Three patients whose bacteriuria was detected early in pregnancy were autopsied after death from causes unrelated to renal infection. Two had characteristic gross and microscopic renal lesions of pyelonephritis. One remained asymptomatic during three years of continuous bacteriuria; the other developed one episode of mildly symptomatic pyelonephritis shortly after bacteriuria was detected. The third patient had no evidence of pyelonephritis at autopsy despite latent diabetes mellitus and history of urinary tract instrumentation. Thus, relatively asymptomatic or minimally symptomatic bacteriuria may be associated with substantial renal scarring and with lesions of chronic inactive pyelonephritis. Conversely, bacteriuria may persist in a patient who has history of urinary tract instrumentation and latent diabetes mellitus and not produce renal lesions.
Thrupp LD, Cotran RS, Kass EH. Relationship of Bacteriuria in Pregnancy to Pyelonephritis. JAMA. 1964;189(12):899–902. doi:10.1001/jama.1964.03070120021005