Pyelonephritis and bacteriuria. A major problem in preventive medicine.

THE CHANGING PATTERN of infectious disease is well illustrated in the problem of pyelonephritis. In the past, clinically important infections were due largely to microorganisms that were "caught," that is, were not indigenous to the host. Socioeconomic patterns played important roles in determining the prevalence and pathogenesis of such infections. Now, increasing numbers of infections are due to Gramnegative rods, staphylococci, enterococci, and similar microorganisms that are not "caught" in the usual sense of the word, but are constantly present within the host. The presence of such organisms, and their capacity to cause clinical disease, seem to be influenced less by specific socioeconomic circumstances than by subtle changes in the equilibrium between host and parasite. The very fact that this equilibrium is constantly operative and constantly subject to change makes it especially likely that autochthonous organisms will be associated with chronic infections as well as with acute symptomatic disturbances. The nature of chronic disease presupposes that