How bad is the back pain qith a kidney infection?

Varies. Varies somewhat based upon the severity of the infection and also the pain tolerance of the patient. That being said, it has the potential to be quite severe and can be associated with fevers, chills, and pain with urination.
Painful. Pain may be mild at first but will become moderate to severe without treatment.
Some time is bad. Back pain with kidney infection usually unilateral unless both kidney involve, also move to the front the leg and to.

Related Questions

How to tell if it's a kidney infection or just back pain?

Check: other signs. Kidney infection is associated with fever, abnormal urine results and abnormal blood count. Back pain is usually worse only with certain positions. Kidney infection is of short term duration. Back pain is a long term issue.