Edward H. Kass

Pyelonephritis and related infections of the urinary tract are among the most frequently encountered, most frequently undiagnosed, and most difficult to manage of all infections. The lack of clear views of the pathogenesis, diagnosis, and treatment of infections of the urinary tract is well recognized.^1-3 A few selected data indicate the magnitude of the problem. 1. Pyelonephritis is the commonest disease of the kidneys at autopsy. Active pyelonephritis has been found in 10% to 20% of autopsies in several general hospitals,^4-6and healed pyelonephritis occurs about as frequently as does active pyelonephritis.⁶ 2. Pyelonephritis has been implicated, with varying degrees of evidence, in such disorders as hypertension, chronic renal insufficiency, toxemias of pregnancy, various disturbances in electrolyte metabolism, diabetes mellitus, pregnancy, and stone formation. 3. Despite the importance of this group of diseases the diagnosis of infection of the urinary tract is made in only about 20%

Pulmonary clearance of bacteria was studied using histologic, bacteriologic, and radiotracer methods. When mice were exposed to an aerosol of P(32)-tagged Staphylococcus aureus or Proteus mirabilis, and the rate of disappearance of viable bacteria compared with the rate of their mechanical removal, it was found that bacterial viability declined 80 to 90 per cent in 4 hours, whereas radioactivity declined by only 14 to 20 per cent. The marked disparity in these rates indicated that mechanical removal comprised a relatively small fraction of the total clearing process. The in situ bactericidal action of the lung predominated over the mechanical removal process in achieving clearance of the inhaled bacteria. By immunofluorescent methods, the inhaled bacteria were found to be localized in the alveolar spaces and within alveolar macrophages. These observations suggest that the bactericidal action of the bronchopulmonary tree is due primarily to the phagocytic activity of the alveolar macrophages, and that the action of the mucociliary stream, in relation to bacterial particles, may be largely related to the transport from the lung of phagocytes containing material of bacterial origin.

The interpretation of bacterial cultures of the urine has been greatly aided by the use of quantitative methods. Analysis of the bacterial colony counts of urines obtained from large numbers of patients has indicated that, except for certain defined clinical circumstances,1a colony count greater than 100,000 per milliliter of freshly obtained urine generally indicates the presence of true bacteriuria, that is, of actual multiplication of bacteria within the urinary tract. Conversely, bacterial colony counts less than 100,000 usually represent contamination attendant upon the collection of the specimen.2,3 The validity of this approach has been amply confirmed,4-6despite some earlier and relatively minor disagreements that have since been largely resolved.7The quantitative approach has been of value not only in defining the presence or absence of infection of the urinary tract in the usual clinical setting, but also it has provided a means for determining the presence of asymptomatic infection