Approach to the Patient with Suspected Enteric Infection

Definition

Enteric infections are endemic in many low-income countries but may also be contracted from contaminated food or water in developed countries. Symptoms may range from minimal gastrointestinal distress to life-threatening watery diarrhea or dysentery.

Epidemiology

Worldwide, enteric infections are a leading cause of morbidity. In low- and middle-income countries without access to clean water and basic sanitation, young children are disproportionately affected with acute diarrheal illness and suffer sequelae ranging from malnutrition ( Chapter 197 ) and its complications to dehydration and death. Although infrequently fatal in industrialized regions, enteric infections are ubiquitous ailments with pathogens that know no borders because of international travel to and from hyperendemic regions, as well as the globalization of food supplies. Foodborne outbreaks remain common in the United States, where pathogens are distributed widely in produce or other foods. For example, one of the largest outbreaks of Salmonella enteritidis , estimated to involve more than 200,000 people in the United States, resulted from national distribution of contaminated ice cream. For foodborne illnesses traced to retail food establishments, about 40% are due to contamination of food by ill or infectious workers. Fortunately, many outbreaks can be mitigated when pathogens that are isolated from individual patients undergo molecular profiling by public health laboratories linked to the U.S. Centers for Disease Control and Prevention (CDC).

Pathobiology

Enteric infections ultimately reflect the successful interaction of individual pathogens with their human hosts. Pathogens must overcome innate and acquired host defenses while competing with the normal human microbiota to colonize intestinal epithelia. Once established, pathogens may then elaborate toxins or produce virulence factors that promote adhesion and invasion.

Not all hosts are equally susceptible to enteric infections. The use of acid-blocking agents, such as proton pump inhibitors, impairs an important first line of host defense by decreasing gastric acidity, thereby reducing the effective inocula required for bacterial pathogens. Recent prior or concurrent use of antibiotics can alter the normal intestinal microflora, thereby reducing its ability to impair the growth of newly introduced pathogens. Host genetics can also play critical roles in determining the outcome of infection. For instance, Vibrio cholerae infections ( Chapter 278 ) tend to be most severe in individuals with O blood group, likely due to more efficient intoxication of O enterocytes with cholera toxin. In contrast, enterotoxigenic E. coli infections ( Chapter 280 ) appear to be more severe in individuals who express the A blood group antigen on intestinal epithelia, likely due to an A-specific lectin expressed by these bacteria.

Some pathogens, particularly norovirus ( Chapter 350 ), Shigella ( Chapter 285 ), and Shiga toxin–producing E. coli ( Chapter 280 ), typically require very low inocula to establish infection. This characteristic has contributed to numerous outbreaks of norovirus on cruise ships and a multitude of foodborne outbreaks of Shiga toxin–producing E. coli ( Chapter 280 ).