Factors That Explain Excretion of Enteric Pathogens by Persons Without Diarrhea

Abstract

Excretion of enteropathogens by subjects without diarrhea influences our appreciation of the role of these pathogens as etiologic agents. Characteristics of the pathogens and host and environmental factors help explain asymptomatic excretion of diarrheal pathogens by persons without diarrhea. After causing acute diarrhea followed by clinical recovery, some enteropathogens are excreted asymptomatically for many weeks. Thus, in a prevalence survey of persons without diarrhea, some may be excreting pathogens from diarrheal episodes experienced many weeks earlier. Volunteer challenges with Vibrio cholerae O1, enterotoxigenic Escherichia coli (ETEC), enteropathogenic E. coli, Campylobacter jejuni, and Giardia lamblia document heterogeneity among enteropathogen strains, with some inexplicably not eliciting diarrhea. The immune host may not manifest diarrhea following ingestion of a pathogen but may nevertheless asymptomatically excrete. Some human genotypes render them less susceptible to symptomatic or severe diarrheal infection with certain pathogens such as Vibrio cholerae O1 and norovirus. Pathogens in stools of individuals without diarrhea may reflect recent ingestion of inocula too small to cause disease in otherwise susceptible hosts or of animal pathogens (eg, bovine or porcine ETEC) that do not cause human illness.

Quantitative PCR for Detection of Shigella Improves Ascertainment of Shigella Burden in Children with Moderate-to-Severe Diarrhea in Low-Income Countries

“…Among children who were culture positive and had a qPCR result of Ն1.4 ϫ 10 4 ipaH copies, some had diarrhea and some did not. Possible explanations for this observation include genetic differences among the isolates of Shigella, protective polymorphic alleles in some children, differences in the gut microbiota that enhance or decrease a child's probability of disease, or an immune response based on prior exposure of either the mother (via breast milk or transplacentally acquired antibody) or child (19).…”

Identifying Etiological Agents Causing Diarrhea in Low Income Ecuadorian Communities

“…Asymptomatic carriage may be caused by several factors, including strain pathogenicity, host immunity against pathogenic factors, intestinal microbiota, and herd immunity. 5,49,50 Asymptomatic Campylobacter spp. carriage among people living in Latin America countries has been documented since the late 1980s 51 ; specifically, C. coli carriage has been documented among people living or handling with pigs, sheep, or chickens.…”

Association Between Stool Enteropathogen Quantity and Disease in Tanzanian Children Using TaqMan Array Cards: A Nested Case-Control Study

“…2,3 Studies of diarrhea in low-and middleincome countries are complicated by the diversity of required diagnostic methods for enteropathogens as well as high rates of asymptomatic detection. 4,5 Furthermore, in most such studies, the etiology of a large percentage of episodes is not determined, likely because of poor test sensitivity. Nucleic acid amplification tests allow the use of a single highly sensitive diagnostic modality for the detection of a wide range of enteropathogens; however, the increased sensitivity comes at the cost of an increase in the background rate of detection for many pathogens.…”