Use of urinary gram stain for detection of urinary tract infection in infants

Diagnostic value of biomarkers for paediatric urinary tract infections in primary care: systematic review and meta-analysis

Background

Accurate diagnosis of urinary tract infection is essential as children left untreated may suffer permanent renal injury.

Aim

To compare the diagnostic values of biomarkers or clinical prediction rules for urinary tract infections in children presenting to ambulatory care.

Design and setting

Systematic review and meta-analysis of ambulatory care studies.

Methods

Medline, Embase, WOS, CINAHL, Cochrane library, HTA and DARE were searched until 21 May 2021. We included diagnostic studies on urine or blood biomarkers for cystitis or pyelonephritis in children below 18 years of age. We calculated sensitivity, specificity and likelihood ratios. Data were pooled using a bivariate random effects model and a Hierarchical Summary Receiver Operating Characteristic analysis.

Results

Seventy-five moderate to high quality studies were included in this review and 54 articles in the meta-analyses. The area under the receiver-operating-characteristics curve to diagnose cystitis was 0.75 (95%CI 0.62 to 0.83, n = 9) for C-reactive protein, 0.71 (95% CI 0.62 to 0.80, n = 4) for procalcitonin, 0.93 (95% CI 0.91 to 0.96, n = 22) for the dipstick test (nitrite or leukocyte esterase ≥trace), 0.94 (95% CI 0.58 to 0.98, n = 9) for urine white blood cells and 0.98 (95% CI 0.92 to 0.99, n = 12) for Gram-stained bacteria. For pyelonephritis, C-reactive protein < 20 mg/l had LR- of 0.10 (95%CI 0.04–0.30) to 0.22 (95%CI 0.09–0.54) in children with signs suggestive of urinary tract infection.

Conclusions

Clinical prediction rules including the dipstick test biomarkers can support family physicians while awaiting urine culture results. CRP and PCT have low accuracy for cystitis, but might be useful for pyelonephritis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12875-021-01530-9.

Utility of point-of-care Gram stain by physicians for urinary tract infection in children ≤36 months

Urinary tract infection (UTI) in children requires early diagnosis and treatment to prevent repeated UTI and renal scarring. This study aimed to evaluate the usefulness of the point-of-care Gram stain by physicians for suspected UTI in children at Okinawa Chubu Hospital as a rapid diagnostic test.A single-center, retrospective study was undertaken between January 2011 and December 2015. Patients aged 36 months or younger who were reviewed had suspected UTI in the emergency room or outpatient clinic. Urine culture, urinalysis, and point-of-care Gram stain were performed on a single specimen. Patients with structural or functional urological defects requiring routine catheterization were excluded. We compared the diagnostic performance among the rapid diagnostic tests (i.e., pyuria, point-of-care Gram stain, or both). Kappa statistics were used to evaluate the agreement between the results of point-of-care Gram stain and morphotypes of urine culture with the 95% CI (bias corrected bootstrap interval). We also analyzed which antibiotics were more susceptible to the bacteria of urine culture results, selected by the results of point-of-care Gram stain or empirical treatment based on the Japanese guidelines by McNemar test.Of 1594 patients reviewed in the study, 1546 were eligible according to our inclusion criteria. Using urine culture as the gold standard for UTI, the sensitivity and specificity of pyuria were 73.2% and 95.1%, whereas those of the point-of-care Gram stain were 81.4% and 98.2%, respectively. The concordance rate between the morphotypes of bacteria detected by point-of-care Gram stain and those of urine culture was 0.784 (kappa coefficient) (95% CI 0.736-0.831). Furthermore, the proportion of "susceptible" in the minimum inhibitory concentration of pathogen-targeted treatment based on the point-of-care Gram stain was higher than that of empirical therapy (exact McNemar significance probability: .0001).Our analysis suggests that the point-of-care Gram stain is a useful rapid diagnostic tool for suspected UTI in young children. Pathogen-targeted treatment based on the point-of-care Gram stain would lead to better antibiotic selection compared with empirical therapy.

Combination of Coral UTI ScreenTM system, gram-stain and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for diagnosis of urinary tract infections directly from urine samples

This study proposes an algorithm for microbiological diagnosis of urinary tract infections based on screening by luminometry and Gram-stain, followed by identification by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Positive urine samples detected with the luminometry screening Coral UTI Screen^TM system underwent Gram staining and identification of the causative organism was performed by MALDI-TOF Microflex LT mass spectrometer (Bruker Daltonics, Germany). Subsequently, the results were compared with those of conventional culture identification using WIDER MIC/id system (Francisco Soria Melguizo SA, Spain). Considering the conventional approach as the gold standard, the proposed algorithm presented both a high specificity (98.1%) and a positive likelihood ratio of 37.42. The implementation of this algorithm would allow diagnosis of urinary tract infection in less than an hour in 92.4% of positive samples. This combination of techniques would be useful particularly for patients with severe UTI, pyelonephritis or urinary sepsis.

Rapid urine preparation prior to identification of uropathogens by MALDI-TOF MS

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF MS) has been introduced in clinical routine microbiology laboratories. For the rapid diagnosis of urinary tract infections, culture-independent methods prior MALDI-mediated identification have been described. Here, we describe a comparison of three of these methods based on their performance of bacterial identification and their potential as a routine tool for microbiology labs : (i) differential centrifugation, (ii) urine filtration and (iii) a 5-h bacterial cultivation on solid culture media. For 19 urine samples, all methods were directly compared and correct bacterial species identification by MALDI was used as performance indicator. A higher percentage of correct MALDI identification was obtained after filtration (78.9 %) and the growth-based method (84.2 %) as compared to differential centrifugation (68.4 %). Additional testing of 76 mono-microbial specimens (bacteriuria > 10(5) CFU/mL) confirmed the good performance of short growth with a 90.8 % correct MALDI score, with a potentially better fit to the routine workflow of microbiology labs.

Using a urine dipstick to identify a positive urine culture in young febrile infants is as effective as in older patients

AIM

There is limited evidence about the diagnostic value of urine dipsticks in young febrile infants. The aim of this study was to determine whether urine dipsticks would identify positive urine cultures in febrile infants of less than 90 days of age.

METHODS

This study was a subanalysis of a prospective multicentre study developed in 19 Spanish paediatric emergency departments belonging to the Spanish Paediatric Emergency Research Network. It focused on febrile infants of less than 90 days of age admitted between October 2011 and September 2013. A positive urine culture was defined as the growth of ≥ 50,000 cfu/mL of a single pathogen collected by a sterile method.

RESULTS

We included 3401 patients, and 176 (12.8%) female patients and 473 (23.3%) males had a positive urine culture. The leucocyte esterase test showed a mean sensitivity of 82.1% and a mean specificity of 92.4%, with a greater mean negative predictive value for females than males (97.8 versus 94.1%) and a greater mean positive predictive value for males than females (79.4% versus 58%).

CONCLUSION

The leucocyte esterase test showed the same accuracy in young febrile infants as previously reported findings for older children. It predicted positive urine cultures and also revealed important gender differences.

Dipstick screening for urinary tract infection in febrile infants

OBJECTIVE

This study compares the performance of urine dipstick alone with urine microscopy and with both tests combined as a screen for urinary tract infection (UTI) in febrile infants aged 1 to 90 days.

METHODS

We queried the Intermountain Healthcare data warehouse to identify febrile infants with urine dipstick, microscopy, and culture performed between 2004 and 2011. UTI was defined as >50 000 colony-forming units per milliliter of a urinary pathogen. We compared the performance of urine dipstick with unstained microscopy or both tests combined ("combined urinalysis") to identify UTI in infants aged 1 to 90 days.

RESULTS

Of 13 030 febrile infants identified, 6394 (49%) had all tests performed and were included in the analysis. Of these, 770 (12%) had UTI. Urine culture results were positive within 24 hours in 83% of UTIs. The negative predictive value (NPV) was >98% for all tests. The combined urinalysis NPV was 99.2% (95% confidence interval: 99.1%-99.3%) and was significantly greater than the dipstick NPV of 98.7% (98.6%-98.8%). The dipstick positive predictive value was significantly greater than combined urinalysis (66.8% [66.2%-67.4%] vs 51.2% [50.6%-51.8%]). These data suggest 8 febrile infants would be predicted to have a false-positive combined urinalysis for every 1 infant with UTI initially missed by dipstick screening.

CONCLUSIONS

Urine dipstick testing compares favorably with both microscopy and combined urinalysis in febrile infants aged 1 to 90 days. The urine dipstick test may be an adequate stand-alone screen for UTI in febrile infants while awaiting urine culture results.

Comparison of routine urinalysis and urine Gram stain for detection of bacteriuria in dogs

OBJECTIVE

To determine the utility of performing urine Gram stain for detection of bacteriuria compared to routine urine sediment examination and bacterial aerobic urine culture.

DESIGN

Prospective, observational study.

SETTING

University teaching hospital.

ANIMALS

Urine samples acquired via cystocentesis through convenience sampling from 103 dogs presenting to a tertiary referral institution.

INTERVENTIONS

All samples underwent routine urinalysis, including sediment examination, as well as urine Gram stain and quantitative bacterial aerobic urine culture.

MEASUREMENTS AND MAIN RESULTS

The urine Gram stain demonstrated improved sensitivity (96% versus 76%), specificity (100% versus 77%), positive predictive value (100% versus 83%), and negative predictive value (93% versus 69%) when identifying bacteriuria, compared to routine urine sediment examination.

CONCLUSIONS

The urine Gram stain is highly sensitive and specific when detecting the presence of bacteria in canine urine samples. Gram staining should be considered when bacteriuria is highly suspected and requires rapid identification while bacterial culture is pending.

What is the risk of bacterial meningitis in infants who present to the emergency department with fever and pyuria?

OBJECTIVE

To determine the rate of bacterial meningitis among febrile infants in the emergency department (ED) who have pyuria detected in an initial catheterized urine specimen.

METHODS

This retrospective chart review, conducted at the Hospital for Sick Children, Toronto, Ont., involved all children aged 0 to 3 months who presented to the ED with fever and pyuria (>/=10 white blood cells/mm(3)) over a 3-year period. Cerebrospinal fluid (CSF) was evaluated using standard methods, and the rate of meningitis in children with pyuria was determined.

RESULTS

The study sample included 211 infants with fever and pyuria -- 79 of these under 1 month of age. Eighty-one percent (171/211) had positive urine cultures, and 143 underwent lumbar puncture to rule out meningitis. Of these, 140 CSF samples were culture negative and 3 grew coagulase negative Staphylococcus -- 2 because of contamination and 1 because of a ventriculo-peritoneal shunt infection. Both children with CSF contamination grew Escherichia coli in the urine. The rate of bacterial meningitis in the study sample was 0% (95% confidence interval, 0%-2.6%).

CONCLUSIONS

In this study of febrile children under 90 days of age with fever and pyuria, the incidence of concurrent meningitis was 0%. This suggests that recommendations for mandatory lumbar puncture in such children should be reconsidered. However, until larger prospective studies define a patient subset that does not require CSF analysis, it is prudent to rule out meningitis, administer parenteral antibiotics for urinary tract infection, and admit for close observation.

Technical report—Diagnosis and management of an initial UTI in febrile infants and young children

OBJECTIVES

The diagnosis and management of urinary tract infections (UTIs) in young children are clinically challenging. This report was developed to inform the revised, evidence-based, clinical guideline regarding the diagnosis and management of initial UTIs in febrile infants and young children, 2 to 24 months of age, from the American Academy of Pediatrics Subcommittee on Urinary Tract Infection.

METHODS

The conceptual model presented in the 1999 technical report was updated after a comprehensive review of published literature. Studies with potentially new information or with evidence that reinforced the 1999 technical report were retained. Meta-analyses on the effectiveness of antimicrobial prophylaxis to prevent recurrent UTI were performed.

RESULTS

Review of recent literature revealed new evidence in the following areas. Certain clinical findings and new urinalysis methods can help clinicians identify febrile children at very low risk of UTI. Oral antimicrobial therapy is as effective as parenteral therapy in treating UTI. Data from published, randomized controlled trials do not support antimicrobial prophylaxis to prevent febrile UTI when vesicoureteral reflux is found through voiding cystourethrography. Ultrasonography of the urinary tract after the first UTI has poor sensitivity. Early antimicrobial treatment may decrease the risk of renal damage from UTI.

CONCLUSIONS

Recent literature agrees with most of the evidence presented in the 1999 technical report, but meta-analyses of data from recent, randomized controlled trials do not support antimicrobial prophylaxis to prevent febrile UTI. This finding argues against voiding cystourethrography after the first UTI.

Absolute and relative accuracy of rapid urine tests for urinary tract infection in children: a meta-analysis

Rapid urine tests, such as microscopy, for bacteria and white cells, and dipsticks, for leucocyte esterase and nitrites, are often used in children that are unwell to guide early diagnosis and treatment of urinary tract infection. We aimed to establish whether these tests were sufficiently sensitive to avoid urine culture in children with negative results and to compare the accuracy of dipsticks with microscopy. Medline, Embase, and reference lists were searched. Studies were included if urine culture results were compared with rapid tests in children. Data were analysed to obtain absolute and relative accuracy estimates. Data from 95 studies in 95 703 children were analysed. Summary estimates for sensitivity and specificity for microscopy for Gram-stained bacteria were 91% (95% CI 80-96) and 96% (92-98), for unstained bacteria were 88% (75-94) and 92% (84-96), for urine white cells were 74% (67-80) and 86% (82-90), for leucocyte esterase or nitrite positive dipstick were 88% (82-91) and 79% (69-87), and for nitrite-only positive dipstick were 49% (41-57) and 98% (96-99). Microscopy for bacteria with Gram stain had higher accuracy than other laboratory tests with relative diagnostic odds ratio compared with bacteria without Gram stain of 8.7 (95% CI 1.8-41.1), white cells of 14.5 (4.7-44.4), and nitrite of 22.0 (0.7-746.3). Microscopy for white cells should not be used for the diagnosis of urinary tract infection because its accuracy is no better than that of dipstick, laboratory facilities are needed, and results are delayed. Rapid tests are negative in around 10% of children with a urinary tract infection and cannot replace urine culture. If resources allow, microscopy with Gram stain should be the single rapid test used.

Leukocyte counts in urine reflect the risk of concomitant sepsis in bacteriuric infants: a retrospective cohort study

BACKGROUND

When urine infections are missed in febrile young infants with normal urinalysis, clinicians may worry about the risk--hitherto unverified--of concomitant invasion of blood and cerebrospinal fluid by uropathogens. In this study, we determine the extent of this risk.

METHODS

In a retrospective cohort study of febrile 0-89 day old infants evaluated for sepsis in an urban academic pediatric emergency department (1993-1999), we estimated rates of bacteriuric sepsis (urinary tract infections complicated by sepsis) after stratifying infants by urine leukocyte counts higher, or lower than 10 cells/hpf. We compared the global accuracy of leukocytes in urine, leukocytes in peripheral blood, body temperature, and age for predicting bacteruric sepsis. The global accuracy of each test was estimated by calculating the area under its receiver operating characteristic curve (AUC). Chi-square and Fisher exact tests compared count data. Medians for data not normally distributed were compared by the Kruskal-Wallis test.

RESULTS

Two thousand two hundred forty-nine young infants had a normal screening dipstick. None of these developed bacteremia or meningitis despite positive urine culture in 41 (1.8%). Of 1516 additional urine specimens sent for formal urinalysis, 1279 had 0-9 leukocytes/hpf. Urine pathogens were isolated less commonly (6% vs. 76%) and at lower concentrations in infants with few, compared to many urine leukocytes. Urine leukocytes (AUC: 0.94) were the most accurate predictors of bacteruric sepsis. Infants with urinary leukocytes < 10 cells/hpf were significantly less likely (0%; CI:0-0.3%) than those with higher leukocyte counts (5%; CI:2.6-8.7%) to have urinary tract infections complicated by bacteremia (N = 11) or bacterial meningitis (N = 1)--relative risk, 0 (CI:0-0.06) [RR, 0 (CI: 0-0.02), when including infants with negative dipstick]. Bands in peripheral blood had modest value for detecting bacteriuric sepsis (AUC: 0.78). Cases of sepsis without concomitant bacteriuria were comparatively rare (0.8%) and equally common in febrile young infants with low and high concentrations of urine leukocytes.

CONCLUSION

In young infants evaluated for fever, leukocytes in urine reflect the likelihood of bacteriuric sepsis. Infants with urinary tract infections missed because of few leukocytes in urine are at relatively low risk of invasive bacterial sepsis by pathogens isolated from urine.

How does study quality affect the results of a diagnostic meta-analysis?

BACKGROUND

The use of systematic literature review to inform evidence based practice in diagnostics is rapidly expanding. Although the primary diagnostic literature is extensive, studies are often of low methodological quality or poorly reported. There has been no rigorously evaluated, evidence based tool to assess the methodological quality of diagnostic studies. The primary objective of this study was to determine the extent to which variations in the quality of primary studies impact the results of a diagnostic meta-analysis and whether this differs with diagnostic test type. A secondary objective was to contribute to the evaluation of QUADAS, an evidence-based tool for the assessment of quality in diagnostic accuracy studies.

METHODS

This study was conducted as part of large systematic review of tests used in the diagnosis and further investigation of urinary tract infection (UTI) in children. All studies included in this review were assessed using QUADAS, an evidence-based tool for the assessment of quality in systematic reviews of diagnostic accuracy studies. The impact of individual components of QUADAS on a summary measure of diagnostic accuracy was investigated using regression analysis. The review divided the diagnosis and further investigation of UTI into the following three clinical stages: diagnosis of UTI, localisation of infection, and further investigation of the UTI. Each stage used different types of diagnostic test, which were considered to involve different quality concerns.

RESULTS

Many of the studies included in our review were poorly reported. The proportion of QUADAS items fulfilled was similar for studies in different sections of the review. However, as might be expected, the individual items fulfilled differed between the three clinical stages. Regression analysis found that different items showed a strong association with test performance for the different tests evaluated. These differences were observed both within and between the three clinical stages assessed by the review. The results of regression analyses were also affected by whether or not a weighting (by sample size) was applied. Our analysis was severely limited by the completeness of reporting and the differences between the index tests evaluated and the reference standards used to confirm diagnoses in the primary studies. Few tests were evaluated by sufficient studies to allow meaningful use of meta-analytic pooling and investigation of heterogeneity. This meant that further analysis to investigate heterogeneity could only be undertaken using a subset of studies, and that the findings are open to various interpretations.

CONCLUSION

Further work is needed to investigate the influence of methodological quality on the results of diagnostic meta-analyses. Large data sets of well-reported primary studies are needed to address this question. Without significant improvements in the completeness of reporting of primary studies, progress in this area will be limited.

Rapid tests and urine sampling techniques for the diagnosis of urinary tract infection (UTI) in children under five years: a systematic review

BACKGROUND

Urinary tract infection (UTI) is one of the most common sources of infection in children under five. Prompt diagnosis and treatment is important to reduce the risk of renal scarring. Rapid, cost-effective, methods of UTI diagnosis are required as an alternative to culture.

METHODS

We conducted a systematic review to determine the diagnostic accuracy of rapid tests for detecting UTI in children under five years of age.

RESULTS

The evidence supports the use of dipstick positive for both leukocyte esterase and nitrite (pooled LR+ = 28.2, 95% CI: 17.3, 46.0) or microscopy positive for both pyuria and bacteriuria (pooled LR+ = 37.0, 95% CI: 11.0, 125.9) to rule in UTI. Similarly dipstick negative for both LE and nitrite (Pooled LR- = 0.20, 95% CI: 0.16, 0.26) or microscopy negative for both pyuria and bacteriuria (Pooled LR- = 0.11, 95% CI: 0.05, 0.23) can be used to rule out UTI. A test for glucose showed promise in potty-trained children. However, all studies were over 30 years old. Further evaluation of this test may be useful.

CONCLUSION

Dipstick negative for both LE and nitrite or microscopic analysis negative for both pyuria and bacteriuria of a clean voided urine, bag, or nappy/pad specimen may reasonably be used to rule out UTI. These patients can then reasonably be excluded from further investigation, without the need for confirmatory culture. Similarly, combinations of positive tests could be used to rule in UTI, and trigger further investigation.

Optimal diagnostic testing for urinary tract infection in young children

Urinary tract infection (UTI) is a major concern in young febrile children. Current recommendations favor use of urine obtained by bladder catheterization or aspiration, but opinion varies as to the best ancillary tests to predict a positive culture and guide initial management. The utility of dipstick leukocyte esterase, blood, and nitrite; unspun urine leukocyte count; gram stain of cytocentrifuged urine; and standard spun sediment examination was evaluated in 142 febrile, < 5-year-old children seen in the Emergency Department, 25 of whom had culture-proven UTI. Using sensitivity and negative predictive values as criteria for performance, unspun urine leukocyte count and gram stain of cytocentrifuged urine used in parallel was the best approach but still failed to detect some UTI. Analysis of the nature of the specimens evaluated provided explanation of differences from previous observations. Adoption of this modified approach to prediction of urinary tract infection appears to improve prediction but has operational implications and creates potential problems for the laboratory.

A preliminary evaluation of the interaction between urine specific gravity and leukocyte esterase results using Bayer Multistix and the Clinitek 500

OBJECTIVES

To determine the sensitivity of the leukocyte esterase (LE) pad to predict microscopically quantified white blood cells in urine sediment and to assess the interaction of urine specific gravity (SG) on leukocyte esterase sensitivity.

METHODS

Microscopic quantification of white blood cells in urine sediment was performed manually and automated chemical urinalysis was performed using the Bayer Clinitek 500 and Multistix 8 SG strips on 422 random urine specimens.

RESULTS

The sensitivity of the leukocyte esterase pad to predict white blood cells in centrifuged urine was 58% (61/106). There was a weak but statistically significant negative correlation between SG and LE pad performance, r = -0.12, p < 0.05.

CONCLUSIONS

The 58% sensitivity of the Multistix leukocyte esterase detection of white blood cells in urine sediment was consistent with previous reports. The negative correlation of specific gravity and leukocyte esterase provides partial explanation for the lack of sensitivity of the leukocyte esterase test.

Nurse practitioners' treatment of febrile infants in Utah: comparison to physician practice nationally

PURPOSE

To determine nurse practitioners' (NPs') knowledge of published guidelines involving the treatment of infants with fever without a source and to compare the practice of NPs in Utah to physicians nationally.

DATA SOURCES

Using a comparative descriptive design, a survey was sent to 450 NPs in Utah replicating the methodology of a 1998 survey of physicians. The NPs were asked about their evaluation decisions and management strategies for various ages of infants/toddlers with fever without a source.

CONCLUSIONS

The practice decisions of NPs in Utah and physicians nationally were similar. Family NPs' clinical decisions aligned more closely with family practice medical doctors and pediatric NPs' with pediatricians. Overall, the younger the patient, the more likely were NPs to order labs and antibiotics or to hospitalize/refer to a physician. The fact that management decisions were not based upon existing protocols may account for the practice variation seen among NPs.

IMPLICATIONS FOR PRACTICE

Management of a febrile infant is a common clinical scenario for the primary care provider. Although evidence-based protocols exist, the treatment of febrile infants remains controversial. Overall, NPs' evaluation and management of these infants were not shown to differ from physicians. Further studies are needed to determine why clinical guidelines are not being followed.

Validity of urinalysis and microscopy for detecting urinary tract infection in the emergency department

This study assessed the validity of standard urinalysis, urinalysis for leucocyte esterase and nitrites, and urgent microscopy in the diagnosis of urinary tract infection (UTI) in 60 female patients with a triage diagnosis of UTI. There were 24 (40%) proven UTIs after culture. Simple urinalysis was sensitive for UTI (95.8%) but the positive predictive value was only 45.1%. The addition of leucocyte esterase and nitrite urinalysis testing did not improve the sensitivity, but if both of these were positive the positive predictive value improved to 100%. Urgent microscopy alone was sensitive (100%) but non-specific (38.9%). The specificity of the diagnosis improved to 94.4% for organism counts of >or=10/microl and to 88.9% for leucocyte counts of >or=50/microl. The negative predictive value of no detectable leucocytes on microscopy was 94.7%. Screening for UTI in the emergency department (ED) population is improved by the addition of leucocyte esterase and nitrite test. A positive urinalysis test for leucocytes and nitrites, or urinalysis positive at levels of >or=500 leucocytes or >or=5 g/l protein should confirm a clinical diagnosis of UTI. Urgent urine microscopy should be performed only if the above criteria are not met yet a minimum of one urinalysis result is positive.

Test characteristics of the urine Gram stain in infants <or= 60 days of age with fever

OBJECTIVE

The utility of the Gram stain for the preliminary diagnosis of urinary tract infections (UTI) in infants <or= 60 days of age has not been clearly defined. Our purpose was to assess the test characteristics of the Gram stain in febrile infants and compare them to urinalysis (UA) and microscopy.

METHODS

The study was prospective and observational. Urine samples were obtained from a consecutive sample of infants <or= 60 days of age with a temperature of >or= 38.0 degrees C presenting to a pediatric emergency department during 2 consecutive winter seasons. Single pathogen growth of >or= 10(4) cfu/mL from a catheterized specimen and >or= 10(3) cfu/mL from a suprapubic specimen was considered positive. A positive Gram stain was defined as the identification of any organisms. Urinalysis was tested for the presence of nitrites and for leukocyte esterase (LE). Urine microscopy was analyzed for white blood cells per high power field (WBC/hpf).

RESULTS

Fourteen of 246 patients were excluded; 11 because no Gram stain was completed. Of the remaining 232 patients, Gram stain had a sensitivity of 85.2% (95% CI 71.9-98.6%), a specificity of 99.0% (95% CI 97.7-100%), a likelihood ratio for a positive test of 87.3 (95% CI 21.8-349.9), and a likelihood ratio for a negative test of 0.15 (95% CI 0.06-0.37). There were 193 specimens for which a Gram stain and a complete UA and microscopy were completed and compared. Urine microscopy had a lower sensitivity and specificity than Gram stain for both >or= 5 WBC/hpf and >or= 10 WBC/hpf. In addition to the Gram stain, a dipstick negative for nitrites and LE had a low negative likelihood ratio (0.16), useful for decreasing the likelihood of a UTI.

CONCLUSIONS

The Gram stain has excellent test characteristics for the preliminary diagnosis of a UTI in febrile infants. Patient disposition and therapy will likely change if clinical protocols and guidelines use the Gram stain rather than urine microscopy for preliminary diagnosis of UTI in infants.

Should we abandon standard microscopy when screening for urinary tract infections in young children?

Dipstick analysis is a screening test for urinary tract infection (UTI) in office practice. Standard urine microscopy is available offsite. We evaluated the usefulness of these tests on consecutive urine samples obtained by bladder catheterization in young children with a possible UTI. Thirty of 230 children had positive cultures. Dipstick analysis was specific (98%) but not sensitive (70%). Standard microscopy was not specific. Dipstick analysis and urine culture are useful tests for the diagnosis of UTI.

Pediatric urine testing

Today, urinalysis is one of the most common clinical tests ordered for adult and pediatric patients. Because urine specimens are usually readily available and are obtained noninvasively, the urine testing is well suited for children. This article discusses the most common urine tests performed in children for screening purposes and also less common tests for diagnosis of specific disorders. Special considerations regarding urine specimen collection in children are discussed. Some simple tests that are underused by clinicians are mentioned, as are some exciting new molecular applications of urine testing.

Predictive model for serious bacterial infections among infants younger than 3 months of age

OBJECTIVE

To develop a data-derived model for predicting serious bacterial infection (SBI) among febrile infants <3 months old.

METHODS

All infants </=90 days old with a temperature >/=38.0 degrees C seen in an urban emergency department (ED) were retrospectively identified. SBI was defined as a positive culture of urine, blood, or cerebrospinal fluid. Tree-structured analysis via recursive partitioning was used to develop the model. SBI or No-SBI was the dichotomous outcome variable, and age, temperature, urinalysis (UA), white blood cell (WBC) count, absolute neutrophil count, and cerebrospinal fluid WBC were entered as potential predictors. The model was tested by V-fold cross-validation.

RESULTS

Of 5279 febrile infants studied, SBI was diagnosed in 373 patients (7%): 316 urinary tract infections (UTIs), 17 meningitis, and 59 bacteremia (8 with meningitis, 11 with UTIs). The model sequentially used 4 clinical parameters to define high-risk patients: positive UA, WBC count >/=20 000/mm(3) or </=4100/mm(3), temperature >/=39.6 degrees C, and age <13 days. The sensitivity of the model for SBI is 82% (95% confidence interval [CI]: 78%-86%) and the negative predictive value is 98.3% (95% CI: 97.8%-98.7%). The negative predictive value for bacteremia or meningitis is 99.6% (95% CI: 99.4%-99.8%). The relative risk between high- and low-risk groups is 12.1 (95% CI: 9.3-15.6). Sixty-six SBI patients (18%) were misclassified into the lower risk group: 51 UTIs, 14 with bacteremia, and 1 with meningitis.

CONCLUSIONS

Decision-tree analysis using common clinical variables can reasonably predict febrile infants at high-risk for SBI. Sequential use of UA, WBC count, temperature, and age can identify infants who are at high risk of SBI with a relative risk of 12.1 compared with lower-risk infants.

Pediatric urinary tract infection

UTIs are common in children. They may present with a range of severity from cystitis to febrile UTI or pyelonephritis. The presentation may be vague and have nonspecific symptoms. Therefore, a UTI should be considered in all children with a fever in whom other sources have been excluded. Treatment depends on the age, location of infection, and degree of illness in the child. Sick children and infants less than 3 months should be treated as inpatients, and healthy children and older infants may be treated as outpatients. Urinalysis provides presumptive evidence of infection, whereas urine culture is definitive. Close follow-up and outpatient evaluations are needed to prevent long-term consequences of infection.

Urinary tract infection in the pediatric patient

Little attention has been focused on the identification of urinary tract infection (UTI) in young febrile children in the emergency department, despite recent information that suggests both a high prevalence and significant associated morbidity in this population. Most UTIs that lead to scarring or diminished kidney growth occur in children younger than age 4 years, especially babies in the first year of life. Overall, prevalence rates of UTI in febrile infants in the emergency department are approximately 3% to 5%, with higher rates for white girls, uncircumcised boys, and those without another potential source for fever. Prevalence and risk factors are given so that clinicians may identify those febrile children at particularly high or low risk of UTI for selective management. Culturing methods, urine screening tests, and culture interpretation are reviewed and management strategies based on these results are suggested.

Screening tests for urinary tract infection in children: A meta-analysis

OBJECTIVE

To review systematically and to summarize the existing literature regarding performance of rapid diagnostic tests for urinary tract infection (UTI) in children.

DESIGN

Systematic review and meta-analysis.

METHODS

Published articles reporting the performance of urine dipstick tests (leukocyte esterase [LE] and/or nitrite), Gram stain, or microscopic analysis of spun or unspun urine in the diagnosis of UTI in children </=12 years of age. Articles were identified through a comprehensive MEDLINE search, and those articles meeting a priori inclusion criteria were selected. Eligibility criteria included the use of urine culture as the reference standard, independent comparison of urine culture with the results of one of the screening tests, definition of positive screening test results provided, only pediatric patients included or evaluable separately, and both gold standard and screening test performed on all patients. For each test, heterogeneity of reported sensitivity and specificity of all studies was determined. The subgroups of studies with similar definitions of UTI and age of study subjects were analyzed separately to account for some of the differences in reported results. When significant unexplained heterogeneity among studies precluded simple combining of results, a summary receiver-operator characteristic curve was fitted for each screening test, from which pooled estimates of true-positive rate (TPR; ie, sensitivity) and false-positive rate (FPR; 1-specificity) were calculated.

PRIMARY RESULTS

A total of 1489 titles were identified by the MEDLINE search; 26 articles met all criteria for inclusion. There was significant heterogeneity among studies for nearly all tests for both TPR and FPR, which was explained only partially by the stringency of the definition of UTI or age of subjects studied. Based on the pooled estimates, the presence of any bacteria on Gram stain on an uncentrifuged urine specimen had the best combination of sensitivity (0.93) and FPR (0.05). Urine dipstick tests performed nearly as well, with a sensitivity of 0.88 for the the presence of either LE or nitrite and an FPR of 0.04 for the presence of both LE and nitrite. Pyuria had lower TPR and higher FPR: for presence of >5 white blood cells/high-power field in a centrifuged urine sample, the TPR was 0.67 and the FPR was 0.21, whereas for >10 white blood cells per mm(3) in uncentrifuged urine, the TPR was 0.77 and the FPR was 0.11.

CONCLUSIONS

Both Gram stain and dipstick analysis for nitrite and LE perform similarly in detecting UTI in children and are superior to microscopic analysis for pyuria.

The validity of the uriscreen test for early detection of urinary tract infection in children

OBJECTIVE

To determine the validity of the Uriscreen, a rapid diagnostic test based on the detection of urine catalase for the early detection of urinary tract infection (UTI) in children, compared with standard urinalysis and dipstick tests. STUDY DESIGN. Cross-sectional study.

STUDY POPULATION

Children 1 month to 17 years of age who presented to the emergency department of a pediatric tertiary care center between March and November of 1996 with symptoms suggestive of UTI.

METHODS

Urine specimens obtained from a random sample of 121 patients were evaluated simultaneously for possible UTI by Uriscreen (catalase test), urinalysis (microscopic pyuria), dipstick (leukocyte esterase and nitrite), and quantitative urine culture. All specimens were collected by one of three sterile techniques (midstream void technique, bladder catheterization, or suprapubic aspiration), as appropriate for age, and tested immediately. Using the quantitative urine culture as the gold standard (reference test), the sensitivity, specificity, and positive and negative predictive values of all the screening tests were determined and compared. Age, sex, temperature, presenting symptoms, and method of urine collection were recorded for each participant.

RESULTS

Of the 121 patients, 35 (28.9%) had positive culture results: 30 girls (85.7%) and 5 boys (14.3%). Compared with urinalysis and dipstick tests, Uriscreen had the highest sensitivity (100% vs 88.6% and 97.1%, respectively) and the highest negative predictive value (100% vs 95% and 98.6%, respectively), but the poorest specificity (68.6% vs 88.4% and 82.5%, respectively) and positive predictive value (56.4% vs 75.6% and 69.4%, respectively).

CONCLUSIONS

The clinical use of Uriscreen for the presumptive diagnosis of UTI in children is limited and not significantly superior to urinalysis or the dipstick test. However, because of its 100% sensitivity and negative predictive value and its ease of use, rapidity, and low cost, it is recommended highly for ruling out the diagnosis of UTI. In laboratories, a negative Uriscreen result may prevent the need for performing expensive urine cultures.

Evaluation of the infant with fever without source: an evidence based approach

The infant with fever without an obvious source upon physical examination offers a challenging clinical problem. A combination of detailed history, physical examination, and selected laboratory tests allows the clinician to discern which infants are at lower risk for bacterial illness. Implications for management and future research are discussed herein.

Screening for urinary tract infection in infants in the emergency department: which test is best?

OBJECTIVE

Comparison of rapid tests and screening strategies for detecting urinary tract infection (UTI) in infants.

METHODS

Cross-sectional study conducted in an urban tertiary care children's hospital emergency department and clinical laboratories of 3873 infants <2 years of age who had a urine culture obtained in the emergency department by urethral catheterization; results of urine dipstick tests for leukocyte esterase or nitrites, enhanced urinalysis (UA) (urine white blood cell count/mm3 plus Gram stain), Gram stain alone, and dipstick plus microscopic UA (white blood cells and bacteria per high-powered field) compared with urine culture results (positive urine results defined as >/=10 colony-forming units per milliliter of urinary tract pathogen) for each sample. Cost comparison of 1) dipstick plus culture of all urine specimens versus 2) cell count +/- Gram stain of urine, culture only those with positive results.

RESULTS

The enhanced UA was most sensitive at detecting UTI (94%; 95% confidence interval: 83,99), but had more false-positive results (16%) than the urine dipstick or Gram stain (3%). The most cost-effective strategy was to perform cultures on all infants and begin presumptive treatment on those whose dipstick had at least moderate (+2) leukocyte esterase or positive nitrite at a cost of $3.70 per child. With this strategy, all infants with UTI were detected. If the enhanced UA was used to screen for when to send the urine for culture, 82% of cultures would be eliminated, but 4% to 6% of infants with UTI would be missed and the cost would be higher ($6.66 per child).

CONCLUSION

No rapid test can detect all infants with UTI. Physicians should send urine for culture from all infants and begin presumptive treatment only on those with a significantly positive dipstick result. The enhanced UA is most sensitive for detecting UTI, but is less specific and more costly, and should be reserved for the neonate for whom a UTI should not be missed at first visit.

Neonatal fever: utility of the Rochester criteria in determining low risk for serious bacterial infections

The purpose of this study was to test the utility of the Rochester criteria in determining which febrile neonates are at low risk for serious bacterial infections (SBI). This was a retrospective study over a 5-year period of 134 patients younger than 29 days old with fever without a source evaluated in the emergency department. Results of urinalysis, lumbar puncture, peripheral white blood cell count, and cultures of blood, urine, cerebrospinal fluid, and stool were recorded. Of the 134 neonates, 71 were high-risk, 48 low-risk, and 15 were not classifiable by the available data. Nineteen of the 71 high-risk patients (26.8%) had SBI (2 patients had 2 SBI). Three of the 48 low-risk neonates (6.3%) had SBI (1 patient had 2 SBI). None of the 15 nonclassifiable patients had SBI. Employing the Rochester criteria to the fully cultured neonates who could be risk-stratified, the sensitivity, specificity, positive predictive value, and negative predictive value were 86.4%, 46.4%, 26.8%, and 93.8%, respectively. Although outpatient management of febrile neonates may be feasible, a small percentage of neonates meeting low-risk criteria will have a SBI.