Gastrointestinal Infections : Defintion, Pathophysiology, Diagnosis, Treatment
Gastrointestinal (GI) infections are among the more common causes of morbidity and mortality around the world. Most are caused by viruses and some are caused by bacteria or other organisms. In underdeveloped and developing countries, acute gastroenteritis involving diarrhea is the leading cause of mortality in infants and children younger than 5 years of age. In the United States, there are approximately 211 million episodes of acute gastroenteritis each year, causing over 900,000 hospitalizations and over 6000 deaths.
- Fluid replacement is the cornerstone of therapy for diarrhea regardless of etiology.
- Initial assessment of fluid loss is essential for rehydration. Weight loss is the most reliable means of determining the extent of water loss. Clinical signs such as changes in skin turgor, sunken eyes, dry mucous membranes, decreased tearing, decreased urine output, altered mentation, and changes in vital signs can be helpful in determining approximate deficits.
- Weight loss of 9% to 10% is considered severe and requires intravenous (IV) fluid replacement with Ringer’s lactate or 0.9% sodium chloride. Intravenous therapy is also indicated in patients with uncontrolled vomiting, the presence of paralytic ileus, stool output greater than 10 mL/kg/h, shock, or loss of consciousness.
- The necessary components of oral rehydration therapy (ORT) solutions include glucose, sodium, potassium, chloride, and water.
- The maintenance phase should not exceed 100 to 150 mL/kg/day and is generally adjusted to equal stool.
- Early refeeding as tolerated is recommended. Age-appropriate diet may be resumed as soon as dehydration is corrected. Early initiation of feeding shortens the course of diarrhea. Initially, easily digested foods, such as bananas, applesauce, and cereal, may be added as tolerated. Foods high in fiber, sodium, and sugar should be avoided.
- The bacterial species most commonly associated with GI infection and infectious diarrhea in the United States are Shigella spp., Salmonella spp., Campylobacter spp., Yersinia spp., Escherichia spp., Clostridium spp., and Staphylococcus spp.
- Antibiotics are not essential in the treatment of most mild diarrheas, and empirical therapy for acute GI infections may result in unnecessary antibiotic courses.
- Most pathology of cholera is thought to result from an enterotoxin that increases cyclic AMP-mediated secretion of chloride ion into the intestinal lumen, which results in isotonic secretion (primarily in the small intestine) exceeding the absorptive capacity of the intestinal tract (primarily the colon).
- The incubation period of V. cholerae is 1 to 3 days.
- Cholera is characterized by a spectrum from the asymptomatic state to the most severe typical cholera syndrome. In the most severe state, this disease can progress to death in a matter of 2 to 4 hours if not treated.
- The mainstay of treatment for cholera consists of fluid and electrolyte replacement with ORT. Rice-based rehydration formulations are the preferred ORT for cholera patients. In patients who cannot tolerate ORT intravenous therapy with Ringer’s lactate can be used.
- Antibiotics shorten the duration of diarrhea, decrease the volume of fluid lost, and shorten the duration of the carrier state . A single dose of oral doxycycline is the preferred agent. In children younger than 7 years of age, trimethoprim-sulfamethoxazole, erythromycin, and furazolidone are preferred.
- Escherichia coli GI disease may be caused by enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), entero- adhesive E. coli (EAEC), and enterohemorrhagic E. coli (EHEC). ETEC is now incriminated as being the most common cause of traveler’s diarrhea.
- ETEC is capable of producing two plasmid-mediated enterotoxins: heat-labile toxin (HLT) and heat-stable toxin (HST). The net effect of either toxin on the mucosa is production of a cholera-like secretory diarrhea.
- Nausea and watery stools, with or without abdominal cramping, are characteristic of the disease caused by ETEC. Most ETEC diarrhea resolves within 24 to 48 hours without complication.
- Most cases respond readily to ORT, and although antibiotic therapy is seldom necessary, prophylaxis has been shown to effectively prevent the development of ETEC diarrhea.
- Fluid and electrolyte replacement should be initiated at the onset of diarrhea.
- Effective prophylactic agents include doxycycline, trimethoprim/ sulfamethoxazole, or a fluoroquinolone.
- Human disease caused by Salmonella generally falls into four categories: acute gastroenteritis (enterocolitis), bacteremia, extraintestinal localized infection, and enteric fever (typhoid and paratyphoid fever), and a chronic carrier state. S. typhimurium is the most common cause of salmonellosis.
- Salmonella enterocolitis occurs secondary to mucosal invasion of microorganisms, but it may involve enterotoxin production or local inflammatory exudates as possible mechanisms of pathology. Organisms may invade beyond the mucosa and enter the mesenteric lymphatics, which then carry bacteria to the general circulation via the thoracic duct. Bacteria not cleared by the reticuloendothelial system may cause metastatic infection in various organs.
- With enterocolitis, patients often complain of nausea and vomiting within 72 hours of ingestion followed by crampy abdominal pain, fever, and diarrhea, although the actual presentation is quite variable.
- Stool cultures inevitably yield the causative organism, if obtained early. However, recovery of organisms continues to decrease with time so that by 3 to 4 weeks, only 5% to 15% of adult patients are passing Salmonella.
- Some patients may continue to shed Salmonella for a year or longer. These â€œchronic carrierâ€ states are rare for serotypes other than S. typhi.
- Salmonella can produce bacteremia without classic enterocolitis or enteric fever. The clinical syndrome is characterized by persistent bacteremia and prolonged intermittent fever with chills. Stool cultures are frequently nega- tive.
- Extraluminal infection and/or abscess formation can occur at any site after any of the other syndromes or may be the primary presentation. Metastatic infections have been reported to involve bone, cysts, heart, kidney, liver, lungs, pericardium, spleen, and tumors.
- Enteric fever caused by S. typhi is called typhoid fever. If caused by any other serotype, it is referred to as paratyphoid fever. The onset of symptoms is gradual. Nonspecific symptoms of fever, dull headache, malaise, anorexia, and myalgias are most common. Initially, fever tends to be remittent but gradually progresses over the first week to temperatures that are often sustained over 104Â°F. Other frequently encountered symptoms include chills, nausea, vomiting, cough, weakness, and sore throat.
- About 80% of patients have positive blood cultures. Bacteremia persists in about one-third of patients for several weeks if not treated. Diagnostic tests other than culture are unreliable.
- Most patients with enterocolitis require no therapeutic intervention. The most important part of therapy for Salmonella enterocolitis is fluid and electrolyte replacement. Antimotility drugs should be avoided since they increase the risk of mucosal invasion and complications.
- Antibiotics have no effect on the duration of fever or diarrhea and their frequent use increases the likelihood of resistance and the duration of fecal shedding. Antibiotics should be used in neonates or infants younger than 6 months, patients with primary or secondary immunodeficiency, severely symptomatic patients with fever and bloody diarrhea, and patients after splenectomy.
- Recommended antibiotics with adult doses include: Fluoroquinolones, Trimethoprim/sulfamethoxazole, Ampicillin,Third-generation cephalosporins
- For bacteremia, life-threatening treatment should include the combination of a third-generation cephalosporin (ceftriaxone 2 g IV daily) and ciprofloxacin 500 mg orally twice daily. The duration of antibiotic therapy is dictated by the site.
- Fluoroquinolones such as ciprofloxacin (500 mg orally twice daily for 10 days in adults) are the drugs of choice for enteric fever, particularly in areas where multidrug resistance is common. A short course of 3 to 5 days is effective but a minimum of 10 days is recommended in severe cases.
- The drug of choice for chronic carriers of Salmonella is norfloxacin, 400 mg orally twice daily for 28 days.
- Vaccines are recommended for high-risk groups. Live oral attenuated vaccine Ty21a and parenteral polysaccharide vaccine have been shown to confer 42% to 77% efficacy for a duration of 3 to 5 years.