key questions answered. Managing UTIs
Dr Peter Whelan advises on managing a problem that commonly presents in primary care
How should UTIs be diagnosed?
A definitive diagnosis is made with the presence of significant bacteruria, the definition of which still remains somewhat controversial. The traditional standard for significant bacteria is >105uropathogens/ml on a voided MSU. This standard has remained for four decades, but several recent studies have shown it to be frequently insensitive in acutely symptomatic women, and a more sensitive definition is >102uropathogens/ ml, which gives a sensitivity of 95 per cent and a specificity of 85 per cent for those diagnosed with acute cystitis.
The Infectious Disease Society of America consensus definition of cystitis used in antimicrobial treatment studies has been a slightly greater concentration of 103uropathogens/ml, which gives a sensitivity of 80 per cent and specificity of 90 per cent, as these concentrations can be identified by the standard microbiological techniques used in most clinical laboratories. This is not generally accepted, however, and some UK laboratories still adhere to the greater than 105 definition.
Antibiotic treatment in patients with a good clinical history is still a sensible clinical decision, even if a subsequent MSU is negative for bacteria. Nitrates are helpful when accompanied by leucocytes on a dipstick test as a ready guide, but no more than that.
Is the empirical use of antibiotics justified in practice?
In a review of trials evaluating short-term treatment of uncomplicated cystitis in women, Norrby concluded that three-day regimes or longer were more efficient than a single dose or single-day regimes. Trimethoprim on its own or trimethoprim and sulfamethoxazole, and ß-lactams were more effective in this regime, although the ß-lactams, amoxicillin and first-generation cephalosporins are thought to have poorer efficacies in short-course regimes because they are in high concentrations in the urine for short periods of time only.
Here is an argument that has two sides to it: given that the majority of patients do well on the standard three to five-day courses, there are still cases where a full seven-day course would be appropriate. Partial responses appear to be related to lack of duration of the appropriate antibiotic in some cases, rather than necessarily exposing partial resistance.
It is also important to know the effects of the antimicrobial on both the faecal and vaginal flora as this may influence long-term cure.
Increasingly, strains of Escherichia coli are becoming resistant to the simpler antibiotics; more than 20 per cent of coliform strains have shown resistance, which is why the long-term agent nitrofurantoin (a drug used for several decades) needs to be given as a seven-day course. Comparatively it has much less resistance and is a good second-line drug, leaving the quinolones, which still retain a very high sensitivity rate (over 90 per cent), to be used for difficult or recurring infections.
Why do so many UTIs seem to recur?
Careful studies have demonstrated that as many as 55 per cent of apparently confined bladder infections are in fact associated with organisms in the upper tracts. This may well explain why recurrences frequently occur within a week of cessation of antibiotics. Similarly, short courses of inadequate antibiotics such as ß-lactams may only suppress rather than eliminate all of the organisms, thus leading to a rapid recurrence of the infection. It is important to identify this problem and to treat it with a longer course of antibiotics rather than subjecting patients to further investigation, which is likely to be of limited value.
These cases, however, need to be differentiated from persistently recurrent infections in which further evaluation for potential functional or anatomical abnormalities is important. More than three episodes a year is a useful rule of thumb for referral to exclude functional or anatomical abnormalities.
Peter Whelan is a consultant urologist at St James's University Hospital in Leeds, an FRCS urology examiner and president-elect of the European Board of Urology