2 days of antimicrobial therapy is generally not necessary if the infant or young child has had the expected clinical response and the uropathogen is determined to be sensitive to the antimicrobial being administered. Antimicrobial sensitivity testing is determined most commonly by the application of disks containing the usual serum concentration of the antimicrobial to the culture plate. Because many antimicrobial agents are excreted in the urine in extremely high concentrations, an intermediately sensitive organism may be fully eradicated. Studies of minimal inhibitory concentration may be required to clarify the appropriateness of a given antimicrobial. If the sensitivity of the organism to the chosen antimicrobial is determined to be intermediate or resistant, or if sensitivity testing is not performed, a "proof-of-bacteriologic cure" culture should be performed after 48 hours of treatment. Data are not available to determine that clinical response alone ensures bacteriologic cure.
Infants and young children 2 months to 2 years of age, including those whose treatment initially was administered parenterally, should complete a 7- to 14-day antimicrobial course orally (strength of evidence: strong).
Most uncomplicated UTIs are eliminated with a 7- to 10-day antimicrobial course, but many experts prefer 14 days for ill-appearing children with clinical evidence of pyelonephritis. Data comparing 10 days and 14 days are not available.
After a 7- to 14-day course of antimicrobial therapy and sterilization of the urine, infants and young children 2 months to 2 years of age with UTI should receive antimicrobials in therapeutic or prophylactic dosages until the imaging studies are completed (strength of evidence: good).
Some Antimicrobials for Prophylaxis of UTI
|TMP in combination with SMX||2 mg of TMP, 10 mg of SMX per kg as single bedtime dose or 5 mg of TMP, 25 mg of SMX per kg twice per week|
|Nitrofurantoin||1-2 mg/kg as single daily dose|
|Sulfisoxazole||10-20 mg/kg divided every 12 h|
|Nalidixic acid||30 mg/kg divided every 12 h|
|Methenamine mandelate||75 mg/kg divided every 12 h|
Infants and young children 2 months to 2 years of age with UTI who do not demonstrate the expected clinical response within 2 days of antimicrobial therapy should undergo ultrasonography promptly, and either voiding cystourethrography (VCUG) or radionuclide cystography (RNC) should be performed at the earliest convenient time. Infants and young children who have the expected response to antimicrobials should have a sonogram and either VCUG or RNC performed at the earliest convenient time (strength of evidence: fair).
Imaging of the urinary tract is recommended in every febrile infant or young child with a first UTI to identify those with abnormalities that predispose to renal damage. Imaging should consist of urinary tract ultrasonography to detect dilatation secondary to obstruction and a study to detect VUR.
Ultrasonography Urinary tract ultrasonography consists of examination of the kidneys to identify hydronephrosis and examination of the bladder to identify dilatation of the distal ureters, hypertrophy of the bladder wall, and the presence of ureteroceles. Previously, excretory urography (commonly called intravenous pyelography) was used to reveal these abnormalities, but now ultrasonography shows them more safely, less invasively, and often less expensively. Ultrasonography does have limitations, however. A normal ultrasound does not exclude VUR. Ultrasonography may show signs of acute renal inflammation and established renal scars, but it is not as sensitive as other renal imaging techniques.
Usually the timing of the ultrasound is not crucial, but when the rate of clinical improvement is slower than anticipated during treatment, ultrasonography should be performed promptly to look for a cause such as obstruction or abscess.
VUR The most common abnormality detected in imaging studies is VUR. The rate of VUR among children younger than 1 year of age with UTI exceeds 50%. VUR is not an all-or-none phenomenon; grades of severity are recognized, designated I to V in the International Study Classification (International Reflux Study Committee, 1981), based on the extent of the reflux and associated dilatation of the ureter and pelvis. The grading of VUR is important because the natural history differs by grade, as does the risk of renal damage. Patients with high-grade VUR are 4 to 6 times more likely to have scarring than those with low-grade VUR and 8 to 10 times more likely than those without VUR.
VCUG; RNC (radionuclide cystography) Either traditional contrast VCUG or RNC is recommended for detecting reflux. Although children may have pyelonephritis without reflux, the child with reflux is at increased risk of pyelonephritis and of scarring from UTI. With VCUG and RNC, a voiding phase is important because some reflux occurs only during voiding. If the predicted bladder capacity is not reached, the study may underestimate the presence or degree of reflux.
VCUG with fluoroscopy characterizes reflux better than does RNC. In addition, RNC does not show urethral or bladder abnormalities; for this reason, boys, whose urethra must be examined for posterior urethral valves, or girls, who have symptoms of voiding dysfunction when not infected, should have a standard fluoroscopic contrast VCUG as part of their initial studies. RNC has a lower radiation dose and therefore may be preferred in follow-up examinations of children with reflux. However, the introduction of low-dose radiographic equipment has narrowed the gap in radiation between the VCUG and RNC.
There is no benefit in delaying performance of these studies as long as the child is free of infection and bladder irritability is absent. While waiting for reflux study results, the child should be receiving an antimicrobial, either as part of the initial treatment or as posttreatment prophylaxis.
Radionuclide Renal Scans Renal cortical scintigraphy (with 99 m Tc-DMSA or 99 m Tc-glucoheptonate) and enhanced computed tomography are very sensitive means of identifying acute changes from pyelonephritis or renal scarring. However, the role of these imaging modalities in the clinical management of the child with UTI still is unclear.
Recurrent urinary tract infections (UTIs) are not uncommon in the pediatric patient, especially during the first year immediately following the original infection. The American Academy of Pediatrics currently recommends that a urine culture be obtained every month for 3 to 6 months following a UTI and every 3 months thereafter in patients who have no renal pathology. The presence of vesicoureteral reflux (VUR), however, warrants more aggressive monitoring and medical prophylaxis (ie, suppressive antibiotics) to prevent subsequent infections. The goal is to minimize renal injury and scarring and the development of long-term complications associated with untreated UTIs, such as hypertension and renal failure.
Radiographic studies in children who have UTIs allow differentiation of those who have normal urinary tracts from those who have underlying renal pathology such as VUR. Renal ultrasonography and voiding cystourethrography are the diagnostic studies performed most commonly. Results of these two studies will dictate further management and follow-up. Intravenous pyelography and cystoscopy generally are not indicated but may be reserved for an immediate preoperative evaluation to allow outlining of pertinent anatomy.
The treatment for presumed cystitis is a 10-day course of antibiotic therapy if the child is known to have no radiographic abnormalities. If the child has normal radiographic findings and is plagued by recurrent UTIs, short-course therapy with 3 days of trimethoprim-sulfamethoxazole is an inexpensive option that discourages the development of resistant organisms. Short-course therapy also is often used to treat uncomplicated cystitis in adolescents.
Several prospective studies have shown that there is no value to identifying or treating asymptomatic children who have bacteriuria, such as the girl in the vignette. Unnecessary treatment only leads to the emergence of resistant strains of bacteria; many patients clear the bacteriuria uneventfully.
Suppressive antibiotic therapy and frequent monitoring for recurrent infections are the preferred management for VUR. For some patients, however, surgical intervention is necessary for relief. Absolute indications for ureteral reimplantation include progressive renal injury, breakthrough infections despite ongoing antibiotic suppressive therapy, and poor compliance or problems tolerating antibiotics. Patients who have grade V reflux or associated anatomic anomalies of ureteral insertion also are candidates for surgical repair of the reflux.
Johnson CE. New advances in childhood urinary tract infections.
Pediatr Rev. 1999;20:335-342
Sheldon CA, Wacksman J. Vesicoureteral reflux. Pediatr Rev. 1995;16:22-27