A kidney infection, also known as pyelonephritis, occurs when harmful bacteria reach the kidneys as part of a urinary tract infection (UTI). Most UTIs only affect the lower urinary tract, meaning the urethra and bladder, but sometimes these infections move into the upper urinary tract, affecting one or both kidneys. While rare, it’s also possible to get a kidney infection following surgery, if bacteria enter the body during the procedure and travel through the bloodstream to the kidneys.
If you have symptoms of a UTI or bladder infection (also known as cystitis), such as pain with urination, smelly urine, low back pain, or discolored urine, it’s important to seek medical treatment to prevent the infection from spreading to your kidneys.
Kidney infections can be quite painful and require prompt evaluation and treatment. If your infection isn’t treated soon enough, it may permanently damage your kidneys or spread to your bloodstream, possibly leading to sepsis and the impairment of other vital organs.
In people ages 65 and older, the above signs and symptoms of a kidney infection may not occur. Instead, these individuals may experience confusion, hallucinations, or difficulty speaking.
In newborns and very young children, the only sign of a kidney infection may be a high fever.
Kidney infections can be caused by bacteria or viruses that spread in your urinary tract, but bacterial infections are much more common. In fact, about 90 percent of kidney infections are caused by a single type of bacteria, Eschericia coli, or E. coli.
The infection is thought to occur from bacteria that travel from your gastrointestinal tract to your skin surface, through your urethra to your bladder, then through the tubes (known as ureters) that connect your bladder and kidneys.
Normally, urine flushes any potentially harmful bacteria out of your ureters before they can cause an infection. But sometimes this process is hindered by:
Structural abnormalities in your ureters or kidneys
Kidney stones
Enlarged prostate (benign prostatic hyperplasia)
Urine backflow (reflux) from your bladder to your kidneys
It’s also possible for bacteria from your bloodstream to enter your kidneys and cause an infection. This happens most commonly with staphylococcus, or staph, bacteria.
Kidney infections that spread from your bloodstream tend to develop after surgery or as a consequence of another infection elsewhere in the body. For example, if an artificial joint or heart valve becomes infected, the kidneys can become secondarily infected.
It’s very uncommon for kidney surgery to lead to a kidney infection.
The following factors can increase your risk of developing a kidney infection:
Being female: In the female anatomy, the urethral opening (where urine exits the body) is close to the vagina and anus, which makes it easy for bacteria from these orifices to enter the urethra. In the male anatomy, the urethral opening is further away from the anus. Female urethras are also shorter than male urethras, which makes it easier for bacteria to travel to the bladder and cause an infection.
Being sexually active: Sexual intercourse can make it easier for bacteria in your genital area or anus to enter your urethra, especially for women. Using condoms with spermicidal coating also increases a woman’s risk of developing a UTI.
Being pregnant: When you’re pregnant, your enlarged uterus can press against and squeeze your ureters, reducing the flow of urine from your kidneys to your bladder. This reduced urine flow can make it easier for bacteria in your bladder to migrate to your kidneys.
Having impaired urine flow: The flow of urine throughout your urinary tract is an important barrier against infection. This flow can be slowed by a narrowed urethra, enlarged prostate, or kidney stone.
Having a weakened immune system: Your immune system can be weakened by health conditions such as diabetes, HIV, and cancer, or by certain drugs.
Wearing a catheter: Long-term use of a urinary catheter to drain urine from the bladder, such as during a surgical procedure or hospital stay, raises the risk of developing a UTI.
Having nerve damage: If you have a spinal cord injury or nerve damage around your bladder, you may not notice when you develop a bladder infection, which can allow it to progress to your kidneys more easily.
Having urine reflux problems: A medical condition called vesicoureteral reflux results in small amounts of urine flowing backward from your bladder into your kidneys, potentially carrying bacteria with it. Vesicoureteral reflux is most likely to be diagnosed during childhood.
Having trouble emptying your bladder: If your bladder doesn’t empty fully, known as urinary retention, the remaining urine can contribute to developing an infection.
A kidney infection is usually diagnosed based on an assessment of your symptoms, a physical exam, and urine test results that indicate bacteria in your urinary tract.
Your doctor will likely ask about your health history and any conditions that might place you at a higher risk of a kidney infection, such as having an enlarged prostate gland or a medical condition that can cause urinary retention, such as multiple sclerosis.
Sometimes a doctor will order imaging tests, such as an ultrasound or computerized tomography scan, to look for signs of swelling or other abnormalities in your kidneys or bladder.
Kidney infections are treated with antibiotics, either oral or intravenous (IV), depending on the severity of your infection and its symptoms.
People with severe illness may need to be hospitalized for several days or longer for initial treatment. During this time, you may receive IV antibiotics in addition to fluids, while your medical team monitors you closely.
The oral antibiotics prescribed for kidney infection treatment are typically taken for 7 to 14 days to make sure all of the bacteria causing the infection have been killed. It’s most common for your doctor to prescribe a 14-day course of antibiotics.
For reasons that aren’t fully understood, kidney infections in men are often resistant to treatment and may require as many as six weeks of antibiotic therapy.
Your doctor may order follow-up tests after the antibiotic treatment to make sure you no longer have an infection.
Medication Options for Kidney Infection
Your doctor will decide what antibiotic to prescribe, and for how long, based on your symptoms and the results of your urine tests. Your doctor may start you on one medication right away but change it later if your urine test results indicate that a different antibiotic may be more effective.
Drugs typically taken by mouth for kidney infection include:
Amoxicillin-clavulanate (Augmentin)
Cephalexin (Keflex)
Ciprofloxacin (Cipro)
Levofloxacin (Levaquin)
Trimethoprim-sulfamethoxazole (Bactrim, Septra)
If additional therapies are needed, you may be given the following drugs via IV in your doctor’s office:
Ceftriaxone (Rocephin)
Ciprofloxacin (Cipro IV)
Gentamicin (Garamycin)
All of these drugs and others may be considered for IV treatment if you need to be hospitalized for a severe kidney infection.
Complementary and Integrative Therapies
There aren’t any effective complementary or integrative methods or therapies for curing a kidney infection.
However, there may be ways you can increase your comfort while being treated with antibiotics, such as by placing a heating pad on your abdomen, back, or side to ease any pain in those areas. Drinking plenty of fluids can also help flush the bacteria causing the infection from your system. Getting plenty of rest will help in your recovery from the infection as well.
Preventing kidney infections usually starts with preventing UTIs in the lower urinary tract. Take the following steps to help prevent UTIs:
Drink lots of water throughout the day.
Urinate when you feel the urge to do so; don’t wait.
After using the toilet, wipe from front to back so you don’t spread bacteria from your anus to your urethra.
Urinate after having sex.
Don’t use unnecessary cleansing or deodorizing products in the genital area.
Steer clear of birth control methods that can raise the risk of a UTI.
If you do develop a UTI, get it treated as soon as possible. See your primary healthcare provider for treatment, or visit an urgent care facility for diagnosis and a prescription for antibiotics.
Treating a UTI promptly may prevent it from spreading from your bladder to your kidneys.
A kidney infection usually starts out as a UTI that affects the bladder. There’s no rule for how long it takes for a UTI to spread from your bladder to your kidneys.
If left untreated, a kidney infection may not resolve on its own, potentially becoming a severe infection, which can cause sepsis or lead to a chronic or recurrent infection.
When treated with antibiotics, you may start to feel better two to three days after starting the drug. It’s important to continue your treatment for the entire course that’s prescribed.
For a mild kidney infection, treatment can last 7 to 14 days. It may take a week or longer for your symptoms to resolve with treatment. A severe or complicated kidney infection may take much longer to treat, depending on how far the infection has spread and what other complications it has caused.
If it isn’t treated promptly, a kidney infection can lead to a number of potentially serious complications.
You’re more likely to develop a complication from a kidney infection if you have:
Prior kidney disease
A history of kidney infections
A structural abnormality in your urinary tract
The following complications can result from a kidney infection:
High blood pressure: Your blood pressure can rise to unhealthy levels as your immune system tries to fight your infection.
Kidney failure: If it’s serious enough, an infection can stop your kidneys from effectively removing waste products from your blood.
Scarring: If you develop scars in your kidneys from an infection, your kidneys may not be able to function properly, potentially leading to chronic kidney disease.
Blood infection: One of the main jobs of your kidneys is to filter waste products out of your blood. A kidney infection can spread to your entire bloodstream in this process. A bloodstream infection can, in turn, lead to sepsis, which is a severe inflammatory reaction to bacteria. Sepsis can be life-threatening.
Renal or perinephric abscess: If the infection in your kidney isn’t treated promptly, the bacteria may create an abscess, or pocket of pus, inside or next to your kidney.
Pregnancy complications: A kidney infection during pregnancy raises the risk of low birth weight in your baby.
It’s estimated that each year, 1 in 2,000 people in the United States develop a kidney infection. Kidney infections are much more common among pregnant women, occurring in about 2 percent of pregnancies. There are also about 200,000 hospital visits for kidney infections annually in the United States.
One important area of research for kidney infection is antibiotic resistance, which occurs when bacteria have developed an ability to block the effect of the drugs designed to kill them. Currently, guidelines for treating kidney infections recommend adding IV antibiotics to oral drugs when a certain percentage of bacteria from a urine sample show signs of resistance.
“Treatment for kidney infections has largely stayed the same over the last several years,” says Amin S. Herati, MD, an assistant professor of urology at Johns Hopkins Medicine in Baltimore. “[But] there are some new therapies in the pipeline that are very exciting,” he says.
One promising potential treatment on the horizon, says Dr. Herati, is bacteriophage therapy, which involves injecting a virus that targets specific bacteria, causing them to burst and die. This approach could be useful for UTIs and kidney infections in which antibiotic resistance is a problem.
While many diseases affect different populations in the United States at different rates, there isn’t much information available on the relative risk of kidney infection among different racial and ethnic groups.
Black Americans are more than three times as likely as white Americans to have kidney failure and are at higher risk of kidney disease than any other group. But kidney infection rarely leads to kidney failure, accounting for only a tiny sliver of cases.
There is some evidence that the risk of getting a UTI during pregnancy, which can develop into a kidney infection, also varies for different groups. Non-Hispanic Native Hawaiian/Pacific Islander women, non-Hispanic Black women, non-Hispanic Asian women, and Hispanic women all present an elevated risk of UTI during pregnancy, compared with non-Hispanic white women.
Kidney infection can develop from or lead to several other health conditions, including:
Urinary tract infection: Most UTIs affect the lower urinary tract, which includes the urethra and bladder. Bacteria can migrate from the bladder to the kidneys, causing infection there.
Benign prostatic hyperplasia: Having an enlarged prostate can reduce the flow of urine, making a person more likely to develop a UTI or kidney infection.
Sepsis: One of the most serious potential complications of a kidney infection, sepsis is an extreme immune system response to infection, resulting in widespread inflammation and sometimes vital organ failure and death.
Potentially starting as a urinary tract infection, a kidney infection occurs when bacteria travel up your urinary tract.
Symptoms of kidney infection include fever, back pain, and nausea. Prompt treatment is required to prevent serious complications, such as kidney damage or sepsis.
Kidney infections are treated with oral or IV antibiotics, depending on the severity of the infection and its symptoms.
It’s important to see a doctor if you suspect you have a UTI, in order to catch an infection early and stop it from spreading to your kidneys.
