Patient Basics: Asymptomatic Bacteriuria

Asymptomatic bacteriuria means a urine test finds bacteria, but you have no signs of a bladder or kidney infection. It is common, especially in older adults, and for most people it causes no harm. Most people with it should not take antibiotics. Pregnancy is the main exception.

Key points

• It means bacteria in the urine without burning, urgency, fever or other signs of infection.
• It is common in older adults, women, people with diabetes and anyone with a urinary catheter.
• For most people, antibiotics don’t help. They can cause side effects, severe diarrhea and germs that resist treatment.
• Pregnant women are tested early in pregnancy and treated if bacteria are found.
• People about to have certain kinds of urinary tract surgery are also tested and treated.
• Cloudy or strong-smelling urine on its own is not a sign of infection.

What asymptomatic bacteriuria means

Many people carry bacteria in their urine and never know it. The germs, often E. coli from the gut, live in the bladder without causing swelling or pain. They may stay for months, or come and go on their own.

Doctors find it with a urine culture. In this lab test, a urine sample is kept warm so any bacteria can grow, and then the type and amount are measured. When a large number of one type grows, but the person feels fine, the result is called asymptomatic (no symptoms) bacteriuria (bacteria in the urine). For women, doctors may want a second sample that shows the same germ before they call it that.

A urine sample can also show white blood cells, the body’s infection fighters. That is common in people with bacteriuria and is not, by itself, a reason to treat.

Who is likely to have it

• Women, more often as they get older
• Older adults, especially people living in nursing homes, where it is very common
• People with diabetes
• Anyone with a urinary catheter. Nearly everyone who has one for more than a few weeks will have bacteria in the urine.
• People with a spinal cord injury or a bladder that doesn’t empty well
• Some pregnant women

Why it usually isn’t treated

Studies in older women, people with diabetes and people with catheters found that killing the bacteria didn’t prevent later infections or help people live longer. The bacteria often came back soon after the antibiotic was stopped.

Antibiotics also carry risks:

• Upset stomach, diarrhea and rashes
• Clostridioides difficile (C. diff), a gut infection that can cause severe diarrhea
• Vaginal yeast infections
• Allergic reactions
• Germs that stop responding to antibiotics, which makes a true infection harder to treat later

Because of this, doctors don’t test the urine of people who feel well, and don’t treat bacteria found by chance, in these groups:

• Healthy women who aren’t pregnant
• Older adults, at home or in nursing homes
• People with diabetes
• People with long-term catheters or spinal cord injury
• People about to have most other kinds of surgery, including hip and knee replacement

When asymptomatic bacteriuria is treated

During pregnancy

In pregnancy, bacteria in the urine raise the risk of a kidney infection (pyelonephritis). They may also raise the chance of an early birth or a small baby. So a urine culture is done at an early prenatal visit, even if you feel fine. If it finds bacteria, you’ll take a short course of an antibiotic that is safe in pregnancy. Your urine may be tested again afterward to make sure the germs are gone.

If the culture finds group B strep, a germ that can make newborns sick, you will also get antibiotics through a vein during labor.

Before some urinary tract procedures

Some operations on the prostate, bladder or kidney can cause bleeding inside the urinary tract. One example is surgery done through the urethra to shrink an enlarged prostate. Bacteria can then get into the blood. Your urologist will test your urine beforehand and, if bacteria grow, give an antibiotic just before the procedure.

Older adults with confusion or falls

When an older person becomes suddenly confused (delirium), falls or seems more tired than usual, a urine test is often one of the first things done. Bacteria are so common in older adults’ urine that a positive test doesn’t prove the urine is the cause.

Unless the person has fever, chills, back or side pain, or new bladder symptoms, current guidelines advise looking for other causes first. These include dehydration, a new medicine, constipation, poor sleep, pain or an infection somewhere else. Antibiotics are started when signs point to a true infection, or right away if the person is very ill. If a family member is in the hospital or a nursing home, it’s fair to ask what else the care team is checking.

Signs of a real urinary tract infection

• Burning or pain when you pee
• Needing to pee often or urgently
• Pain low in the belly
• Blood in the urine
• Fever, chills or pain in the back or side, which can mean a kidney infection

Cloudy or smelly urine on its own

Many people look up bacteriuria after noticing urine that looks or smells different. Without burning, urgency, fever or pain, these changes usually have a simple cause.

• A strong or ammonia-like smell. Urine smells stronger when it is concentrated, from drinking too little or sweating a lot. Asparagus, coffee and some vitamins and medicines can change the smell too.
• Cloudy or hazy urine. Harmless minerals called phosphates can cloud urine, especially after a meal. Vaginal discharge or semen mixed into the sample can do the same.
• Mucus threads. A few thin threads in a urine test are normal. They come from the lining of the urinary tract or, in women, from the vagina.

Drink more water for a day or two. See a doctor if the change lasts, or if it comes with signs of infection, blood in the urine, or new thirst and weight loss.

When to see a doctor

• Any of the infection signs listed above
• You are pregnant and haven’t had a urine test yet
• You have a catheter and develop fever, chills or new pain
• An older family member has new confusion along with fever or bladder symptoms

Get emergency care for a high fever with shaking chills, vomiting, confusion or feeling faint, which can mean infection has spread to the blood.

Common questions about asymptomatic bacteriuria

Is asymptomatic bacteriuria dangerous?

For most people, no. Bacteria in the urine without symptoms rarely lead to a serious infection, and treating them doesn’t lower that small risk. The main exceptions are pregnancy and planned surgery on the urinary tract. In those cases, testing and treatment do prevent problems.

Will asymptomatic bacteriuria go away on its own?

Often, yes. The bacteria may clear without treatment, or one type may be replaced by another over time. In older adults and people with catheters, bacteria may stay for months or years. That is usually fine as long as no signs of infection appear.

Can asymptomatic bacteriuria turn into a UTI?

Sometimes, but not often, and taking antibiotics ahead of time doesn’t prevent it. If you later get burning, urgency, fever, or pain in your back or side, call your doctor. A new urine test can then help choose the right antibiotic for the germ.

What does nitrite in urine mean?

It usually means bacteria are in the urine. Some germs, such as E. coli, turn natural chemicals in urine called nitrates into nitrites, which a dipstick test picks up. A positive result doesn’t prove an infection. If you feel well and aren’t pregnant, it usually doesn’t need antibiotics.

Questions to ask your doctor

• Why was my urine tested?
• Do I need treatment, or is it safe to leave it alone?
• Which symptoms should make me call you?
• If I’m pregnant, will my urine be checked again after treatment?
• Could something other than the urine explain how my parent has been feeling?

Learn more

• Urine culture (MedlinePlus, U.S. National Library of Medicine)
• Urinary tract infection basics (CDC)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.