Urine Concentration and Pyuria for Identifying UTI in Infants

Urine specific gravity, pyuria, and neutrophil gelatinase-associated lipocalin for identifying urinary tract infection in young children

BACKGROUND

To determine whether urine neutrophil gelatinase-associated lipocalin (uNGAL) might be superior to pyuria for detecting urinary tract infection (UTI) regardless of urine specific gravity (SG) in young children.

METHODS

We conducted a retrospective analysis of children aged < 3 years who were evaluated for UTI with urinalysis, urine culture, and uNGAL measurements during a 5-year period. Sensitivity, specificity, likelihood ratios (LRs), predictive values (PVs), area under the curves (AUCs) of uNGAL cut-off levels, and various microscopic pyuria thresholds for detecting UTI were calculated for dilute (SG < 1.015) and concentrated urine (SG ≥ 1.015).

RESULTS

Of 456 children included, 218 had UTI. The diagnostic value of urine white blood cell (WBC) concentration to define UTI changed with urine SG. For detecting UTI, uNGAL cut-off of 68.4 ng/mL had higher AUC values than pyuria ≥ 5 WBCs/high power field (HPF) for dilute and concentrated urine samples (both P < 0.05). Positive LR and PV and specificity of uNGAL were all greater than those of pyuria ≥ 5 WBCs/HPF regardless of urine SG, although the sensitivity of pyuria ≥ 5 WBCs/HPF was higher than that of uNGAL cut-off for dilute urine (93.8% vs. 83.5%) (P < 0.05). At uNGAL ≥ 68.4 ng/mL and ≥ 5 WBCs/HPF, posttest probabilities of UTI were 68.8% and 57.5% for dilute urine and 73.4% and 57.3% for concentrated urine, respectively.

CONCLUSIONS

Urine SG can affect the diagnostic performance of pyuria for detecting UTI and uNGAL might be helpful for identifying UTI regardless of urine SG in young children. A higher resolution version of the Graphical abstract is available as Supplementary information.

Treatment and Epidemiology of Third-Generation Cephalosporin-Resistant Urinary Tract Infections

BACKGROUND AND OBJECTIVES

Limited data are available on the contemporary epidemiology, clinical management, and health care utilization for pediatric urinary tract infection (UTI) due to third-generation cephalosporin-resistant Enterobacterales (G3CR) in the United States. The objective is to describe the epidemiology, antimicrobial treatment and response, and health care utilization associated with G3CR UTI.

METHODS

Multisite, matched cohort-control study including children with G3CR UTI versus non-G3CR UTI. UTI was defined as per American Academy of Pediatrics guidelines, and G3CR as resistance to ceftriaxone, cefotaxime, or ceftazidime. We collected data from the acute phase of illness to 6 months thereafter.

RESULTS

Among 107 children with G3CR UTI and 206 non-G3CR UTI with documented assessment of response, the proportion with significant improvement on initial therapy was similar (52% vs 57%; odds ratio [OR], 0.81; 95% confidence interval [CI], 0.44-1.50). Patients with G3CR were more frequently hospitalized at presentation (38% vs 17%; OR, 3.03; 95% CI, 1.77-5.19). In the follow-up period, more patients with G3CR had urine cultures (75% vs 53%; OR, 2.61; 95% CI, 1.33-5.24), antimicrobial treatment of any indication (53% vs 29%; OR, 2.82; 95% CI, 1.47-5.39), and subspecialty consultation (23% vs 6%; OR, 4.52; 95% CI, 2.10-10.09). In multivariate analysis, previous systemic antimicrobial therapy remained a significant risk factor for G3CR UTI (adjusted OR, 1.91; 95% CI, 1.06-3.44).

CONCLUSIONS

We did not observe a significant difference in response to therapy between G3CR and susceptible UTI, but subsequent health care utilization was significantly increased.

Role of 16S Ribosomal RNA Analysis in Identification of Microorganisms in Febrile Urinary Tract Infection of Infants

OBJECTIVES

To assess the role of 16S ribosomal RNA analysis in microbial identification in febrile infants under six months of age diagnosed with UTI, and compare it with the conventional culture results.

METHODS

Young infants under 6 mo of age who were suspected UTI from May 2018 to April 2019 had been enrolled. Uropathogens were analyzed by the traditional microbiologic culture system and the 16S rRNA analysis. The 16S rRNA analysis included 16S rRNA amplicon band confirmation and bacterial identification through the sequencing analysis.

RESULTS

A total of 57 infants with the febrile UTI were enrolled, and the median age was 3 mo. Uropathogens were identified in 43 patients (75.4%) in a conventional culture method: Escherichia coli in 38 patients (88.4%), Klebsiella pneumoniae in 3 (7.0%), Enterobacter cloacae in 1 (2.3%), and Pseudomonas aeruginosa in 1 (2.3%). Fifty urine samples (87.8%) had positive 16S rRNA amplicon band on electrophoresis. Among the 16S rRNA-positive urines, 40 samples were available for the sequence analysis of 16S rRNA, and the identification of bacteria were as follows: E. fergusonii in 36, K. pneumoniae in 3, and Shigella flexneri in 1. The sensitivity of 16S rRNA sequencing was 81.4% [95% confidence interval (CI), 67.4-90.3%] and the specificity was 64.3% (95% CI, 38.8-83.7%).

CONCLUSION

Uropathogen identification using 16S rRNA analysis could be applied to manage the febrile UTI in young infants clinically in combination with the conventional culture.

Urinary tract infections in children: Testing a novel, noninvasive, point-of-care diagnostic marker

OBJECTIVES

Urinary neutrophil gelatinase-associated lipocalin (uNGAL) appears highly accurate to identify urinary tract infections (UTIs) when obtained via catheterization. Our primary aim was to determine the agreement in uNGAL levels between paired catheter and bag urine specimens. Our secondary aim was to compare the diagnostic test characteristics of quantitative uNGAL, dipstick uNGAL (a potential point-of-care test), and urinalysis (UA).

METHODS

This was a prospective study of febrile children < 24 months evaluated for UTIs. We evaluated quantitative uNGAL at a previously identified threshold of 39.1 ng/mL, dipstick uNGAL at its built-in threshold of >50 ng/mL, and UA at standard thresholds for leukocyte esterase (LE). A positive urine culture was defined as >100,000 CFUs/mL of a pathogen.

RESULTS

A total of 211 patients were included (10% with positive urine cultures); 116 had paired catheterized and bagged samples. The agreement between catheterized and bagged samples at a quantitative uNGAL cutoff of ≥39.1 ng/mL was 0.76 (95% confidence interval [CI] = 0.67 to 0.83) and 0.77 (95% CI = 0.68 to 0.84) at a uNGAL dipstick threshold of >50 ng/mL. The area under the receiver operating characteristic curve for uNGAL from a catheterized sample was 0.96 (95% CI = 0.89 to 1.00) compared to 0.93 (95% CI = 0.87 to -0.99) from a bagged sample. The sensitivities of catheterized sample quantitative and dipstick uNGAL (90.5%) were higher than UA at a LE threshold of ≥1+ (57.1%). Bagged-sample uNGAL had lower quantitative and dipstick specificities (both 73.8%) than from catheterized samples (94.3% and 95.3% respectively), similar to UA.

CONCLUSIONS

uNGAL from bagged and catheterized samples showed insufficient agreement to be used interchangeably. The low specificity of uNGAL from bagged samples suggests that sampling technique affects uNGAL levels.

Urinary neutrophil gelatinase-associated lipocalin: a marker of urinary tract infection among febrile children

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as a valuable biomarker of urinary tract infection (UTI) in children.

PURPOSE

This study aimed to compare the diagnostic accuracy of urinary NGAL (uNGAL) with those of serum C-reactive protein (CRP) and white blood cell (WBC) count for predicting UTI and acute pyelonephritis (APN) in febrile children.

METHODS

The medical charts of children undergoing uNGAL measurements between November 2017 and August 2019 were retrospectively reviewed. Patients with a suspected or diagnosed UTIs were included. The diagnostic accuracies of uNGAL, serum CRP, and WBC count for detecting UTI and APN were investigated. Independent predictors of UTI and APN were investigated using multivariable logistic regression analyses.

RESULTS

A total of 321 children were enrolled in this study. The uNGAL levels were higher in the UTI group (n=157) than in the non-UTI group (n=164) (P<0.05). Among children with a UTI, uNGAL levels were higher in the APN group (n=70) than, the non-APN group (n=87) (P<0.05). In the multivariate analysis, uNGAL was independently associated with UTI and APN (both P<0.05). Serum CRP and WBC count were not correlated with the presence of UTI and APN. Receiver operating curve analyses showed that the uNGAL level had the highest area under the curve (AUC) for predicting UTI and APN, respectively (AUC, uNGAL vs. CRP vs. WBC count, 0.860 vs. 0.608 vs. 0.669 for UTI; 0.780 vs. 0.680 vs. 0.639 for APN, all P<0.05, respectively). The predictive values and likelihood ratios of uNGAL were superior to those of serum CRP and WBC count for detecting UTI and APN at each cutoff level.

CONCLUSION

UNGAL may be more useful than serum CRP and WBC count for identifying and assessing UTI in febrile children.

The Differential Diagnosis of Sterile Pyuria in Pediatric Patients: A Review

Sterile pyuria is a common finding in pediatric patients. Literature describing the diagnoses as well as clinical characteristics of children with sterile pyuria is lacking. This review was performed to establish an evidence-based approach to the differential diagnosis by way of an extensive literature search. The definition of pyuria is inconsistent. The various causes of pediatric sterile pyuria identified were classified as either Infectious or Non-Infectious. Sub-categories of Infectious causes include: Viral Infection, Bacterial Infection, Other Infections (tuberculosis, fungal, parasitic), Sexually Transmitted Infections, Recent Antibiotic Therapy. Non-Infectious causes include: Systemic Disease, Renal Disease, Drug Related, Inflammation adjacent to Genitourinary Tract. Clinicians that encounter pediatric patients with sterile pyuria and persistent symptoms should consider the substantial differential diagnosis described in this study.

Urine Specific Gravity and the Accuracy of Urinalysis

BACKGROUND

A recent study in young infants found that different cutoffs maximized the accuracy of the urine white blood cell count in dilute versus concentrated urine samples. We aimed to confirm this finding and to determine its impact on clinical care.

METHODS

We conducted a retrospective analysis of data gathered on consecutive children <24 months of age with visits to the emergency department during a 5-year period. We evaluated the accuracy of screening tests for urinary tract infection (UTI) in dilute and concentrated urine samples. We also calculated the number of children who would have been treated differently in a hypothetical cohort of 1000 children presenting with fever had urine specific gravity (SG) been taken into consideration.

RESULTS

We included 10 078 children. The ability to rule in UTI (as measured by the positive likelihood ratio [LR]) was similar in dilute and concentrated urine for the leukocyte esterase test (11.76 vs 10.71, respectively). The positive LR for urine white blood cell count per high-powered field was higher in dilute urine (9.83 vs 6.12). In contrast, the positive LR for the nitrite test was lower in dilute urine (20.54 vs 47.44). Despite these differences, we found little change in the number of children treated with antibiotics in predictive models that took urine SG into consideration.

CONCLUSIONS

Although we found that urine SG influences the accuracy of some components of the urinalysis, its inclusion in the decision-making process had negligible effect on the clinical care of children with UTI.

Evaluation of BacterioScan 216Dx in Comparison to Urinalysis as a Screening Tool for Diagnosis of Urinary Tract Infections in Children

Urinalysis (UA) has routinely been used as a screening tool prior to urine culture set up. BacterioScan 216Dx is an FDA-cleared semiautomated system to detect bacterial growth in urine. The aim of this study was to evaluate 216Dx in comparison to UA for diagnosis of urinary tract infection (UTI) in children. Clean-catch, unpreserved urine samples from children aged <18 years were tested by 216Dx, and positive urine samples in media were processed for direct bacterial identification by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Sensitivity and specificity of 216Dx and urinalysis (UA) were determined against urine culture. Of 287 urine samples obtained from children (median age, 108 months), 44.0% and 56.0% were UA positive and negative, respectively, while 216Dx detected 27% and 73% as positive and negative, respectively. Compared to culture, the overall sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 216Dx versus UA were 92.1% versus 97.3%, 82.7% versus 63.8%, 44.8% versus 29.1%, and 98.6% versus 99.3%, respectively. Among 216Dx true-positive (TP) samples (n = 35), 77.0% were successfully identified directly from broth by MALDI-TOF. Among urine samples that were identified as contaminated by culture (n = 127; 44%), the 216Dx detected 93 (73.0%) as negative while UA detected 69 (54.0%) as negative. Although the sensitivities of 216Dx and UA are comparable, the specificity of 216Dx was higher than that of UA. The 216Dx can be used as an alternative/adjunct screening tool to UA to rule out urinary tract infection (UTI) in children. Compared to culture, the faster turnaround time (3 hours) of 216Dx has the potential to reduce unnecessary antibiotic use and improve patient management.

Update on Associated Risk Factors, Diagnosis, and Management of Recurrent Urinary Tract Infections in Children

Recurrent urinary tract infection (rUTI) continues to challenge pediatric care providers. The diagnosis of an rUTI can be difficult, especially in young febrile children. Antibiotic resistance rates continue to rise, which limits oral treatment options. Prophylactic antibiotics are used commonly to manage rUTI, but their use increases the risk of rUTI with antibiotic-resistant strains without significantly reducing renal scarring. Alternative therapies for rUTI include probiotics and anthocyanidins (eg, cranberry extract) to reduce gut colonization by uropathogens and prevent bacterial adhesion to uroepithelia, but efficacy data for these treatments are sparse. The future of rUTI care rests in addressing the following contemporary issues: best diagnostic practices, risk factors associated with rUTI, and the prevention of recurrent infection. In this review, we summarize the state of the art for each of these issues and highlight future studies that will aim to take an alternative approach to managing rUTI.

Approach to Neonates and Young Infants with Fever without a Source Who Are at Risk for Severe Bacterial Infection

INTRODUCTION

Among neonates and infants <3 months of age with fever without a source (FWS), 5% to 15% of cases are patients with fever caused by a serious bacterial infection (SBI). To favour the differentiation between low- and high-risk infants, several algorithms based on analytical and clinical parameters have been developed. The aim of this review is to describe the management of young infants with FWS and to discuss the impact of recent knowledge regarding FWS management on clinical practice.

MATERIALS AND METHODS

PubMed was used to search for all of the studies published over the last 35 years using the keywords: "fever without source" or "fever of unknown origin" or "meningitis" or "sepsis" or "urinary tract infection" and "neonate" or "newborn" or "infant <90 days of life" or "infant <3 months".

RESULTS AND DISCUSSION

The selection of neonates and young infants who are <3 months old with FWS who are at risk for SBI remains a problem without a definitive solution. The old Rochester criteria remain effective for identifying young infants between 29 and 60 days old who do not have severe bacterial infections (SBIs). However, the addition of laboratory tests such as C-reactive protein (CRP) and procalcitonin (PCT) can significantly improve the identification of children with SBI. The approach in evaluating neonates is significantly more complicated, as their risk of SBIs, including bacteremia and meningitis, remains relevant and none of the suggested approaches can reduce the risk of dramatic mistakes. In both groups, the best antibiotic must be carefully selected considering the clinical findings, the laboratory data, the changing epidemiology, and increasing antibiotic resistance of the most common infectious bacteria.

Microscopic Bacteriuria Detected by Automated Urinalysis for the Diagnosis of Urinary Tract Infection

OBJECTIVE

To evaluate the test performance of microscopic bacteriuria by automated urinalysis for presumptive urinary tract infection (UTI) in young children.

STUDY DESIGN

This is a retrospective cross-sectional study of children aged <2 years evaluated for UTI in a single large emergency department with paired automated microscopic urinalysis and culture. Test characteristics were calculated for automated microscopic bacteriuria and pyuria, and a practical diagnostic threshold of bacteriuria was determined. Standard test performance measures and receiver operator characteristic curves were generated. The diagnostic performance of bacteriuria was compared with microscopic pyuria.

RESULTS

Two thousand five hundred fifty-four children with a median age of 6.1 months were studied, 19% of whom had a positive urine culture. Automated microscopic bacteriuria ≥1+ resulted in a positive likelihood ratio (LR+) of 4.5 (95% CI, 3.9-5.2) and negative LR (LR-) of 0.52 (95% CI, 0.47-0.57). Pyuria alone (≥5 WBC/high-power field) had a LR+ of 4.5 (95% CI, 4.1-5.0) and a LR- of 0.14 (95% CI, 0.11-0.18), whereas the addition of automated microscopic bacteriuria ≥1+ improved the LR+ to 16.3 (95% CI, 12.6-21.1) but raised the LR- to 0.51 (95% CI, 0.47-0.56). Test performance of automated microscopic bacteriuria measured by area under the curve analysis was lower (0.73; 95% CI, 0.70-0.76) than for pyuria (0.92; 95% CI, 0.90-0.93). Isolated automated microscopic bacteriuria without pyuria occurred in only 204 patients (8.0%), among whom only 20 (9.8%) had a positive urine culture.

CONCLUSIONS

Microscopic bacteriuria measured by automated urinalysis augments the diagnostic value of pyuria for identifying presumptive UTI in young children aged <2 years. Bacteriuria is diagnostically inferior to microscopic pyuria, and in children with bacteriuria without pyuria, presumptive UTI is unlikely.

Mass spectrometric measurement of urinary kynurenine-to-tryptophan ratio in children with and without urinary tract infection

BACKGROUND

Indoleamine-2,3-dioxygenase (IDO) catalyzes the first step of tryptophan (Trp) catabolism, yielding kynurenine (Kyn) metabolites. The kynurenine-to-tryptophan (K/T) ratio is used as a surrogate for biological IDO enzyme activity. IDO expression is increased during Escherichia coli urinary tract infection (UTI). Thus, our objective was to develop a method for measurement of Kyn/Trp ratio in human blood and urine and evaluate its use as a biomarker of UTI.

METHODS

A mass spectrometric method was developed to measure Trp and Kyn in serum and urine specimens. The method was applied to clinical urine specimens from symptomatic pediatric patients with laboratory-confirmed UTI or other acute conditions and from healthy controls.

RESULTS

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was linear to 500 μmol/L for both Trp and Kyn. Imprecision ranged from 5 to 15% for Trp and 6-20% for Kyn. Analytical recoveries of Trp and Kyn ranged from 96 to 119% in serum and 90-97% in urine. No correlation was found between the K/T ratio and circulating IDO mass (r = 0.110) in serum. Urinary Kyn and Trp in the pediatric test cohort demonstrated elevations in the K/T ratio in symptomatic patients with UTI (median 13.08) and without UTI (median 14.38) compared to healthy controls (median 4.93; p < 0.001 for both comparisons). No significant difference in K/T ratio was noted between symptomatic patients with and without UTI (p = 0.84).

CONCLUSIONS

Measurement of Trp and Kyn by LC-MS/MS is accurate and precise in serum and urine specimens. While urinary K/T ratio is not a specific biomarker for UTI, it may represent a general indicator of a systemic inflammatory process.

Urinary Neutrophil Gelatinase-Associated Lipocalin for the Diagnosis of Urinary Tract Infections

OBJECTIVES

To determine the accuracy of the novel biomarker urinary neutrophil gelatinase-associated lipocalin (uNGAL) to diagnose urinary tract infections (UTIs) in febrile infants and young children.

METHODS

Prospective cross-sectional study of febrile infants <3 months ( ≥ 38.0°C) and children 3 to 24 months (≥ 39.0°C) evaluated for UTIs. uNGAL levels, urinalysis, Gram-stain and culture were obtained. UTI was defined by colony counts.

RESULTS

Of 260 patients, 35 (13.5%) had UTIs. Median uNGAL levels were 215.1 ng/mL (interquartile range: 100.3-917.8) and 4.4 ng/mL (interquartile range: 1.6-11.8) in the groups diagnosed with and without UTIs, respectively. The area under the receiver-operating characteristic curve for uNGAL was 0.978 (95% confidence interval [CI]: 0.948-1.000). At a threshold uNGAL level of 39.1 ng/mL, sensitivity was 97.1% (95% CI: 83.4-99.9) and specificity was 95.6% (95% CI: 91.7-97.7). uNGAL had higher sensitivity than the combination of leukocyte esterase (in trace or greater amounts) or nitrite (+) (97.1%, 95% CI: 83.4-99.9 vs 74.3%, 95% CI: 56.4-86.9), with similar specificity (95.6%, 95% CI: 91.7-97.7 vs 97.3%, 95% CI: 94.0-98.9). uNGAL had higher sensitivity than Gram-stain (97.1%, 95% CI: 83.4-99.9 vs 74.3%, 95%: CI: 56.4-86.9), with similar specificity (95.6%, 95% CI: 91.7-97.7 vs 100.0%, 95% CI: 97.9-100.0).

CONCLUSIONS

uNGAL has substantial accuracy to identify those with and without UTIs in infants and young children. Further studies will need to confirm our findings and determine if uNGAL is a more cost-effective test than standard screening tests.

Febrile infant update

PURPOSE OF REVIEW

The approach to febrile young infants remains challenging. This review serves as an update on the care of febrile infants less than 90 days of age with a focus on the changing epidemiology of serious bacterial infection (SBI), refinement of management strategies based on biomarkers, and the development of novel diagnostics.

RECENT FINDINGS

There is high variability in the emergency department management of febrile young infants without significant differences in outcomes. C-reactive protein (CRP) and procalcitonin have emerged as valuable risk-stratification tests to identify high-risk infants. When interpreting automated urinalyses for suspected urinary tract infection (UTI), urine concentration influences the diagnostic value of pyuria. Novel diagnostics including RNA biosignatures and protein signatures show promise in better identifying young febrile infants at risk of serious infection.

SUMMARY

The majority of febrile infants with an SBI will have a UTI but the diagnosis of invasive bacterial infection in infants continues to be challenging. The use of procalcitonin and CRP as biomarkers in prediction algorithms facilitates identification of low-risk infants.