UTI (urinary tract infection) covers a spectrum of illness from asymptomatic bacteriuria to acute pyelonephritis with septic shock. Cystitis describes a superficial mucosal infection confined to the lower urinary tract. Acute pyelonephritis is due to infection and inflammation of the renal parenchyma. Chronic pyelonephritis is a histological pattern of diffuse interstitial inflammation which may be due to many causes, some of them infective. It may follow acute pyelonephritis in childhood, particularly in association with vesicoureteral reflux.
Urinary tract infection may be usefully classified into uncomplicated (acute cystitis in females) and complicated (urinary tract infection with acute pyelonephritis in females, all urinary tract infections in males). Special cases include children, urinary tract infection during pregnancy and catheter-associated infections.
Community-acquired urinary tract infection usually occurs by ascending infection following colonization of the vagina, periurethral area and anterior urethra by uropathogenic bacteria.
Risk factors: Vary with age:
• Neonates-1 yr: Functional or anatomical abnormalities (e.g. congenital stenosis, urethral valves).
1-15 yrs: Infection more common in girls, particularly associated with vesicoureteral reflux. Infection during first 5yrs is associated with vesicoureteral reflux or congenital abnormalities and may give rise to renal scarring and subsequent risk of chronic pyelonephritis.
16-35 yrs: Risk of infection increases in females, associated with sexual intercourse. Diaphragm and spermicide use convey higher risk.
• After 35 yrs the sex incidence starts to equalize — risk factors include gynaecological surgery and bladder prolapse in women, prostatic hypertrophy and chronic prostatitis in men and stones, tumours and catheter use in both sexes.
• Prolonged recumbency, catheter use, dehydration and antibiotic use, which promote introital colonization and cross-infection by uropathogenic strains, increase the risk of urinary tract infection for hospital in-patients.
urinary tract infection is normally prevented by mucosal defences (e.g. secreted proteins which prevent bacterial adhesion), the composition of the urine (low pH, high urea, high osmolarity) and mechanical factors (e.g. regular complete emptying of the bladder).
Clinical features: Adults: Dysuria, urgency, frequency, low-grade fever, suprapubic discomfort and cloudy, bloodstained urine. Flank pain and tenderness with rigors and vomiting suggest acute pyelonephritis, but lack of these clinical features does not reliably exclude it. Young children present more non-specifically with fever, abdominal pain, vomiting and poor feeding. Infection in neonates presents as failure to thrive, vomiting, fever and jaundice and is frequently associated with bacteraemia. Urinary tract infection in the elderly is common and may present non-specifically with nocturia, incontinence and confusion.
Organisms: Escherichia coli (80%) — a limited range of E. coli serogroups which have surface molecules that allow them to adhere to urinary tract epithelium (‘adhesins’) are ‘uropathogenic’ accounting for most urinary tract infections (>278). Other coliforms such as Klebsiella spp., Proteus spp., Enterobacter spp. are isolated less often, but are more likely to be antibiotic-resistant. Staphylococcus saprophyticus is a relatively common cause of uncomplicated urinary tract infection in young women. Hospital infections (particularly catheter-associated or in patients on antibiotics) are associated with a wider range of organisms, including Pseudomonas aeruginosa, Staphylococcus epidermidis, yeasts and Enterococcus spp. Staphylococcus aureus bacteriuria may follow haematogenous seeding of the kidney from infection elsewhere. Adenovirus infection is a rare cause of epidemic haemorrhagic cystitis in children.
Microbiological investigations: It is good practice to send a mid-stream urine for microscopy and culture in all patients before starting therapy. Some question the cost-effectiveness of this in uncomplicated urinary tract infection, but it allows monitoring of antibiotic resistance rates. Dipstixhave ahigh false-negative rate and are not cost- or clinically effective. Interpreting the results of mid-stream urine: Epithelial cells suggest contamination of the specimen by skin organisms. Pus cells are usually present in urinary tract infection. Their absence favours contamination. Pyuria without bacterial growth may be due to previous antibiotics, tumour, stones, urethritis or tuberculosis. A bacterial count of >105 organisms/mL is considered to indicate urinary tract infection, but many patients with clinical evidence of infection have lower counts. Some authorities consider counts over 102 organisms/mL significant if they represent a pure growth of a known urinary pathogen, but few laboratories culture to detect this low level. Suprapubic puncture is rarely used, but is useful if an aseptically taken specimen is essential. Blood cultures should be taken if systemic infection is a possibility. Chlamydial infection may need to be excluded (>87).
Other investigations: Urological assessment (ultrasound scan, in the first instance, followed by IVP) for stones, tumours and anatomical abnormalities should be carried out in recurrent uncomplicated urinary tract infection, all complicated urinary tract infections and in all males, children and infants. Rectal examination is required in men.
Differential diagnosis: Urethritis is suggested by pyuria without bacteriuria. Historical clues include a change in sexual partner, gradual onset of relatively mild dysuria, urethral or vaginal discharge and associated cervicitis (>87). Candidal or bacterial vaginitis and genital herpes often cause burning ‘external’ dysuria. Genitourinary tuberculosis should be considered, especially in the elderly and in immigrants.
Antibiotic management: All symptomatic urinary tract infections should be treated. For uncomplicated urinary tract infection, a large range of oral antibiotics is available: trimethoprim, co-amoxiclav, oral cephalosporin (e.g. cephalexin) norfloxacin or ciprofloxacin. Amoxicillin is less suitable due to =50% resistance rates. Single-dose oral therapy with co-amoxiclav (500/125 mg), norfloxacin (400 mg) or trimethoprim (400 mg) is slightly less effective than treatment for 7 days, but has a lower incidence of side effects. Three-day treatment regimens are as effective as 7-day schedules, with no more side effects than single-dose oral therapy, and are recommended for uncomplicated urinary tract infection when there is no suggestion of upper tract involvement, or complication such as pregnancy. Short-course therapy is not suitable for children. For complicated urinary tract infection, 7-14 days’ treatment is recommended (acute pyelonephritis: 14 days). In severe illness, intravenous therapy is required initially. Amoxicillin + gentamicin or co-amoxiclav or cefotaxime or ciprofloxacin are all suitable whilst awaiting the results of urine and blood cultures. All empirical regimens should be based on local contemporary resistance data.
Supportive management: Patients should drink as much fluid as possible. Intravenous rehydration may be necessary particularly if vomiting is a prominent symptom. Urinary obstruction is the most common cause of treatment failure and will require surgery or nephrostomy. In hyperglycaemic diabetics, fermentation of glucose by coliforms can produce gas in the renal parenchyma (emphysematous pyelonephritis). Less severe cases may be managed medically, but surgery, including nephrectomy, may be required.
Complications: Renal abscess, bacteraemia with sepsis syndrome.
The prevalence of asymptomatic bacteriuria is 1% in children and rises to 4% in adult women and 10-20% in elderly women. The significance of this finding varies with the clinical context. Pregnant women should be screened for bacteriuria at booking and treated (10-14 days normally recommended) if two MSUs are positive. urinary tract infection is common during pregnancy, often develops into acute pyelonephritis (=30%) and may result in prematurity and fetal loss. Amoxicillin, cefalexin and nitrofurantoin are safe. Avoid tetracyclines (dental discoloration), fluoroquinolones (possible fetal arthropathy) and trimethoprim (risk of teratogenicity) during pregnancy, and sulphonamides (risk of neonatal jaundice) during the last trimester. Monthly MSUs should then be performed until delivery. There is little evidence that treating adults, including the elderly, with asymptomatic bacteriuria is beneficial except in patients with neutropenia or immunosuppression. Children should be treated with antibiotics, and investigated for urinary tract abnormality.
Catheter-associated urinary tract infection
The risk of bacteriuria with an indwelling catheter is proportional to duration since insertion, and is reduced by careful asepsis during insertion and maintenance of a closed system of drainage. Infection is often asymptomatic, but is the commonest cause of hospital-acquired Gram-negative bacteraemia. Scrupulous aseptic technique at insertion may delay infection. Many recommend a single-dose of intravenous gentamicin at catheterization. Asymptomatic catheter urinary tract infection should not be treated. If infection is symptomatic, it is unlikely to be eradicated by antibiotics whilst the catheter remains in situ. Try to remove the catheter, begin treatment and then recatheterize if necessary. Antiseptic or antibiotic irrigation is of no benefit.
Acute urethral syndrome (AUS)
This describes acute dysuria and frequency in women whose mid-stream urine is sterile or contains only low bacterial counts. Vaginitis and sexually transmitted causes of urethritis should be excluded. Most women with this syndrome have acute bacterial urethrocystitis, and should be treated with antibiotics as above.
Recurrent urinary tract infection
Many women have occasional attacks of cystitis, but some have frequent recurrences (e.g. more than twice/yr). Patients with recurrent urinary tract infection require urological evaluation for urinary tract abnormality, but in the majority none will be found. Risk factors such as diaphragm and spermicide use should be avoided, and patients should void after sexual intercourse. Antibiotic prophylaxis may be needed. Successful regimens include continuous low-dose therapy (e.g. co-amoxiclav 375 mg q24h, trimethoprim 100 mg q24h, cephalexin 250 mg q24h or norfloxacin 400 mg q24h), self-administered single-dose or short course therapy or postcoital single-dose prophylaxis.
Acute bacterial prostatitis
Risk factors: Usually none; may follow urethral instrumentation or surgery.
Clinical features: Fever, perineal pain, symptoms of urinary tract infection. Rectal examination reveals a swollen, tender prostate. Patients are often very unwell with bacteraemia.
Organisms: Coliforms including Escherichia coli (25%), less often Pseudomonas aeruginosa, Enterococcus spp.
Microbiological investigations: Mid-stream urine: Pyuria and bacteriuria are usually present. Blood cultures if unwell. Results of urine culture should guide antibiotic therapy; prostatic massage is not required.
Antibiotic management: Ciprofloxacin. Parenteral cephalosporin if bacteraemic. Antibiotics should be given for 4 weeks to prevent relapse.
Complications: Prostatic abscess may develop. This may rupture spontaneously into the urethra, or more rarely the rectum, or it may require cystoscopic drainage. Urological advice should be sought 2 and antibiotic cover extended to cover anaerobes.
This is a difficult diagnosis to make; urological opinion should be sought. In some men, the prostate may serve as a reservoir of infection, resulting in recurrent urinary tract infection. Prostatic localization studies involve collecting urine samples before and after prostatic massage. Expressed prostatic secretions are also collected and quantitative bacterial culture is used to determine the likelihood of persistent bacterial prostatitis. There is rarely a history of acute prostatitis. Some patients complain of perineal or low back pain and may have difficulty voiding. The prostate is sometimes tender on palpation. Chronic prostatitis may follow chlamydial urethritis (>87) and treatment with doxycycline for 4 weeks helps some patients.
Inflammation of the epididymis is acquired via ascending infection from the urethra, particularly if the urethra is instrumented in the presence of bacteriuria. Pain, fever and swelling of the epididymis are present and symptoms of concurrent urinary tract infection or urethritis may also be present. In sexually active men, infection may follow urethritis due to chlamydiae or Neisseria gonorrhoea, which should be treated appropriately (>87). Non-sexually transmitted epididymitis is caused by coliforms, Enterococcus spp. and occasionally Staphylococcus spp. or Streptococcus spp. Other causes include Mycoplasma spp. and viruses. Non-sexually acquired infection should be treated with trimethoprim or a fluoroquinolone for 2 weeks. TB should be considered in appropriate risk groups.
Orchitis is usually viral, associated in particular with mumps (>128). Pyogenic orchitis usually arises as a complication of epididymitis, due to the same organisms. Parenteral antibiotics are required and urgent urological advice should be sought, in particular to exclude testicular torsion.
Intrarenal and perinephric abscess
Risk factors: Renal cortical abscesses:
haematogenous spread of Staphylococcus aureus (most commonly) usually from a skin infection. IVDU, diabetes mellitus and haemodialysis predispose. Corticomedullary abscesses: ascending infection usually secondary to urinary tract abnormality, especially calculi and obstruction in adults and vesicoureteric reflux in children.
Clinical features: Onset is characteristically insidious. Fever, rigors and flank pain. There may be renal angle tenderness with a flank bulge or kyphosis. Corticomedullary abscess is usually associated with nausea and vomiting and urinary symptoms, but these are usually absent in cortical abscess, which rarely communicates with the lower urinary tract.
Organisms: Staphylococcus aureus (cortical abscess); coliforms, in particular Escherichia coll and Proteus spp. (corticomedullary abscess).
Microbiological investigations: mid-stream urine (often normal in cortical abscess). Blood culture. Culture of aspirated pus.
Other investigations: Ultrasound and/or CT scan are required to localize the abscess, and may be used to guide aspiration or percutaneous drain insertion.
Differential diagnosis: Renal carcinoma.
Antibiotic management: For staphylococcal cortical abscess, high-dose fiucloxacillin (2g 6hly, iv) for 2 weeks (+ iv gentamicin or oral fucidin) followed by 2 weeks of oral flucloxacillin. For corticomedullary abscess, gentamicin plus either ampicillin or ciprofloxacin initially, guided thereafter by the results of cultures.
Supportive management: Smaller abscesses are treated with antibiotics alone, but large abscesses or those that fail to respond after 2-4 days’ therapy with appropriate antibiotics will require drainage (often percutaneous). Obstruction should be relieved if present.
Complications: Rupture through the renal capsule leads to perinephric abscess. Onset is often insidious, with symptoms as above; extension towards the diaphragm causes pleuritic pain and raised fixed hemidiaphragm with pleural effusion. There may be signs of psoas irritation with scoliosis and pain on hip flexion. Drainage is always required.
Prolonged severe infection, particularly with Proteus spp. and obstruction may lead to xanthogranulomatous pyelonephritis. The renal pelvis is dilated, often with a staghorn calculus. There may be an abscess cavity, and the surrounding tissue is replaced by a yellow zone, histology of which shows macrophages laden with cholesterol and lipid material. Nephrectomy is usually required.
Urine culture positive for Staphylococcus aureus in patients who have not been catheterized should suggest previous staphylococcal bacteraemia and possible secondary renal abscess.