A PCR Based Assay for the Detection of Diarrheagenic Escherichia coli from Occult Blood Detection Cards in U.S. Travelers to Mexico with Acute Diarrhea

Division of Infectious Diseases, The University of Texas Medical School, Center for Infectious Diseases, The University of Texas School of Public Health, Baylor College of Medicine, Houston, TX, Instituto Nacional de Salud Publica, Cuernavaca, and Universidad Autónoma de Guadalajara, México

^* To whom correspondence should be addressed. Email: Pablo.C.Okhuysen{at} uth.tmc.edu.

	Abstract

Large field studies in travelers' diarrhea (TD) in multiple destinations are limited by the need to perform stool cultures on site in a timely manner. A method for the collection, transport and storage of fecal specimens that does not require immediate processing, refrigeration and is stable for months would be advantageous. The study was designed to determine if enterotoxigenic Escherichia coli (ETEC) and enteroaggregative E. coli (EAEC) DNA could be identified from cards processed for evaluation of fecal occult blood. U.S. students traveling to Mexico during 2005-2007 were followed for occurrence of diarrheal illness. When ill, students provided a stool specimen for culture and occult blood by the standard method. Cards were then stored at room temperature prior to DNA extraction. Fecal PCR was performed to identify ETEC and EAEC in DNA extracted from stools and from occult blood cards. Significantly more EAEC cases were identified by PCR performed on DNA extracted from cards (49%) or from frozen feces (40%) than by culture followed by HEp-2 adherence assays (13%) (P < 0.001). Similarly, more ETEC cases were detected in card DNA (38%) than fecal DNA (30%) or culture followed by hybridization (10%) (P < 0.001). Sensitivity and specificity of the card test was 75% and 62%, when compared to EAEC by culture, and 50% and 63%, when compared to ETEC respectively. DNA extracted from fecal cards used for detection of occult blood is of use in identifying diarrheagenic E. coli.