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Asymptomatic and Symptomatic
Urinary Tract Infections: Magnitude,
Special Settings and Diagnostic Testing
Kehinde Lawal
Definition
From a microbiological view point, urinary tract
infection (UTI) is indicated when pathogenic microorganisms are found in the urine, bladder, urethra, kidney, and prostate and a microorganism
growth of 105 per ml is isolated from a mid-stream
or clean catch urine specimen. Asymptomatic urinary tract infection is the absence of symptoms in a
patient having urinary tract infection. The presence
of symptoms in a patient having infection of the urinary tract is referred to as symptomatic urinary tract
infection. In both cases, urine culture may be positive or negative. In symptomatic patients, fewer
(102 - 104 per ml) may signify infection. Urine specimen from catheterization with colony counts of
102 - 104per ml indicates infection. Occasionally,
however, due to mid-stream urine contamination, a
colony count of >105 per ml accompanied by multiple bacteria specie growth may occur. Acute urinary
tract infection can either be lower urinary tract infection (urethritis and cystitis ) or upper urinary tract
infection (acute pyelonephritis).
Clinical Features
Acute cystitis and acute pyelonephritis are two
major clinical syndromes mostly encountered. Patients with acute cystitis have infection localized in
the bladder. In a typical acute pyelonephritis patient,
in which the infection has spread to the kidney, localized kidney pain, fever, nausea, vomiting, chills,
malaise are usually observed. Acute urethritis patients
often present with symptoms of dysuria, urgency, frequency and non-significant bacteria growth. Catheterassociated UTIs cause minimal symptoms and are
often resolved after catheter is removed.
Kehinde Lawal,
MLT(AMT),
AIMLS, FIMLS,
MS, Wausau,
Wisconsin
Pathogenesis
Most UTIs result when bacteria gain access to the
bladder via the urethra. Ascent of bacteria from the
bladder may follow and is probably the pathway for
most renal parenchyma infections. Some strains of
E. coli and Proteus are uropathogenic. These strains
have violent genes (e.g., genes encoding fimbriae)
that mediate attachment to uroepithelial cells. UTIs
are caused by a subset of fecal microbial, flora of
88 August 2012 • Continuing Education Topics & Issues
which E. coli is the most common. Some hosts, primarily women, are especially susceptible to infection. In females prone to the development of cystitis,
however, enteric Gram-negative organisms residing
in the bowel colonize the introitus, the periurethral
skin, and distal urethral before and during bacteriuria episodes. Alteration of the normal vaginal flora
of normal dominant H2 02- producing lactobacilli appears to facilitate colonization of E. coli. Antibiotic
treatment and other genital infections or contraceptive are contributive factors.
Etiology
Uncomplicated community-acquired UTIs are
caused by E. coli in 80-85% of cases; other organisms such as Klebsiel1a, Proteus and Enterobacter
are Gram-negative rods which account for smaller
proportions of UTI cases. Gram-positive etiologic
agents of UTI include Staphylococcus saprophyticus
which causes 5-10% acute UTIs among schoolgirls.
E. coli, Proteus, Klebsiella, Enterobacter, Serratia,
and Pseudomonas are commonly associated with recurrent UTIs and UTI of the calculi. Sexually transmitted organisms such as Chlamydia trachomatis
and Neisseria gonorrhoeae are urethritis producing
agents. Ureaplasma urealyticum is associated with
acute dysuria while Candida and other fungi species
have frequently been isolated from the urine of
catheterized patients.
Epidemiology
The magnitude of the epidemiology of UTI can be
considered from two perspectives: catheter-associated
(nosocomial) and non-catheter associated (community acquired) infections. In both groups, UTIs can either be symptomatic or asymptomatic.
Community-acquired UTIs result in more than
7 million doctor’s office visits and 1 million hospital emergency department visits, resulting in
100,000 hospitalizations annually in the United
States. These visits involve about 1.2-3.2% of sexually active young girls. Acute symptomatic infection is common among young women, accounting
for about 0.9% infections per patient every year
among this category.
Asymptomatic bacteriuria is frequently reported
among elderly men and women with rates up to 50% in
some case studies. UTIs are uncommon in males under
the age of 50 years. However, the incidence of UTI in
men tends to rise after the age of 50 years. Among older
patients residing in nursing homes, UTIs are the most
common bacterial infection. UTIs are also the most
common reason for antimicrobial drug prescriptions.
About 20%-60% of antimicrobial drug treatments are
initiated among older patients in nursing homes.
The occurrence of not so complicated UTIs among
females who reside in the communities and who are between the ages of 18-49 years is about 28.2% among
every 10,000 women. Approximately 10% of adult
women in the United States have at least one UTI each
year. Nearly one in three women will experience UTI
by the age of 24, which requires antimicrobial therapy.
The incidence of UTI among hospitalized patients with
indwelling catheters is about 10.2-15.2%.The risk of infection is 3-5% per day of catheterization. Catheterized
urinary tract is found to facilitate Gram-negative bacteremia in about 1.2-2.3% cases of hospitalized patients
with indwelling catheters.
Risk Factors
Under certain special settings, an individual may
become predisposed to symptomatic or asymptomatic urinary tract infection. These special settings
include:
• Socio-economic status: UTI is prevalent among
individuals who belong to very low socio-economic
class.
• Pregnancy: UTIs are detected among 3-9% of
pregnant women. Twenty to 30 percent of pregnant
women with asymptomatic bacteriuria subsequently
develop pyelonephritis structural urinary tract abnormality.
• Obstruction to the free flow of urine: Any obstruction to the free flow of urine results in hydronephrosis which greatly increases the frequency of UTI.
Figure 1
A centrifuged mid-stream urine showing abnormal pyuria and
bacteriuria. More than 2-5 leukocytes (white blood cells) and rodshaped bacteria per high power field x400 is shown.
• Sexual behavorial practices: UTI is prevalent
among young schoolgirls and women who are sexually
active.
• Menopause: Post menopausal women have reduced natural estrogen levels which favors the colonization of uropathogenic Gram-negative bacilli.
• Vesicoureteral reflux: An anatomically impaired
vesicoureteral junction facilitates the reflux of bacteria,
hence, upper urinary tract infection.
• Genetic factors: Host genetic factors influence
susceptibility to UTIs. Women with maternal history of
UTI often experience recurrent UTIs.
• Bacterial virulence factors: Certain uropathogenic organisms like E.coli and Proteus specie have
fimbriae that mediate bacterial attachment to specific
receptors on epithelial cells. This stimulates UTIs.
• Diabetes: The presence of glucose in urine favors
the growth of glucose utilizing bacteria; women who
have hyperglycemia and poorly managed diabetes are at
risk of UTIs.
• Other special conditions under which UTIs may
be engendered include history of UTI relapse after
treatment, prior history of acute pyelonephritis, frequent
UTIs with symptoms longer than 7 days and neurogenic bladder dysfunction.
Diagnostic Testing
Laboratory evaluation of mid-stream urine specimen
or a sample from urethral catheterization is essential.
The mid-stream urine should be analyzed for nitrite and
leukocyte reactions, pyuria, bacteriuria and hematuria.
A positive urine nitrite strongly suggests the diagnosis
of UTI. A positive urine leukocyte esterase reaction
from pyuria is also a strong indicator. Abnormal pyuria
in women is defined as 2 to 5 leukocytes per high power
field from a centrifuged urine specimen. The presence
of 1 to 2 leukocytes per high power field from the centrifuged urine specimen of a man, accompanied by bacteriuria, is a strong indicator of UTls. Systemic leukopenia may produce a false negative urine leukocyte
Figure 2
Microscopic hematuria is seen in a centrifuged urine patient with
UTI. More than 5 red blood cells (RBCs) per high power field x400
is shown.
Continuing Education Topics & Issues • August 2012 89
Table 1. Clinical laboratory evaluation of mid-stream urine
esterase reaction. In women with Chlamydia UTls, bacteriuria may be absent. However, more than 15 bacteria
per oil immersion field in a centrifuged urine suggests
the diagnosis of UTI. In symptomatic patients, Gramstained uncentrifuged urine specimen should be microscopically evaluated. The detection of bacteria by urine
microscopy accompanied by colony count of 105 per ml
is an evidence of UTI. Asymptomatic bacteriuria is defined as a urine culture with more than 105 per ml of a
single bacterial specie in an asymptomatic patient. In
the urinalysis for hematuria, confirmatory microscopic
urine analysis should be performed since a false positive blood urine test strip reaction can occur due to the
presence of free hemoglobin, myoglobin, porphyrins or
providone-iodine in urine. More than 5 red blood cells
(RBC) per high power field in a centrifuged urine is one
of the indicators of UTI.
Treatment of UTI
Flouroquinolone therapy is a first-line treatment
choice since bacteria resistance is sometimes observed
when patients with UTI are treated with routinely used
antibiotics. Flouroquinolon, such as ciprofloxacin, levofloxacin or ofloxacine, can be used. Other routinely
used antibiotics include co-trimoxazole or trimethoprim, Amoxicillin/Clavulanate, amoxicillin, cephalexin
and nitrofurantoin.
Table 2. UTI recommended empirical treatment
Amoxicillan
90 August 2012 • Continuing Education Topics & Issues
References
1. Gulmifa et al. 2007. Upper urinary tract obstruction and trauma,
sections 36 and 37, in Campbell’s Urology, 9th ed, PC Walsh et al
(eds). Philadelphia, Saunders.
2. Guinto VT, De Guia B,Festin MR, Dowswll T. 2010. “Different
antibiotic regimens for treating asymptomatic bacteriuria in pregnancy”. Cochrane Database Syst Rev (9): CD 007855.
3. Gupta K, Houten TM, Stamm WE. 2001. Increasing antimicrobial resistance and the management of uncomplicated community-acquired urinary tract infections. Intem. Med. 135 :41-50.
4. Ramakrishnan K, Scheid DC. 2005. “Diagnosis and Management
of acute pyelonephritis in adults.” Am. Fam. Physician 71 (5):
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prevention of recurrent urinary tract infection in children: a systemic review and meta-analysis. Archives of desease in childhood
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(1): 21-8.
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R, Schaeffer, Anthony J, Stamm, Walter E, 1999. Guidelines for
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Cystitis and Acute Pyelonephritis in Women. Clinical Infectious
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Questions for STEP Participants
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1.
U.T.I may involve just the lower urinary tract.
A. True
B. False
6.
Sex is a major risk factor for U.T.I.
A. True
B. False
2.
The two major clinical features mostly
encountered in acute U.T.I are:
A. Urethritis and Cystitis
B. Cystitis and Pyelonephritis
C. Prostatitis and Dysuria
D. Cystitis and Prostatitis
7.
The most common fecal microbial flora
associated with U. T. I. is
A. Staphylococcus aureus
B. Klebsiella pneumonia
C. Entamoeba coli
D. Escherichia coli
3.
U.T.I. is indicated when a microorganism
growth of what number is isolated?
A. < 105 per milliliter
B. > 105 per milliliter
C. = 102 per milliliter
D. = 105 per milliliter
8.
Hydrogen peroxide-producing Lactobacilli
facilitates U.T.I.
A. True
B. False
9.
Which of the following special settings is not
associated with U.T.I.?
A. Virulence factor
B. Pregnancy
C. Abnormal urinary tract
D. Race
4.
5.
The most probable pathway for most renal
parenchymal infection is
A. Bladder via Ureter
B. Bladder via Urethra
C. Urethra via Urethra
D. Bladder via Loop of Henley
Asymptomatic U.T.I. is indicated when there
is
A. Colony count of less than 105 /ML of
single bacteria specie.
B. Colony count of more than 105 /ML of
single bacteria specie
C. Colony count of less than 105/ML of
mixed bacteria specie
D. Colony count of more than 105/ML of
mixed bacteria specie
10. In laboratory diagnostic testing, which of the
following suggests the diagnosis of U.T.I.?
A. 2-5 leukocytes per HPF
B. A positive nitrite
C. Less than 5 RBCs in an uncentrifuged
urine
D. Both A and B
Continuing Education Topics & Issues • August 2012 91