A kidney infection typically causes fever, pain in your back or side, and painful urination. These symptoms often develop quickly, sometimes within hours, and feel noticeably worse than a standard bladder infection. Knowing what to look for helps you recognize when a urinary tract infection has moved beyond the bladder and into more serious territory.
The Core Symptoms
Kidney infections produce a distinct combination of urinary symptoms and whole-body illness. The most common signs include:
- Fever and chills
- Pain in your back, side, or groin
- Burning or pain during urination
- Frequent or urgent need to urinate
- Nausea and vomiting
- Cloudy, foul-smelling, or blood-tinged urine
- Belly pain
The back and side pain is often the clearest signal. It typically hits on one side, in the area between your lower ribs and hip, and can range from a deep ache to sharp, intense pain. Tapping on that spot usually makes it worse. This pain reflects inflammation in the kidney itself, which sits in that region of your body.
Nausea and vomiting catch many people off guard because they don’t expect stomach symptoms from a urinary problem. But the kidneys sit close to the digestive organs, and the body’s inflammatory response to a kidney infection frequently spills over into gastrointestinal distress. Some people experience these gut symptoms as their most prominent complaint.
How It Differs From a Bladder Infection
A bladder infection (cystitis) and a kidney infection (pyelonephritis) share some overlapping symptoms, but they feel meaningfully different. A bladder infection stays localized: you get burning with urination, frequent trips to the bathroom, urgency, and sometimes lower abdominal pressure or blood in the urine. You generally feel okay otherwise.
A kidney infection adds systemic illness on top of those urinary symptoms. Fever, chills, flank pain, nausea, and vomiting are the hallmarks that separate the two. You feel sick in a way that a bladder infection doesn’t cause. One important detail: kidney infections can occur with or without the typical urinary symptoms like burning and frequency. Some people jump straight to fever and back pain without ever noticing classic bladder symptoms first, which can make the infection harder to recognize.
Symptoms in Older Adults
Adults over 65 often present differently. The classic symptoms may be muted or absent entirely, replaced by signs that don’t obviously point to a urinary infection. Confusion or sudden mental cloudiness is one of the most recognized atypical signs in older adults. A person who was clear-headed yesterday and seems disoriented today may have a kidney or urinary tract infection as the underlying cause.
Other signs to watch for in older adults include mid-to-lower back pain, nausea, cloudy or reddish urine, and low-grade fever (often starting around 99°F or higher). Not every older adult with a kidney infection will show these symptoms, which is part of what makes infections in this age group easy to miss. Caregivers and family members are often the first to notice something is off.
Symptoms in Babies and Young Children
Infants and toddlers can’t tell you their back hurts or that urination burns. In children under two, a kidney infection may show up as fever, irritability or unusual fussiness, poor feeding, vomiting, or diarrhea. Some babies gain weight poorly as the only visible sign. In older children, the symptoms start to look more like what adults experience: fever with chills, nausea or vomiting, and pain in the back, side, or groin. Prompt treatment matters in children because kidney infections can cause lasting damage to developing kidneys.
Warning Signs That Need Emergency Care
Most kidney infections are treatable at home with antibiotics, but a small percentage progress to a dangerous condition called urosepsis, where the infection enters the bloodstream. This is a medical emergency. The signs that a kidney infection has become something more serious include a rapid heart rate or heart palpitations, difficulty breathing, a weak pulse, very low blood pressure, and an inability to urinate. If you already have kidney infection symptoms and notice your heart racing, you feel lightheaded, or breathing becomes labored, go to an emergency room.
What Happens When You Get Diagnosed
Diagnosis usually starts with a urine test. The lab checks for white blood cells (which your body produces to fight bacterial infections) and blood in the urine. A urine culture identifies the specific bacteria causing the infection, which helps determine the best treatment.
The physical exam often involves your provider pressing on your back near the kidneys. Tenderness in that spot, combined with fever and abnormal urine results, is usually enough to confirm the diagnosis.
Treatment and Recovery Timeline
Antibiotics are the standard treatment. Current guidelines from the Infectious Diseases Society of America recommend 5 to 7 days of treatment for most kidney infections when patients are improving on therapy. This is shorter than the 10 to 14 day courses that were standard for years. Some cases, particularly in men where a prostate infection is suspected, may still require 10 to 14 days.
Most people start feeling noticeably better within 48 to 72 hours of starting antibiotics, though it’s important to finish the full prescribed course even after symptoms improve. Fever is usually the first symptom to resolve. The back and side pain tends to linger a bit longer but should steadily improve over the first week. If your symptoms aren’t improving within two to three days of treatment, that’s a signal to follow up, as the bacteria may be resistant to the antibiotic you were prescribed.
Severe cases, particularly those involving vomiting that prevents you from keeping pills down, high fevers, or signs of sepsis, may require a hospital stay for intravenous treatment until symptoms stabilize enough to switch to oral medication.