URINARY TRACT INFECTIONS
The diagnosis and management of urinary tract infections (UTI) must be tailored to each patient category. The natural history of UTI in each group must be taken into account before a specimen is submitted for culture and before antibiotics are given.
In the laboratory, specimens are processed and results interpreted according to the patient category and clinical data provided Please give relevant clinical data. frequency dysuria etc. Indicate if screening for bacteriuria e.g. in pregnancy or in an asymptomatic patient with positive dipstick results.
Dipstick tests are best used to help assess the likelihood of infection in a symptomatic patient. Positive leucocyte esterase and bacterial nitrite tests suggest that UTI is likely and that an antibiotic should be prescribed. Negative tests indicate that infection is unlikely but urine should be cultured as false negative dipstick tests do occur.
Dipstick tests are not reliable as a means of screening for UTI in pregnancy and in children.
Specimens which have been found to be positive for protein etc. on routine dipstick testing are sometimes submitted for culture. Please indicate this on the request form "proteinuria: exclude UTI".
When patients are screened for haematuria positive results should be confirmed by microscopy. Please state "haematuria screen" on request form.
See manufacturers data sheet for the limitations of dipstick tests. Specimens must be fresh (not more than two hours old). Boric acid will invalidate some dipstick tests.
The first morning voided urine is a standard specimen for quantitative culture and cell counts. Studies establishing >108 cfu/l as "significant" were based on first morning specimens which lie within a narrow concentration range. Random specimens are acceptable in acute infections if antibiotic treatment is to be started. Boric acid preserves cells and bacteria for up to 48 hours but it is inhibitory to some organisms so containers should not be underfilled and storage times should be minimised.
Voided urine is always contaminated by the commensal flora of the urethra and peri urethral areas. Careful collection of a mid-stream specimen of urine will reduce the degree of contamination. After the first part of the stream of urine is passed, the flow of urine is continued and the "mid-stream " portion is collected in a receptacle and transferred into the transport container.
Plastic universal containers with added Boric acid crystals are provided for the transport of urine specimens. Boric acid prevents overgrowth of organisms, which may result in a false positive culture. Under filled containers will result in a high concentration of Boric acid, which may kill some organisms and result in a false negative culture. Use of Boric acid preserves urine during transport to the laboratory but specimens should ideally be cultured within 24 hours. Boric acid also preserves the cell count. Boric acid does not interfere with pregnancy tests but will invalidate some dipstick tests.
Urinalysis - Flow Cytometry
We currently use particle flow cytometry (FC) to screen urines submitted for suspected urinary tract infection (UTI). This technology has been in use for many years in haematology but is new to microbiology.
Leucocytes: Estimation of WBC by FC is fast, accurate and reproducible. Patients with symptomatic UTI have pyuria, but pyuria without infection may occur in a variety of conditions. Note that nappy material retains cells so nappy specimens are often negative for leucocytes. This may also affect dipstick test results.
Bacteriuria: FC is a sensitive and accurate method for the detection of organisms in urine. Sample that are negative for bacteria by FC are reported on the day of receipt with the comment "Significant bacteriruia not detected by Flow Cytometry". Samples are cultured only when organisms are detected by FC. Since both viable and non-viable organisms are detected by FC some samples with turnout to be negative on culture.
Erythrocytes (RBC): FC is sensitive but accurate only in "clean" specimens free of contaminating epithelial cells, crystals and debris. Contaminated specimens require light microscopy (using a Kova slide) for an accurate RBC count. RBC may be present in an infected urine but an accurate red cell count is not relevant to the diagnosis of UTI. The erythrocyte count will no longer be reported routinely when the request is for "C& S".
If screening for haematuria. Please indicate clearly e.g. "HAEMATURIA SCREEN".
Squamous epithelial cells: Indicate perineal contamination and casts doubt on the validity of a positive culture report. Repeat with a carefully collected specimen.
Quantitation of bacteria in the urine helps to identify true infections. Patients with infection usually have >108 bacteria per litre in an early morning specimen of urine. When a growth of >108 cfu/l is reported the probability of true infection is 95% in symptomatic women so there is a 5% chance that the result is a false positive. A result shouldalways therefore be reviewed in the light of clinical data. A repeat specimen may also help when culture results are inconclusive.
About a third of women with symptomatic UTI will have lower numbers of bacteria in their urine. We will report lower numbers when relevant clinical data are provided.
Follow-up urine culture after two weeks post treatment is recommended.
ADULT NON PREGNANT WOMEN
The prevalence of bacteriuria in this group is 1-3%. Asymptomatic bacteriuria and mild symptomatic infections are often self-limited.
Lower urinary tract infection (cystitis) results in painful urination and frequency with supra pubic heaviness or pain. Fever and backache or flank pain usually indicates involvement of the upper urinary tract (pyelonephritis) but absence of these symptoms does not exclude it.
Culture of urine is not essential but confirmation of infection is useful. If urine culture is negative and especially if pyuria is present consider other causes of dysuria such as chlamydial infection, candida or other vaginitis or atrophic vaginitis in the elderly.
trimethoprim 3 days
NB: Short course therapy is not advocated in pregnancy, in complicated infections, in diabetics, infections lasting over seven days, or if there is a history of antibiotic resistant infections or previous pyelonephritis. The patient must be relied on to return if symptoms recur and follow-up urine culture after symptoms recur. Follow-up urine culture after one week is recommended. Failure to respond to short course therapy is virtually diagnostic of pyelonephritis which should be treated as below
(Pyelonephritis, abnormal host defences i.e. diabetes, urinary tract abnormality)
trimethoprim 7 – 10 days
or ciprofloxacin 500 mg bd 10 days if previous recent antibiotics
If the same infecting organism is isolated at follow-up give a course of a suitable antibiotic for two to six weeks. Consider the possibility of structural abnormalities of the urinary tract.
If more than two to three episodes of UTI occur per year, consider chemoprophylaxis for six months to one year with a single dose at night or post coital-
nitrofurantoin 50- 100 mg
or cephalexin 125 mg
Also consider early self treatment with a short course of a suitable antibiotic.
All pregnant women should be screened for bacteriuria early in pregnancy as 20-40% of pregnant women with asymptomatic bacteriuria will develop acute pyelonephritis later in pregnancy.
Culture is mandatory. Dipstick testing is an inappropriate screening test for asymptomatic bacteruria.
cephalexin 7 days
The prevalence of bacteriuria in adult men is low (0·1% or less) until the later years when infection is associated with prostatic disease. In young men confirmed infection suggests the possibility of anatomic abnormalities of the urinary tract or prostatic infection.
Chlamydial and gonococcal urethritis are also associated with dysuria and frequency. Urine will show pyuria and will be negative on culture.
trimethoprim, 7 days
The prevalence of asymptomatic bacteriuria is high among the elderly. At least 10% of men and 20% of women older than 65 years have bacteriuria, which runs a natural course of clearance and re-infection. Repeated courses of antibiotics do more harm than good and should be avoided unless the infection is symptomatic.
Symptoms of frequency, dysuria, hesitancy and incontinence are not diagnostic of UTI in the elderly. Atrophic vaginitis with overgrowth of coliforms is, for example, a common cause of dysuria in elderly women, which may require appropriate oestrogen therapy rather than a course of antibiotics.
Symptoms of pyelonephritis are likely to be non-specific e.g. confusion, drowsiness and being generally unwell. Suspected pyelonephritis must be treated promptly as it is a common cause of septicaemia in the elderly.
A clean specimen of urine is difficult to obtain in this age group. Evaluate symptoms carefully and repeat culture if result is of dubious significance.
trimethoprim 200 mg bd, 7 days
The intake of cranberry juice has been shown to be useful in suppressing urinary tract infection.
Whenever possible submit two specimens to exclude false positives due to contamination. In children, pyuria may occur in the absence of urinary tract infection. Remember that nappy specimens retain cells so such specimens may be falsely negative for pyuria.
See NICE guidance for management of UTI in children.
A clean catch specimen of urine should be obtained from older children. In infants and young children a bag urine may be collected by the application of a sterile adhesive collection bag. The baby should be sat up and the bag removed as soon as urine is voided in order to prevent contamination of the perineum. Urine may be extracted from nappies. Since the material retains cells, nappy specimens do not give reliable results on microscopy. Urine cannot be extracted from the super absorbent type of nappy. Indicate collection method on request form. Plastic universal containers with added boric acid crystals are provided for the transport of urine specimens with a special 7 ml container for young children. If only very small specimens are available use a sterile universal plastic or glass container.
or cephradine / cephalexin
Sterile pyuria occurs in children during pregnancy. In adults consider chlamydial infection and TB.
CATHETER ASSOCIATED UTI (Longterm Catheters)
Colonisation/infection commonly occurs following longterm catheterisation. Limit the duration of catheterisation whenever possible and consider other forms of bladder function management.
A specimen should only sent if the patient is symptomatic with low abdominal pain or fever. A change in the appearance or smell of urine are not indications for urine culture. When culture is indicated, a fresh specimen should be collected via the catheter and not taken from the collection bag. Culture usually shows a mixed growth. The presence of absence of WBC in the specimen is irrelevant.
Antibiotic treatment is unlikely to eradicate the infection and may lead to the emergence of resistant organisms and yeasts. It should be limited to patients who are clinically unwell. Give a short course of a suitable antibiotic (trimethoprim or ciprofloxacin 5-7 days) changing the catheter under antibiotic cover. A single dose of an antibiotic may also be useful prior to catheter change if the urine is infected e.g. trimethoprim 400 mg or ciprofloxacin 500 mg given 2 hours pre manipulation. Blockage of the catheter will not be resolved by treating infection, occasionally however, specific organisms e.g.Proteus mirabilis may be relevant. Seek advice.
1. Stamm W.E., Hooton T.M. Management of Urinary Tract Infections in Adults. New Eng J Med. 1993; 329: 1328-1334.
2. Kontiokari T., Sundqvist Kaj, Nuutinen M., Pokka T., Koskela M., Uhari M. Randomised trial of cranberry-lingonberry juice andLactobacillus GG drink for the prevention of urinary tract infections in women. BMJ. 2001; 322: 1571-1573.