Asymptomatic bacteriuria

Asymptomatic bacteriuria in the
Dr Grace Sluga
Consultant Microbiologist
Urine dipstick
• Leucocyte esterease
– Detects the presence of pyuria in the urine
• False positives with vaginal secretions, nephrolithiasis, bladder
tumours, corticosteroids, etc…
• Nitrites
– Detect the presence of bacteria (Enterobacteriaceae and
some gram positive organisms, which converts urinary
nitrate in nitrite) – Does not distinguish asymptomatic
bacteriuria from symptomatic UTI
• False positive with contamination, exposure to the air
• false negatives with bacteria that dose not reduce nitrates
(Enterococcus spp and Streptococcus spp) and low dietary nitrates
Value of urine dipstick analysis
• Abnormal leucocytes:
Specificity: 17-86%
PPV: 0.38
NPV: 0.93
• NPV and PPV value in the
general population with
pre-test probability of 0.15
• Abnormal nitrates
Sensitivity: 45-60%
Specificity: 85-98%
PPV: 0.41
NPV: 0.92
The urine dipstick test useful to rule out
infections. A meta-analysis of the
accuracy BMC Urol 2004
Value of urine dipstick analysis
• Do not do routine urine dipstick: lack
specificity for UTI
• Use urine dipstick to rule out UTI in patient
with unclear symptoms/signs: high negative
predictive value
• However, a positive dipstick requires further
evaluation and does not rule in UTI
Asymptomatic bacteriuria
• Definitions:
– Significant number of bacteria in a urine culture: >10^5
CFU with no symptoms of UTI
– Regardless of the presence of WBCs in the urine
• Microbiology is similar to that of symptomatic UTI
and pyelonephritis
• But subtle changes in the organism pathogenicity
factors may predispose to asymptomatic bladder
colonisation rather than infection (eg: lack of fimbria
in E coli)
Prevalence of asymptomatic bacteriuria in selected populations.
Nicolle L E et al. Clin Infect Dis. 2005;40:643-654
© 2005 by the Infectious Diseases Society of America
Randomized clinical trials of treatment of asymptomatic bacteriuria in elderly populations.
Nicolle L E et al. Clin Infect Dis. 2005;40:643-654
© 2005 by the Infectious Diseases Society of America
Asymptomatic bacteriuria
• Very common – do not treat
• Treatment:
– Does not significantly reduce the risk of
symptomatic UTI
– Does not decrease mortality
– Does not improve continence
– Increase risk of drug adverse events and
antimicrobial resistance
Asymptomatic bacteriuria
• Best prevention: do not send urine samples
unless patient have symptoms of UTI
(frequency, dysuria, suprapubic pain) or
evidence of systemic infection
• Screening or treatment for asymptomatic
bacteriuria is never indicated unless:
– Patient is pregnant
– Patient is undergoing a urological procedure
where mucosal bleeding is anticipated
Catheter specimen urines: THE STATS
– Incidence of bacteriuria in CSU: 3-8% per day
– By 1 month: nearly 100% with CSU will be
– Around 90% of patients with CA-bacteriuria are
asymptomatic and apyrexial
– Bacteraemia complicates <1% of CA-bacteriura
– Virtually all patients with long term catheter will
have positive urine dipstick
CA-bacteriuria: when to treat
• Symptoms of UTI in catheterised patients:
– New costovertebral angle tenderness or loin pain or pelvic
– Fever >38 or 1.5C above baseline on two occasions during
12 hours.
– New onset delirium
– Acute, unexplained haematuria
» IDSA/NICE/SIGN guidelines
• Peripheral high WBC: low predictive value for
diagnosing CA-UTI
Antimicrobial resistance data
• All urine samples sent from 1 January 2013 to
31 March 2013
• Source: GPs and MTW patients
• 5319 positive urine samples
– E coli: 83%
– Klebsiella spp: 7.8%
– Proteus spp: 5.6%
– Serratia/enterobacter/citrobacter group: 3%
Antimicrobial resistance data
33% - Resistant to trimethoprim
21% - Resistant to nitrofurantoin
14% - Resistant to co-amoxiclav
5.5% - Resistant to gentamicin
Limitations of the data:
– Data from last year – new data being collected
– Data may be skewed as urine from straighforward,
unclomplicated cases may not be sent and
samples include hospitalised patients
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