Urinary Tract Infections

This is a general term which describes a bacterial infection anywhere of the urinary tract.

– It is usually caused by an infection which arises from the enteric bacteria in the gut.

– It is also classified as uncomplicated (normal renal structure/function) or complicated (producing a structural/functional abnormality of urinary tract)


Risk factors:

– Decreased urine flow –> due to dehydration, or obstructions within the urinary tract

– Increased bacterial entry –> due to sexual intercourse, incontinence

– Higher bacterial growth –> due to diabetes, immunosuppression + catheter + pregnancy

– Female –> they have a less vertical urethra making bacterial travel easier



Although we can use diagnostic tests, in non-pregnant women, if they have >3 symptoms of cystitis and no vaginal discharge, treat without further tests using a clinical diagnosis:

– Urine dipstick –> Gives cloudy urine (pyuria = pus in urine) + positive leukocyte esterase and nitrites

– MSU culture –> threshold value is > 10^5 colony forming units/ml. This is the gold standard test

– Blood tests –> FBC, U&E and blood culture

– Ultrasound –> can be used in people with upper UTI and those who do not respond to treatment.


N.B. You can get sterile pyuria = Pus (WBC and enzymes in urine) but a negative urine culture:

– Commonly due to Urinary tract TB –> Gives dysuria, frequency and pain but negative culture.

Also due to appendicitis or urethritis due to Chlamydia trachomatis or Neisseria Gonorrhea


Urinary tract infections can be subdivided into lower and upper UTI which share similarities, but also different symptoms:

Cystitis (lower UTI)

This is an infection of the bladder which is normally due to E. Coli bacteria. 


– Usually due to Gram-negative bacteria from bowel and vaginal flora. Most common = E. coli

– Staphylococcus saprophyticus –> skin commensal bacteria which gives higher incidence in

young, sexually active women

– Proteus mirabilis –> gives alkaline urine with ammonia smell


– Triad of dysuria (pain urinating) + frequency + urgency

– Suprapubic pain + pungent urine smell

– But systemic signs like fever/vomiting are usually absent


Nitrofurantoin or Trimethoprim


Acute Pyelonephritis (upper UTI)

This is an infection of the kidney. Similarly to cystitis, it is usually due to an enteric infection which rises up the tract.

– Therefore, a significant risk factor for developing pyelonephritis is vesicoureteral reflux, which is more apparent in young boys.



E. Coli (90%) + Enterococcus faecalis + Klebsiella



– All symptoms of cystitis but also vomiting and fever

Also presents with flank pain + fever

Hallmark is finding white cell casts in the urine



Broad spectrum cephalosporin or quinolone (Ciprofloxacin) for 10-14 days


N.B. If you have repeated UTIs, this eventually causes gives interstitial fibrosis and atrophy of tubules

– The atrophic tubules will start to resemble thyroid follicles histologically, so it is called thyroidization of the kidney.

NICE Referral Guidelines

Urgent (2 weeks):

if Age > 45 AND visible hematuria (without UTI or persistent/recurrent after UTI)

if Age > 60 and nonvisible hematuria AND dysuria or raised WCC

Non-urgent referral:

if Age > 60 with recurrent/persistent UTI