Yes. Kidney infections are usually caused by bacteria, but viruses can cause them less often. Many kidney infections begin when germs enter the urinary tract and travel from the bladder to one or both kidneys. In some cases, a virus from another part of the body may reach the kidneys through the bloodstream. Because treatment depends on the cause, prompt medical assessment is important.
What usually causes a kidney infection?
A kidney infection, also called pyelonephritis, affects one or both kidneys. It is a type of urinary tract infection (UTI). According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), bacteria are the most common cause, while viruses are a less common cause.
Most bacterial kidney infections develop when bacteria enter the urinary tract and move upward. They may first infect the bladder before traveling through the ureters, which are the tubes connecting the kidneys to the bladder. The Merck Manual Professional Edition identifies bacteria, particularly certain types of bacteria that normally live in the digestive tract, as common causes of these infections. Escherichia coli (E. coli) is a leading example.
Kidney infections do not always begin in the bladder. In some cases, harmful organisms can reach the kidneys through the bloodstream from another part of the body. This provides one possible route for a viral infection to affect the kidneys, although viral causes are less common than bacterial causes.
How can a virus cause a kidney infection?
Viruses are infectious agents that enter the body's cells to reproduce. Most kidney infections are not caused by viruses, but some viral infections can involve the kidneys. A virus may reach the kidneys through the bloodstream rather than following the usual route of a bladder infection spreading upward.
The term viral kidney infection can be used to describe an infection involving the kidneys in which a virus is responsible. However, viral illnesses can also affect kidney function or cause other kidney-related problems without producing the same kind of infection as typical bacterial pyelonephritis. These conditions should not automatically be treated as interchangeable because their causes and management may differ.
Having a cold, flu-like illness, or another viral illness does not by itself mean that the kidneys are infected. A healthcare professional considers the symptoms, medical history, examination findings, and appropriate test results to determine whether the kidneys are involved and what may be causing the problem.
What symptoms may occur with a kidney infection?
The symptoms of a kidney infection can overlap whether the underlying cause is bacterial or viral. The Mayo Clinic describes several possible symptoms, including fever, chills, pain in the back or side, and changes in urination. These experiences can occur for different reasons, so they do not establish which organism is responsible.
- Fever or chills.
- Pain or a burning feeling when urinating.
- Needing to urinate more often or feeling an urgent need to urinate.
- Pain in the back, side, or groin.
- Cloudy, foul-smelling, dark, or bloody urine.
- Nausea or vomiting.
Children may show different signs. In children younger than 2 years, a kidney infection may cause a high fever without the more recognizable urinary symptoms. Feeding difficulties and poor weight gain may also occur. Older adults and people who have difficulty communicating their symptoms may need particular attention to changes in their overall condition.
Prompt medical assessment is important when a kidney infection is suspected, especially when fever or chills occur with back or side pain, painful urination, or vomiting. Confusion, rapid breathing, shortness of breath, or a marked decline in general condition may indicate a serious infection requiring emergency care.
How do doctors determine whether a kidney infection is viral or bacterial?
Symptoms alone generally cannot identify the organism responsible for a kidney infection. According to the NIDDK's guidance on kidney infection diagnosis, healthcare professionals may consider medical history, a physical examination, and laboratory or imaging tests when assessing a possible kidney infection.
Common investigations include:
- Urinalysis: A urine sample is examined for findings such as blood and white blood cells that may be associated with inflammation or infection.
- Urine culture: This test identifies certain bacteria in the urine and may help determine which antibiotics are appropriate when a bacterial infection is present.
- Blood tests: These may help assess whether there is a serious infection and provide information about kidney function.
- Imaging tests: Ultrasound or other imaging may be used when the clinical situation suggests that additional investigation is necessary.
A urine culture is useful for identifying many common bacterial causes, but the full evaluation depends on the circumstances. If a viral cause or another kidney condition is suspected, the healthcare professional determines whether additional testing is appropriate. The choice of tests depends on the findings rather than on a single symptom.
Does treatment differ for viral and bacterial kidney infections?
Yes. Treatment depends on the organism involved and the person's clinical condition. The NIDDK's kidney infection treatment guidance explains that bacterial kidney infections are treated with antibiotics. Depending on the situation, these medicines may be taken by mouth or given through a vein, and hospital treatment may be needed when someone is seriously ill.
Antibiotics do not treat viruses. As explained by MedlinePlus, antibiotics work against certain bacterial infections, not viral infections. Therefore, an antibiotic is not a treatment for a virus itself. If the cause is uncertain, a healthcare professional should determine the appropriate approach rather than assuming that antibiotics or antiviral medicines are necessary.
There is no single treatment plan that applies to every viral infection involving the kidneys. The approach depends on the specific cause, the effects on kidney function, and whether another infection or complication is present. Do not use leftover antibiotics or take prescription medicines intended for another person.
When should you seek medical care?
Contact a healthcare professional promptly if you have symptoms that could indicate a kidney infection. Early assessment matters because an untreated kidney infection can sometimes lead to lasting kidney damage or allow bacteria to enter the bloodstream. A person who is already receiving treatment should seek further medical advice if symptoms persist, return, or worsen.
Seek emergency medical care for symptoms such as confusion, difficulty breathing, rapid breathing with marked illness, or a sudden and significant deterioration in your condition. People who are pregnant, have a weakened immune system, have known kidney problems, or are caring for a young child with a high fever should seek timely professional guidance rather than delaying assessment.
The main point is that kidney infections are usually bacterial, but viruses can cause them less often. Because the symptoms can overlap and treatment differs according to the cause, appropriate medical evaluation is the safest way to establish what is happening and determine the next steps.