10. Urinary tract infection Flashcards
What is bacteriuria?
Presence of bacteria in the urine
Asymptomatic bacteriuria is NOT usually relevant. When is it relevant?
Asymptomatic bacteriuria with coliform is significant in PREGNANCY. It is associated with complications in the pregnancy. Therefore, it should be treated.
What is cystitis?
inflammation of the bladder, often caused by infection
What is an uncomplicated UTI?
Infection in a structurally and neurologically normal urinary tract
What is a complicated UTI?
Infection in a urinary tract with functional or structural abnormalities (including indwelling catheters and calculi). Groups of patients in which it is regarded a complicated UTI: Men, pregnant women, children, patients who are hospitalised or in healthcare-associated settings.
What is the prevalence of bacteriuria in young non-pregnant women?
1-3%
What percentage of the female population will experience a symptomatic urinary tract infection at some point during their life?
40-50% of the female population
What percentage of UTIs are caused by a single bacterial species?
95%
What is the most common infection organism in acute infection?
E. coli
What is a reason why E. coli causes UTIs?
These E. coli tend to have adherence factors that allow it to prevent being flushed out by the passage of urine
What other organisms cause UTIs?
Proteus mirabilis; Klebsiella aerogenes; Enterococcus faecalis; Staphylococcus saprophyticus; Staphylococcus epidermidis
Why does Staphylococcus saprophyticus cause UTIs?
Associated with infections in young women. Has virulence factors (P-fimbriae) that allow adherence to the epithelium
Is Staphylococcus saprophyticus coagulase negative or positive?
Coagulase negative
Which organism can cause UTI in the presence of prosthesis (e.g. procedures or long-term indwelling catheter)?
Staphylococcus epidermidis
What is the pathogenesis of UTIs caused by non-E.coli organisms?
In recurrent UTI, especially in the presence of structural abnormalities, the relative frequency of infection caused by non-E. coli organisms (Proteus, Pseudomonas, Klebsiella and Enterobacter and enterococci and staphylococci) increases greatly
What are antibacterial host defences in the urinary tract?
Urine (osmolality, pH, organic acids), urine flow and micturition, urinary tract mucosa (bactericidal activity, cytokines)
How does ascending UTI occur?
The urethra is colonised by bacteria, and the female urethra is short and close to the vulvar and perianal areas, making contamination likely. Organisms that cause UTI colonise the vaginal introitus and the periurethral area before the urinary infection manifests. Massage of the urethra and sexual intercourse can force bacteria into the female bladder. Once in the bladder, bacteria may multiply and pass up the ureters (especially in VUR) to the renal pelvis and parenchyma.
Why does obstruction cause UTIs?
Obstruction inhibits the normal flow of urine, and the resulting stasis is important in increasing susceptibility to infection
What are causes of mechanical obstruction, leading to UTIs?
Extrarenal: valves, stenosis or band; calculi; BPH. Intrarenal: Nephrocalcinosis; uric acid nephropathy; analgesic nephropathy; polycystic kidney disease; hypokalaemic nephropathy; and renal lesions of SCD
What are causes of neurogenic malfunction, leading to UTIs?
Poliomyelitis; tabes dorsalis; diabetic nephropathy; spinal cord injuries
What is a cause of reflux, leading to UTIs?
• Vesicoureteric Reflux (VUR) tends to perpetuate infection by maintaining a residual pool of infected urine in the bladder after voiding. The reflux can result in scarring of the kidneys.
How can UTIs occur via the haematogenous route?
Infrequent. The kidney is a frequent site of abscesses in patients with S. aureus bacteraemia or endocarditis. NOTE: S. aureus does NOT have appropriate virulence factors to cause ascending infection
What type of bacteria rarely causes UTIs via the haematogenous route, and more likely an ascending UTI?
In humans, infection of the kidney with Gram-negative bacilli rarely occurs by the haematogenous route. Seeing E. coli in the urine is much more likely to be due to ascending infection
Symptoms of UTI in neonates and children < 2 years?
NON-SPECIFIC: Failure to thrive, vomiting, fever
Symptoms of UTI in children > 2 years?
Frequency, dysuria, abdominal or flank pain
What are symptoms of lower UTIs, resulting from bacteria causing irritation of urethral and vesical mucosa?
This causes frequent and painful urination of small amounts of turbid urine. Suprapubic heaviness or pain. Occasionally, the urine may be grossly bloody or show a bloody tinge at the end of micturition. Fever tends to be ABSENT in infections that are confined to the lower urinary tract.
What are upper UTI symptoms?
Fever (sometimes with rigors); flank pain; lower urinary tract symptoms (frequency, urgency and dysuria); sometimes, the lower urinary tract symptoms may precede the upper urinary tract symptoms by 1-2 days; symptoms may vary greatly
What are symptoms of UTI in older patients?
Vast majority will be ASYMPTOMATIC. Symptoms, if present, are often NOT diagnostic because non-infected older patients often experience frequency, dysuria, hesitancy and incontinence. Symptoms of upper urinary tract infections are often atypical (e.g. abdominal pain, confusion)
Investigations for uncomplicated UTIs/pyelonephritis?
Urine dipstick; MSU for urine MC&S; bloods - FBC, U&E, CRP
What are further investigations for complicated UTI?
Renal USS and IV urography
In what case is no dipstick needed, and should you give empirical ABx treatment?
When there are 3 or more typical symptoms of UTI, no vaginal discharge or irritation and is 90% culture positive
Typical UTI symptoms?
Dysuria, urgency, frequency, polyuria, suprapubic tenderness, haematuria
What do leucocytes produce?
Leucocyte esterase
Why are nitrites very specific?
Because they are produced by E. coli. So positive nitrites is suggestive of coliforms being present in the urine
What shows that coliforms are present in urine?
Positive nitrites
What investigation results suggests a UTI caused by a non-coliform bacterium?
Nitrite-negative and leucocyte-positive
When should laboratory testing for culture and sensitivities be done?
Pregnancy, suspected UTI in children, suspected pyelonephritis, suspected UTI in men, catheterised patients, failed antibiotic treatment (resistance), abnormalities of the genitourinary tract, and renal impairment
Why is it important to get a midstream urine sample (MSU)?
Much more representative of what is going on in the bladder (first catch urine may be contaminated by urethral bacteria that has no part to play in the disease process)
What can killing normal bacteria by giving unnecessary antibiotics for UTI result in?
Thrush because yeasts are not affected by antibiotics
What urine culture result is indicative of infection?
White cells pyuria
What urine culture result is indicative of contamination?
Squamous epithelial cells
What urine culture results are usually diagnostic of UTI?
Culture of single organisms > 10^5 colony forming units (CFUs)/mL with urinary symptoms. Lower numbers are used for organisms that are typical of UTI (E. coli and S saprophyticus), where the cut-off is > 10^3 CFU/mL. (REMEMBER: a proportion of patients with both symptomatic and asymptomatic infection will have < 10^5 CFU/mL so always interpret the results in light of the clinical picture)
What urine culture result may represent inflammation?
White cells > 10^4/mL (or 10^7/L)
Some labs may screen the number of white cells in the urine before sending urine for culture. Who should this not be done in?
Immunocompromised patients, pregnant women or children. Pyuria is usually ABSENT in children.
What does mixed growth in a urine culture mean?
Mixed growth reduces the significance of culture (suggests contamination)
What do epithelial cells in a urine culture mean?
Epithelial cells present in high numbers in the sample also suggest that it is NOT an MSU, and suggest that the culture has been contaminated by lots of urethral organisms thereby reducing the significance of the culture
What could sterile pyuria (raised WCC but no growth on culture) in urine culture mean?
Consider Chlamydia trachomatis or other vaginal infections and other non-culturable organisms (e.g. TB).
What are causes of sterile pyuria?
Prior treatment with antibiotics (MOST COMMON), calculi, catheterisation, bladder neoplasm, TB, STI
Culture is done on chromogenic agar, what does this mean?
It turns different colours based on the bacteria that is grown
What is pink on chromogenic agar suggestive of?
E. coli
What is blue on chromogenic agar suggestive of?
Other coliforms
What is light blue on chromogenic agar suggestive of?
Gram-positives
What are methods of sampling?
MSU (best method), catheterisation (may introduce organisms), suprapubic aspiration (sometimes used in very young children)
What is empirical treatment?
Treatment given without knowledge of the cause or nature of the disorder and based on experience rather than logic. Sometimes urgency dictates empirical treatment, as when a dangerous infection by an unknown organism is treated with a broad-spectrum antibiotic while the results of bacterial culture and other tests are awaited.
What may infections with organisms producing ESBL be treated with?
OPAT (outpatient parenteral antimicrobial therapy).
What is the treatment for an uncomplicated lower UTI in a non-pregnant woman?
- local antibiotic guidelines should be followed if available
- NICE Clinical Knowledge Summaries recommend trimethoprim or nitrofurantoin for 3 days
- send a urine culture if:
aged > 65 years - visible or non-visible haematuria
What is the treatment for a lower UTI in a SYMPTOMATIC pregnant woman?
- if the pregnant woman is symptomatic:
a urine culture should be sent in all cases - should be treated with an antibiotic for
first-line: nitrofurantoin (should be avoided near term) - second-line: amoxicillin or cefalexin
- trimethoprim is teratogenic in the first trimester and should be avoided during pregnancy
What is the treatment for asymptomatic bacteriuria in pregnant woman?
- a urine culture should be performed routinely at the first antenatal visit
- Clinical Knowledge Summaries recommend an immediate antibiotic prescription of either nitrofurantoin (should be avoided near term), amoxicillin or cefalexin.
- This should be a 7-day course
- the rationale of treating asymptomatic bacteriuria is the significant risk of progression to acute pyelonephritis
- a further urine culture should be sent following completion of treatment as a test of cure
What is the treatment for UTI in men?
- an immediate antibiotic prescription should be offered for 7 days
- as with non-pregnant women, trimethoprim or nitrofurantoin should be offered first-line unless prostatitis is suspected
- NICE Clinical Knowledge Summaries state: ‘Referral to urology is not routinely required for men who have had one uncomplicated lower urinary tract infection (UTI).’
What is the treatment for UTI in catheterised patients?
- do not treat asymptomatic bacteria in catheterised patients
- if the patient is symptomatic they should be treated with an antibiotic
- a 7-day, rather than a 3-day course should be given
What is the treatment for patients with acute pyelonephritis?
- For patients with sign of acute pyelonephritis hospital admission should be considered
- local antibiotic guidelines should be followed if available
- the BNF currently recommends a broad-spectrum cephalosporin or a quinolone (for non-pregnant women) for 10-14 days
How do most Candida UTIs occur?
In patients with indwelling catheters
What is the treatment for fungal/Candida UTI?
- Removal of the catheter may result in cure
- Oral fluconazole is NO MORE EFFECTIVE than no therapy
- There is NO BENEFIT in the therapy of asymptomatic infection (so therapy is generally not recommended)
- There are exceptions
Therapy is generally not recommended in fungal UTIs. What are the exceptions?
Renal transplant patients, patients waiting to undergo elective urinary tract surgery. In these cases, attempts should be made to eliminate or suppress candiduria.
What are most cases of candiduria likely due to, rather than infection of the urinary tract?
Most cases of candiduria are due to vaginal thrush
What number of organisms are needed to infect the renal medulla and cortex?
Very few organisms are needed to infect the renal medulla. Many more organisms are needed to infect the cortex.
What is pyelonephritis associated with?
Commonly associated with sepsis and septicaemia?
What is the treatment for pyelonephritis?
Requires aggressive treatment. Broad-spectrum antibiotics. Co-amoxiclav with or without gentamicin. NOTE: ciprofloxacin is NOT used very often because it is associated with C. difficile and there is a lot of resistance.
What can you see in imaging in pyelonephritis?
Calculi, structural cause
What are complications of pyelonephritis?
Perinephric abscess, chronic pyelonephritis (scarring, chronic renal impairment), septic shock, acute papillary necrosis
What is prophylaxis for pyelonephritis?
ABx given prophylactically for UTI. This is controversial. Likely to promote resistance and have adverse effects.
