Certain illnesses may increase a person's likelihood of contracting pyelonephritis. Individuals who have suffered nerve damage in the lower torso are at increased risk of developing pyelonephritis, as they may not be able to sense the early symptoms of a urinary tract infection that could progress to the kidneys. Kidney stones and an enlarged prostate are two conditions that inhibit the normal flow of urine through the urinary tract, and people who experience one or both of these conditions are more likely to contract an infection in the kidneys. Additionally, a condition known as vesicoureteral reflux can cause urine to flow the wrong way within the urinary tract and greatly increases a person's probability of developing pyelonephritis.
Illnesses such as cancer, diabetes, and HIV damage the immune system and impair the body's ability to fight off infection. A person with a suppressed immune system will be less able to fight an infection in the urinary tract or kidneys, and is therefore not only more likely to contract pyelonephritis, but also more at risk from complications once the infection has begun.