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 ?

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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

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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

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Dipstick : WBC

• False Negative

– Neutropaenia

Poor predictor of positive Urine culture

• Leukocytes esterase to detect > 10 WBC

~ 75-95% sensitivity

~ 65-95% specificity

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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

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Significant growth: Kass criteria

Urine specimens are almost

inevitably

contaminated during collection

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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

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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)

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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

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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

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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

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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