Bacteriuria and Urinary Tract Infections
In infants, bacteriuria can be diagnosed with certainty only by culturing samples obtained by invasive techniques (bladder catheterization or suprapubic aspiration). There is no consensus, however, about the magnitude of bacteriuria required to reach significance (Table 42-18). Bacteriuria in newborn infants can be either asymptomatic or an indication of pyelonephritis, which is characterized by local and systemic inflammatory response. Similarly, candiduria can be asymptomatic, cause hydronephrosis, or be part of a disseminated infection. Lower UTI, i.e., cystitis usually cannot be diagnosed on clinical grounds in newborn infants, except when associated with hematuria.
Frequency in Newborn Infants
The frequency of bacteriuria ranges between 0% and 2.0% in an unselected neonatal population and between 0.6% and 10% in an NICU population (782,783,784,785,786,787,788). Risk factors include prematurity (frequency of bacteriuria is 0.1%-10%) (783,785,787,788), male gender (male-to-female ratio
ranges from 1:1 to 9:1 in newborn infants) and urinary tract anomalies (785,786,787,788). The higher incidence of UTI in boys than in girls in infancy results from the higher frequency of structural abnormalities (785,786) in males and from the higher bacterial counts and higher prevalence of Escherichia coli in uncircumcised infants (789). Circumcision reduces the risk for UTI in infancy (790) to a rate that is similar to that in females (786). However, the risk for UTI rises for 2 weeks after ritual Jewish circumcision (791). VUR is less frequent in extremely LBW infants who developed UTI than in infants weighing 1001-1500g (792). UTI often occurs in association with neonatal sepsis (785). In one series, Candida spp were responsible for 25 of 60 (42%) hospital-acquired UTI in a NICU (793).
ranges from 1:1 to 9:1 in newborn infants) and urinary tract anomalies (785,786,787,788). The higher incidence of UTI in boys than in girls in infancy results from the higher frequency of structural abnormalities (785,786) in males and from the higher bacterial counts and higher prevalence of Escherichia coli in uncircumcised infants (789). Circumcision reduces the risk for UTI in infancy (790) to a rate that is similar to that in females (786). However, the risk for UTI rises for 2 weeks after ritual Jewish circumcision (791). VUR is less frequent in extremely LBW infants who developed UTI than in infants weighing 1001-1500g (792). UTI often occurs in association with neonatal sepsis (785). In one series, Candida spp were responsible for 25 of 60 (42%) hospital-acquired UTI in a NICU (793).
Pathophysiology
The risk of UTI depends on bacteriologic factors (see Chapter 48) and host characteristics. Periurethral cultures obtained in uncircumcised infants show higher total bacterial counts, and a higher prevalence of E. coli than cultures obtained in circumcised infants (789). The normal defense against UTI includes maintenance of an adequate flow of urine; complete emptying of the bladder, and presence of an anatomic barrier, i.e., the bladder outlet. These defense mechanisms may be compromised by urinary tract obstruction, VUR (see Chapter 43), bladder dysfunction (e.g., neurogenic bladder), or manipulation (e.g., prolonged or repeated bladder catheterization) (794,795). Immune defenses in general are described in Chapter 45. In the case of pyelonephritis, endocytosis of bacteria is performed by inflammatory cells and by proximal tubular cells.
Pathology
Acute pyelonephritis is characterized by the presence of polymorphonuclear leukocytes in the glomeruli, tubules, and interstitium (796). Some glomeruli are completely destroyed, whereas others are infiltrated with leukocytes and surrounded by fibrin. The tubules are necrotic, dilated, and their lumens are filled with leukocytes and bacteria. Suppuration may develop in the kidney, often with multiple abscesses, and in other parts of the genitourinary tract. Chronic or recurrent pyelonephritis is characterized by infiltration of inflammatory cells, loss or hyalinization of glomeruli, and atrophy of tubules, with obstruction of the lumen with colloid casts. The development of renal scars may not occur until after 1 year of life.
Clinical Presentation
The clinical presentation of UTI in newborn infants may include one or more of the following signs:
Growth failure and gastrointestinal symptoms. Failure to thrive, excessive weight loss, poor feeding, diarrhea, and vomiting are the most common clinical features of neonatal UTI.
Jaundice. The hyperbilirubinemia observed in newborn infants with UTI may be either direct or indirect and sometimes is associated with hemolytic anemia. It is commonly the main clinical feature at presentation and may be the only sign of UTI in some infants (797).
Temperature instability or fever (temperature ≥38°C). UTI has been reported in 7.5% to 11% of febrile infants presenting to the emergency room during the first 8 to 12 weeks of life (798,799).
Irritability, lethargy.
Abnormal urination. This includes poor urinary stream, malodorous urine, and polyuria, which may lead to severe dehydration.
Signs associated with bacteremia (e.g., respiratory distress) or with focal infection (e.g., mucocutaneous candidiasis, omphalitis).
Hypertension. This may develop as a result of hydronephrosis associated with the UTI (see Complications) (800).
Laboratory Features
Urinalysis
Based on specimens obtained by bladder catheterization or suprapubic aspiration, only one-half of febrile outpatients with documented UTI during the first 3 months of life had an abnormal urinalysis, defined either by the presence of more than five leukocytes per high power field or by the presence of any bacteria (798). The positive predictive value of pyuria on samples obtained by suprapubic aspiration ranges between 71% (pyuria greater than 10 leukocytes/mm3) (782) and 96% (pyuria ≥20 leukocytes/mm3) (787). Thus, the presence of pyuria, at least on a sample obtained by suprapubic aspiration, is suggestive of UTI, whereas the absence of pyuria is insufficient to rule it out (788,801,802). Microscopic demonstration of yeast cells in urine obtained by suprapubic aspiration or bladder catheterization is very suggestive of candiduria.
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