Acute pyelonephritis is a serious bacterial infection that ascends from the lower urinary tract to involve the kidney’s tissue and collecting system. This condition causes inflammation of the renal parenchyma and pelvis, sometimes leading to kidney swelling. Since this infection can rapidly progress to severe illness, immediate medical evaluation is necessary for anyone experiencing the characteristic symptoms.
Recognizing the Signs and Symptoms
Acute pyelonephritis often presents with a sudden, dramatic onset of systemic symptoms. The classic presentation includes a triad of high fever, intense flank pain, and gastrointestinal distress such as nausea or vomiting. Fever often exceeds 102°F (38.9°C), accompanied by uncontrollable shaking and chills, indicating the body’s strong inflammatory response.
The localized pain is typically felt in the flank, the area on either side of the body between the ribs and the hip. This discomfort is often described as a constant, deep ache that may radiate toward the back or abdomen. Costovertebral angle (CVA) tenderness, where sharp pain is elicited upon gentle tapping over the kidney area during a physical exam, is a strong indicator of kidney inflammation.
Patients often experience symptoms related to the lower urinary tract, such as painful or burning urination, increased urgency, and frequent urination. The urine may appear cloudy or contain visible pus or blood, reflecting the presence of white blood cells and bacteria. These symptoms usually develop rapidly, often over the course of a day, demanding prompt attention.
Common Causes and Risk Factors
Acute kidney infections most frequently develop when bacteria ascend from the bladder into the ureters and reach the kidneys. Escherichia coli (E. coli) is the organism responsible for 70–80% of community-acquired cases. These bacteria originate in the bowel and gain entry to the urinary tract through the urethra.
Certain factors increase the likelihood of this ascending infection, including anatomical differences. Women are five times more likely than men to experience pyelonephritis because their shorter urethra provides a quicker pathway for bacteria. Any condition that causes urine to pool or obstructs its flow significantly raises the risk. This includes kidney stones and conditions like vesicoureteral reflux, where urine flows backward from the bladder into the ureters.
Compromised immune systems, such as those caused by diabetes mellitus, increase susceptibility to severe infection. Pregnancy is a specific risk factor due to hormonal changes and the physical pressure of the uterus, which can impede urine drainage. Men with an enlarged prostate, which causes incomplete bladder emptying, are also at increased risk.
Diagnosis and Treatment Pathways
Diagnosing an acute kidney infection involves a combination of reported symptoms, a physical examination, and laboratory tests. A doctor will check for costovertebral angle tenderness and evaluate for signs of systemic illness. Laboratory testing begins with a urinalysis, which typically reveals high levels of white blood cells and bacteria in the urine, often accompanied by nitrites and leukocyte esterase.
A urine culture is performed to specifically identify the causative pathogen and determine its susceptibility to antibiotics. This test is performed before starting treatment to ensure the most effective medication is selected. Blood tests are also standard, checking for signs of widespread infection, such as an elevated white blood cell count, and assessing kidney function.
Treatment relies on the immediate administration of antibiotics to halt the infection’s progression. For uncomplicated cases in healthy individuals who can tolerate oral intake, outpatient treatment with oral antibiotics, such as a fluoroquinolone, may be appropriate. Hospitalization and intravenous (IV) antibiotics are necessary for patients with severe dehydration, persistent vomiting preventing oral medication absorption, or signs of sepsis.
Patients initially treated in the hospital with IV antibiotics are typically switched to an oral regimen once fever subsides and symptoms improve, usually within 48 hours. Imaging, such as a CT scan or ultrasound, is reserved for individuals who do not show improvement after 72 hours of appropriate antibiotic therapy, or if an obstruction or kidney abscess is suspected. The course of antibiotic treatment typically lasts seven to fourteen days, and a follow-up urine culture may be recommended to confirm the infection has cleared.
Potential Complications
When an acute kidney infection is not promptly or adequately treated, there is a risk of severe and potentially life-threatening complications. One serious outcome is urosepsis, which occurs when the bacterial infection spreads from the kidney into the bloodstream. Sepsis is a medical emergency that can lead to septic shock and multi-organ failure.
Intense inflammation and pus formation within the kidney tissue can lead to a renal abscess, a pocket of pus requiring drainage in addition to antibiotics. Repeated or severe episodes of pyelonephritis can cause permanent damage to kidney structures, resulting in scarring and atrophy. This damage may eventually impair kidney function, contributing to the development of chronic kidney disease.