Acute Pyelonephritis

Acute pyelonephritis is a bacterial infection of the kidneys that can cause sudden and severe symptoms, including fever, flank pain, and nausea. While most cases can be treated successfully with antibiotics, prompt medical attention is essential to prevent serious complications.

Table of contents

• What is acute pyelonephritis?
• What causes kidney infections?
• Who is at risk?
• Signs and symptoms
• How is it diagnosed?
• Treatment options
• Possible complications
• Prevention

What is acute pyelonephritis?

Acute pyelonephritis is a bacterial infection that causes inflammation of the kidneys. It is one of the most common kidney diseases and is considered a serious type of urinary tract infection (UTI), which is an infection anywhere in the urinary system^[1]. The infection typically affects the renal parenchyma (the functional tissue of the kidney), calices (cup-shaped structures that collect urine), and pelvis (the central collecting area of the kidney)^[4].

Kidney infections are more serious than lower urinary tract infections, which affect the bladder or urethra. About 1 in 2,000 people get a kidney infection every year in the United States^[1]. The condition accounts for approximately 250,000 office visits and 200,000 hospital admissions annually in the United States^[3].

Most episodes of acute pyelonephritis are uncomplicated and can be cured with no lasting kidney damage^[4]. However, if not treated properly, the infection can cause permanent damage to the kidneys or spread to the bloodstream, creating a dangerous situation^[1].

What causes kidney infections?

Bacterial infections are the most common cause of kidney infections. Viruses can also cause them, but this is rare in people who are healthy^[1]. The infection usually begins when bacteria enter the body through the urethra (the tube that carries urine out of the body) and travel upward through the bladder to reach the kidneys^[9].

Escherichia coli, more commonly known as E. coli, is by far the most common bacteria causing acute pyelonephritis, accounting for approximately 75 to 95 percent of uncomplicated cases^[13]. This bacteria is normally found in the gastrointestinal tract^[7]. Other bacteria that can cause kidney infections include Proteus mirabilis, Enterobacter, and Staphylococcus^[1].

In rare cases, bacteria can reach the kidneys through the bloodstream from another part of the body^[1].

Who is at risk?

The highest incidence of acute pyelonephritis is among otherwise healthy women between 15 and 29 years of age^[3]. Young women are particularly at risk, possibly because of the role of frequent sexual intercourse in introducing bacteria to the exterior opening of the urethra and from there to the bladder^[7]. Women have a shorter urethra than men, which makes it easier for bacteria to move up to their bladder and kidneys^[1].

Several factors can increase your risk of developing a kidney infection:

• Blockages in the urinary tract: Anything that keeps you from emptying urine out of your urinary tract can allow bacteria to grow and back up into your kidneys. This includes kidney stones, enlarged prostate, and uterine prolapse. Pressure on the bladder during pregnancy can also increase risk^[1].
• Vesicoureteral reflux: This is a condition where urine flows backward from the bladder toward the kidneys^[1].
• Medical conditions: Diabetes, HIV, and being on immunosuppressive medications put you at increased risk for infections^[1].
• Use of spermicidal contraceptives: These can increase the risk because they destroy the natural protective barrier of bacteria in the vaginal area^[7].
• Urinary catheters: Having a catheter or other foreign body in the urinary tract increases risk^[4].
• Previous urinary tract infections: Having a UTI increases susceptibility to kidney infections^[7].

Men are at relatively low risk of acute pyelonephritis unless they are older than 65 years of age^[7].

Signs and symptoms

The most distinctive features of acute pyelonephritis are pain in the back, flank (the area just below the rib cage and above the waist on either side of the back), or belly, along with fever at or above 38°C (100.4°F)^[7]. Symptoms usually appear within two days of infection^[1].

Common symptoms include:

• Fever, often greater than 38°C (100.4°F)^[7]
• Chills^[1]
• Pain in the lower back, side, or flank^[1]
• Pain or burning when urinating^[1]
• Bloody or cloudy urine that might smell bad^[1]
• Urgent or frequent need to urinate^[1]
• Nausea^[1]
• Vomiting^[1]
• General aching or feeling unwell^[2]

Most patients have fever, although it may be absent early in the illness. Flank pain is nearly universal, and its absence should raise suspicion of an alternative diagnosis^[8].

Symptoms can vary with age. In babies and toddlers, a high fever may be the only symptom^[7]. Newborns may show poor feeding and vomiting^[6]. In older adults (those over 65 years of age), the typical symptoms may be absent, and additional symptoms may include confusion, jumbled speech, or hallucinations^[7].

How is it diagnosed?

To check for a kidney infection, you may be asked to provide a urine sample to test for bacteria, blood, or pus in your urine^[16]. A positive urinalysis (urine test) confirms the diagnosis in patients with a compatible history and physical examination^[3]. The absence of pyuria (pus in the urine) and bacteriuria (bacteria in the urine) suggests an alternative diagnosis^[13].

Urine culture with antimicrobial susceptibility testing (a test that shows which antibiotics will work against the bacteria) should be performed in all patients before starting treatment and used to guide antibiotic therapy^[3]. Bacterial colony counts are typically greater than 100,000 CFU/mL (colony-forming units per milliliter)^[13]. Urine cultures are positive in 90 percent of patients with acute pyelonephritis^[15].

Your healthcare provider might also take a blood sample for a culture, which is a lab test that checks for bacteria or other organisms in your blood^[16]. Although blood cultures are positive in 20 to 30 percent of cases, there is little evidence that results influence management or outcome^[13].

Physical examination should include checking for tenderness when the area over the kidneys is tapped (called costovertebral angle tenderness), abdominal examination, and possibly pelvic examination^[13]. Pregnancy testing should be performed for all women of childbearing age^[13].

Imaging studies, such as ultrasound, CT scan (a test that uses X-rays and computers to create detailed pictures of the inside of the body), or a type of X-ray called a voiding cystourethrogram, are not necessary in uncomplicated cases^[3]. However, imaging is warranted for patients with sepsis (a life-threatening response to infection), concern for kidney stones, new kidney injury, or lack of improvement within 48 to 72 hours of appropriate therapy^[13]. Contrast-enhanced CT (CT scan with dye injected into a vein) of the abdomen and pelvis is the preferred imaging method when needed^[3].

Treatment options

Antibiotics are the first line of treatment for kidney infections^[16]. The drugs used and the length of treatment depend on your health and the bacteria found in your urine tests^[16]. Symptoms of a kidney infection often begin to clear up within a few days of treatment, but you need to take the full course of antibiotics even if you start feeling better^[16]. Most patients respond to appropriate management within 48 to 72 hours^[3].

Outpatient treatment is appropriate in patients who have uncomplicated disease and can tolerate oral therapy^[3]. Ambulatory younger women who present with signs and symptoms of uncomplicated acute pyelonephritis may be candidates for outpatient therapy if they are otherwise healthy and not pregnant^[11].

For outpatient treatment, fluoroquinolones (such as ciprofloxacin for 7 days or levofloxacin for 5 days) are appropriate first-line oral antibiotic therapies when the bacteria is known to be susceptible and local resistance rates are low (less than 10 percent)^[3]. Trimethoprim/sulfamethoxazole for 14 days is also an appropriate choice when the organism is known to be susceptible, but should not be used for initial treatment because of high resistance rates^[3].

When local resistance to a chosen oral antibiotic likely exceeds 10 percent, one dose of a long-acting broad-spectrum parenteral antibiotic (given by injection or through a vein) such as ceftriaxone, ertapenem, or an aminoglycoside should be given while awaiting susceptibility data, followed by oral therapy^[3].

Extended emergency department or observation unit stays are an appropriate option for patients who initially warrant intravenous therapy^[3].

Hospitalization is usually appropriate for patients who are severely ill, pregnant, elderly, or who have conditions that increase the complexity of management^[11]. If your kidney infection is severe, you may need to go to the hospital. Treatment might include antibiotics and fluids through a vein in your arm^[16].

Patients admitted to the hospital should receive parenteral antibiotic therapy, and those with sepsis or risk of infection with a multidrug-resistant organism should receive antibiotics with activity against extended-spectrum beta-lactamase-producing organisms (bacteria that are resistant to many common antibiotics) until susceptibility data are available^[3].

In addition to antibiotics, pain relief may be needed. Hot showers or heating pads set on low can help relieve pain. Drinking plenty of water may help wash out bacteria causing the infection^[19].

Emergency surgery may be indicated if fever or positive blood culture results persist longer than 48 hours, if the patient’s condition deteriorates, or if the patient appears toxic for longer than 72 hours^[11].

Pregnant patients with pyelonephritis are at significantly elevated risk of severe complications and should be admitted and treated initially with parenteral therapy^[3].

Possible complications

Sometimes, kidney infections can lead to life-threatening complications, especially in people with a weakened immune system or other underlying health issues^[1]. An episode of acute pyelonephritis may lead to significant kidney damage, acute kidney injury, abscess formation (collections of pus in or around the kidney), sepsis, septic shock, and multiorgan system failure^[2].

The inflammation and dehydration from just one kidney infection can result in scarring that can cause high blood pressure and reduced kidney function^[6]. Repeat acute kidney infections can ultimately lead to the need for a kidney transplant^[6].

Specific complications include:

• Emphysematous pyelonephritis: This is a condition where bacteria start destroying parts of the kidneys and create gas. It is most common in people with diabetes^[1].
• Renal papillary necrosis: This is a condition that damages the kidneys^[1].
• Renal or perinephric abscess: Collections of pus in or around the kidney^[2].

Patients who do not respond to appropriate management within 48 to 72 hours should be evaluated with imaging and repeat cultures while alternative diagnoses are considered^[3].

Prevention

Several steps can help prevent kidney infections:

• Drink plenty of water each day. This helps you urinate often, which clears bacteria from your system^[19].
• Urinate when you have the urge. Do not hold your urine for a long time^[19].
• Urinate right after sexual intercourse if you are a woman^[19].
• After using the toilet, wipe from front to back if you are a woman^[19].
• Change sanitary pads often. Avoid douches, feminine hygiene sprays, and other feminine hygiene products that have deodorants^[19].
• Men should keep the tip of the penis clean^[19].
• If you have symptoms of a bladder infection, such as burning when you urinate or having to urinate often, call your doctor so you can treat the problem before it gets worse and spreads to the kidney^[19].