11
Urinary Tract Infections
SALT: November 2007
Dr Nizam DamaniMBBS, MSc, FRCPI, FRCPath, CIC, DipHIC
Consultant Microbiologist
Southern Health and Social Care Trust
UTI: Case 1
• A A A A 24 year24 year24 year24 year----old female calls her GP complaining of increased old female calls her GP complaining of increased old female calls her GP complaining of increased old female calls her GP complaining of increased
frequency & burning pain when urinating for last 2 days. frequency & burning pain when urinating for last 2 days. frequency & burning pain when urinating for last 2 days. frequency & burning pain when urinating for last 2 days.
• STD ?
• Pregnancy ?
• 1st episode ?
• Do a Urine dipstick ?
• Send Urine specimen to the Lab ?
• Advise on how to take proper MSU ?
• 104 cfu/ml ?
• Which antibiotic to prescribe ?
• Why ?
• Duration ?
UTI: Case 1
• 2nd episode?
• Previous culture ?
• Organisms ?
• Recurrent UTIs ?
• Any prophylaxis ?
• Which antibiotic ?
• Is it working ?
• Advice given on how to take prophylaxis ?
44
Case Study: Two
• 69 year old gentleman with enlarged prostate
• Catheterised for 10 months
• On waiting list for surgery
• Low dose prophylactic Ciprofloxacin
Day 1: Present complaints – 2 days history of feeling unwell.
– Nausea
– No fever
Dipstick result
– RBC ±
– WBC +++
– Nitrate : negative
55
Case Study: One
Day 2
• General condition worse• Febrile
• CSU specimen sent to the Lab. for Urine analysis
• GP contacted
• Advised to stop Ciprofloxacin and replace with Cephlaxin 250 mg TID
Day 4
• No real change ? Worse
• Developed rigor
• Phoned microbiology Lab : – Microscopy : RBC and WBC not seen
– Culture : Staph aureus ? MRSA
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Urine analysis: Which one to believe ?
Dipstick Microbiology Lab
RBC ± Not seen
Microscopy
WBC +++
Leukocyte esterase
Not seen
Microscopy
Nitrate Negative Staph. aureus
Culture
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Diagnosis of UTI: Microscopy
WBC 10/mm3 (Unspun MSU )
• ↓ if WBC are lysed during transport
• Febrile children often have pyuria in absence of
UTI
• Pyuria is less strongly correlated with UTI in
catheterized patients
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Dipsticks : WBC
• Leukocyte esterase in WBC
• Detect both intact and lysed WBCs
• Must be combined with Nitrate testing
• False Positive:
– Specimen with vaginal secretion
– Decreased sensitivity• Cephalexin, oxalic acid ( iced tea drinkers)
• High glucose, high specific gravity
• Albumin & ascorbic acid inhibit this method
99
Dipstick : WBC
• False Negative
– Neutropaenia
Poor predictor of positive Urine culture
• Leukocytes esterase to detect > 10 WBC
~ 75-95% sensitivity
~ 65-95% specificity
1010
Organisms of UTI (%)
Organism Community Hospital
Esch coli 80-90 45-55
Proteus 5-8 10-12
Klebsiella 1-2 15-20
Entero/citro 2-5
Pseudomonas 10-15
Acinetobacter < 1
Coag -ve staph 1-2 1-2
Staph aureus < 1
Enterococci < 1 10-12
In patients with indwelling catheters,
infections are frequently polymicrobial and
multi-resistant
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Kass Criteria
• Study in asymptomatic female
• First morning Mid Stream Urine specimen
• Positive predictive value for MSU – 80% for one specimen & 95% for two specimens :
• 20 % of women and 10 % of men > 65 years have significant bacteriuria
_______________________________________________
• Transported within 2 -4 hours11 or refrigerate at 4ºC
• Use ice box during transportation
• Boric acid ( 0.1g/10ml ) can be used as a preservative to inhibit bacterial growth
• Lower count if not first-morning MSU
1212
Significant growth: Kass criteria
Urine specimens are almost
inevitably
contaminated during collection
1313
Diagnosis of UTI: Culture
Culture ● 105 cfu/ml for MSU only
● Candida infections: 104 cfu/ml
● 102 - 103 for CSU cfu/ml obtained
from urine collected with a needle from
the sampling port of the catheter
Not for ● Suprapubic specimen in non-
catheterised patient
● Urine obtained during cystoscopy
1414
Dipstick : Nitrite testing
• Need enzyme reductase to convert Nitrate to Nitrite
• Absent if the infection is caused by the following organisms as they don't contain reductase to convert nitrate to nitrite. : – Enterococci spp,
– Streptococci spp
– Staphylococci spp eg Staph saprophyticus
– Neisseria gonorrhoeae
– M Tuberculosis
• Urine has to be in the bladder for 4 hours so that adequate reduction of nitrate can occur
• Obstetric patients: detect only 50% of patients with asymptomatic UTI
• Moderate sensitivity & specificity
• Catheterised patients may have polymicrobial infection
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Dipstick : Nitrite testing
• False negative
– Dipstick stored in an ambient humidity
– Storage of sample at Room temp for > 2 hours
( reduce nitrite to Nitrogen)
1616
Dipstick for MSU: Bottom line
• Dipsticks ( leucocytes esterase & nitrate)
– Highly specific: Negative predictive value of 90%-100%
– Low sensitivity: Positive predictive value of 30%.
– Must not use in pregnancy & younger children to detect
asymptomatic bacteriuria
– Not a replacement for microscopy & culture
Treatment of UTI
• Recommended therapy for uncomplicated UTI– Trimethoprim 200 g BD for 3 days
– Nitrofurantoin 100 mg QID for 3 days
• Single dose therapy: high failure rate (12%-35%)
• 14 days for Pyelonephritis
• Lab reports higher rate of resistance due to :– Selected patients who have received antibiotic therapy for
• Recurrent UTI
• CSU specimen from Catheterized Patients
• Multiple specimens from same patients
• Higher clinical cure rate due↑ concentration of antibiotic in bladder
• Encourage fluid intake
Recurrent UTI
• Two or more episodes of urinary tract infection with
acute pyelonephritis or upper urinary tract infection
• One episode of urinary tract infection with acute
pyelonephritis or upper urinary tract infection plus
one or more episodes of urinary tract infection with
cystitis or lower urinary tract infection
• Three or more episodes of urinary tract infection
with cystitis or lower urinary tract infection
NICE Guidelines, 2007
1919
Bacteriuria in catheterized patient
• Incidence of bacteriuria in patients with indwelling catheter :
– Average daily risk : 5 % (range 3 -10 %)
– 2- 10 days : 25 %
– 30 days : 100 % patients are bacteriuric
– Develop bacteraemia : 1-4 %
Urinary catheter interferes with normal defences, allows attachment & colonization of microorganisms
2020
Risk factors associated with development of UTIs
in catheterized patients
• Increasing duration of catheterization
– Avoid catheterization, if possible
– Remove when it is no longer needed
– ‘Method of last resort ‘ NICE guideline, 2003
• Faulty aseptic management
– Strict asepsis during insertion and maintenance is
essential
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Formation of Biofilm
• Antibiotic is not effective in presence of
biofilm because:
– microorganisms are embedded in the
biofilm grow slower therefore they have
reduced uptake of antimicrobial agents
– biofilms may also escape the protective
action of phagocytes
– Presence of foreign body may initiate gene
activation which increases antibiotic
resistance
Saint S, Biofilms and catheter-associated urinary tract infections.
Infectious Disease Clinics of North America. 2003;17(2):411-32
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Antibiotic treatment
• Treat patient and not the Laboratory report !
• Asymptomatic colonisation does not warrant treatment
• Choice of antibiotic depends on the susceptibility testing; difficult if infection is polymicrobial
• Recommended duration : 7-10 days
• Because of presence of biofilm, treatment will work best if catheter removed
• Removal of catheter may be necessary if the catheter is in placefor > 1 week.
• Candiduria usually resolves without treatment if the catheter can be removed
• Don’t perform bladder wash out or put antiseptic in the urinary bag
• Strict aseptic technique during insertion and maintenance and keep system closed !
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Prophylactic antibiotics
• Routine use of prophylactic antibiotics in catheterized patients is notrecommended because of – Cost
– Adverse effects
– Selection of antibiotic-resistant organisms
– Bacteriuria will develop resistance regardless of antibiotic therapy
• Removal of a catheter in presence of infection can cause bacteraemia. – Antibiotic prophylaxis is recommended for
• Instrumentation or surgery on Urinary tract
• Previous history of CA-UTI
• Heart valve replacement
• Septal defect
• Patent ductus arteriosus
• Prosthetic valve
• ? other conditions
2424
Bottom line
Bacteriuria Symptoms Treatment
+ No No
+ YesPresence of fever, urgency,
frequency, dysuria or suprapubic
tenderness.
YesAntibiotics are unable to penetrate biofilm
to eradicate microorganisms; removal of
catheter may be necessary if the catheter
is in place for > 1 week.
Routine use of prophylactic antibiotics
in catheterized patients is not recommended