Urinary Tract Infections

Here we'll learn about urinary tract infections (UTIs), which affect approximately 60% of women and 12% of men at some point in their lives. Infections that affect the urethra and urinary bladder are "lower tract" infections, those that affect the ureters and kidneys are "upper tract" infections. Most infections remain in the "lower tract."

• Sexual intercourse (risk correlates with frequency and use of spermicide)
• Changes in bacterial flora
• Personal and family history of UTIs
• Conditions that affect urinary voiding also increase the risk of UTIs, including:

Catheterization - catheterization is a significant cause of UTIs in hospitalized patients, and the risk correlates with duration. Pregnancy Diabetes mellitus Neurogenic bladder or spinal cord injuries Prostatic hypertrophy "Recurrent" UTIs are defined as 2 or more symptomatic episodes within a 6-month period, or more 3 or more episodes within a 12-month period. In the general population, UTI's are far more common in women. This is largely due to their shorter urethras, which gives pathogens quicker access to the urinary bladder. However, be aware that males with the risk factors we listed above, particularly older males with prostatic hypertrophy, also have elevated rates of UTIs. Many authors distinguish between "complicated" and "uncomplicated" UTIs, which can be useful in choosing a treatment strategy; however, definitions of these terms vary widely across publications, so we will avoid them, here. Nearly all UTI's are caused by bacteria, but they can also be caused by some fungi and viruses. The top bacterial causes are:

• Uropathogenic Escherichia coli
• Klebsiella pneumoniae
• Enterococcus faecalis,
• Proteus mirabilis
• Staphylococcus aureus, which is rare but is associated with increased morbidity/mortality. You can learn more about these bacteria via the links in our notes.

Uropathogenic E. coli By far the most common cause of UTIs in all settings; these bacteria have the following special virulence factors: Type 1 and P fimbriae, which allows them to "crawl" up the urinary tract and invade cells. The bacteria release alpha-hemolysin and other pro-inflammatory toxins, and use siderophores to "steal" iron from the host. They produce a biofilm, which protects them from the host's anti-pathogen mechanisms, They are resistant to many of our current antibiotic medications. Though most symptomatic infections involve the urinary bladder, infections can occur all along the tract. UTI-causing pathogens typically spread via the "ascending" route – bacteria from the anus and perineum enter the urethra and ascend through the urinary tract. In rarer cases, pathogens can spread hematogenously and reach the urinary tract; this is more likely in immunocompromised or debilitated patients and is more often associated with Staphylococcal or fungal infections. Primarily rely on urinalysis; however, we may also use imaging studies to look for obstructions, organ damage or enlargement, or for anatomic anomalies that contribute to infection. Typically require treatment with antibiotics such as trimethoprim and sulfamethoxazole, cephalexin, or ceftriaxone. Choice of antibiotic therapy should be based on the results of urine culture and local antibiotic resistance. Cranberries and other supplements provide little to no prevention or treatment. Refers to the finding of bacteria in urine collected from an asymptomatic patient.

• In the general population, there is no apparent benefit to administering antibiotics to these patients.
• However, indicate three patient groups where screening and treatment of asymptomatic bacteriuria is recommended: those who are pregnant, about to undergo urologic interventions, and those who have recently received renal transplants.

Urethritis is infection of the urethra, which is usually asymptomatic but may cause dysuria and urethral discharge. Urethritis is usually caused by a sexually transmitted bacteria, most often Neisseria gonorrhea or Chlamydia trachomatis, which require specific pathogen-specific antibiotic treatments (gonococcal urethritis is treated with ceftriaxone, C. trachomatis is treated with azithromycin or doxycycline). These infections are more common in males. Infection of the bladder is called "cystitis" – this is the most common type of urinary tract infection. Patients experience frequent and urgent urination, usually accompanied by a burning sensation. Despite multiple voiding episodes, urine output is reduced; on urinalysis, we'll see white blood cells and hematuria. In approximately 1 out of every 30 UTIs, infection ascends to the kidneys – we call this pyelonephritis ("pyelo" refers to the renal pelvis, from the Greek word for trough or basin). Patients with acute pyelonephritis experience the signs and symptoms of cystitis (frequent, urgent urination with burning sensation, etc.), in addition to the following manifestations: Fever with chills, flank and abdominal pain, nausea and vomiting, and tenderness in the costovertebral angle – this is the area between the 12th rib and the spine, posteriorly, where the kidney sits. Chronic pyelonephritis can occur when kidney infections are persistent or recurrent; this can lead to inflammation and fibrosis. Chronic pyelonephritis is more likely to occur in patients with anatomic anomalies, for example, in children with ureterovesical reflux (urine moves "backwards" from the bladder to the ureters, usually due to a valve defect). Complications of UTIs: Can cause renal damage, especially pyelonephritis. Abscesses are collections of pus that can form anywhere along the urinary tract; abscesses can cause pain, fever, and other non-specific signs and symptoms. Papillary necrosis is caused by inflammation and ischemia. Signs and symptoms of papillary necrosis include: Back pain, painful and frequent urination with pieces of renal tissue, protein, and blood in the urine, fever, and increased serum creatinine. Be aware that renal papillary necrosis is not unique to urinary tract infections; it can also be caused by NSAIDs, diabetes mellitus, sickle cell, urinary tract obstructions, analgesic nephropathy. Sepsis: Called urosepsis when it originates in the urinary tract; 25% of sepsis cases start as urinary tract infections. UTI's are common in children, but can be an indication of congenital anomalies. We need to treat UTIs in children promptly to avoid renal fibrosis and scarring, which can lead to hypertension later in life.

• For references, please see full tutorial.