Acute Pyelonephritis I: Introduction

Pyelonephritis is a bacterial infection that affects the renal pelvis, tubules, and interstitial tissue of one or both kidneys.

It can be classified as acute, a sudden severe infection, or chronic due to repeated infections or structural abnormalities that damage the kidney.

The primary cause of acute pyelonephritis is a bacterial infection, typically Escherichia coli. However, other bacteria, such as Proteus, Klebsiella, Enterococcus, and Pseudomonas, also cause the disease.

Acute pyelonephritis typically begins with bacterial colonization of the urethra, followed by migration to the bladder, causing cystitis.

From the bladder, bacteria can ascend through the ureters to the kidneys, particularly in cases of urinary stasis or vesicoureteral reflux.

Once bacteria reach the kidneys, they invade the renal interstitium, triggering the immune system to release cytokines and other inflammatory mediators.

This response leads to renal edema, neutrophil infiltration, and injury to renal tissue, causing symptoms like high fever and chills, leukocytosis, bacteriuria, flank and lower back pain, painful urination, nausea, and vomiting.