Clinical and laboratory features of urinary tract infections in young infants

ABSTRACT Introduction: Urinary tract infection (UTI) is the most common serious bacterial infection in young infants. Signs and symptoms are often nonspecific. Objectives: To describe clinical, demographic and laboratory features of UTI in infants ≤ 3 months old. Methods: Cross-sectional study of infants ≤ 3 months old with UTI diagnosed in a pediatric emergency department, for the period 2010-2012. UTI was defined as ≥ 50,000 colony-forming units per milliliter of a single uropathogen isolated from bladder catheterization. Paired urinalysis and urine culture from group culture-positive and group culture-negative were used to determine the sensitivity and specificity of pyuria and nitrite tests in detecting UTI. Results: Of 519 urine cultures collected, UTI was diagnosed in 65 cases (prevalence: 12.5%); with male predominance (77%). The most common etiologies were Escherichia coli (56.9%), Klebsiella pneumoniae (18.5%) and Enterococcus faecalis (7.7%). Frequent clinical manifestations were fever (77.8%), irritability (41.4%) and vomiting (25.4%). The median temperature was 38.7°C. The sensitivity of the nitrite test was 30.8% (95%CI:19.9-43.4%), specificity of 100% (95%CI:99.2-100%). Pyuria ≥ 10,000/mL had a sensitivity of 87.7% (95%CI:77.2-94.5%), specificity of 74.9% (95%CI:70.6 -78.8%). The median peripheral white blood cell count was 13,150/mm3; C-reactive protein levels were normal in 30.5% of cases. Conclusions: The male: female ratio for urinary tract infection was 3.3:1. Non-Escherichia coli etiologies should be considered in empirical treatment. Fever was the main symptom. Positive nitrite is highly suggestive of UTI but has low sensitivity; whereas pyuria ≥ 10,000/mL revealed good sensitivity, but low specificity. Peripheral white blood cell count and C-reactive protein concentration have limited usefulness to suggest UTI.

摘要
## 引言
尿路感染（Urinary tract infection, UTI）是婴幼儿最常见的重症细菌性感染，其临床表现常缺乏特异性。
## 研究目的
描述月龄≤3个月婴幼儿尿路感染的临床、人口统计学及实验室特征。
## 研究方法
本研究为横断面研究，纳入2010-2012年于儿科急诊确诊为尿路感染的月龄≤3个月婴幼儿。尿路感染的定义为：经膀胱导尿采集的尿液标本中分离出单一尿路致病菌，菌落形成单位≥50000 CFU/mL。本研究通过纳入尿培养阳性组与尿培养阴性组的配对尿液分析与尿培养结果，评估脓尿检测与亚硝酸盐试验诊断尿路感染的灵敏度与特异度。
## 研究结果
共收集519份尿培养标本，其中65例确诊为尿路感染，患病率为12.5%；男性占比77%，存在性别优势。最常见的致病菌为大肠埃希菌（56.9%）、肺炎克雷伯菌（18.5%）与粪肠球菌（7.7%）。常见临床表现包括发热（77.8%）、烦躁不安（41.4%）与呕吐（25.4%），中位体温为38.7℃。亚硝酸盐试验的灵敏度为30.8%（95%置信区间：19.9%~43.4%），特异度为100%（95%置信区间：99.2%~100%）。脓尿≥10000/mL的灵敏度为87.7%（95%置信区间：77.2%~94.5%），特异度为74.9%（95%置信区间：70.6%~78.8%）。外周血白细胞计数的中位数为13150/mm³；30.5%的患儿C反应蛋白（C-reactive protein, CRP）水平处于正常范围。
## 研究结论
婴幼儿尿路感染的男女比例为3.3:1。经验性治疗时需考虑非大肠埃希菌致病菌感染的可能。发热为最主要的临床表现。亚硝酸盐试验阳性高度提示尿路感染，但灵敏度较低；而脓尿≥10000/mL的灵敏度较好，但特异度偏低。外周血白细胞计数与C反应蛋白浓度对尿路感染的诊断价值有限。