The kidneys are vital organs responsible for filtering waste from the blood and excreting it from the body in the form of urine. When abnormalities occur in the urinary tract, many people may overlook minor symptoms such as painful urination or back pain. However, these symptoms may actually be warning signs of pyelonephritis. If left untreated without proper care, it can progress into a serious health problem. Understanding the causes, symptoms, and self-care approaches is therefore important to help manage this condition appropriately.
What is pyelonephritis?
Pyelonephritis is a condition in which there is a bacterial infection in the kidney tissue or renal pelvis. In most cases, it begins with an infection in the lower urinary tract, such as the urethra or bladder. The pathogen then travels upward to the kidneys, causing inflammation. This condition is considered more severe than typical cystitis. If the patient is not evaluated and treated by a physician, it may lead to complications that can be dangerous to kidney function and other body systems.
How many types of pyelonephritis are there?
Infections in the renal pelvis can present with different symptoms and levels of severity. Medically, pyelonephritis is classified into two main types in order to plan appropriate treatment, as follows:
Acute pyelonephritis (Acute Pyelonephritis)
This is an infection that develops rapidly and presents with severe symptoms. Patients often have high fever, chills, pain in the flank/lower back area, and abnormal urination. Although symptoms may appear severe, if diagnosed and treated promptly with antibiotics, symptoms often begin to improve within 2–3 days after starting medication, and full recovery may take about 2–3 weeks depending on severity.
Chronic pyelonephritis (Chronic Pyelonephritis)
This is a condition of recurrent, ongoing infection and inflammation over a long period, often associated with abnormalities of the urinary tract, such as vesicoureteral reflux (urine flowing back up to the kidneys) or chronic obstruction, such as kidney stones, which allow bacteria to embed and accumulate, making treatment difficult. Repeated inflammation damages kidney tissue, and in some cases may lead to chronic kidney failure with progressively declining kidney function.
What causes pyelonephritis?
The main causes of pyelonephritis are often related to bacteria and abnormalities within the urinary tract that promote microbial growth. Common factors include the following:
Bacterial infection in the urinary tract
A key cause is often Escherichia coli (E. coli), a bacterium that lives in the gastrointestinal tract and large intestine. When this bacterium from the anal area contaminates the area around the urethral opening and enters the urethra, it can spread to the bladder and ascend to the renal pelvis, ultimately causing infection.
Urinary tract obstruction
When obstruction occurs in the urinary tract, urine cannot flow and be excreted normally, leading to retention and accumulation in the bladder, ureters, or kidneys. This urinary stasis provides an ideal environment for bacterial growth and multiplication. Causes of obstruction may include urinary stones, benign prostatic enlargement, or urethral stricture/obstruction.
What are the symptoms of pyelonephritis?
People with pyelonephritis often have warning signs indicating inflammation and infection within the body. Early symptoms that can be observed include:
- High fever with severe chills
- Pain in the flank, lower back, or radiating pain at the side
- Frequent urination, persistent urge to urinate, or passing small amounts of urine
- Burning or painful urination
- Cloudy urine, unusually foul odor, or urine mixed with blood and pus
- Nausea and vomiting
- Fatigue, loss of appetite, rapid physical decline
Who is at risk for pyelonephritis?
Although pyelonephritis can occur in people of any sex and age, certain groups have anatomical or health conditions that make them more prone to infection and inflammation than usual, as follows:
Women and pregnant women
Women are at higher risk than men because the urethra is shorter and located closer to the vagina and anus, making it easier for bacteria to enter the urinary tract. In addition, in pregnant women, hormonal changes cause the ureters to dilate, and the enlarging uterus may compress the urinary tract, impairing urine drainage and making infection more likely.
People with immunodeficiency or underlying diseases
Patients with underlying conditions such as diabetes, people living with HIV, or those who must take immunosuppressive drugs have weaker immune systems than usual. This reduces the body’s ability to fight bacteria, making it harder to eliminate invading pathogens and increasing the risk of pyelonephritis.
People with problems or abnormalities in urination
Patients who cannot fully empty their bladder—such as those with stones, benign prostatic enlargement, or those who require long-term urinary catheterization—are at risk for bacterial accumulation and ascending infection that can damage tissue in the renal pelvis.
Complications if pyelonephritis is not treated promptly
Pyelonephritis is not just ordinary pain or fever. If symptoms are misjudged or left untreated without promptly consulting a physician, it may lead to life-threatening complications, including:
- Bloodstream infection (sepsis): Bacteria may spread from the kidneys into the bloodstream, causing systemic inflammation, a critical condition that can be fatal.
- Kidney failure: Severe infection or chronic inflammation can damage kidney tissue, causing the kidneys to lose their ability to filter waste, leading to toxin buildup in the body.
- Kidney abscess: A pocket of pus may form within the kidney tissue, damaging the kidney structure.
- Complications during pregnancy: If it occurs in pregnant women, it may increase the risk of preterm birth or low birth weight.
Diagnosis of pyelonephritis
When patients present with suspicious symptoms, a detailed medical history and laboratory testing help physicians assess severity and plan appropriate treatment. The steps include:
- Medical history and physical examination: The physician will ask about pain and urination patterns and gently tap the back/flank area to check for tenderness.
- Urinalysis: To look for white blood cells, red blood cells, or bacteria in the urine, which are signs of infection.
- Urine culture: To identify the bacteria causing the disease, allowing appropriate antibiotic selection.
- Blood tests: To assess complete blood count and kidney function, and to check for bloodstream infection.
- Imaging studies: Such as ultrasound or CT scan to detect anatomical abnormalities or causes of obstruction such as stones—especially in patients with severe symptoms, no improvement within 48–72 hours after starting medication, or suspicion of stones or obstruction.
Treatment approaches for pyelonephritis
Treatment of pyelonephritis focuses on eliminating the causative bacteria, relieving pain, and preventing complications. Physicians will select treatment based on disease severity, as follows:
Oral antibiotics
For patients in the early stage without severe complications, the physician will prescribe oral antibiotics to kill the bacteria. Typically, antibiotics must be taken continuously for about 7–14 days. Patients must complete the full course exactly as prescribed, even if symptoms improve. This helps prevent antibiotic resistance and recurrence. If symptoms do not improve within 48–72 hours after starting medication, patients should return to the physician to evaluate for obstruction or a kidney abscess.
Intravenous antibiotics
In cases of high fever, severe vomiting that prevents taking oral medication, dehydration, high-risk patients with low immunity, pregnant women, or urinary tract obstruction, the physician may recommend hospital admission for intravenous antibiotics and fluids. This allows the medication to act quickly against the infection under close medical and nursing supervision.
Surgical treatment
If pyelonephritis is caused by structural abnormalities or urinary tract obstruction—such as a large stone, ureteral narrowing, or a severe renal abscess—the physician will relieve the obstruction along with antibiotic treatment. When kidney infection occurs together with obstruction, it is an emergency that requires drainage of infected urine from the kidney first, either by placing a ureteral stent (Ureteral Stent) or performing percutaneous nephrostomy. After the infection is controlled, surgery is then performed to remove the obstruction, such as endoscopic stone fragmentation, pus drainage, or structural correction so that the urinary tract can return to normal function.
How to prevent pyelonephritis and prevent recurrence
Small lifestyle changes in daily life can effectively reduce the risk of pyelonephritis and urinary tract infections. Recommendations include:
- Drink enough clean water, at least 7–8 glasses per day, to help flush and eliminate bacteria from the urinary tract. However, people with kidney disease or heart disease, or those whose physicians restrict fluid intake, should consult a physician first.
- Avoid holding urine for long periods; if you feel the urge, go to the restroom immediately.
- Clean the genital area and around the anus properly. Especially for women, always wipe from front to back to prevent transferring bacteria from the anus into the urethra.
- Urinate and clean the body every time after sexual intercourse to flush out bacteria that may have entered.
- Avoid vaginal douching with harsh chemicals, as it reduces beneficial bacteria that help maintain balance and allows pathogenic bacteria to grow.
- People with recurrent urinary tract infections, men with urinary tract infections, or those with stones should see a urologist to evaluate underlying abnormalities, because addressing the root cause helps prevent recurrence.
Urology Center, Bangkok Hospital, ready to care for urinary tract disorders
Urinary tract disorders are common issues that deserve close attention. The Urology Center at Bangkok Hospital is fully equipped to provide care and treatment for urinary tract disorders, with a team of experienced specialist physicians working collaboratively with a multidisciplinary team to design treatment plans appropriate to each patient’s condition. Combined with medical technology for diagnostic evaluation and surgery, the focus is on patient health and restoring quality of life so patients can return to daily activities to their fullest potential.
Article summary
Pyelonephritis is a disease caused by a urinary tract infection that spreads into kidney tissue, accompanied by high fever, chills, back pain, and abnormal urination. If recognized early and treated promptly by a physician with antibiotics, it can be treated and kidney damage can be prevented. Monitoring for bodily abnormalities and improving drinking and urination habits can help reduce the risk of developing this disease.
Frequently asked questions (FAQ) about pyelonephritis
1. How is pyelonephritis different from cystitis?
Cystitis is an infection in the lower urinary tract. Symptoms are often limited to painful urination or lower abdominal pain. Pyelonephritis occurs when the infection ascends to the kidneys, leading to more severe symptoms such as high fever, chills, and back pain, with a higher risk of complications.
2. Can pyelonephritis resolve on its own?
You should not wait for it to resolve on its own. Treatment requires antibiotics to kill the bacteria. If left untreated, the infection may spread into the bloodstream or damage kidney tissue and lead to kidney failure.
3. Can pyelonephritis be transmitted sexually?
This is not a sexually transmitted infection. However, sexual activity can be a factor that pushes bacteria from the genital or anal area into the urethra and may lead to infection.
4. If pyelonephritis occurs during pregnancy, can it harm the baby?
Yes, it can. Severe infection can increase the risk of preterm birth and may cause the newborn to have a lower-than-normal birth weight. Pregnant women should see a physician immediately if abnormal symptoms occur.
5. What symptoms of pyelonephritis require going to the emergency room immediately?
If you develop rapidly rising high fever, severe back or flank pain, inability to urinate, nausea/vomiting to the point of being unable to drink or eat, or confusion/decreased alertness, you should go to the emergency room immediately, as these may be signs of bloodstream infection.
