Of the several million people who travel from temperate industrialized countries to tropical regions of Asia, Africa, and Central and South America each year, 20–50% experience a sudden onset of abdominal cramps, anorexia, and watery diarrhea; thus traveler’s diarrhea is the most common travel-related infectious illness (Chap. 6). The time of onset is usually 3 days to 2 weeks after the traveler’s arrival in a resource-poor area; most cases begin within the first 3–5 days. The illness is generally self-limited, lasting 1–5 days. The high rate of diarrhea among travelers to underdeveloped areas is related to the ingestion of contaminated food or water.
The organisms that cause traveler’s diarrhea vary considerably with location (Table 30-3), as does the pattern of antimicrobial resistance. In all areas, enterotoxigenic and enteroaggregative strains of E. coli are the most common isolates from persons with the classic secretory traveler’s diarrhea syndrome. Infection with Campylobacter jejuni is especially common in areas of Asia.
TABLE 30-3CAUSES OF TRAVELER’S DIARRHEA ||Download (.pdf) TABLE 30-3 CAUSES OF TRAVELER’S DIARRHEA
|ETIOLOGIC AGENT ||APPROXIMATE PERCENTAGE OF CASES ||COMMENTS |
|Bacteria ||50–75 || |
|Enterotoxigenic Escherichia coli ||10–45 ||Single most important agent |
|Enteroaggregative E. coli ||5–35 ||Emerging enteric pathogen with worldwide distribution |
|Campylobacter jejuni ||5–25 ||More common in Asia |
|Shigella ||0–15 ||Major cause of dysentery |
|Salmonella ||0–15 || |
|Others ||0–5 ||Including Aeromonas, Plesiomonas, and Vibrio cholerae |
|Viruses ||0–20 || |
|Norovirus ||0–10 ||Associated with cruise ships |
|Rotavirus ||0–5 ||Particularly common among children |
|Parasites ||0–10 || |
|Giardia lamblia ||0–5 ||Affects hikers and campers who drink from freshwater streams |
|Cryptosporidium ||0–5 ||Resistant to chlorine treatment |
|Entamoeba histolytica ||<1 || |
|Cyclospora ||<1 || |
|Other ||0–10 || |
|Acute food poisoninga ||0–5 || |
|No pathogen identified ||10–50 || |
Closed and semi-closed communities, including day-care centers, schools, residential facilities, and cruise ships, are important settings for outbreaks of enteric infections. Norovirus, which is highly contagious and robust in surviving on surfaces, is the most common etiologic agent associated with outbreaks of acute gastroenteritis. Other common organisms, often spread by fecal-oral contact in such communities, are Shigella, C. jejuni, and Cryptosporidium. Rotavirus is rarely a cause of pediatric diarrheal outbreaks in the United States since rotavirus vaccinationwas broadly recommended in 2006. Similarly, hospitals are sites in which enteric infections are concentrated. Diarrhea is one of the most common manifestations of nosocomial infections. C. difficile is the predominant cause of nosocomial diarrhea among adults in the United States, and outbreaks of norovirus infection are common in health care settings. Klebsiella oxytoca has been identified as a cause of antibiotic-associated hemorrhagic colitis. Enteropathogenic E. coli has been associated with outbreaks of diarrhea in nurseries for newborns. One-third of elderly patients in chronic-care institutions develop a significant diarrheal illness each year; more than one-half of these cases are caused by cytotoxin-producing C. difficile. Antimicrobial therapy can predispose to pseudomembranous colitis by altering the normal colonic flora and allowing the multiplication of C. difficile (Chap. 31).
Globally, most morbidity and mortality from enteric pathogens involves children <5 years of age. Breast-fed infants are protected from contaminated food and water and derive some protection from maternal antibodies, but their risk of infection rises dramatically when they begin to eat solid foods. Exposure to rotavirus is universal, with most children experiencing their first infection in the first or second year of life if not vaccinated. Older children and adults are more commonly infected with norovirus. Other organisms with higher attack rates among children than among adults include enterotoxigenic, enteropathogenic, and enterohemorrhagic E. coli; Shigella; C. jejuni; and G. lamblia.
Immunocompromised hosts are at elevated risk of acute and chronic infectious diarrhea. Individuals with defects in cell-mediated immunity (including those with AIDS) are at particularly high risk of invasive enteropathies, including salmonellosis, listeriosis, and cryptosporidiosis. Individuals with hypogammaglobulinemia are at particular risk of C. difficile colitis and giardiasis. Patients with cancer are more likely to develop C. difficile infection as a result of chemotherapy and frequent hospitalizations. Infectious diarrhea can be life-threatening in immunocompromised hosts, with complications including bacteremia and metastatic seeding of infection. Furthermore, dehydration may compromise renal function and increase the toxicity of immunosuppressive drugs.
If the history and the stool examination indicate a noninflammatory etiology of diarrhea and there is evidence of a common-source outbreak, questions concerning the ingestion of specific foods and the time of onset of the diarrhea after a meal can provide clues to the bacterial cause of the illness. Potential causes of bacterial food poisoning are shown in Table 30-4.
TABLE 30-4BACTERIAL FOOD POISONING ||Download (.pdf) TABLE 30-4 BACTERIAL FOOD POISONING
|INCUBATION PERIOD, ORGANISM ||SYMPTOMS ||COMMON FOOD SOURCES |
|1–6 h |
|Staphylococcus aureus ||Nausea, vomiting, diarrhea ||Ham, poultry, potato or egg salad, mayonnaise, cream pastries |
|Bacillus cereus ||Nausea, vomiting, diarrhea ||Fried rice |
|8–16 h |
|Clostridium perfringens ||Abdominal cramps, diarrhea (vomiting rare) ||Beef, poultry, legumes, gravies |
|B. cereus ||Abdominal cramps, diarrhea (vomiting rare) ||Meats, vegetables, dried beans, cereals |
|>16 h |
|Vibrio cholerae ||Watery diarrhea ||Shellfish, water |
|Enterotoxigenic Escherichia coli ||Watery diarrhea ||Salads, cheese, meats, water |
|Enterohemorrhagic E. coli ||Bloody diarrhea ||Ground beef, roast beef, salami, raw milk, raw vegetables, apple juice |
|Salmonella spp. ||Inflammatory diarrhea ||Beef, poultry, eggs, dairy products |
|Campylobacter jejuni ||Inflammatory diarrhea ||Poultry, raw milk |
|Shigella spp. ||Dysentery ||Potato or egg salad, lettuce, raw vegetables |
|Vibrio parahaemolyticus ||Dysentery ||Mollusks, crustaceans |
Bacterial disease caused by an enterotoxin elaborated outside the host, such as that due to Staphylococcus aureus or B. cereus, has the shortest incubation period (1–6 h) and generally lasts <12 h. Most cases of staphylococcal food poisoning are caused by contamination from infected human carriers. Staphylococci can multiply at a wide range of temperatures; thus, if food is left to cool slowly and remains at room temperature after cooking, the organisms will have the opportunity to form enterotoxin. Outbreaks following picnics where potato salad, mayonnaise, and cream pastries have been served offer classic examples of staphylococcal food poisoning. Diarrhea, nausea, vomiting, and abdominal cramping are common, while fever is less so.
B. cereus can produce either a syndrome with a short incubation period—the emetic form, mediated by a staphylococcal type of enterotoxin—or one with a longer incubation period (8–16 h)—the diarrheal form, caused by an enterotoxin resembling E. coli LT, in which diarrhea and abdominal cramps are characteristic but vomiting is uncommon. The emetic form of B. cereus food poisoning is associated with contaminated fried rice; the organism is common in uncooked rice, and its heat-resistant spores survive boiling. If cooked rice is not refrigerated, the spores can germinate and produce toxin. Frying before serving may not destroy the preformed, heat-stable toxin.
Food poisoning due to Clostridium perfringens also has a slightly longer incubation period (8–14 h) and results from the survival of heat-resistant spores in inadequately cooked meat, poultry, or legumes. After ingestion, toxin is produced in the intestinal tract, causing moderately severe abdominal cramps and diarrhea; vomiting is rare, as is fever. The illness is self-limited, rarely lasting >24 h.
Not all food poisoning has a bacterial cause. Nonbacterial agents of short-incubation food poisoning include capsaicin, which is found in hot peppers, and a variety of toxins found in fish and shellfish (Chap. 136).