Prevalence and antimicrobial susceptibility pattern of urinary tract infection among hospitalized children in a single center

Abstract

Introduction

Urinary tract infection (UTI) is one of the most common disease caused by some bacteria in daily practice and is relatively easy to detect by routine urine culturing. Approximately 8.4% of girls and 1.7% of boys by the age of 7 years are diagnosed with UTI, and 30% of infants and children experience recurrent infections during the first six to 12 months after initial UTI^1,2. The common pathway of UTI is the ascent of bacteria from the urethra and hematogenous spread of infection. The short-term symptoms of UTI usually are fever, dysuria, and flank pain³. If not properly treated, it often develops public health problems of recurrent UTI, inflammatory scars of kidney, permanent decline of renal function, even significant morbidity and mortality with a poor outcome, particularly in infants less than 2 months of age^4,5. It has reported that children are more susceptible to UTI due to an indwelling urinary catheter, congenital anomalies of the genitourinary tract, long-term use of broad-spectrum antibiotic, or compromised immune system^6,7.

But in practice, it is vital to differentiate complicated UTI from simple UTI based on the presence of functional or structural abnormalities of the genitourinary tract. Other common risk factors of complicated UTI include foreign bodies, stones, kidney transplantation, immunosuppression, and pregnancy. Complicated infection are at risk of treatment failure and development of serious complications, which may require further evaluation and more extensive treatment⁸. UTI may be a clinical presentation for potential abnormalities in children⁹.These abnormalities can allow for the prolongation of bacteruria due to poor drainage. In addition, urinary stones are a consequence of UTI in 10–15% of patients with stone disease, while approximately 10% of hospitalized patients with stones are complicated by UTI that necessitates drainage^10,11. Thus, the therapeutic goals of complicated UTI in childhood consist of eradication of the bacterial pathogen, identification of abnormalities, and avoidance of recurrent infections¹² .

The gold standard for the diagnosis of UTI is the detection of the pathogen in urine. The pathogen is detected and identified in urine which contributes to antibacterial treatment. Rapid administrations of empirical antibiotics are required before urine culture testing. Meanwhile, complicated UTI often increase the prevalence of inappropriate antibacterial treatment, which in turn increases antibiotic resistance (ABR)¹³. In pediatric UTI, ABR is also being raised as a clinical challenge. Therefore, there is an urgent need to identify which bacterial strains in children and explore their susceptibility to commonly used antimicrobials. It could guide effective antibacterial therapy and reduce the multi-drug resistance prevalence in children. This study was aimed at determining the prevalence and the bacteria and susceptibility of UTI.

Materials And Methods

Ethics approval and consent to participate

The present study was approved by the Institutional Review Board of Anhui Provincial Children’s Hospital. The local ethics committee of our hospital approved this study, which conformed to the provisions of the Declaration of Helsinki. All methods were carried out in accordance with relevant guidelines and regulations. Written informed consent was routinely obtained from each surgical patient.

Study design 

A retrospective analysis of urine culture results was performed at department of Urology, Anhui Provincial Children’s Hospital during the 8 years, from January 2014 to December 2021. The age and sex, the general characteristics of patients, the microorganism isolated, and the antimicrobial susceptibility profiles were collected in patients who had been diagnosed with UTI.

Culture and identification

A midstream urine sample had taken from all patients who diagnosed with UTI. The urine specimen was inoculated on CysteineLactose-Electrolyte-Defcient (CLED) agar using a sterile loop (0.001 ml). Then colonies from CLED were sub-cultured into MacConkey agar and blood agar plates (BAP) (Oxoid, UK) After overnight incubation at 37℃ for 24-48 hours colonies were counted to check significant growth. A colony count of ≥10⁵ CFU/ml of urine was regarded as significant for bacteriuria. The identification of bacteria was done using gram staining, colony characteristics, and biochemical test following standard procedure¹⁴. The Analytical Profile Index (API 20E) was used to support the bacterial identification process (bioMerieux, France) 

Antimicrobial susceptibility testing 

Susceptibility testing was performed with the disk-diffusion method according to the criteria of National Committee for Clinical Laboratory Standards (NCCLs) (13). The drugs included ampicillin (AMP), ampicillin-sulbactam (SAM), ciprofloxacin (CP), levofloxacin (LEV), nitrofurantoin (FM), piperacillin-tazobactam (TZP); cephazolin (CZO), cefotetan (CTT), ceftazidine (CAZ), ceftriaxone (CRO), imipenem (IMP),  amikacin (AN); tobramycin (TOB), trimethoprim‑sulfamethoxazole (TMP‑STX), cefoxitin (CXT); imipenem (IPM), cefotaxime (CTX), aztreonam, ertapenem, gentamicin, cefepime, quinupristin, tigecycline,   penicillin-G (PG), gentamycin (GM), erythromycin (E), linezolid (LZD), vancomycin (VA), tetracycline (TC), nitrofurantoin (FM). Regarding to the resistance rate, antibiotic resistance rate under 20% was set as the green zone, 20%–30% as the yellow zone, and the ratio over 30% as the red zone.

Used binary logistic regression to determine the independent effect of the variables (age, gender, birth weight, feeding pattern, premature delivery, primigravida, history of catheterization and surgery) by calculating the strength of the association between UTI and associated factors using odds ratio (OR) and 95% confidence interval (CI). Adjusted OR (for variables which were statistically significant in binary logistic analysis) was computed using multivariable logistic regression to control the confounding variables. 

Statistical analysis

In this study, analysis of data was performed by SPSS statistical software package (version 16) (IBM Corp., Armonk, NY, USA). A descriptive study of data such as bacterial patterns, bacterial resistance patterns, sex and age of patients, frequencies, and its percentage, age of patients performed by mean±standard deviation (SD). Pearson’s Chi‑squared test is used for comparing qualitative variables and analysis of variance test is used for average age expression in bacterial pattern and antibiotic resistance pattern. In all cases P-value less than 0.05 was taken as statistically significant. 

In this study, analysis of data was performed by SPSS statistical software package (version 16) (IBM Corp., Armonk, NY, USA). The proportion of children with positive urine cultures was expressed as a percentage of the total included children. Isolated and identified pathogens were each quantified as percentage of total isolated organisms. The susceptibility patterns and MDR to commonly prescribed antibiotics were expressed as frequencies and percentages. In addition, univariable logistic regression analyses were utilized to identify the independent risk factors for culture positive UTI. In all cases P-value less than 0.05 was taken as statistically significant. 

Results

A total of 840 pediatric patients including 569 males and 271 females were hospitalized for UTI in our center, indicating that the male to female ratio was 2.10:1. The age of UTI children in this study ranges from 1 month to 14 years. From 840 pediatric patients, 694 (82.62%) children were diagnosed with complicated UTI and the remaining 146 (17.38%) children were simple UTI. The general characteristics of patients are shown in Table 1. 

Table 1. Clinical characteristics of study participants by diagnosis of UTI.

 The proportion of culture-positive UTI was 54.52% (458/840) with majority of the isolates being Gram-negative bacteria. There were 694 children with complicated UTI in those children. 30 of these 694 patients (4.32%) had urinary stones and 664 had urogenital abnormalities (95.68%). Abnormalities of the genitourinary tract  included VUR, duplicated collecting system, PUV, NB, ureteral obstruction and UPJO. Consequently, the proportion of culture-positive UTI was 397/694 (57.20%). Gram-negative bacteria mainly included Escherichia coli 121 (30.48%), Klebsiella pneumoniae 32(8.06%), Pseudomonas aeruginosa 20 (5.04%), Enterobacter cloacae 11 (2.77%) and Citrobacter 13 (3.28%). The isolated Gram-positive bacteria mainly contained Enterococcus faecalis (14.61%) and Enterococcus faecium (16.62%). In addition, there were 146 children diagnosed simple UTI. We detected that the proportion of culture-positive UTI was 61/146 (41.78%). The predominant bacteria were Escherichia coli (73.77%, 45/61) followed by Enterococcus faecium and CoNS (each 6.56%) (Table 2). 

Table 2. Bacterial profile isolated from urine culture of children in both simple and complicated UTI.

The antimicrobial susceptibility pattern of each bacterial isolate are shown in Table 3. In the group of complicated UTI, Escherichia coli isolates were highly sensitive to amikacin (95.87%), ertapenem (91.74%), nitrofurantoin (92.56%), imipenem (90.08%), and cefotetan (87.60%) and high rate of resistant were also detected to ampicillin (93.39%), cephazolin (76.03%), ceftriaxone (73.55%), trimethoprim‑sulfamethoxazole (63.64%) aztreonam (64.46%). Klebsiella pneumoniae isolates showed sensitive to ertapenem (96.87%), amikacin (96.87%), imipenem (93.75%) and piperacillin-tazobactam (90.62%), while highly resistant were observed to ampicillin (96.87%), cephazolin (75.00%), ceftazidine (62.50%), ceftriaxone (62.50%), aztreonam (62.50%) and ampicillin-sulbactam (59.37%). As shown in Table 4, The isolated Gram-positive Enterococcus faecalis were sensitive to vancomycin, penicillin-G, tigecycline, linezolid and nitrofurantoin (100%, 94.83%, 88.48%, 87.93%, 86.20, respectively) and resident to tetracycline (86.21%), quinupristin (84.48%), erythromycin (75.86%). Likewise, Enterococcus faecium were sensitive to vancomycin, linezolid, tigecycline, quinupristin (98.48%, 95.45%, 84.85% , 83.33%), while resident to ampicillin (93.94%), erythromycin (89.39%), penicillin-G (84.85%), ciprofloxacin (77.27%), levofloxacin (68.18%) and tetracycline (66.67%). In the group of simple UTI, Escherichia coli were highly sensitive to ertapenem (100%), imipenem (100%), and cefotetan (100%), amikacin (95.56%) and nitrofurantoin (91.11%) and high rate of resistant were also detected to ampicillin (91.11%), trimethoprim‑sulfamethoxazole (64.44%), cephazolin (62.22%) and ceftriaxone (53.33%). 

Table 4. Antimicrobial susceptibility patterns of Gran-positive bacteria from simple UTI samples. PG = penicillin-G, Amp = Ampicillin; GM: Gentamycin, CP = Ciprofloxacin, LEV = Levofloxacin, E = erythromycin, LZD = Linezolid, VA = Vancomycin, TC = Tetracycline, FM = Nitrofurantoin, S, I, R = sensitive, intermediate, resistant. 

 Among complicated UTI patients, there were 8 children with fungal infection. Multiple drug resistances (MDR) was found in 315/389 (80.98%) of bacteria isolated (Table 5). In the group of simple UTI, MDR were also detected in 47/61 (77.05%). The detailed distribution was shown in Table 6. 

Table 5. Multi drug resistance pattern of bacterial isolates from children with complicated UTI. MDR = multiple drug resistance, R1 = resistance to one drugs, R2 = resistance to two drugs, R3 = resistance to three drugs, R4 = resistance to four drugs, R5 = resistance to five drugs, R6 = resistance to six drugs, R7 = resistance to seven drugs.

Table 6. Multi drug resistance pattern of bacterial isolates from children with simple UTI. MDR = multiple drug resistance, R1 = resistance to one drugs, R2 = resistance to two drugs, R3 = resistance to three drugs, R4 = resistance to four drugs, R5 = resistance to five drugs, R6 = resistance to six drugs, R7 = resistance to seven drugs.

Discussion

Pediatric UTIs are infectious disease of urinary tract in nearly 0.7% girls and 2.7% boys by the age of 1 year¹⁵. About 5% girls and 20% boys under two months are diagnosed with UTI among febrile infants¹⁶. Meanwhile, UTIs are more common in premature infants than term infants during neonatal period¹⁷. There are 30% children within 6 months and even up to 50% school-age girls with recurrent UTIs (RUTIs) after initial UTIs^18,19. The high prevalence of UTI and fear of its recurrence results in the irrational use of antibiotics, especially for children with recurrent and complicated UTI. Moreover, empirical treatment is also prevalent in primary hospital. These continued and irrational use of antibiotics has led to microbiota dysbiosis and antibiotic resistance, even other diseases^20,21. Thus, antibiotic resistance is an experienced problem to be urgently solved in treating UTI.

Complicated UTIs are defined as those infections causing severe complications, such as urosepsis, renal scarring, and end-stage renal disease. Among children, major complicating factors are infection stones, indwelling catheters, and abnormalities of the genitourinary tract²². Anatomical or functional abnormalities allow for the prolongation of bacteruria and decreasing the clearance of invading pathogens due to poor drainage²³. Boys with PUV have increased risks of UTI voiding dysfunction, elevating bladder pressure stemming and ongoing renal damage. The continued bladder pressure from urine stasis or obstruction can cause VUR and increase the potential risk of renal function damage by an ascending infection (24). Approximately 20% of neonatal cases with VUR were diagnosed with UTI and then led to renal scars^25,26. In addition, UTIs remain the first cause of morbidity and the second cause of mortality in patients with neurogenic bladder due to high bladder pressure, detrusor exyernal sphincter dyssynergia and post-void residual²⁷. These children often perform clean intermittent catheterisation, which can further increase the UTI risk caused by catheter contamination and the introduction of external pathogens into the bladder^28,29. It is important to identify these abnormalities early because they may serve as a reservoir for bacterial growth or recurrent infections. Once the diagnosis of UTI has been made, further examinations are necessary for children to identify the complicating risk factors. 

      The genitourinary tract is a sterile environment, except for the distal urethra. UTI is mostly caused by Gram-negative bacillus because of its unique structure which promotes the epithelial cells attachment and prevents bacteria from urinary lavage³⁰. E. coli is the most predominant bacterium isolated from urine, accounting for 85-90% of all cases³¹. It often originates from the faecal flora, spreads across the perineum, and then invades the bladder through the opening of urethra. Other common Gram-negative pathogens include Klebsilla pneumoniae, Proteus mirabilis, Enterobacter, Citrobacter, and P. aeruginosa. Besides, Streptococcus species and Staphylococcus species are the frequent Gram-positive bacteria. In the present study, we also found that Gram-negative bacterial isolate were more prevalent than Gram-positive bacterial isolates in two paired groups. Escherichia coli, was the most common Gram-negative uropathogen followed by Klebsiella pneumoniae. In addition, there were Enterococcus faecalis and Enterococcus faecium in Gram-positive pathogens. Knowing the prevalence of drug-resistant uropathogens could help the clinicians to make the right choice of antibiotics among children with UTIs.

In the group of complicated UTI, we found that all Gram-negative isolates in this study were shown sensitivity to amikacin, ertapenem, nitrofurantoin, imipenem, and cefotetan. Among antibiotics used in this study, these isolates were highly resistant to ampicillin, cephazolin, ceftriaxone, trimethoprim‑sulfamethoxazole and aztreonam. This implies that they cannot be used as empirical therapy for UTI particularly in children with urinary abnormalities or stones. Of Gram positive bacteria, they showed high sensitivity to vancomycin, penicillin-G, tigecycline, linezolid and nitrofurantoin and resident to tetracycline, quinupristin and erythromycin. For simple UTI patients, the most common uropathogen was Escherichia coli. It was highly sensitive to ertapenem, imipenem, cefotetan, amikacin and nitrofurantoin and high rate of resistant was also observed to ampicillin, trimethoprim‑sulfamethoxazole, cephazolin and ceftriaxone. Majority of the isolates were resistant to the commonly prescribed antibiotics, therefore culture and antibiotic susceptibility testing was recommended before giving treatment to prevent antimicrobial resistance at least. Empirical treatment of UTI should be minimized as sensitivity always varies for each organism, for each drug over time. If a urine culture is obtained, appropriate antibiotic treatment was applied. A patient who has not been markedly improved after 1-2 days of antibiotics requires re-evaluation with further testing. Imaging to evaluate for a UTI mimic, complicated UTI, or urinary obstruction may be required as well as urine culture. Further large-scale studies are warranted to examine the generalizability of our findings.

Antibiotic resistance (ABR) is a major problem in treating infectious diseases, and is increasingly aggravated by muddled empirical treatments worldwide, especially in regions with limited resources. Presence of multi-drug resistant (MDR) organisms (resistance to ≥3 drugs) was detected in children with UTI. In the present study, MDR was relatively high in both groups. Complicated UTI organisms showed an overall higher MDR than simple UTI organisms.

There are some limitations in our study. Firstly, this present study was merely carried out in a single center, which could not be representative of the overall values of prevalence and antimicrobial susceptibility pattern of pediatric UTIs in China. Secondly, our study is a retrospective study based on incomplete or sometimes missing information in patient charts. Thirdly, some asymptomatic patients with simple UTIs were not included in this study and received outpatient antibiotics. Therefore, it is urgently needed to conduct multicenter studies on the prevalence and antibiotic susceptibility in future. 

Conclusion

Our study revealed a higher prevalence of complicated UTI among children compared to simple UTI. The majority of the isolates was Gram-negative bacteria in both groups. Escherichia coli was the most prevalent isolate followed by Enterococcus faecium and Enterococcus faecalis in complicated UTI patients. Likewise, Escherichia coli was the predominant bacteria in those patients with simple UTI. These organisms were highly resistant to the most commonly used antibiotics. Culture and susceptibility test is vital for appropriate management of UTI in the study.

Declarations

Data availability 

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Acknowledgements 

This work was supported by the Natural Science Foundation of Anhui Province (1908085MH246) and the Natural Science Foundation of China (82070724).

Author contributions 

K.Z., Y.Z., M.C. and Z.H. conceived the study and participated in data analysis. K.Z., wrote and revised the manuscript. All authors read and approved the final manuscript. 

Competing interests 

The authors declare no competing interests.

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Tables

Table 3 is available in the Supplemental Files section.