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Bacteriuria without symptoms is present in about 3% of otherwise healthy middle aged women. In nursing homes rates are as high as 50% among women and 40% in men. In those with a long term indwelling urinary catheter rates are 100%. Up to 10% of women have a urinary tract infection in a given year and half of all women have at least one infection at some point in their lives.
Signs and symptoms
Asymptomatic bacteriuria is bacteriuria without accompanying symptoms of a urinary tract infection. It is more common in women, in the elderly, in residents of long-term care facilities, and in people with diabetes, bladder catheters and spinal cord injuries. People with a long-term Foley catheter always show bacteriuria. Chronic asymptomatic bacteriuria occurs in as many as 50% of the population in long-term care.
There is an association between asymptomatic bacteriuria in pregnant women with low birth weight, preterm delivery, and infection of the newborn. However, most of these studies were graded as poor quality. Bacteriuria in pregnancy also increases the risk of preeclampsia.
Testing for bacteriuria is usually performed in people with symptoms of a urinary tract infection. Certain populations which are not able to feel or express symptoms of an infection are also tested when showing nonspecific symptoms. For example, confusion or other changes in behaviour can be a sign of an infection in the elderly. Screening for asymptomatic bacteriuria in pregnancy is common routine in many countries, but controversial.
The gold standard for detecting bacteriuria is a bacterial culture which identifies the actual concentration of bacterial cells in the urine. The culture is usually combined with subsequent MALDI-TOF, which allows to identify the causal bacterial species, and antibiotic susceptibility testing. Urine culture is quantitative and very reliable, but takes at least one day to obtain a result. Therefore clinicians will often treat symptomatic bacteriuria based on the results of the urine dipstick test while waiting for the culture results.
Bacteriuria can usually be detected using a urine dipstick test. The nitrite test detects nitrate-reducing bacteria if growing in high numbers in urine. A negative dipstick test does not exclude bacteriuria, as not all bacteria which can colonise the urinary tract are nitrate-reducing.The leukocyte esterase test indirectly detects the presence of leukocytes (white blood cells) in urine which can be associated with a urinary tract infection. In elderly, the leukocyte esterase test is often positive even in the absence of an infection. The urine dipstick test is readily available and provides fast, but often unreliable results.
Microscopy can also be used to detect bacteriuria. It is rarely used in clinical routine, since it requires more time and equipment and does not allow reliable identification or quantification of the causal bacterial species.
Bacteriuria is assumed if a single bacterial species is isolated in a concentration greater than 100,000 colony forming units per millilitre of urine in clean-catch midstream urine specimens. In urine samples obtained from women, there is a risk for bacterial contamination from the vaginal flora. Therefore, in research, usually a second specimen is analysed to confirm asymptomatic bacteriuria in women. For urine collected via bladder catheterization in men and women, a single urine specimen with greater than 100,000 colony forming units of a single species per millilitre is considered diagnostic. The threshold for women displaying UTI symptoms can be as low as 100 colony forming units of a single species per millilitre. However, bacteria below a threshold of 10000 colony forming units per millilitre are usually reported as "no growth" by clinical laboratories.
The decision to treat bacteriuria depends on the presence of accompany symptoms and comorbidities.
Asymptomatic bacteriuria generally does not require treatment. Exceptions include those undergoing surgery of the urinary tract, children with vesicoureteral reflux or others with structural abnormalities of the urinary tract. In many countries, regional guidelines recommend treatment of pregnant women.
There is no indication to treat asymptomatic bacteriuria in diabetics, renal transplant recipients, and in those with spinal cord injuries.
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