Frequency of identification of cytotoxigenic strains of Escherichia coli in cases of diarrhea from rural and urban communities.

It has been suggested that strains of Escherichia coli producing Vero-Toxin (VTEC) may cause diarrhea or hemorrhagic colitis; however, there are not enough studies to support this hypothesis. We studied the frequency of isolation of VTEC strains in patients with acute diarrhea from rural and urban communities. A total of 1430 strains were analyzed, 361 coming from 118 patients from the rural community (Cadereyta, Qro.) and 1069 from the urban district (D.F.); 95 of these patients were asymptomatic, 213 suffered from watery diarrhea and 43 had bloody diarrhea. For production of toxins, strains were grown in tryptic soy broth for 24h and the culture supernatant was inoculated on HeLa cells; strains were considered cytotoxic when they caused lysis in at least 50% of the cells. In the rural community, VTEC strains were isolated in 20% of the asymptomatics, in 45% of the watery diarrhea patients and in 76% of patients with bloody diarrhea. Frequency of isolation was significantly higher in patients with diarrhea than in asymptomatics (P less than 0.05). The relative risk to present watery diarrhea was 3 and to present bloody diarrhea was 12. In the urban district, VTEC strains were isolated in 13, 7.9 and 4.5% from asymptomatics, watery diarrhea and bloody diarrhea patients, respectively; the relative risk for diarrhea was 1. Colonization by VTEC strains is significantly higher in patients from the rural community and these infected patients have an important risk to develop diarrhea.