Urinary tract infections (UTIs) are primarily bacterial infections caused by enteric bacteria, which are normally found in the gut but become problematic when they colonize the urinary tract. The most common causative agent is Escherichia coli (E. coli), responsible for over 70% of UTIs, with some studies reporting up to 95%. Other bacteria such as Proteus, Pseudomonas, Klebsiella, Staphylococcus, Enterococcus, and Streptococcus can also cause UTIs, but these are less frequent. Viral UTIs are extremely rare in healthy individuals but may occur in immunocompromised patients. Fungal UTIs, often caused by Candida albicans, are uncommon and usually indicate underlying conditions like diabetes.
UTIs are significantly more common in females, occurring approximately eight times more often than in males. This increased prevalence is due to anatomical differences, such as a shorter female urethra and its proximity to the anus, which facilitates bacterial migration. Factors like diarrhea and sexual activity can increase the risk by spreading bacteria near the urethral opening. Notably, Staphylococcus saprophyticus is associated with UTIs linked to sexual activity, especially in sexually active females aged late teens to twenties. Catheterization, involving the insertion of a tube into the bladder, can also lead to catheter-associated UTIs (CAUTIs) by introducing bacteria directly into the urinary tract.
UTI symptoms depend on the infection's location within the urinary tract. Lower UTIs involve the urethra (urethritis) or bladder (cystitis) and typically cause dysuria (painful or difficult urination), frequent urination, and sometimes a mild fever. These infections are uncomfortable but generally less severe. The primary concern is preventing the infection from ascending to the upper urinary tract, which includes the ureters (ureteritis) and kidneys (pyelonephritis). Kidney infections present with high fever, flank pain, and can lead to serious complications such as kidney damage, kidney failure, or bacteremia (bacteria in the blood), often requiring hospitalization and intravenous antibiotics.
Diagnosis of UTIs commonly involves a dipstick test that detects nitrites and leukocyte esterase in urine. Nitrites indicate bacterial conversion of nitrates, while leukocyte esterase signals the presence of white blood cells, both markers of infection. Quantitative urine cultures measure colony-forming units (CFUs) per milliliter, with 100,000 CFU/mL typically indicating infection, although lower counts may also be significant when combined with symptoms.
Treatment primarily involves antibiotics. Nitrofurantoin is a first-line antibiotic specifically used for UTIs. Sulfa drugs such as trimethoprim-sulfamethoxazole are also common treatments. In cases of antibiotic resistance, fluoroquinolones may be prescribed. For severe upper UTIs like pyelonephritis, intravenous broad-spectrum antibiotics such as cephalosporins are often necessary, usually requiring hospitalization.
There is no lasting immunity to UTIs; in fact, having one infection increases the risk of subsequent infections. Preventative measures include proper hygiene, such as wiping from front to back in females to avoid bacterial spread, and urinating after sexual activity to flush out bacteria from the urethra. Understanding these factors is crucial for managing and reducing the incidence of UTIs effectively.
