Asymptomatic bacteriuria occurs when bacteria is present in a voided urine sample. It’s caused by bacterial colonization of the urinary tract.

A urinary tract infection (UTI) causes symptoms such as frequent urination, painful urination, or pelvic pain. But asymptomatic bacteriuria doesn’t cause any noticeable symptoms. The condition simply refers to the detection of a high number of bacteria in a urine sample.

Nonetheless, there’s good reason to be concerned about this infection, particularly if you’re pregnant. It can lead to a symptomatic upper UTI (namely, pyelonephritis). Pyelonephritis is a type of kidney infection that can lead to complications during pregnancy.

Asymptomatic bacteriuria affects 1 to 5 percent of healthy premenopausal women and 1.9 to 9.5 percent of pregnant women. Asymptomatic bacteriuria is less prevalent in men.

Bacteria are typically introduced into the urinary tract during intercourse or when wiping after a bowel movement. The bacterium E. coli is responsible for most cases of asymptomatic bacteriuria.

Other bacterial species can also cause colonization, including:

  • Klebsiella pneumoniae
  • Proteus mirabilis
  • Pseudomonas aeruginosa
  • Staphylococcal species
  • Enterococcus species
  • Group B streptococci

Because asymptomatic bacteriuria doesn’t cause symptoms, it’s important to know what increases your risk of infection. You can avoid the consequences of untreated asymptomatic bacteriuria through early detection and treatment.

Researchers have identified a number of risk factors, including:

If you have or might have any of these medical concerns or conditions, you may be at risk for asymptomatic bacteriuria.

In nonpregnant women, asymptomatic bacteriuria rarely causes serious problems. However, in pregnant women this infection can progress upward, causing acute urethritis, acute cystitis, and acute pyelonephritis.

Bacteriuria can lead to adverse pregnancy outcomes such as low birth weight and preterm labor. Preterm labor is the most common cause of serious complications — including death — in newborn babies.

According to the World Health Organization (WHO), up to 45 percent of pregnant women with untreated asymptomatic bacteriuria will develop pyelonephritis.

A kidney infection can also lead to acute respiratory distress syndrome (ARDS) or sepsis. Sepsis occurs when pathogenic organisms or toxins invade the blood or tissue. Both can be life-threatening.

Since people with this condition are by definition without symptoms, a positive urine culture is the only means of diagnosis.

If you’re pregnant, your doctor will likely perform a screening. Pregnant women should be screened early in their pregnancies, between the 12th and 16th weeks.

The doctor will have you provide a midstream clean-catch urine sample. This sample will then be sent to a lab to be cultured. This sample can help your doctor identify the type and number of bacteria present.

The lab uses a measurement called colony-forming units per milliliter (CFU/mL) to count the number of bacteria present in your urine sample. In the case of asymptomatic bacteriuria, a positive urine sample is defined as at least 100,000 CFU/mL.

If your urine sample is positive and you have no symptoms of a UTI, you can be diagnosed with asymptomatic bacteriuria.

Diagnostic criteria vary between men and women, and more specifically, pregnant women. Non-pregnant women must provide two consecutive positive samples of the same bacterial species before receiving a diagnosis of asymptomatic bacteriuria.

Most doctors will treat a pregnant woman with one urine sample collection that shows adequate bacterial growth. Men and people with a catheter inserted need only to provide one positive sample.

Bacterial infections are usually treated with antibiotics. However, non-pregnant individuals with asymptomatic bacteriuria generally don’t require treatment. This is because no ill effects are present, and the bacteria may clear spontaneously over time.

Taking antibiotics can also disrupt the normal balance of bacteria in your body. Additionally, overprescription of antibiotics can promote the emergence of antibiotic-resistant bacterial strains.

However, antibiotic treatment of asymptomatic bacteriuria is recommended for the following groups:

  • pregnant women
  • people who’ll be undergoing a procedure involving their urinary tract or prostate
  • people who’ll be receiving a kidney transplant

People in the above groups should be screened for asymptomatic bacteriuria so that treatment can begin promptly if the condition is identified.

A short course of oral antibiotics is usually sufficient for treatment. Your doctor will probably prescribe a seven- to ten-day course of antibiotics. You should be sure to finish your entire course of antibiotics as directed by your doctor.

Many studies have compared different antibiotic regimens and shown them to be equally effective at treating asymptomatic bacteriuria. Your doctor will most likely receive a report with your urine culture that shows the most effective antibiotics for your specific bacteria.

Antibiotics that are typically used to treat pregnant women with the condition include:

Your doctor will be sure to prescribe an antibiotic that’s considered safe for use during pregnancy. Some antibiotics, such as ciprofloxacin (Cipro), are often used to treat urinary infections in nonpregnant women, but aren’t used frequently in pregnancy due to safety concerns for the developing fetus.

Once you’ve completed your treatment program, you’ll visit your doctor again to check for resolution.

After taking antibiotics, pregnant women will have another urine culture done to make sure the bacteria were killed. If that culture is negative, they may be screened for reinfection periodically until they give birth.

You can help to prevent bacterial colonization of your urinary tract by following these guidelines:

  • Drink plenty of fluids. Aim to drink several glasses of water each day. This can help flush bacteria out of your urinary tract.
  • Wipe front to back after a bowel movement. Wiping from back to front can introduce bacteria from a woman’s bowels into her urinary tract.
  • Urinate shortly after having sex. This helps to flush any bacteria out of your urinary tract.
  • Drink cranberry juice. Although studies aren’t conclusive, cranberry juice may slow or prevent bacterial growth in your urinary tract.

Asymptomatic bacteriuria is typically a benign condition in most people. However, it puts pregnant women at increased risk for infections such as pyelonephritis. As a result, it also increases the risk of preterm labor and other complications.

Pregnant women should be screened early on and, if the condition is present, treated with a short course of antibiotics.

See a doctor if you eventually develop symptoms, including frequent urination, pelvic pain, or other indicators of a UTI.