In developing countries of the world, infectious diarrhea kills about 4 million people per year. In the United States, it is esti-mated that children younger than 5 years of age experience more than 20 million episodes of diarrheal diseases each year, with about 400 deaths per year attributed to such episodes. Dehydra-tion is the most important factor for the morbidity and mortality associated with diarrheal disease. Dehydration is largely control-lable by using rehydration therapy (Guerrant & Steiner, 2000).
The portal of entry of all diarrheal pathogens is oral ingestion. Although the food we eat is far from sterile, the high acidity of the stomach and the antibody-producing cells of the small bowel generally serve to decrease the potential of pathogens. If the num-ber of organisms is large enough, or if the food neutralizes the acidic environment, infection can occur. Decreased gastric acidity with disruption of normal bowel flora (as occurs after surgery), use of antimicrobial agents, and the immune dysfunction of AIDS all decrease intestinal defenses.
There are many viral, bacterial, and parasitic causes for diarrheal diseases. Rotavirus is the most significant viral cause of diarrhea in young children. Common causes of bacterial infection in-clude Escherichia coli and Salmonella, Shigella, Campylobacter, and Yersinia species. Parasitic infections of importance include Giardia and Cryptosporidium species and Entamoeba histolytica.
E. coli is the most common aerobic organism colonizing the largebowel. When E. coli organisms are cultured from fecal specimens, the results seldom suggest pathology, but rather reflect normal flora. However, certain strains of E. coli with increased virulence (ie, degree of pathogenicity of an organism) have been responsible for significant outbreaks in recent years. These stronger patho-logic strains are subgrouped as enterotoxigenic E. coli (ETEC) be-cause of their production of enterotoxins. ETEC strains often cause cholera-like disease, with rapid, severe dehydration and an increased risk of death.
Recent outbreaks of an E. coli species, 0157:H7, have often been linked to the ingestion of undercooked beef. This bacterium lives in the intestines of cattle and can be introduced into meat at the time of slaughter. Prevention of disease from this strain of E. coli is aimed at teaching the public to cook ground beef thor-oughly (ie, until the meat is no longer pink and the juices run clear).
Salmonella is a gram-negative bacillus with many species, includ-ing the very pathogenic Salmonella typhi (ie, typhoid fever). Of the nontyphi species, most organisms are prevalent in animal food sources. It is estimated that Salmonella species contaminate more than 50% of commercially available chicken products and are fre-quently found in eggs (intact and with broken shells), in raw milk, and occasionally in beef (Crump et al., 2002). Approxi-mately 40% of the deaths caused by Salmonellaoccur in nursing home residents. The high mortality rate reflects the seriousness of the infection in the elderly, who often have weakened immune systems (CDC, 2000a).
There is great variability of symptoms associated with Salmo-nella species infection, including an asymptomatic carrier state,gastroenteritis, and systemic infection. Diarrhea with gastro-enteritis is common. Disseminated disease and bacteremia, whether accompanied by diarrhea or not, is less common.
The person with Salmonella-caused diarrhea can be a source for transmission to others. The importance of good hygiene should be emphasized, and health care workers should use special care when handling bedpans, stool specimens, or other objects that may have fecal contamination. Hand washing is imperative after any con-tact with a person with Salmonella diarrhea. Patients with gastro-enteritis generally are not treated with antibiotics because antibiotic use may increase the period of time that the patient carries the bac-teria while not improving the clinical outcome. However, those with systemic salmonellosis require antimicrobial therapy.
The Shigella species is a gram-negative organism that invades the lumen of the intestine and causes disease and severe watery (possibly bloody) diarrhea. Shigella species spread through the fecal-oral route, with easy transmission from one person to another. Small numbers of organisms are needed to cause disease. Because transmission occurs easily with improper hygiene, it is not sur-prising that Shigella organisms disproportionately affect pediatric populations. Disease in the very young may infrequently be com-plicated by pulmonary or neurologic symptoms.
Antimicrobial therapy should be instituted early. Frequently, initial therapy choices must be altered when final microbiologic testing reveals the organism’s sensitivity.
In the United States, diarrheal disease attributed to Campylobacter species surpasses that recorded for Salmonella and Shigella species. The organism is found abundantly in animal food sources. It is especially common in poultry but can also be found in beef and pork. Transmission appears to be almost entirely by the fecal-oral route, with food sources representing the reservoir of organism. Direct person-to-person transmission appears to be less common than for other enteric pathogens, such as Shigella.
Cooking and storing food at appropriate temperatures pro-tects against Campylobacter. It is important that kitchen utensils used in meat preparation be kept away from other food to prevent Campylobacter transmission.
After a person is infected, the organism directly attacks the lumen of the intestine and may cause disease through enterotoxin release. Symptoms can range from mild abdominal cramping and minimal diarrhea to severe disease with profuse watery bloody di-arrhea and debilitating abdominal cramping. Antimicrobial ther-apy is recommended only for those who are seriously ill.
Giardia lamblia is a protozoan. Transmission occurs when foodor drink is contaminated with viable cysts of the organism. People often become infected while traveling to endemic areas in in-dustrialized and nonindustrialized countries of the world or by drinking contaminated water from mountain streams within the United States. The organism can be transmitted by close contact, as occurs in day care settings. Transmission by sexual contact has also been documented.
Frequently, the infection goes unnoticed. Infection is often recognized more easily in children than in adults. In extreme cases, the patient may experience abdominal pain and chronic di-arrhea, usually described as containing mucus and fat but not blood. Microscopic examination of stool specimens reveals the trophozoite or cyst stages of the parasitic life cycle.
Metronidazole (Flagyl) is commonly used to treat Giardia, but success rates for this and alternative therapies are inconsistent. Patients with Giardia infections should be instructed that the or-ganism can be easily transmitted in family or group settings. Per-sonal hygiene measures should be reinforced, and those who travel or camp where water is not treated and filtered should be ad-vised to avoid local water supplies unless water is purified before drinking or used in cooking.
Although reported cases of cholera have been rare in the United States in recent decades, no discussion of infectious diarrhea is complete without mention of this very serious infectious disease. Historically, epidemics of cholera have influenced all aspects of life—from medical to political—and infection rates have been significant enough to destroy governments and armies. Cholera is always a concern when wars or natural disasters result in inad-equately processed wastewater. Vibrio cholera also may be found naturally in brackish rivers and coastal waters.
The V. cholera organism is a gram-negative organism with sev-eral different serotypes. The type usually associated with epidemics is toxigenic V. cholera 01. The organism is transmitted by contam-inated food or water. Most recent cases in the United States have been from contaminated shellfish found in the Gulf of Mexico or by visitors who have brought contaminated shellfish into the United States.
Cholera causes disease with a very rapid onset of copious di-arrhea in which up to 1 L of fluid per hour can be lost. Dehydra-tion, with subsequent cardiopulmonary collapse may cause rapid progression from onset of signs and symptoms to death. The principal therapy is rehydration. Rehydration efforts should be vigorous and sustained. If oral rehydration cannot be accom-plished, the patient should be hospitalized for intravenous ther-apy support.
In the United States, cholera should be suspected in patients who have watery diarrhea after eating shellfish harvested from the Gulf of Mexico. Confirmation of the causative organism can be made by stool culture. It is imperative that all cases are reported to local and state public health authorities. People traveling to areas where cholera occurs regularly should remember the simple rule of thumb: “boil it, cook it, peel it, or forget it”.
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