Travelers' Diarrhea in Thailand: A Quantitative Analysis Using TaqMan® Array Card

Abstract

Background: Travelers' diarrhea (TD) is a common illness experienced by travelers from developed countries who visit developing countries. Recent questionnaire-based surveillance studies showed that approximately 6%-16% of travelers experienced TD while visiting Thailand; however, a majority of TD information was limited mainly to US military populations.

Methods: A TD surveillance study was conducted at Bumrungrad International Hospital in 2012-2014 in Bangkok, Thailand. Enteropathogens were identified using conventional methods and the TaqMan® array card (TAC), which uses real-time polymerase chain reaction for the simultaneous detection of multiple pathogens. Analyses to determine pathogen-disease and symptoms association were performed to elucidate the clinical relevance of each enteropathogen.

Results: TAC identified more pathogens per sample than conventional methods. Campylobacter spp. were the most prevalent, followed by the diarrheagenic Escherichia coli and norovirus GII. These agents had significant pathogen-disease associations as well as high attributable fractions among diarrheal cases. A wide range of pathogen loads for Campylobacter spp. was associated with TD, while heat-labile toxin enterotoxigenic Escherichia coli was associated with an increased pathogen load. Most cases were associated with inflammatory diarrhea, while Campylobacter spp. and Shigella spp. were associated with dysentery.

Conclusions: A pan-molecular diagnostic method such as TAC produces quantifiable and comparable results of all tested pathogens, thereby reducing the variability associated with multiple conventional methods. This allows better determination of the clinical relevance of each diarrhea etiologic agent, as well as their geographical relevance in Thailand.

Figure 1.

Pathogen load and disease association. Positive threshold cycle (Ct) values (<35) were stratified into 4 groups as indicated on the x-axis and analyzed with binary logistic regression using negative results (Ct >35) as the reference group for each pathogen. *A statistically significant odds ratio at respective Ct cycles. Abbreviations: B. fragilis, Bacteroides fragilis; Ct, threshold cycle; EAEC, enteroaggregative Escherichia coli; EIEC, enteroinvasive E. coli; EPEC, enteropathogenic E. coli; ETEC, enterotoxigenic E. coli; LT, heat-labile toxin; ST, heat-stable toxin; STEC, Shiga toxin-producing E. coli.

Figure 2.

Associations between clinical symptoms, stool characteristics, and pathogen, as determined by conventional and TaqMan® array card methods. *A statistically significant odds ratio of each pathogen with respect to clinical symptoms and stool characteristics. Abbreviations: Conv., conventional; EAEC, enteroaggregative Escherichia coli; EIEC, enteroinvasive E. coli; EPEC, enteropathogenic E. coli; ETEC, enterotoxigenic E. coli; LT, heat-labile toxin; RBC, red blood cell; ST, heat-stable toxin; STEC, Shiga toxin-producing E. coli; TAC, TaqMan® array card; WBC, white blood cell.