Urinary tract infections

4. Urinary tract infections or UTI: It is an infection of any part of the urinary tract involving the kidneys, ureters, bladder and/or urethra. It is most common in young women. Upper UTI involves infections in the kidneys and ureters while lower UTI involves infections of the lower tract i.e. bladder, prostate and urethra. A complicated UTI is associated with a structural or functional abnormality of the genitourinary tract or the presence of an underlying disease like diabetes, sickle cell anemia etc. which may lead to more severe UTI. In the absence of such conditions UTIs are milder and are called uncomplicated UTI and have a good prognosis.

   Significant bacteriuria: It is defined as the presence of 100 000 or more colony forming units (CFU) per ml of urine, also known as Kass criteria. The cutoff limit can be lowered in the presence of clinical symptoms, pyuria (>10 WBC/mm3), cystitis and pyelonephritis.

   Pregnant women with asymptomatic bacteriuria are at increased risk of pyelonephritis and premature delivery.

   Clinical features: Clinical features include dysuria, frequency and urgency in lower UTIs; chills and fever, flank pain, malaise in pyelonephritis. Chlamydia trachomatis is a common cause of urethritis in women and men, other causes being Neisseria gonorrhoeae and HSV type 2. Acute bacterial prostatitis presents with acute onset of chills and fever, urinary frequency and urgency, dysuria, perineal and low back pain and constitutional symptoms. Rectal examination is contraindicated in acute bacterial prostatitis due to the risk of precipitating sepsis. Chronic bacterial prostatitis is milder and presents with relapsing UTIs with urinary frequency, dysuria, nocturia and low back and perineal pain. Prostatic massage followed by urine culture gives a better yield in chronic prostatitis. Nonbacterial prostatitis is a chronic form that presents similarly but with sterile culture of urine and prostatic secretions. Prostatodynia is chronic noninflammatory prostatitis but no inflammatory cells are present and the culture is sterile.

   Reinfection is a recurring infection due to a different or same microorganism that is usually drug susceptible. Unlike relapse, reinfection does not represent failure to eradicate infection from the urinary tract but is due to reinvasion of the system. Relapse is a return of infection due to the same microorganism which is often drug resistant, typically happens within 3 weeks of completing treatment. The term treatment failure has been used to describe failure to eradicate bacteriuria during treatment and failure to prevent relapse.

   Pathogenesis: Bacteria in the enteric flora periodically gain access to the genitourinary tract. Close proximity of anus in women to peri-urethra is a likely factor. Bacterial colonization of periurethral area often precedes the onset of bladder bacteriuria. P-fimbriated strains of Escherichia coli adhere to uroepithelial cells to glycolipid receptors. Acidic pH and commensal vaginal flora protects against colonization. After periurethral colonization, uropathogens gain access to the bladder via the urethra, to kidney via ureters and to prostate via the ejaculatory ducts. Urine is a good growth medium for bacteria. Tamm-Horsfall protein prevents colonization by adhering to fimbria. Renal calculi, structural anomalies of the urinary tract, VUR, residual urine in bladder, BPH, urethral stricture, instrumentation of the urinary tract, catheterization etc. increases the risk of UTI.

   Diagnosis: Centrifuged sample of urine should be examined microscopically and culture done. Pus cells are present, typically >10/mm3.

   Common microorganisms causing UTI

   • Acute uncomplicated cystitis and uncomplicated pyelonephritis: E.coli
   • Staghorn calculi: Proteus, Ureaplasma
   • Hospital acquired UTI: Klebsiella, Pseudomonas, Enterobacter
   • Recent catheterization or instrumentation: Coagulase negative Staphylococci,Enterococci
   • Relapsing UTIs, long term antibiotic use: Candida albicans

   Treatment: Asymptomatic patients should have colony counts greater than or equal to 100,000 per ml on at least 2 occasions before treatment is considered. Bacteriuria developing after urinary catheterization should be treated with antibiotics.

   Treatment of asymptomatic bacteriuria

   • Pregnancy: Treat with cephalexin or amoxicillin
   • Children: Treat with antibiotics; evaluate for VUR
   • General population: No need to treat except in neutropenia, catheterization, instrumentations of urinary tract
   • Diabetes mellitus: Treat with antibiotics, blood sugar control

Uncomplicated cystitis is treated with nitrofurantoin, fosfomycin, cephalexin or trimethoprim/sulfamethoxazole. Fluoroquinolones can be used if local resistance is low.

Patients with uncomplicated pyelonephritis i.e. no DM, non-pregnant, mild symptoms, can be treated on an outpatient basis. Other cases are admitted. Outpatient treatment of pyelonephritis is with oral fluoroquinolone (if resistance is low) like ciprofloxacin or levofloxacin or trimethoprim/sulfamethoxazole. Initial intravenous gentamicin plus ceftriaxone is given as a single dose. Inpatient treatment is with intravenous fluoroquinolone, aminoglycoside with ampicillin, cephalosporins or carbapenems.

Acute prostatitis is treated with oral Bactrim or ciprofloxacin for 4- 6 weeks; severely ill patients need intravenous ampicillin plus gentamicin. Therapy should be guided by culture and sensitivity. Chronic prostatitis is treated with oral fluoroquinolones. Second line drugs are doxycycline, Bactrim, azithromycin and clarithromycin. Treatment may be needed for up to one year. Nonbacterial prostatitis is treated with doxycycline or azithromycin. Prostatic abscess needs drainage.

Catheter associated UTIs should be treated with antibiotics and removal of infected catheter.