Asymptomatic Bacteriuria occurs in about 5% of woman and is important in pregnancy where, untreated, 20-30% of cases will develop acute pyelonephritis. Bacteriuria in pregnancy is also associated with premature birth, low birth weight and increased perinatal mortality. It is therefore important that all women have their urine cultured early in pregnancy. Those with positive cultures must be treated (with a safe and effective agent such as nitrofurantoin or a cephalosporin) and follow-up cultures obtained to ensure clearance.
In catheterised patients the incidence of UTI is about 1-5% per catheterisation and about 50% at 4-7 days post catheterisation with modern closed systems. The potential entry points for infection are:
a. urethral meatus around catheter
b. junction between catheter and connection tube
c. sample port
d. reflux from bag to tubing
e. drainage outlet
UTIs in catheterised patients should only be treated if patients have systemic features. Whenever possible the catheter should be removed before treatment. Where indicated, use antibiotics determined by susceptibility testing. Do not use prophylaxis in catheterised patients as this generally leads to the emergence of resistance. A catheter/catheterisation policy should address the basic issues, including the following points to reduce catheter- associated UTIs:
i. Only catheterise when absolutely necessary
ii. Remove catheter as soon as possible
iii. Use intermittent rather than continuous catheterisation
iv. Insert catheter with good aseptic technique
v. Use closed sterile drainage system
vi. Ensure urine drains by gravity to avoid reflux
Bacteriuria is more common in both children and the elderly. The prevalence of UTI
in infants is about 1-2%, (higher in pre-term babies) being more common in boys during the first three months and thereafter more common in girls. In pre-school children the prevalence of bacteriuria in girls is about 4.5% and 0.5% in boys. Many of these infections will be symptomatic but some will be clinically silent.
Identifying UTIs in children is difficult and it is recommended that all febrile illnesses in children without localising features should be investigated for the possibility of UTI. The importance of bacteriuria in young children is that it may lead to renal infection and scarring. Vesico-ureteric reflux is found in 30-50% of children with symptomatic or asymptomatic bacteriuria and it is therefore important that children with UTIs are carefully investigated for underlying abnormalities.
At least 10% of men and 20% of women over 65 years have bacteriuria. Reasons for this increase include obstruction with poor emptying (prostatic enlargement in men, uterine prolapse in women), loss of antibacterial secretions, faecal incontinence, neuromuscular disorders and increased instrumentation/catherisation.
Whilst it is important to identify and treat UTIs in children, screening for asymptomatic infections has not been shown to be cost-effective. In elderly patients there is no evidence that asymptomatic bacteriuria increases morbidity or mortality. There is, therefore, no value in routine screening in such patients. It follows that routine treatment for asymptomatic bacteriuria in elderly patients is not indicated.
Haematogenous infection of the kidneys is well recognised with Staph. aureus. Despite the contribution of Gram-negative bacteria to pyelonephritis, it is thought that this generally occurs by the ascending route rather than by the blood stream, although bacteraemia may then result from the infected focus. Candida infection may also spread to the kidneys by the blood stream as may Salmonella typhi and Mycobacterium tuberculosis. The parasite Schistosoma haematobium causes infection with haematuria in parts of Africa and the Middle East.
Staphylococcal and salmonella infections require investigation by blood and urine cultures. Salmonella serology has limited clinical value and is generally no longer performed. Candida may be cultured from urine and/or blood. Mycobacterial infection of the urinary tract is generally diagnosed by culture of multiple early morning urines. Microscopy for acid-fast bacilli is of limited value because non-pathogenic mycobacteria may give false/positive results. Schistosomes are detected by microscopy of the spun deposit of the terminal portion of an early morning urine. Serology may become positive a few weeks after the clinical onset.