A kidney infection (pyelonephritis) is a serious progression of a common urinary tract infection (UTI) that has traveled up to one or both kidneys. This condition involves the inflammation of the kidney tissue and the renal pelvis, typically caused by bacteria. Pyelonephritis is generally not contagious in the way illnesses like the common cold or influenza are. This distinction is based on the internal origin of the bacteria causing the infection.
Why Kidney Infections Are Not Transmissible
The bacteria responsible for a kidney infection originate almost exclusively from within the patient’s own body. Unlike airborne viruses or surface-stable pathogens, the bacteria involved in pyelonephritis are part of the normal flora of the human digestive tract. These internal bacteria, most commonly Escherichia coli (E. coli), migrate from the perianal region into the urethra, starting the infection process.
The infection is considered endogenous, arising from the patient’s own microbial environment rather than an external source. This mechanism prevents the infection from being passed on through casual contact, sharing food, or close physical proximity. While E. coli can be spread by touch, it does not result in a kidney infection in another person, as the complex internal migration and colonization process must occur in the recipient.
The Internal Mechanism of Development
A kidney infection typically begins as a lower urinary tract infection (UTI) in the bladder, known as cystitis, and then progresses upward. The journey starts when bacteria, primarily E. coli from the colon, colonize the skin around the urethra and enter the urinary opening. Once inside the urethra, these bacteria travel against the normal flow of urine into the bladder.
If the bacteria are not flushed out or are particularly virulent, they multiply rapidly. From the bladder, the infection travels upward through the ureters, the narrow tubes connecting the bladder to the kidneys. This ascent causes the inflammation and infection of the kidney tissue that defines pyelonephritis.
Certain factors can facilitate this upward spread, increasing the risk of pyelonephritis development:
- Any condition that obstructs the urinary tract, such as kidney stones or an enlarged prostate, which prevents complete bladder emptying.
- Vesicoureteral reflux (VUR), a condition where urine flows backward from the bladder into the ureters, particularly in children.
- A short urethra in females.
- Underlying conditions like diabetes.
Recognizing the Signs and Symptoms
The symptoms of a kidney infection are severe. A hallmark of pyelonephritis is the sudden onset of a high fever, often accompanied by shaking chills. These systemic signs indicate the infection has moved beyond the lower urinary tract.
Another distinguishing feature is severe pain located in the flank, the area on the back or side just below the ribs. This pain is often tender to the touch, reflecting the inflammation of the kidney itself. Many patients also experience nausea and vomiting, which can lead to dehydration. Although lower urinary tract symptoms like painful and frequent urination may be present, the combination of fever, chills, and flank pain strongly suggests a kidney infection. Because of the risk of the infection spreading to the bloodstream and causing sepsis, anyone experiencing these severe symptoms should seek emergency medical attention.
Medical Treatment and Recovery
Medical intervention is necessary to treat a kidney infection and prevent serious complications like permanent kidney damage or sepsis. Treatment primarily involves antibiotics to target the bacteria. The initial choice of antibiotic is often based on the most likely causative organism, typically E. coli, but this may be adjusted once a urine culture identifies the specific bacteria and its sensitivities.
If the infection is severe, or if the patient is unable to keep down fluids and medication due to vomiting, hospitalization may be required. Antibiotics and fluids are administered intravenously (IV) for a faster response. Patients are also given pain relievers to manage flank pain and fever. Even after symptoms improve, it is important to complete the entire course of antibiotics, which can last one to two weeks, to ensure the infection is eradicated and prevent recurrence.