Asymptomatic bacteriuria in the elderly

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:– Sensitivity:48-86%– Specificity: 17-86%– PPV: 0.38– NPV: 0.93

• NPV and PPV value in the general population with pre-test probability of 0.15 (prevalence)

• 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

bacteriuric– 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

disconfort– 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