Urinary Tract Infections

Urinary Tract Infections

Investigations

·        Dipstick: Under-rated

o  Nitrites (produced by an enzyme in most infectious bacteria which breaks nitrates down to nitrites) Þ presumptive diagnosis

o  If no leukocytes, nitrates, protein or blood then no infection. Ie high negative predictive value. Positive predictive value only about 30 – 40%

o  Culture should be done (ie not just dipstick) in pregnancy, diabetics, atypical presentations recurrent attacks and non-response to treatment

·        Urine Microscopy:

o  Some RBC and WBCs are normal

o  Look for casts, crystals, bacteria.  Absence of bacteria not significant (treat empirically)

o  If RBC > WBC then ?stone

·        Culture:

·        Bacteruria Þ 10E5 colony forming units (cfu) per ml of urine. However, this was set using morning samples in young women via catheterisation Þ not much value.

o   In kids, a much smaller number may be significant, especially if:

§  In a boy

§  Obtained by catheter.  In a supra-pubic aspirate any growth is important

o   Most UTIs are caused by a single bug. If multiple organisms then contaminated sample. Bugs can grow in transit ® send to lab straight away or refrigerate

o   Antibiotic sensitivity: if multi-resistant then usually from Asia where antibiotics are freely available

·        Haematuria in 50% - but if asymptomatic ® ?bladder carcinoma

·        Intravenous pyleogram / urogram (same thing)

Microbiology

·        Hospital acquired are more antibiotic resistant

·        Pathogenesis: bacterial adherence

o   Uropathic strains: fimbriae – microbial adhesions. Different types in different bugs, and different densities of receptors in hosts ® genetic predisposition

o   Catheter adhering strains:

§  Tightly adherent ® none grown from urine

§  Thick layer of „biofilm‟ forms in lumen of catheter containing bugs. Antibiotics can‟t penetrate Þ change catheter

§  Risk factors: ­ duration of use (but regular changing makes it worse), female sex, absence of systemic antibiotics, catheter care violations

§  Prevention: avoid catheterisation, lots of fluid, alternative method for bladder drainage (eg condom catheter), closed, sterile bladder drainage, appropriate aseptic technique at insertion

Adults

·        Epidemiology:

o   More common in women, older people, and long term care

o   20% in women 65 – 75, 3% of men

·        Definition: Lots of terms with subtle variations in meaning: UTI, bacteruria, bladder bacteruria, asymptomatic, etc, etc

·        Presentation:

o   Acute symptomatic urinary infection = urgency, frequency and dysuria (pain on urination). NB urgency and frequency may be unrelated to infection (eg bladder instability)

o   In elderly may present atypically: delirium, falls, immobility

o   Cloudy urine, dark urine (volume depletion), and smelly urine are all normal! 

o   Asymptomatic bacteruria = 2 consecutive positive cultures without symptoms attributable to the urinary tract

·        Classification:

o   Uncomplicated: normal urinary tract and normal renal function

o   Complicated if:

§  Abnormal urinary tract: eg calculi, reflux, obstruction, paraplegia, catheter, prostatitis, etc

§  Impaired host defences: immunosuppressed, diabetes, etc

§  Impaired renal function

§  Virulent organism (eg Proteus)

§  Male

·        Causes of dysuria:

o   Urinary tract infection +/- vaginitis

o   Vaginitis (Candida albicans, trichomonas vaginalis, gardnerella vaginalis)

o   STDs

o   Other: trauma, urethral syndrome

·        Treatment:

o   Oral trimethoprim in uncomplicated infections.  ­E coli resistance ® will need to change this soon

o  Oral quinolones are the main second line agents (eg norfloxacine)

o  Don’t treat asymptomatic positive urine cultures (ie don‟t test unless symptoms) unless diabetic or pregnant

o  Single dose therapy is worse than conventional therapy (7 – 10 days). For adult women, single does therapy has an odds ratio compared to conventional treatment (5 days or more) of 0.7 for TMP/SMZ (trimethoprim/sulphamethoxazole), and 0.4 for amoxycillin

o  Short course possibly as effective as conventional (watch this space)

·        Complications: Ascending infection ® renal scarring ® hypertension, etc

·        Prophylaxis: 

o  Consider if recurrent infections, eg low dose nightly antibiotics for 3 – 6 months, post-coital antibiotics

o  Bladder emptying at night and after intercourse

o  Topical oestrogen cream if post-menopausal

o  Adequate fluid intake (> 2 litres per day)

·        Men:

o  If unknown cause - ?referral to urologist for kidney scan (e.g. stone)

o  Always do urine culture in addition to antibiotics

o  Do swab if discharge

Urethral syndrome

·        No bacteria isolatable

·        Can be chlamydia (need to do right test)

·        Can become very sensitive after a number of infections (general inflammation) 

·        Acidic urine will hurt more if inflamed ® drink lots (dilute urine) and Uracil

·        More common in older women

UTIs in Children

·        Epidemiology:

o  UTI is common:

§  Males usually have them in their first year, for girls it‟s on going

§  By age 7, 9% of girls and 2% of boys will have had at least one episode 

o  Caused by E coli in over 80% of cases. Others are associated with complicated UTIs or long term antibiotic therapy (eg Candida)

o  Of 1000 kids with UTI: 

§  400 have vesico-ureteric reflux, 100 have renal scars, 10 will develop premature hypertension (eg in older childhood or pregnancy), end stage renal failure in 1 

§  10 – 20 will have obstruction due to urethral valves, VU or PUJ obstruction

§  Greatest risk usually kids < 4 and especially in first year of life

·        Risk Factors for UTI:

o  Previous infection

o  Normal anatomy but functional problem: e.g. vesico-urethral reflux (in child, sibling or parent) 

o  Structural abnormality: e.g. urethral stenosis/stricture (more common in boys – congenital, trauma or inflammation)

o  Vulvoanitis from poor perineal hygiene

o  Incomplete or infrequent voiding

o  In first year of life, uncircumcised male is 10 times that of circumcised 

o  Sexual abuse: only 2% of patients investigated for sexual abuse have UTI as a symptom. UTI without other indications (lesions, bleeding, bruising) is very unlikely to be sexual abuse 

o  Antibiotics: disrupt normal peri-urethral flora ® predispose to infection

o  Constipation a risk factor: ask about this

o  Indwelling catheter

·        Risk factors for VUR:

o  Children with UTI (30 – 40%)

o  Siblings affected

o  Antenatal dilation of the urinary tract (8 – 22%) 

o  No evidence that prophylaxis ® ¯renal scars (controversial)

·        Always have appendicitis as differential diagnosis: can have white cells in urine with appendicitis where appendix is in the pelvis (or elsewhere)

·        Symptoms are highly variable:

o   0 – 2: Fever/hypothermia (?sepsis), lethargy, poor feeding, diarrhoea, vomiting, abdominal distension, failure to thrive

o   2 – 5: fever, rigours, vomiting, diarrhoea, colic, abdominal pain, some dysuria, offensive urine, haematuria, weak urine stream

o   5 – 12: fever, rigours, abdominal pain (Þ upper tract infection), dysuria, frequency, urgency, incontinence, haematuria

o   If systemic illness then ­ likelihood of pyelonephritis as well as cystitis. If under one, can have Pyelonephritis without systemic signs ® if UTI under age 1 then presume Pyelonephritis

·        Diagnosis:

o   Urine bag:

§  Wash genitalia before application 

§  Test with urine dipstick. If positive, obtain definitive sample with catheter or supra-pubic aspiration (SPA)

§  Do not routinely send bag specimens for culture. Boys have 93% false positive

o   Catheter: 

§  For children who can‟t void on request and where the bladder is in the pelvis (SPA won‟t work)

§  Uncomfortable.  Discard first few mls

§  Growth > 10E6/litre suggest infection

o   Supra-pubic aspirate:

§  If child too young to obtain an MSU 

§  Gold standard: any growth suggests infection (but beware contamination with skin commensals)

o   MSU: discard first few mls

·        Exam:

o   Often normal, other than fever 

o   Do blood pressure, search for loin, abdominal and supra-pubic tenderness, inspect spine and external genitalia, and brief neuro exam of the lower limbs. Check and plot growth

·        Management:

o   Admitted for IV antibiotics if:

§  Neonate or immunocompromised

§  Shocked

§  Vomiting frequently (ie oral antibiotics won‟t stay down)

o   Hospital treatment:

§  Bloods: FBC, blood cultures, electrolytes and Cr.  If toxic, consider LP and glucose 

§  Antibiotics: Amoxycillin 50 mg/kg/6hr (max 2g) (for enterococcus) and gentamicin 2.5 mg/kg/8hr (if older than 1 week and normal renal function) to cover everything else. 

§  Discharge on oral antibiotics to take total treatment to 10 – 14 days. Then prophylaxis until follow-up

§  Repeat urines to check it‟s cleared

§  Follow-up: 

·        US within, say, 12 hours: checking for obstruction and kidney size. Poor sensitivity for reflux 

·        If < 2 years then MCU (Miturocysto-urethrogram, for reflux ® risk of scarring) + delayed DMSA scan (eg after 6 months, look for filling defects ® renal scarring) 

·        If > 2 years then delayed DMSA

§  If reflux, then prophylactic antibiotics until out of nappies and 6 months since last UTI

o   Oral Antibiotic treatment:

§  Don‟t give antibiotics unless a definitive urine specimen has been obtained

§  Antibiotics standard treatment: 

·        Cotrimoxazole 200/40mg in 5 ml, 0.5 ml/kg bd 5 days (= trimethoprim + sulphamethoxazole – less concern about allergy in kids),

·        Amoxycillin 15 mg/kg tds po (max 500 mg) for 5 days

·        Augmentin 15 mg/kg tds po (max 500 mg) for 5 days 

§  Prophylaxis in children with recurrent infection is common – but duration, drug and dose all remain variable. Cotrimoxazole 200/40mg in 5 ml, 0.25 ml/kg po od

·        Repeat urines at conclusion of antibiotics to check it‟s cleared

·        Referral to urologist:

o   Boys: always refer for confirmed UTI, especially if circumcised

o   Girls: At least repeat urines after first UTI to check cleared.  Refer after second UTI