Korean J Pediatr 2015;58(5):183-189
Korean J Pediatr 2015;58(5):183-189 http://dx.doi.org/10.3345/kjp.2015.58.5.183 pISSN 1738-1061•eISSN 2092-7258
Korean J Pediatr
Validity of bag urine culture for predicting urinary tract infections in febrile infants: a paired comparison of urine collection methods Geun-A Kim, MD, Ja-Wook Koo, MD, PhD Department of Pediatrics, Inje University Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea
Purpose: Catheter urine (CATH-U) and suprapubic aspiration (SPA) are reliable urine collection methods for confirming urinary tract infections (UTI) in infants. However, noninvasive and easily accessible collecting bag urine (CBU) is widely used, despite its high contamination rate. This study investigated the validity of CBU cultures for diagnosing UTIs, using CATH-U culture results as the gold standard. Methods: We retrospectively analyzed 210 infants, 2- to 24-month-old, who presented to a tertiary care hospital’s pediatrics department between September 2008 and August 2013. We reviewed the results of CBU and CATH-U cultures from the same infants. Results: CBU results, relative to CATH-U culture results (≥10 4 colony-forming units [CFU]/mL) were widely variable, ranging from no growth to ≥105 CFU/mL. A CBU cutoff value of ≥105 CFU/mL resulted in false-positive and false-negative rates of 18% and 24%, respectively. The probability of a UTI increased when the CBU bacterial count was ≥105/mL for all infants, both uncircumcised male infants and female infants (likelihood ratios [LRs], 4.16, 4.11, and 4.11, respectively). UTIs could not be excluded for female infants with a CBU bacterial density of 104 –105 (LR, 1.40). The LRs for predicting UTIs based on a positive dipstick test and a positive urinalysis were 4.19 and 3.11, respectively. Conclusion: The validity of obtaining urine sample from a sterile bag remains questionable. Inconclusive culture results from CBU should be confirmed with a more reliable method.
Corresponding author: Ja-Wook Koo, MD, PhD Department of Pediatrics, Inje University Sanggye Paik Hospital, Inje University College of Medicine, 1342 Dongil-ro, Nowon-gu, Seoul 139-707, Korea Tel: +82-2-950-1074 Fax: +82-2-950-1246 E-mail: [email protected]
Received: 14 July, 2014 Revised: 17 August, 2014 Accepted: 24 September, 2014
Key words: Catheter urine culture, Collecting bag urine culture, Febrile infants, Paired comparison, Urinary tract infection
Introduction Urinary tract infections (UTIs) are common causes of generalized pyrexia in infants, occurring in approximately 5% of 2- to 24-month-old febrile children1,2). Fevers associated with UTIs are usually caused by pyelonephritis3,4), the early diagnosis and treatment of which are important for the prevention of complications, including renal scarring which are associated with later renal dysfunction and progressive septicemia5,6). The diagnosis of a UTI is most commonly accomplished using a urine culture, but the collection of urine samples from infants is difficult. Regardless, choosing an appropriate urine collection method for young children is important to avoid misdiagnosing a UTI. Over-diagnosis of UTIs can lead to unnecessary radiological evaluations and antibiotic treatment7), and the consequences of under-diagnosis were previously stated. Suprapubic aspiration (SPA) is regarded as the gold standard method for collecting urine samples with minimal false-positive results2,8). However, this method is more invasive and painful than the others9). Transurethral catheterization is a less painful method that
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Kim GA and Koo JW • Validity of bag urine culture in febrile infants
has comparable sensitivity and specificity as SPA, making it more routinely used2,6). The noninvasive and easily accessible collection and culturing of collecting bag urine (CBU) is widely used in outpatient clinics and emergency units, despite its high contamination rate2,10). A few authors have performed paired examinations of the different urine culture methods used for diagnosing UTIs in children of various ages (9 days to 9 years)11) and in asymptomatic infants during voiding cystourethrograms7), and with prior selection (by urinalysis) for febrile infants12). In this study, we compared the results of CBU cultures and catheter urine (CATH-U) cultures, following the recovery of both sample types from the same patients. The culture results were used to estimate the ability of CBU cultures to diagnose UTIs, when CATH-U samples were considered the “gold standard” for diagnosing UTIs in infants.
Materials and methods The study population consisted of infants examined in the pediatrics department of Inje University Sanggye Paik Hospital (Seoul, Korea), between September 2008 and August 2013. We retrospectively analyzed patient records to determine if the patients had a potential risk of UTI, based on the following inclusion criteria: (1) a tympanic fever >38°C of unknown origin, (2) patient age of 2–24 months, (3) non–toilet-trained patients, and (4) all female infants and uncircumcised male infants. Demographic and clinical profiles, laboratory findings, uri nalyses, and urine culture results were reviewed for each patient. Only infants with collecting bag and CATH-U cultures, obtained on the same day, were included. Patients already receiving antibiotics or having incomplete data for evaluation were ex cluded from the study, as were patients with contaminated CATH-U or CBU cultures. Urine specimens were collected using an aseptic technique, according to our departmental guidelines. After cleansing the perineum with antibacterial cotton (povidone iodine), a urine collection bag was attached to the patient’s perineum by trained pediatric nurses. The urine bag was left in place for up to 1 hour, without changing the bag, unless there was evidence of leakage, stool contamination, or the bag separated from the skin. The perineum was also cleaned with povidone iodine before catheterization, which involved inserting an uncontaminated, lubricated, 5-Fr feeding tube into the urethra. Whether the urine was collected via a urine bag or catheterization, the first few drops were routinely discarded because of potential bacterial contamination from the distal urethra2,13). Within 30 minutes of collection, the urine specimens were sent to the laboratory for prompt urinalysis and culture. This study received ethical approval from the institution`s research board.
1. Definitions The following definitions were based on published descriptions . Dipstick tests were defined as positive if either nitrite or leukocyte esterase (LE) was positive. Microscopy was positive if either the white blood cell (WBC) counts were ≥10/mm3 or bacteria were present. Positive urinalysis was defined when the dipstick and/or microscopy evaluations were positive. A CATH-U culture was considered indicative of a UTI if the culture grew only a single species of bacteria at a density of ≥104 colonyforming units (CFU)/mL. CBU cultures were stratified, based on the presence of a single uropathogen species at densities of ≥103, ≥104, and ≥105 CFU/mL, and were compared to the positive/negative CATH-U results. The definition of CBU conta minants was similar to that of CATH-U, except for the bacterial colony count. Contaminants of CATH-U results were defined as: (1) bacteria present at densities of