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Kidney infection (pyelonephritis): the signs, sepsis, and the treatment
For anyone with a fever and pain in the back or side, anyone whose bladder infection may be spreading, and anyone looking after someone who might have a kidney infection. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says a kidney infection is a type of urinary tract infection that usually starts in the bladder and moves up to one or both kidneys; that it can be very painful and cause serious health problems; that you should seek care right away if you have the signs; and that, although it is uncommon, it could lead to sepsis, which can be life threatening. This page passes on, by name, what NIDDK says: the signs at each age, sepsis, how common it is, the causes and who is more likely to get one, the tests, the treatment, what to do if it comes back, and preventing the next one. It builds the words to say, so you do not have to find them, and prints a card to keep with you.
A word with a dotted line under it, like this, opens its official definition, quoted from a U.S. government glossary.
Right now
- Confused, breathing fast, a racing heart, or very hard to wake, with an infection? NIDDK says a kidney infection could lead to sepsis, which can be life threatening. Ours: call 911 or go to an emergency room now.
- A fever and chills with pain in your back or side, or vomiting? NIDDK says to seek care right away. Ours: call your health care professional today, or go to an urgent care or an emergency room if you cannot reach them; go now if you cannot keep liquids down.
- Pregnant, or is it a baby or young child with a fever? Ours: call the pregnancy team or the child’s doctor today.
- Worn down, or thinking of ending your life? Call or text 988, any hour (ours).
More help
- On this site: Kidneys and bladder: find the right page · Bladder infection (UTI) · Sepsis · Kidney stones · Urinary retention.
- A baby, a child, or a pregnancy: A UTI in a baby or child · Fever in a baby or child · Pregnancy and a new baby.
- What can raise the risk: Enlarged prostate (BPH) · Diabetes · Sickle cell disease · Kidney disease.
- Getting ready: My medicines list · Getting ready for urinary tract imaging · Get ready for your appointment · When you can’t afford your medicine · When you need a doctor and can’t pay.
- In a crisis: Help right now (988, 911). All our free tools.
Kidneys, bladder or urine, and not sure this is the right page? The pages on this site for bladder infections, kidney stones, blood in the urine, bladder pain, bladder leaks, the prostate, kidney disease and bedwetting, on one list.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor or nurse has reviewed it. The facts were read on October 18, 2026 on NIDDK’s (NIH) page Kidney Infection (Pyelonephritis) (last reviewed October 2024) and its Spanish page Infección renal (pielonefritis) (last reviewed April 2017). The two pages differ: this English guide follows the English page, and where it uses something only the Spanish page says (an older adult who has only confusion, a rash among the sepsis signs, bacteria in healthy people’s urine, a repeat culture after treatment, six to eight glasses a day, peeing every 3 to 4 hours and after sex), it says “NIDDK’s Spanish page (2017)”. The numbers (about 250,000 office visits and 200,000 hospital admissions a year in the United States; under age 2; over 65) are NIDDK’s. Ours: 911 or the emergency room for the sepsis signs, sudden confusion or someone hard to wake; going in now if you cannot keep liquids or the antibiotic down; calling the pregnancy team or the child’s doctor today; not taking leftover antibiotics or anyone else’s; asking about the cost; the after-hours number on your card; 988; and the order of the steps. What we left out: the references, the clinical-trials section, the step-by-step of the rectal exam, and NIDDK’s outside links. This page saves nothing and loads no trackers.