Syndromic Diagnosis
Three major diarrhea syndromes exist. They are acute watery diarrhea, which results in varying degrees of dehydration; persistent diarrhea, which lasts 14 days or longer, manifested by malabsorption, nutrient losses, and wasting; and bloody diarrhea, which is a sign of the intestinal damage caused by inflammation. The three are physiologically different and require specific management. Syndromic diagnosis provides important clues to optimal management and is both programmatically and epidemiologically relevant.
Acute watery diarrhea can be rapidly dehydrating, with stool losses of 250 milliliters per kilogram per day or more, a quantity that quickly exceeds total plasma and interstitial fluid volumes and is incompatible with life unless fluid therapy can keep up with losses. Such dramatic dehydration is usually due to rotavirus, enterotoxigenic E. coli, or V. cholerae (the cause of cholera), and it is most dangerous in the very young.
Persistent diarrhea is typically associated with malnutrition, either preceding or resulting from the illness itself (Ochoa, Salazar-Lindo, and Cleary 2004). Even though persistent diarrhea accounts for a small percentage of the total number of diarrhea episodes, it is associated with a disproportionately increased risk of death. In India, persistent diarrhea accounted for 5 percent of episodes but 14 percent of deaths, and a mortality rate three times higher than briefer episodes (Bhan and others 1989). In Pakistan, persistent diarrhea accounted for 8 to 18 percent of episodes but 54 percent of deaths (Khan and others 1993). In Bangladesh, persistent diarrhea associated with malnutrition was responsible for nearly half of diarrhea deaths, and the relative risk for death among infants with persistent diarrhea and severe malnutrition was 17 times greater than for those with mild malnutrition (Fauveau and others 1992). Persistent diarrhea occurs more often during an episode of bloody diarrhea than an episode of watery diarrhea, and the mortality rate when bloody diarrhea progresses to persistent diarrhea is 10 times greater than for bloody diarrhea without persistent diarrhea. HIV infection is another risk factor for persistent diarrhea in both adults and children (Keusch and others 1992). Management focuses on overcoming the nutritional alterations initiated by persistent diarrhea.
Bloody diarrhea, defined as diarrhea with visible or microscopic blood in the stool, is associated with intestinal damage and nutritional deterioration,often with secondary sepsis.Some dehydration—rarely severe—is common, as is fever. Clinicians often use the term bloody diarrhea interchangeably with dysentery; however,dysentery is a syndrome consisting of the frequent passage of characteristic, small-volume, bloody mucoid stools; abdominal cramps; and tenesmus, a severe pain that accompanies straining to pass stool. Those features show the severity of the inflammation. Agents that cause bloody diarrhea or dysentery can also provoke a form of diarrhea that clinically is not bloody diarrhea, although mucosal damage and inflammation are present, and fecal blood and white blood cells are usually detectable by microscopy. The release of host-derived cytokines causes fever, altering host metabolism and leading to the breakdown of body stores of protein, carbohydrate, and fat and the loss of nitrogen and other nutrients. Those losses must be replenished during convalescence, which takes much longer than the illness does to develop. For these reasons, bloody diarrhea calls for management strategies that are markedly different than those for watery or persistent diarrhea. New bouts of infection that occur before complete restoration of nutrient stores can initiate a downward spiral of nutritional status terminating in fatal protein-energy malnutrition (Keusch 2003).
