What is the cause of fever in pyelonephritis (pyelonephritis is an infection of the kidney)

From the Guidelines

Fever in pyelonephritis is a common symptom that occurs due to the body's immune response to bacterial infection of the kidney, typically presenting with a temperature greater than 38 °C, as noted in the 2024 European Association of Urology guidelines 1. The immune response is triggered when bacteria, such as E. coli, invade the kidney tissue, leading to the release of cytokines and other inflammatory mediators. These substances act on the hypothalamus, resetting the body's temperature setpoint higher, resulting in fever. Some key points to consider in the management of pyelonephritis include:

• The use of urinalysis, urine culture, and antimicrobial susceptibility testing for diagnosis 1
• The recommendation for prompt differentiation between uncomplicated and potentially obstructive pyelonephritis to prevent progression to urosepsis 1
• The use of fluoroquinolones and cephalosporins as the only antimicrobial agents recommended for oral empiric treatment of uncomplicated pyelonephritis 1
• The consideration of a short outpatient course of antibiotic treatment, but with awareness of the potential for a higher recurrence rate within 4-6 weeks 1 It is essential to manage fever and other symptoms promptly, as untreated pyelonephritis can lead to severe complications, including sepsis or kidney damage. Key considerations for treatment include:
• Increasing fluid intake
• Using acetaminophen for fever management
• Seeking prompt medical attention if symptoms worsen or do not improve with treatment.

From the Research

Fever in Pyelonephritis

• Fever is a common symptom of acute pyelonephritis, a bacterial infection of the kidney and renal pelvis 2
• The presence of fever can help in the clinical diagnosis of acute pyelonephritis, with a positive predictive value of 0.98 in febrile patients 2
• However, the absence of fever does not rule out the diagnosis, as some patients may not present with fever 2
• Other symptoms and laboratory evidence, such as flank pain and pyuria, should also be considered in the diagnosis of acute pyelonephritis 3

Pathogenesis of Fever in Pyelonephritis

• The exact mechanism of fever in pyelonephritis is not fully understood, but it is thought to be related to the body's immune response to the bacterial infection 2
• The infection causes inflammation in the kidney and renal pelvis, which can lead to the release of pyrogens and the production of fever 2
• The type and severity of the fever can vary depending on the severity of the infection and the individual's overall health 2

Treatment of Pyelonephritis

• The treatment of pyelonephritis typically involves antibiotics, such as fluoroquinolones or trimethoprim/sulfamethoxazole, which can help to reduce fever and other symptoms 3
• In some cases, hospitalization and intravenous antibiotics may be necessary, especially if the patient has a severe infection or is at risk of complications 3
• The choice of antibiotic and treatment regimen should be based on the results of urine culture and antimicrobial susceptibility testing, as well as the patient's individual needs and medical history 4, 5, 6