A urinary tract infection (UTI) is a common bacterial infection, typically localized to the lower urinary tract, involving the urethra or bladder. While often perceived as a minor nuisance, a UTI requires prompt treatment. Neglecting the infection allows bacteria to multiply and travel upward, leading to increasingly severe and potentially life-threatening conditions throughout the body.
The Ascent to Kidney Infection (Pyelonephritis)
The progression of an untreated lower UTI involves bacteria ascending the ureters, the tubes connecting the bladder to the kidneys. This results in pyelonephritis, an infection of the kidney tissue itself. Pyelonephritis is a substantially more serious illness than a simple bladder infection, demanding immediate medical intervention.
Once the infection reaches the kidneys, symptoms shift dramatically from local discomfort to systemic illness. Patients often experience acute-onset high fever, shaking chills, and intense pain in the flank or lower back area. Nausea and vomiting are also common, which can complicate treatment by making it difficult to tolerate oral antibiotics and fluids. Treatment often requires intravenous (IV) antibiotics administered in a hospital setting to ensure the medication reaches the site of infection rapidly.
Systemic Infection and Sepsis
If the kidney infection remains untreated, the bacteria can breach the confines of the kidney tissue and enter the bloodstream, leading to urosepsis. Sepsis is a life-threatening complication where the body’s response to the infection begins to damage its own tissues and organs. This dysregulated response triggers widespread inflammation.
The signs of sepsis reflect this systemic inflammatory state and the onset of organ dysfunction. Symptoms include a rapid heart rate, an elevated respiratory rate, confusion or delirium, and dangerously low blood pressure, which signifies septic shock. The spread of bacteria (bacteremia) compromises circulation, reducing blood flow to vital organs like the brain, heart, and lungs. Septic shock requires immediate, intensive care involving IV fluids, antibiotics, and medications to support blood pressure.
Complications in High-Risk Populations
Certain populations face an accelerated risk of complications due to underlying physiological factors or difficulties in diagnosis. In elderly patients, a UTI may not present with typical symptoms like burning urination or pain. Instead, the infection may manifest as sudden confusion, delirium, or a behavioral change, which can delay diagnosis.
Pregnant women are also at heightened risk because hormonal changes cause the ureters to widen, increasing the likelihood of bacteria traveling to the kidneys. Pyelonephritis during pregnancy can lead to serious adverse outcomes, including premature labor and low birth weight for the infant. Individuals with diabetes, kidney stones, or structural abnormalities are more susceptible because these conditions impair the natural flow of urine, allowing bacteria to multiply and ascend the tract.
Potential for Long-Term Kidney Damage
Beyond the immediate acute threats of pyelonephritis and sepsis, a severe or recurrent untreated UTI can result in long-term structural damage to the kidneys. Prolonged inflammation within the renal tissue can lead to the formation of permanent scar tissue, known as renal scarring. This scarring is distinct from the acute injury that occurs during septic shock.
The formation of scar tissue reduces the functional capacity of the kidney over time because the damaged tissue cannot be regenerated. Repeated bouts of pyelonephritis progressively diminish the kidneys’ ability to filter waste and regulate fluid balance, eventually leading to chronic kidney disease (CKD). In advanced cases, this permanent loss of function may necessitate long-term treatments such as dialysis or a kidney transplant.