Transcript Urinary Tract Infections

Urinary Tract Infections
Sina Mobasherizadeh
Ph.D Candidate of Bacteriology
IUMS
Urinary tract infection
A urinary tract infection (UTI) is an infection that involves any of the
organs or structures of the urinary tract, including the kidneys, ureters,
bladder, and urethra.
Some of the common symptoms of a urinary tract infection are burning or
pain in the lower abdomen, fever, burning during urination, or an
increase in the frequency of urination.
UTIs are the most common type of healthcare-associated infection (HAI)
and are most often caused by the placement or presence of a catheter in
the urinary tract.
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Uncomplicated UTIs occur primarily in sexually active young women with
normal GU tracts and no prior instrumentation and are usually caused by
antibiotic-susceptible bacteria.
Complicated UTls occur in individuals who have one or more structural or
functional GU abnormalities or have indwelling catheters and whose conditions
cannot be controlled with therapy.
Bacteriuria, which can be symptomatic or asymptomatic, is the presence of
bacteria in the urine.
Asymptomatic bacteriuria (ASB) is the isolation of bacteria from the urine
insignificant quantities, but without GU signs or symptoms of infection. ASB
requires treatment only in some populations, such as pregnant women and
patients about to undergo instrumentation of the GU tract.
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Signs and Symptoms of Upper Urinary Tract Infection
• Fever and chills (systemic reaction)
• Flank pain
• Lower urinary tract signs and symptoms (frequency,
urgency, and dysuria)
Signs and Symptoms of Lower Urinary Tract Infection
• Frequent and painful urination of small volumes of turbid
urine
• Inflammatory irritation of urethral and bladder mucosa
• Occasional suprapubic pain or sensation of heaviness
• Fever generally absent
Catheter-associated urinary tract infection (CAUTI)
A catheter-associated urinary tract infection (CAUTI) are the most common
type of healthcare-associated infection, accounting for more than 30% of
infections reported by acute care hospitals.
CAUTIs have been associated with increased morbidity, mortality, healthcare
costs, and length of stay.
The risk of CAUTI can be reduced by ensuring that catheters are used only
when needed and removed as soon as possible; that catheters are placed using
proper aseptic technique.
The clinical significance of ASB in catheterized patients is undefined.
Approximately 75% to 90% of patients with ASB do not develop a systemic
inflammatory response or other signs or symptoms to suggest infection
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Epidemiology
Between 15% and 25% of hospitalized patients may receive short-term
indwelling urinary catheters. fewer than 5% of bacteriuric cases develop
bacteremia, CAUTI is the leading cause of secondary nosocomial bloodstream
infections; about 17% of hospital-acquired bacteremias are from a urinary
source, with an associated mortality of approximately 10%.
UTIs in kidney transplant recipients most often present as cystitis, however,
pyelonephritis may occur in almost 25% of them and can lead to allograft injury.
may be responsible for more than 50% of bacteremias in this population.
An estimated 17% to 69% of CAUTI may be preventable with recommended
infection control measures, which means that up to 380,000 infections and
9000 deaths related to CAUTI per year could be prevented.
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Pathogenesis and Microbiology
The source of microorganisms causing CAUTI can be endogenous, typically
via rectal, or vaginal colonization, or exogenous, such as via contaminated
hands of healthcare personnel or equipment.
The daily risk of bacteriuria with catheterization is 3% to 10%, approaching
100% after 30 days.
Formation of biofilms by urinary pathogens on the surface of the catheter
occurs universally with prolonged duration of catheterization.
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Microbiological agents
The most frequent pathogens associated with CAUTI (combining both ASB
and SUTI) in hospitals reporting to NHSN (National Healthcare Safety
Network)between 2006-2007 were :
Escherichia coli (21.4%) and Candida spp (21.0%),
followed by Enterococcus spp (14.9%), Pseudomonas aeruginosa (10.0%),
Klebsiella pneumoniae (7.7%), and Enterobacter spp (4.1%).
A smaller proportion was caused by other gram-negative bacteria and
Staphylococcus spp.
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Antimicrobial resistance
Antimicrobial resistance among urinary pathogens is an ever increasing
problem. About a quarter of E. coli isolates and one third of P. aeruginosa
isolates from CAUTI cases were fluoroquinolone-resistant.
Resistance of gram-negative pathogens to other agents, including
third-generation cephalosporins and carbapenems, was also considerable .
The proportion of organisms that were multidrug-resistant, defined by
non-susceptibility to all agents in 4 classes, was 4% of P. aeruginosa, 9% of
K. pneumoniae, and 21% of Acinetobacter baumannii.
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EPIDEMIOLOGY AND RISK FACTORS
Age
Pediatrics
Adults to Age 65
Geriatrics
Institutionalized Care
Pregnancy
Bladder Catheterization
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Pediatrics:
• During the neonatal period, about I% of all babies have bacteria in
bladder urine; the incidence is higher in boys, and bacteremia often is
present.
• Non circumcised males younger than 6 months of age have a 12-fold
increased risk of UTI compared with circumcised cohorts.
• Among preschool-aged children, girls develop UTIs more often than
boys, and infection frequently is associated with severe congenital
abnormalities. These infections are often asymptomatic.
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Adults to Age 65
the incidence of UTIs in men is extremely low.
Infections associated : with anatomic abnormalities or prostatic
disease and the consequent instrumentation, such as catheterization.
women :as many as one fifth experience a symptomatic UTI.
In terms of antibacterial activity, urine from men is more inhibitory
than urine from women because of the presence of prostatic fluids in
the urine of men, and the difference in pH and osmolarity.
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Geriatrics
The diagnosis and management of UTI in the geriatric population can be challenging.
Older adults frequently have an atypical clinical presentation including delirium, fevers
alone, or failure to thrive.
the incidence of UTIs increases dramatically for both genders, and the female to-male
ratio progressively declines.
The increased incidence of UTIs in men arises from obstructive uropathologic conditions
caused by the loss of the bactericidal activity of prostate secretions. In women, bladder
prolapse contributes to the occurrence of infection, as does soiling of the perineum
from fecal incontinence in women afflicted with dementia.
In both genders, neuromuscular disease and increased instrumentation and bladder
catheterization are contributing factors.
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Pregnancy
Pregnant women are at higher risk for UTI for several reasons.
Hormonal changes lead to changes in the ureter and urethra, making them more
susceptible to bacterial adherence and infection. The enlarging uterus can put
pressure on the bladder and impair urinary flow.
Asymptomatic bacteriuria in pregnant women should be treated because infection
can lead to premature labor.
Susceptibility testing is particularly important in this patient population because
not all antibiotics can be given to pregnant women.
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Specimen Collection
Preventing contamination by normal vaginal, perianal, and interior
urethral flora is the most important consideration in collecting a clinically
relevant urine specimen
The voided midstream collection, in which the patient collects the urine
specimen, is the most commonly used method in clinical practice. The
urine is contaminated with bacteria from the urethra unless the first
portion of the voided specimen is discarded.
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Catheterized Specimen Collection
When specimens are collected from an existing,
indwelling urinary catheter, the catheter collection port
should be cleaned with an alcohol pad and punctured
directly with a needle and syringe. The specimen should
never be collected from the drainage bag.
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straight catheter
Before collecting urine with a single, straight
catheter, the urethral opening or vaginal vault
is cleansed with a soap solution and rinsed
with sterile water.
Ileal Conduit
Samples obtained from an ileoconduit
are collected from the stoma opening after the
area has been swabbed with an alcohol wipe.
The urine on the external appliance is never
used for culture, because it is similar to the
urine in a drainage bag in patients with
indwelling catheters.
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Suprapubic Aspiration
Suprapubic aspiration is the definitive method for collecting uncontaminated
specimens.
Although most consider any organism isolated on these specimens to be clinically
significant, this may not be correct because transient colonization of the bladder
can occur.
Suprapubic aspirations are collected :
Infants
Patients in whom the interpretation of the results of voided specimens is difficult.
Anaerobic culture.
With the bladder full, the urine is collected with a needle and syringe following skin
antisepsis
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Specimen Transport
Urine is an excellent supportive medium for the growth of most uropathogens
and therefore must be immediately refrigerated or preserved.
Generally, urine should be refrigerated, received, and processed in the
laboratory within 2 hours.
Longer delays render examination for significant pyuria unreliable, and the
extremes of pH and urea concentration and the presence of antimicrobial
agents may adversely affect the recovery of uropathogens.
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MICROBIAL DETECTION
Microscopy
Uncentrifuged urine samples may be used for a stained smear.
The presence of one or more bacterial cells per oil immersion field in at least
five fields in a smear of uncentrifuged urine correlates with more than
100000CFU/mL.
If the uncentrifuged preparation tests negative, the sedimented preparation for
leukocyte examination should be stained.
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Detection of Pyuria
Detection of leukocytes may be performed by microscopic examination of a
wet mount of a urinary sediment resulting from centrifugation of 10 mL of a
specimen at 2000-2500 rpm on a tabletop centrifuge for 5 minutes.
At least five fields should be examined, and each leukocyte seen per highpower field (hpf) (40x) represents approximately 5 to 10 cells per cubic
millimeter of urine. In this way, 5 to 10 leukocytes/hpf in the sediment is the
upper limit of normal, representing 50 to 100cells/mm3
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Chemical Methods
WBC leukocyte esterase test
White blood cells in the urine usually indicate a urinary tract infection.
A positive leukocyte esterase test indicates the presence of granulocytic white blood cells.
Lymphocytes do not contain granules, and would not produce a positive leukocyte
esterase test.
False Positives:
•Females due to contamination of the specimen by vaginal discharge.
•The presence of strong oxidizing agents in the collection container.
•The presence of trichomonas and eosinophils.
False Negatives:
•The presence of significant levels of protein or glucose and in urines with high specific
gravity.
• The presence of ascorbic acid
•The presence of boric acid in the collection container.
• Some drugs such as Cephalexin ,Cephalothin, Tetracycline, or high concentrations of
oxalic acid.
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A nitrite test is a standard component of a urinary test strip.
A positive test for nitrites in the urine is called nitrituria.
A positive nitrite test indicates that the cause of the UTI is a gram egative organism,
most commonlyEscherichia coli.
False negative:
• nitrite tests in urinary tract infections occur in cases with a low colony forming
unit count, or in recently voided or dilute urine.
•The presence of high ascorbic acid
•PH< 6
• In addition, a nitrite test does not detect organisms unable to reduce nitrate to
nitrite, such as enterococci, staphylococci, or adenovirus
•False Positive
•Use of Phenazopyridine
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Rejection Criteria
Specimens may be rejected because of an inadequate or inappropriate
method of collection or transport.
Samples to be rejected include 24-hour urine specimens.
Antibiotic therapy may not have been initiated.
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LABORATORY DIAGNOSIS
Significance of Colony Counts:
Since 1956, the interpretation of quantitative urine cultures has been
considered one of the more straightforward and simpler laboratory tests to
diagnose UTls.
It was "dogma“ that a finding of 100,000 (105)colony-forming units per
milliliter
(CFU/mL) or more was a "positive" test result symbolizing
infection. hence the 105CFU/mL so-called "cut off" positive infection point.
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Culture for Etiologic Agents of Urinary Tract Infections
Generally, routine urine culture should include plating onto one selective
(e.g., MAC) and one nonselective medium.
Calibrated loops of 0.0 I mL should be used, not 0.00 I mL loops, because
quantitation is difficult to obtain with a low inoculum.
The urine specimen should be mixed thoroughly and the calibrated loop
should be inserted vertically; inserting the loop in a more horizontal position
may increase the volume beyond calibration; it should also be observed
visually for bubbles that would decrease the volume.
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