Urinary Tract Infections

The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. The bladder acts as a reservoir for urine until micturition is appropriate. Regulation of micturition relies on the CNS and the spinal cord.

The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. The kidneys also play a major role in homeostatic processes, including electrolyte concentration, blood pressure, and acid–base regulation. Grossly, they consist of an outer cortex and inner medulla. Microscopic functional units known as nephrons filter the blood through a structure called the glomerulus, and this filtrate is then modified and concentrated as it moves through a complex tubular system. The renal arteries supply the kidneys via a central opening, known as the renal hilum, on its medial side; large renal veins empty directly into the vena cava.

The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. The primary indication for use is treatment of urinary tract infection (although significant resistance has emerged). In addition, the drugs are used to treat and prevent opportunistic infections such as toxoplasmosis encephalitis and pneumocystis pneumonia in immunosuppressed individuals. The most common adverse events are hypersensitivity reactions, fever, rash, GI upset, and hematologic reactions. The drugs are generally contraindicated in pregnancy, young/ill infants, and individuals with megaloblastic anemia or severe renal impairment.

Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. The chronic type depends on the underlying pathology. The diagnosis is established via clinical presentation, supported by laboratory findings (in blood and urine). Imaging studies are performed if severe illness is noted or there is no response to initial treatment (antibiotics). CT is the study of choice, given its ability to detect renal abnormalities associated with the infection, including the extent of the disease. Perinephric abscess is an infection involving the perinephric space between the kidney and Gerota’s fascia. Perinephric abscess can be an extension from pyelonephritis or from hematogenous spread of a systemic infection. The diagnosis is established via CT scan. The treatment includes antibiotics, with abscess drainage (which is both diagnostic and therapeutic).

The kidneys, solid organs located in the lower back, are extremely important in regulating homeostasis through their role in maintaining blood volume, electrolyte balance, acid–base equilibrium, blood-pressure regulation, and removal of metabolic waste from the blood. Evaluation of renal function and early detection of kidney dysfunction is of primary importance. Tests of renal function are useful in identifying the presence of renal disease, monitoring the response of kidneys to treatment, and determining the progression of renal disease.

Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Depending on the location of the infection, patients can present with dysuria, urinary urgency, increased urinary frequency, suprapubic pain, and fever. Urinalysis and urine culture along with the clinical presentation help in the diagnosis of UTIs. Management options include oral or IV antibiotics such as trimethoprim-sulfamethoxazole, nitrofurantoin, and ceftriaxone. In certain instances, further workup may be needed to determine the underlying conditions that predispose an individual to UTIs.