Chapter 39: Infectious Gastrointestinal Disorders

Gastroenteritis, characterized by stomach and intestinal inflammation manifesting through anorexia, nausea, vomiting, and diarrhea, typically results from infectious agents transmitted via contaminated food or water through the fecal-oral route. The pathophysiology involves pathogens breaching the gastrointestinal tract's natural defenses including gastric acidity, peristalsis, commensal microbiota, and secretory immunoglobulin A, subsequently increasing fecal water content and disrupting normal bowel patterns. Clinical presentations range from non-inflammatory watery diarrhea to dysentery with blood and mucus, with symptom characteristics helping localize the infection to either the small or large intestine. Diagnosis relies primarily on clinical assessment supplemented by stool studies when severe symptoms warrant investigation, while management centers on oral rehydration therapy with antimotility agents reserved for non-dysenteric cases and antibiotics indicated for traveler's diarrhea or severe infections. Viral hepatitis encompasses five distinct pathogens causing liver inflammation and necrosis through different transmission routes and disease trajectories; hepatitis A and E follow fecal-oral transmission and remain acute, while hepatitis B, C, and D carry substantial chronicity risks potentially progressing to cirrhosis and hepatocellular carcinoma. Recognition of the prodromal, icteric, and convalescent disease phases guides clinical management, with prevention through vaccines for A and B and modern direct-acting antiviral therapies for hepatitis C providing highly effective interventions. Appendicitis results from vermiform appendix obstruction by fecaliths or other materials triggering bacterial overgrowth, mucosal fluid accumulation, vascular compromise, and potential perforation with peritonitis development. The classic clinical presentation features pain migration from periumbilical to right lower quadrant locations within hours, accompanied by constitutional symptoms, with specific physical examination maneuvers including Rovsing's sign, psoas sign, and obturator sign confirming localized peritoneal irritation. Diagnosis integrates clinical findings with supportive laboratory and imaging evidence to exclude alternative diagnoses, while definitive management requires surgical appendectomy preceded by appropriate antimicrobial and fluid resuscitation.