Enteric Infections and Food Poisoning
Acute infections of the gastrointestinal tract are among the most frequent of all illnesses, exceeded only by respiratory tract infections such as the common cold. Diarrhea is the most common manifestation of these infections; however, because it is usually self-limiting within hours or days, most of those afflicted do not seek medical care. Nonetheless, in the United States, gastrointestinal infection remains one of the three most common syndromes seen by physicians who practice general medicine. Worldwide, diarrheal disease remains one of the most important causes of morbidity and mortality among infants and children. It has been estimated that in Asia, Africa, and Latin America, depending on socioeconomic and nutritional factors, a child’s chance of dying of a diarrheal illness before the age of 7 years can be as high as 50%. In developed countries, mortality is very much lower, but it is still significant.
The most prominent clinical features of gastrointestinal infections are fever, vomiting, ab-dominal pain, and diarrhea. Their presence varies with different diseases and different stages of infection. The occurrence of diarrhea is a central feature, and its presence and nature form the basis for classification of gastrointestinal infections into three major syn-dromes: watery diarrhea, dysentery, and enteric fever.
The most common form of gastrointestinal infection is the rapid development of fre-quent intestinal evacuations of a more or less fluid character known as diarrhea (derived from the Greek “dia,” for “through,” and “rhein,” meaning to flow like a stream). Nau-sea, vomiting, fever, and abdominal pain may also be present, but the dominant feature is intestinal fluid loss. Diarrhea is produced by pathogenic mechanisms that attack the proximal small intestine, the portion of the bowel in which more than 90% of physio-logic net fluid absorption occurs. The purest form of watery diarrhea is that produced by enterotoxin-secreting bacteria such as Vibrio cholerae and enterotoxigenic Escherichiacoli (ETEC), which cause fluid loss without cellular injury. Other common pathogensthat damage the epithelium, such as rotaviruses, also cause fluid loss, but are more likely to cause fever and vomiting as well. Most cases of watery diarrhea run an acute but brief (1 to 3 days) self-limiting course. Exceptions are those caused by V. cholerae, which usually produces a more severe illness, and those caused by Giardia lamblia, which pro-duces a watery diarrhea that may last for weeks.
Dysentery begins with the rapid onset of frequent intestinal evacuations, but the stools are of smaller volume than in watery diarrhea and contain blood and pus. If watery diarrhea is the “runs,” dysentery is the “squirts.” Fever, abdominal pain, cramps, and tenesmus are frequent complaints. Vomiting occurs less often. The focus of pathology is the colon. Or-ganisms causing dysentery can produce inflammatory and/or destructive changes in the colonic mucosa either by direct invasion or by production of cytotoxins. This damage produces the pus and blood seen in the stools but does not result in substantial fluid loss because the absorptive and secretory capacity of the colon is much less than that of the small bowel. Dysenteric infections generally last longer than the common watery diar-rheas, but most cases still resolve spontaneously in 2 to 7 days.
Enteric fever is a systemic infection, the origin and focus of which are the gastrointestinal tract. The most prominent features are fever and abdominal pain, which develop gradually over a few days in contrast to the abrupt onset of the other syndromes. Diarrhea is usually present but may be mild and not appear until later in the course of the illness. The patho-genesis of enteric fever is more complex than that of watery diarrhea or dysentery. It generally involves penetration by the organism of the cells of the distal small bowel with subsequent spread outside the bowel to the biliary tract, liver, mesentery, or reticuloen-dothelial organs. Bacteremia is common, occasionally causing metastatic infection in other organs. Typhoid fever caused by Salmonella enterica serotype Typhi is the only in-fection for which these events have been well studied. Although it is usually self-limiting, enteric fever carries a significant risk of serious disease and significant mortality.