Asymptomatic bacteriuria is the presence of bacteria in a voided urine sample and is caused by bacterial colonization of the urinary tract. It affects about 5 to 10 percent of both sexually active and pregnant women. Asymptomatic bacteriuria is less prevalent in men.

As the name indicates, asymptomatic bacteriuria does not cause symptoms. The condition simply refers to the detection of bacteria in a urine sample. Nonetheless, there is good reason to be concerned about this infection, particularly if you are pregnant, because it can lead to a symptomatic upper urinary tract infection (namely, pyelonephritis), which can complicate pregnancy.

Bacteria are typically introduced into the urinary tract during intercourse or when wiping after a bowel movement. The bacterium E. coli is responsible for at least 75 to 80 percent of asymptomatic bacteriuria. Klebsiella pneumoniae, Proteus species, staphylococcal species, enterococci, and group B streptococci can also establish colonization.

Because asymptomatic bacteriuria does not cause symptoms, it is important to know what increases your risk of infection. By being aware, you can help avoid the consequences of untreated asymptomatic bacteriuria by early detection and treatment. Researchers have identified a number of risk factors, which include:

  • sickle cell trait or sickle cell disease;
  • diabetes;
  • immunosuppressive disorders;
  • urinary tract obstructions (from stones);
  • loss of bladder control (due to neuromuscular disease); and
  • need for chronic instrumentation of the bladder (self-catherization).

If you have or might have any of these conditions, you are at risk for asymptomatic bacteriuria. You should talk to your doctor immediately.

In non-pregnant women, asymptomatic bacteriuria rarely causes serious problems. However, in pregnant women this infection can progress upward, causing acute urethritis, acute cystitis, and acute pyelonephritis (kidney infection). Pyelonephritis, in turn, can lead to adverse outcomes such as preterm labor, which is the most common cause of serious complications-including death-in newborn babies. A kidney infection can also lead to sepsis (pathogenic organisms or toxins invading the blood or tissue) and adult respiratory distress syndrome (ARDS)-both can be life threatening. Approximately 25 to 30 percent of asymptomatic bacteriuria cases in pregnancy will progress to symptomatic infection, three to four times as great a progression as in non-pregnant women.

Since patients with this condition are by definition without symptoms, a positive urine culture is the only means of diagnosis. If you are pregnant or have other risk factors for asymptomatic bacteriuria, you should have a midstream ?clean catch? urine sample cultured (grown in a lab) to identify the type and number of bacteria present.

Because pregnant women with asymptomatic bacteriuria have a 25 to 30 percent risk of progressing to acute pyelonephritis, pregnant women with bacteria in their urine, even without symptoms, should be treated to reduce this risk. A short course of oral antibiotics is usually sufficient. If this is your first infection, your doctor will probably prescribe a three-day treatment program. For recurrent infections, your doctor will probably prescribe a seven- to ten-day course of antibiotics.

Typical antibiotics used for treatment include sulfisoxazole (Gantrisin), ampicillin (Principen) or amoxicillin (Amoxil), cephalexin (Keflex), nitrofurantoin (Macrodantin), and trimethoprim-sulfamethoxazole (Bactrim). Quinolone antibiotics (ciprofloxacin, Cipro) are often used to treat urinary infections in non-pregnant women, but are not used frequently in pregnancy due to safety concerns for the developing fetus. Many studies have compared different antibiotic regimens and shown them to be equally effective in treating asymptomatic bacteriuria.

Once you have completed your treatment program, visit your doctor again to check for reinfection. If you are pregnant, you will have another urine culture done one week after taking antibiotics to make sure the bacteria were killed. If that culture is negative, you should be screened for reinfection periodically until your baby is born.

Antibiotics To Treat Asymptomatic Bacteriuria

DrugOral Dose*Relative CostRemarks
Sulfisoxazole (Gantrisin)2 grams initially, then 1 gram 4 times dailyLowestshould not be used near the time of delivery; may aggravate neonatal jaundice
Trimethoprim-sulfamethoxazole double strength (Bactrim-DS, Septra-DS)One twice dailyLowshould not be used near the time of delivery; may aggravate neonatal jaundice
Nitrofurantoin monohydrate macrocrystals (Macrobid)100 mg twice dailyIntermediateshould not be used in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency; may cause hemolysis
Cephalexin (Keflex)500 mg twice dailyIntermediate to Highuse with caution if allergic to penicillin
Ampicillin or amoxicillin250-500 mg four times dailyLowmay cause diarrhea, monilia vulvovaginitis, and allergic reaction; many strains of uropathogens are now resistant; should only be used if enterococcus is the cause of infection
Amoxicillin-clavulanate (Augmentin)875 mg twice dailyHighshould be used for recurrent infections caused by resistant organisms
Quinolone antibiotics (ciprofloxacin, Cipro)500 mg twice dailyHighshould be used for recurrent infections caused by resistant organisms; should not be used in pregnancy

*Drug dosages may vary; your doctor will prescribe what is right for you.