What causes kidney infection?

Bacteria may enter through the urethra, multiply in the bladder, and then move through a ureter to the kidney. A blockage, such as a stone, can slow urine flow and make it harder for the urinary system to clear bacteria. Symptoms can include fever, chills, pain in the side or back, nausea, and burning or frequent urination. A bladder infection does not always cause kidney infection, but worsening urinary symptoms with fever or flank pain deserve prompt assessment.

Arrange medical assessment promptly if you have fever with urinary symptoms, pain near the ribs or back, vomiting, or feel suddenly unwell. A clinician may test a urine sample and choose treatment based on the findings. Drink fluids if you can keep them down, rest, and follow prescribed treatment exactly. Do not use leftover antibiotics, because the wrong medicine may delay effective care.

Seek urgent help for confusion, fainting, severe weakness, repeated vomiting, inability to keep fluids down, or severe pain. Pregnancy, a known urinary blockage, kidney disease, or a weakened immune system lowers the threshold for same-day medical advice. Rapid deterioration with fever and shaking chills can signal a serious infection.

Ask whether the symptoms fit a kidney infection or another urinary problem, whether a urine culture is needed, and which warning signs should bring you back. You can also ask how to reduce the chance of another urinary infection.