This study demonstrated that the prevalence of culture-proven UTI in neonates was 6.67%. Urinary tract infection was non-significantly more frequent (70%) among full-term neonates. Moreover, both fever and pyuria were the only findings that showed significant association with UTI. Neonates that showed pyuria in urine analysis were 5.44 times more likely to have UTI, while the presence of fever constituted a risk of only 0.166.
In the present study, the prevalence of culture-proven UTI in neonates admitted to NICU was 6.67%. In comparison, lower incidence (1–2.4%) of UTI was reported among asymptomatic term neonates who were not admitted to NICU [14]. Additionally, our study revealed that the rate of UTI was non-significantly higher among full-term neonates. In contrast, Mohseny et al. [3] reported a high risk (11.3%) of UTI in NICU-admitted premature infants (less than 32 weeks) with central line and suspected sepsis. They attributed this high frequency to the presence of many risk factors for infection in preterm neonates.
The most commonly isolated organism in this study was E. coli. There were no fungal organisms isolated in culture. These results are in agreement with Tamim et al. [15] who have reported E. coli and Klebsiella sp. as the most commonly isolated species from urine culture of nosocomial UTI in NICU patients. On the other hand, an earlier study reported a higher proportion of hospital-acquired UTI caused by Candida sp. [16]. A lower average gestational age and lower average birth weight than our population explains this difference in the isolated pathogen [17].
Urinary tract infection is an important cause of serious bacterial infection in neonates, affecting 1 in 3 babies with proven bacterial infection [18]. Neonatal infections present with non-specific signs. In some cases, the diagnosis is not clearly established. This is particularly true for UTI, where there are no direct symptoms related to the urinary tract [19] Pyuria has been recognized as a sign of urinary infection in neonate. However, there is no distinct cutoff of the number of pus cells for establishing the diagnosis in suspected neonates [2]
Actually, the diagnostic validity of urine analysis is affected by many factors: first, sample collection technique like bag, catheter, or suprapubic sample; second, preparation of the specimen whether centrifuged or not; and third, the method of quantifying and reporting leukocytes per microscopic high-power field or per cubic millimeter. These differences have important consequences for the diagnostic and therapeutic management of neonates with suspected UTI [20].
In this study, the urine collected by suprapubic bladder aspirate technique revealed pyuria in 14.7% of the studied neonates. Comparable to our findings, a prospective study which included consecutive infants < 28 days of age admitted to the NICU of Liaquat National Hospital, Karachi, reported a higher (31.8%) incidence of pyuria [4]. This higher prevalence may be attributed to urine collection using urethral catheterization.
Furthermore, our study revealed that pyuria (> 5 cell/hpf) was the only laboratory finding in urine analysis that showed significant association with UTI. Similarly, Rahman et al. [4] reported a significant relationship between any number of pus cells in urine and a positive culture. They showed that pyuria 1–9 cells/hpf was associated with positive urine culture. In contrast, most authors support pyuria of < 10 cell/hpf as being indicative of presence of low risk of bacterial infections [21, 22]. So, it seems that no clear consensus has been established regarding the cutoff number of pus cells in urine that should be considered abnormal.
Neonates have an immature immune system. Further, responses of uroepithelium have not been extensively studied in this age group. So, data supporting leucocyte urothelial responses are limited [17]. Consequently, the significance of pyuria as a screening tool remains controversial in this age group [4]. Some authors agree with the fact that the sensitivity and specificity of the urine analysis is low. Hence, urine analysis may miss a lot of cases of UTI in neonates especially in premature neonates.
Binary logistic regression analysis revealed a model consisting of both pyuria and fever for prediction of UTI with an accuracy of 93.3%. It was noted that this regression model had a high specificity (94.5%) and negative predictive value (98.57%), while its sensitivity (50%) and positive predictive value (20%) was lower. Hence, the absence of pyuria and fever in a neonate excluded the diagnosis of UTI by 98.57%, whereas in 20% of neonates the presence of both pyuria and fever confirmed the diagnosis of UTI. In comparison, Tzimenatos et al. [23] revealed that urine analysis was highly sensitive and specific (87 and 91%) for the diagnosis of UTI in febrile infants 60 days or younger for UTIs with colony counts with ≥ 10 000 CFUs/mL. Furthermore, binary regression analysis has also revealed that neonates that showed pyuria in urine analysis were 5.44 times more likely to have UTI. On the other hand, the presence of fever constituted a risk of only 0.166. The observed lower risk (odds ratio) of fever might be attributed to the higher frequency of pyuria than fever among UTI patients in our study (50 versus 30%). Moreover, fever is a nonspecific manifestation that can be seen in neonatal sepsis and it is not specific to UTI [24].
This study is limited by lack of randomization and follow-up of patients.