LONG-TERM SHEDDING AND CLONAL TURNOVER OF ENTEROHEMORRHAGIC ESCHERICHIA-COLI O157 IN DIARRHEAL DISEASES

To investigate the length of time that Shiga-like toxin-producing Esch erichia coli O157 is excreted after the onset of diarrhea, 456 serial stool specimens were obtained from 53 children, E, coli O157 cells wer e identified by the use of DNA probes followed by agglutination with a specific antiserum, Specimens were collected until three consecutive stool samples (collected within 9 days) were negative for E, coli O157 , The median durations of shedding were 13 days (range, 2 to 62 days) in patients with diarrhea or hemorrhagic colitis and 21 days (range, 5 to 124 days) in patients that developed hemolytic uremic syndrome, In 36 (68%) of the patients, only the first culture was O157 positive, a nd the three cultures that followed were negative, In 7 (13%) of the p atients, E, coli O157 cells were shed for more than 32 days after the onset of diarrhea; these long-term shedders were clinically asymptomat ic by the end of this period. In 12 patients, one or two serial O157-n egative cultures, obtained up to 8 days after a positive culture, were followed by another positive culture, Comparison of the first and las t E, coil O157 isolates by pulsed-field gel electrophoresis revealed t hat in three of the seven long-term shedders, pulsed-field gel electro phoresis types varied. In two cases, a Shiga-like toxin gene was appar ently lost during infection, The observation of long-term shedding acc ompanied by genotypic turnover has epidemiological and diagnostic impl ications.