by H. Cody Meissner, M.D., FAAP
Following the dramatic reduction in bacteremia as
a cause of fever (due to widespread use of bacterial
vaccines), urinary tract infections (UTIs) have become one of the most common occult infections in
young children. UTI includes infection of urethra
(urethritis), bladder (cystitis), ureter (ureteritis) or
During the first decade of life, approximately 2%
of boys and 8% of girls will experience a UTI. The
prevalence of UTI is about 7% among febrile children between birth and 24 months of age.
Which of the following statements regarding
UTIs is false?
a) A cloudy urine with a bad smell is a reliable
indication of a UTI.
b) Asymptomatic bacteriuria has not been associated with long-term adverse outcomes such as
pyelonephritis, renal failure or hypertension,
and antimicrobial treatment is not indicated.
c) To diagnose a UTI, both a urine culture and a
urinalysis should be obtained.
d) In an appropriately collected specimen, 50,000
colony-forming units/milliliter (CFU/mL)
should be considered the threshold for diagnosis of UTI.
e) For infants under 6 months, boys (especially
if uncircumcised) are more likely than girls to
experience a UTI; after 6 months, UTIs are five
times more common in girls.
Uropathic bacteria are part of the fecal flora and
colonize the perirectal and perineal areas. A UTI
occurs following adherence of E. coli to uroepithe-lial cells of the distal urethra. At the termination of
micturition with constriction of the external urethral
sphincter, bacteria colonizing the distal urethra may
reflux into the bladder.
In the absence of frequent voiding, the concentration of bacteria in the urine in the bladder increases, resulting in an inflammatory response and the
symptoms of cystitis. The presence of foreskin in
uncircumcised males may result in a higher density
of bacteria at the meatus and a greater chance of
colonization of the distal urethra.
The ability of bacteria to ascend to the upper uri-
nary tract and cause pyelonephritis depends on vir-
ulence genes, such as those that produce tissue-dam-
aging toxins. Adhesion of bacteria to epithelial cells
of both upper and lower tract depends on fimbriae or
pili on the surface of the pathogen (see illustration).
Adhesins at the end of the fimbriae attach to specific
epithelial cell receptors, increasing the ability of the
bacteria to adhere and avoid being washed off during
urination. Conditions that result in urinary stasis
predispose a child to UTI. These include obstruc-
tive uropathy, a voiding abnormality and anatomic
abnormalities of the urinary tract.
Asymptomatic bacteriuria refers to the presence
of bacteria in the urine in the absence of pyuria and
is associated with school-age and older girls. Studies
suggest that treatment of asymptomatic bacteriuria
may be harmful based on the observation that a
higher incidence of pyelonephritis occurs in children
with asymptomatic bacteriuria who receive antibi-
otic therapy compared to similar children who do
not receive treatment.
Appropriate collection of a urine specimen is es-
sential for accurate diagnosis of a UTI. If a young
child is suspected of having UTI and cannot provide
a clean-catch urine, a specimen should be obtained
by catheterization or suprapubic aspiration prior to
initiation of antimicrobial therapy.
A urine specimen obtained from a bag applied to
the perineum is valid only when the culture yields
a negative result because of high rates of contami-
nation by perineal flora. Overdiagnosis of UTI will
result in excessive antibiotic use and unnecessary im-
aging studies. Once antimicrobial therapy is started,
the urine will be sterilized rapidly, and an accurate
diagnosis will not be possible.
AAP guidelines state that bacterial counts greater
than 50,000 CFU/mL of a single recognized urinary
pathogen may be diagnostic for UTI in symptomatic
infants or young children (Pediatrics. 2011;128:595-
610, http://bit.ly/2mi7VIu). Reducing the thresh-
old for a significant level from 100,000 CFU/mL
to 50,000 CFU/mL increases the sensitivity but
reduces the specificity of the definition. However,
the additional requirement for pyuria (more than
10 white blood cells/high power field) reduces the
likelihood of confusion with asymptomatic bacte-
riuria or contamination.
Biochemical assays on the urine specimen (leuko-
cyte esterase, nitrite) may be helpful in the diagnosis
of UTI. However, the sensitivity and specificity of
leukocyte esterase and nitrite tests are insufficient
to diagnose a UTI in the absence of other findings.
The leukocyte esterase assay is a surrogate for pyuria.
A positive nitrite test may indicate a UTI caused
by a gram-negative organism that converts endogenous nitrates to nitrites. False-negative nitrite tests
may occur when an organism causing a UTI is unable to reduce nitrate to nitrite (such as enterococcus
or staphylococcus) or when urine was not present
in the bladder long enough for the metabolic conversion to occur.
Dr. Meissner is professor of pediatrics
at Floating Hospital for Children, Tufts
Medical Center. He also is an ex officio
member of the AAP Committee on Infectious Diseases and associate editor of
the AAP Visual Red Book.
Courtesy of the Centers for Disease Control and Prevention
Illustration of Escherichia coli, the cause of more than 80% of urinary tract infections in males and females.
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Common misconceptions about urinary tract infections in children