Pyelonephritis

Pyelonephritis is a bacterial infection of the kidneys that can cause serious health problems if not treated quickly. While most cases begin as bladder infections that spread upward, prompt treatment with antibiotics can prevent lasting kidney damage and life-threatening complications.

Table of contents

• What is pyelonephritis?
• How does the infection develop?
• Signs and symptoms
• Who is at higher risk?
• How doctors diagnose the condition
• Treatment approaches
• Possible complications
• Preventing kidney infections

What is pyelonephritis?

Pyelonephritis is the medical term for a kidney infection. It is a type of urinary tract infection (UTI), which refers to infections anywhere in the system that produces and eliminates urine from your body^[1]. When bacteria or other germs infect the kidneys specifically, this causes inflammation and swelling that can lead to serious health problems^[2].

Kidney infections affect about 1 in 2,000 people each year in the United States, with approximately 250,000 office visits and 200,000 hospital admissions annually^[1][4]. The condition is more common in females than males and occurs frequently during pregnancy^[2].

There are two main types of pyelonephritis. Acute pyelonephritis is a sudden and severe kidney infection that develops rapidly^[5]. Chronic pyelonephritis refers to repeated or persistent kidney infections that occur over time, though this form is rare^[8].

Healthcare professionals also distinguish between complicated and uncomplicated pyelonephritis. Complicated cases include those affecting pregnant women, people with diabetes that is not well controlled, individuals with immune system problems, or those with structural abnormalities in the urinary system^[2].

How does the infection develop?

Bacterial infections are the most common cause of pyelonephritis. The bacteria Escherichia coli (E. coli) causes the majority of cases, accounting for 75 to 95 percent of infections^[1][13]. Other bacteria that can cause kidney infections include Proteus mirabilis, Enterobacter, and Staphylococcus^[1].

The infection usually starts in the lower urinary tract. Your body normally removes bacteria and germs through urination. The kidneys make urine to eliminate waste products. This urine travels through tubes called ureters to your bladder, which stores the urine until you use the bathroom. From the bladder, urine leaves your body through another tube called the urethra^[1].

Sometimes bacteria enter through the urethra and travel upward into the bladder, causing a bladder infection. If the bacteria continue moving upward through the ureters, they can reach one or both kidneys and cause pyelonephritis^[2]. Less commonly, bacteria can reach the kidneys through the bloodstream from another part of your body^[1].

Signs and symptoms

Symptoms of pyelonephritis typically develop rapidly, often within a few hours or over one to two days after infection begins^[5][8]. The most common symptoms include fever and pain in the lower back or side, just beneath the ribs^[2].

Common symptoms of a kidney infection include^[1][3]:

• Fever, often above 102°F (38.9°C)
• Chills and shaking
• Pain in your lower back, side, or flank area (the area just below the ribs)
• Pain or burning sensation when you urinate
• Cloudy urine that may contain blood or pus
• Urine that has a strong or foul smell
• Urgent or frequent need to urinate
• Nausea and vomiting
• General feeling of being unwell or tired

The pain from a kidney infection may travel around your side toward your lower abdomen. Unlike a simple bladder infection, a kidney infection is more likely to suddenly make you feel very sick and cause high fever^[1].

Symptoms can vary depending on age. Newborns may not have fever but show poor feeding and vomiting. Children under age 2 may have fever, poor appetite, vomiting, and diarrhea. In older adults, mental confusion may be the only symptom or the main sign of infection^[5][6].

Who is at higher risk?

Several factors increase your chances of developing pyelonephritis^[1][4]:

Being female. Women have a shorter urethra than men, which makes it easier for bacteria to travel from outside the body up to the bladder and kidneys. The incidence is highest in otherwise healthy women between 15 and 29 years of age^[1][11].

Pregnancy. Kidney infections are more common during pregnancy. Pressure on the bladder from pregnancy can increase risk, and these infections also increase the risk of premature delivery^[1][21].

Current or recent bladder infections. Having a urinary tract infection or bladder infection makes it more likely that bacteria will move up to the kidneys^[4].

Urinary blockages. Anything that prevents you from fully emptying your bladder allows bacteria to grow and move up to your kidneys. This includes kidney stones, an enlarged prostate in men, and uterine prolapse (when the uterus drops into the vagina)^[1].

Vesicoureteral reflux. This is a condition where urine flows backward from the bladder up into the ureters and kidneys instead of moving in the correct direction^[1][4].

Certain health conditions. Diabetes, HIV, weakened immune systems, and taking medications that suppress the immune system all increase infection risk^[1][4].

Problems with urination. Spinal cord injury, nerve damage affecting the bladder, or difficulty completely emptying the bladder increase the likelihood of infection^[4].

How doctors diagnose the condition

Diagnosis of pyelonephritis is typically based on your symptoms combined with laboratory tests^[2]. Your healthcare provider will ask about your symptoms and medical history, check your temperature, heart rate, and blood pressure, and examine your abdomen and back to check for tenderness near the kidneys^[11].

Urine tests are essential for diagnosis. A urinalysis checks your urine for white blood cells, red blood cells, bacteria, and other signs of infection^[3][11]. The absence of white blood cells and bacteria in the urine suggests an alternative diagnosis unless there is a blockage present^[13].

A urine culture should be obtained in all patients with suspected pyelonephritis. This test identifies the specific type of bacteria causing the infection and determines which antibiotics will be most effective for treatment^[11][13]. Results typically take 24 to 48 hours.

Your doctor may also order blood tests to check for bacteria in your bloodstream, evaluate kidney function, and measure your white blood cell count^[3][11]. Blood cultures are positive in 20 to 30 percent of cases, though they rarely change treatment plans^[13].

Imaging tests are not always necessary but may be recommended if you do not improve within 48 hours of starting treatment, if symptoms return after initial improvement, if complications are suspected, or if you have severe illness^[2][13]. Tests may include ultrasound, computed tomography (CT) scans, or other imaging studies to look at your kidneys and urinary tract^[3].

Treatment approaches

Antibiotics are the main treatment for kidney infections. The specific antibiotic and length of treatment depend on your health status and the bacteria found in your urine tests^[3][14].

Outpatient treatment. Most patients with uncomplicated pyelonephritis can be treated at home with oral antibiotics. Common antibiotic choices include fluoroquinolones such as ciprofloxacin or levofloxacin if local resistance rates are low (below 10 percent). Treatment typically lasts 5 to 7 days^[11][13].

If fluoroquinolone resistance in your community exceeds 10 percent, your doctor may give you an initial dose of an intravenous antibiotic (such as ceftriaxone or gentamicin) followed by oral antibiotics^[11]. Once culture results identify which bacteria are causing your infection, your doctor may adjust your antibiotic based on what will work best^[13].

Inpatient treatment. Hospital admission is recommended for people who are severely ill, pregnant, elderly, or have conditions that complicate treatment. Those who cannot keep down oral medications due to vomiting also need hospital care^[12][13]. Hospital treatment includes intravenous antibiotics and fluids^[14].

Most people begin to feel better within one to two days of starting antibiotics, though it is crucial to complete the full course of treatment even if you feel well^[3][14][21]. Stopping antibiotics early can cause the infection to return and may make future infections harder to treat.

Your healthcare provider may also recommend pain relievers, drinking plenty of fluids, and using a heating pad on your back or side for comfort^[17].

In rare cases, surgery may be necessary if you have an abscess, obstruction, kidney stones, or if the infection does not respond to antibiotics within 48 to 72 hours^[12].

Possible complications

When diagnosed early and treated properly, most kidney infections do not lead to complications^[4]. However, without treatment or in certain high-risk individuals, pyelonephritis can cause serious, potentially life-threatening problems^[1].

Possible complications include^[1][4]:

• Kidney scarring and damage that can lead to chronic kidney disease or reduced kidney function
• Acute kidney injury or kidney failure
• High blood pressure
• Abscesses (collections of pus) in or around the kidney
• Sepsis, a severe bloodstream infection that can lead to organ failure and death
• Emphysematous pyelonephritis, a serious condition where bacteria destroy kidney tissue and create gas, most common in people with diabetes
• Renal papillary necrosis, which damages parts of the kidney

Your risk of complications is higher if you are male, older, frail, pregnant, have structural problems in your urinary tract, have experienced repeated kidney infections, have diabetes or kidney disease, or have a weakened immune system^[4].

Even one episode of acute pyelonephritis can result in kidney scarring that may cause high blood pressure and reduced kidney function, particularly in children under age 2. This is why prompt medical care is critical^[6].

Preventing kidney infections

You can take several steps to reduce your risk of developing pyelonephritis^[17][21]:

• Drink plenty of water each day. This helps you urinate often, which flushes bacteria from your urinary system.
• Urinate when you feel the urge. Do not hold urine in your bladder for long periods.
• Treat bladder infections promptly. If you have symptoms such as burning when you urinate or needing to urinate frequently, contact your healthcare provider right away to prevent the infection from spreading to your kidneys.
• Urinate after sexual intercourse. This helps flush out any bacteria that may have entered the urethra.

For women, additional preventive measures include^[17]:

• Wiping from front to back after using the toilet
• Keeping the genital area clean using mild soap and water
• Changing sanitary pads frequently
• Avoiding feminine hygiene sprays and douches

If you have structural problems of the urinary tract or experience repeated kidney infections, your doctor may refer you to a kidney specialist (nephrologist) or urinary surgeon (urologist) to evaluate whether surgery or other treatments might help prevent future infections^[14].