Corresponding Author: Moslehi Mohammad Ashkan, MD, Department of Pediatrics, Nemazee Hospital , Shiraz University of Medical Sciences, Shiraz , Iran . E-mail: moslehim@sums.ac.ir

PATHOGENESIS

• Most UTIs in newborns affects upper tract infection rather than lower parts (simple cystitis). Approximately one-third of infants with UTI have bacteremia with the same organism ^18-20. This may be more common in preterm infants. Associated bacteremia becomes less important with increasing postnatal age. As an example, in a review of 100 infants with UTI, sepsis occurred in 31, 21, and 5 percent of infants less than one, one to three, and more than three months of age, respectively.¹⁶
  
  Hematogenous spread of infection has been thought to be responsible for neonatal UTI because upper tract infection with associated bacteremia is common. However, the microbiology of these infections and the high incidence of urinary tract abnormalities raise the question of whether neonatal UTI truly arises from hematogenous spread from a remote source (e.g., intravascular catheter) or, in the majority of cases, actually represents an ascending urinary tract infection with an associated bacteremia.
 
• Urinary tract abnormalities: Approximately 30 to 50 percent of newborns with UTI have urinary tract abnormalities, of which vesicoureteric reflux (VUR) is most common.^{4, 8, 16-20} This incidence was illustrated in one report of 45 males younger than eight weeks old with UTI; urinary tract abnormalities were observed in 22 of which 19 had VUR, two had VUR and another problem (double collecting system and posterior urethral valves), and one had ureteropelvic junction stricture. ²⁰
  
  The risk of acute pyelonephritis and subsequent renal scarring is related to the severity of VUR, which is graded according to whether the reflux reaches the kidney and by the degree of dilatation of the collecting system ²¹. Children with high-grade VUR are four to six times more likely to have renal scarring than are those with low-grade VUR and 8 to 10 times more likely than are those without VUR.22-24 Other lesions found in infants with UTI include obstructive abnormalities (ureteropelvic junction or ureterovesical junction obstruction; posterior urethral valves), malformations (ectopic ureter), or renal conditions (polycystic diseases, renal dysplasia).
  
  Urinary tract abnormalities may contribute to UTI by several mechanisms, including inadequate urine flow, incomplete emptying of the bladder and incompetent anatomic junctions that permit reflux of contaminated urine. As a result, infection can occur with organisms lacking virulence factors. In a study of children with UTI, for example, infections caused by P-fimbriated stains of E. coli were less common with than without VUR (36 versus 71 percent).²⁵
 
• Uncircumcised males: The incidence of UTI is increased in uncircumcised males. In one report of approximately 136,000 boys in United States Army hospitals, the frequency of UTI during the first month after birth was significantly higher in uncircumcised than circumcised infants (0.19 versus 0.02 percent).¹⁹ The increased incidence in uncircumcised males persists during the first year after birth.²⁶ The higher incidence of UTI in uncircumcised males is related to an increased rate of bacterial colonization and enhanced bacterial adherence.^27-29 In one study, E. coli and other Gram negative uropathogenic organisms were cultured more frequently from the urethras of uncircumcised than from those of circumcised boys, and bacterial colony counts were higher .²⁷ In another report, uropathogenic organisms preferentially adhered to the mucosal inner surface of the foreskin rather than the keratinized external surface, increasing the likelihood of ascending infection.²⁹

CLINICAL FEATURES

The signs and symptoms of UTI in newborns are nonspecific. Infants can have lethargy, irritability, tachypnea, or cyanosis, and may appear acutely ill. Preterm infants frequently present with apnea. ⁹

The most common clinical findings are:

• Fever (20 to 40 percent)>
 
• Failure to thrive (15 to 43 percent)
 
• Jaundice (3 to 41 percent)
 
• Vomiting (9 to 41 percent)
 
• Loose stools (3 to 5 percent)
 
• Poor feeding (3 to 5 percent)

The hyperbilirubinemia that occurs with UTI typically is conjugated and related to cholestasis, although it may be unconjugated. Jaundice may be the first sign of UTI in some infants. In one report, UTI was diagnosed in 12 (7.5 percent) of 160 asymptomatic jaundiced infants less than eight weeks of age who presented to an emergency department.30 Onset of jaundice after eight days was more common in infants with positive compared to negative cultures (50 versus 10 percent). Other findings that occur less commonly include abdominal distension resulting from ileus or enlarged kidneys caused by hydronephrosis.