Biology and pathology of urinary tract infections.

The normal urinary tract is resistant to colonisation by bacteria.' Presence of significant bacteriuria (> 105 bacteria/ml) is, however, not necessarily indicative of an infection of the urinary tract with serious consequences to the host. In fact, urinary tract infections (UTI) should be regarded as a group of infectious diseases of varying clinical severity and prognosis and therefore they demand different levels of priority-that is, for treatment, investigation, including radiology and follow-up. In patients with obstructive malformation UTI is always potentially dangerous and surgical procedures or other radical measures may be required. This review concentrates on the main group of patients with UTI-that is, those without obstructions of the urine flow, or other obvious underlying defects. In school screening programmes the prevalence of significant bacteriuria is around I % in girls.2 3 4 About 3% of all girls will have had at least one symptomatic infection before the age of 10 years.2 The figures for adult women are similar. In males UTI is less common, but a high frequency is found during the first years of life.2 There are two main problems associated with UTI: the first is quantitative. A very large proportion of bacterial infections in our society can be ascribed to UTI. Although the majority of infections are undramatic, a large population suffers from recurrent symptomatic UTI and this makes considerable demands on medical resources. The second problem concerns complications, in that some of these patients suffer renal parenchymal reduction resulting in renal insufficiency and hypertension. The classical radiological sign of renal damage caused by pyelonephritis is calyceal deformity with reduction of the corresponding parenchyma.5 In the epidemiological studies of Winberg et al.2 such changes were found in 5 % of 440 girls followed from their first symptomatic UTI. In a group of 156 boys