Diarrhea caused by Clostridium difficile related to antibiotic therapy was discussed previously. Many cases of diarrhea produced by bacterial infection are also part of the spectrum of “food poisoning.” Clostridium botulinum generates a preformed neurotoxin and in adults is associated with improperly canned food. Usually there is no diarrhea. The organism was discussed earlier with the clostridia. Staphylococcus aureus also generates a preformed toxin after it is allowed to grow in certain foods (typically custards, creams, potato salad, and ham, usually when allowed to remain warm). Symptoms most often occur less than 7 hours after ingestion of the food (average, 3 hours) and consist of nausea, vomiting, abdominal cramps, and diarrhea.

Clostridium perfringens occasionally may contaminate food, typically meat or gravy, that has been cooked and then allowed to cool slowly. Symptoms are due to exotoxin formed within the intestine, occur about 12 hours after eating, and consist of simultaneous abdominal cramps and diarrhea without fever or vomiting. Bacillus cereus uncommonly causes food poisoning, usually in fried rice that is kept warm. Bacillus cereus forms an endotoxin that can either be preformed (such as C. botulinum or S. aureus) or produced as the bacteria multiply after being ingested by the patient (such as C. perfringens). Diarrhea without vomiting is the major symptom. Vibrio parahaemolyticus is ingested with raw or poorly cooked fish or shellfish. The organism may invade tissue or may produce an exotoxin. Average onset of symptoms is 12-24 hours after ingestion. Symptoms are vomiting, nausea, cramps, diarrhea, chill, and fever.

Other bacteria associated with diarrhea. Several bacterial species cause infectious diarrhea but are not ordinarily considered to be agents of food poisoning because of their relatively long incubation periods. These include Salmonella, Shigella, Yersinia enterocolitica, Campylobacter fetus ssp. jejuni, E. coli, Vibrio cholerae, and possibly V. parahaemolyticus. Other bacteria less often involved that should be mentioned are Aeromonas hydrophila and Plesiomonas shigelloides. Recent reports suggest the possibility that Bacteroides fragilis may cause diarrhea. Most of the bacteria listed are associated with contaminated water. Several of them, such as E. coli, may be transmitted via contaminated food or water. E. coli may invade tissue or may produce an exotoxin. Symptoms occur 10-12 hours after contact and consist of vomiting, nausea, cramps, diarrhea, chills, and fever. Salmonella or Shigella gastroenteritis is due to tissue infection by the organisms, although Shigella is capable of toxin production. Shigella dysentery symptoms ordinarily occur 36-48 hours after infection, but the time is variable. Salmonella gastroenteritis (due to species other than Salmonella typhi) is most frequently associated with ingestion of poultry, eggs and egg products, powdered milk, and fresh pork. Symptoms most often manifest in 8-48 hours, with an average onset at 24 hours. Symptoms of both Shigella and Salmonella gastroenteritis are similar to those of E. coli. Salmonella dysentery should be differentiated from typhoid and paratyphoid fever, which have considerably longer incubations and different emphasis in symptoms.

Nonbacterial causes of diarrhea. There are other causes for food poisoning that do not involve bacterial agents. Some of these are ingestion of toxins from certain fish (e.g., ciguatera or scombroid fishes) or shellfish, and the Chinese restaurant syndrome (due to excess monosodium glutamate seasoning; however, at least one report disputes this etiology). Other causes for nonbacterial infectious diarrhea include viral infection (especially by rotavirus) and infection by the parasite Giardia lamblia. Ulcerative colitis and other conditions may also have to be considered.

Differential diagnosis. Some differential points include incubation time and presence of fever, vomiting, or diarrhea. Incubation time less than 7 hours without fever suggests S. aureus or ingestion of the preformed toxin of B. cereus. Both of these usually are associated with vomiting, but S. aureus is more likely to cause diarrhea (about 75% of cases) than B. cereus (<40% of cases). Incubation of about 12 hours favors C. perfringens and B. cereus without preformed toxin; in both disorders toxin is formed after the organism is ingested rather than before. Symptoms of both are predominantly abdominal cramps and diarrhea, usually without fever or vomiting. Presence of neurologic symptoms suggests C. botulinum or chemical poisoning (mushrooms or fish toxins).

Laboratory diagnosis. Includes stool culture and culture of possibly contaminated food or water. Diagnosis of C. botulinum or C. difficile infections usually requires demonstration of toxin, which was discussed earlier in the section on clostridia. Gram stain of the stool may be helpful in some patients. Patients with infection by bacteria that invade the mucosa of the GI tract tend to have WBCs in the stools, whereas those whose effect is produced by toxin usually do not. However, this is only a general rule. Many WBCs in the stool are typical of Shigella, Campylobacter, or C. difficile infection, although it also frequently occurs with Salmonella gastroenteritis, E. coli, Y. enterocolitica, or V. parahaemolyticus. Grossly visible blood in the stools is frequently found with Campylobacter, but gross blood may occasionally appear with severe infection by the other enteroinvasive bacteria, and microscopic blood is fairly frequent. Diagnosis of S. aureus or C. perfringens contamination usually necessitates culture of the affected food, since these organisms are considered normal stool flora.

Traveler’s diarrhea. Diarrhea is common among visitors to many third-world countries; although it should be remembered that diarrhea may occur in persons who never leave the United States, and one half or more of the visitors to these countries (especially those on guided tours) do not get diarrhea. Several studies have shown that the most common cause for so-called traveler’s diarrhea in the majority of these countries is a subgroup of E. coli bacteria known as toxigenic E. coli. A much smaller number of persons develop diarrhea because of infection by other bacteria such as Salmonella, Shigella, and cholera vibrios; and by parasites such as Amoeba histolytica and Giardia lamblia. Infection by traveler’s diarrhea bacteria or by parasites most often is caused by use of water containing the organisms or food contaminated by the water.

At present, there are three ways to control diarrhea: take precautions to avoid infection; take medicine to prevent infection (so-called prophylactic medication); or take medicine after diarrhea starts in order to quickly end the diarrhea.

The best way to prevent traveler’s diarrhea is to avoid getting infected. This means avoiding local water unless there is no doubt that the water is safe. It is not advisable to take the word of the local people that the water is safe—it may be safe for them but not for visitors. Travelers must remember that local water may be present in ways they do not suspect; they should avoid ice, cocktails, drinks that need water or ice added, juice made from concentrate, and fresh salads with lettuce or ingredients that could have been washed. When tourists order orange juice they often cannot be certain it is 100% freshly squeezed from the fruit (even if a waiter says it is), so it is better to eat freshly cut fruit than to take a chance with the juice. It is also wise not to eat the outside skin of fruit (such as apples or pears) that could have been washed with local water. Alcohol—even 86 proof—may not sufficiently sterilize contaminated ice or water.

Raw fish or shellfish (such as oysters or clams) can be contaminated by the bacteria that cause cholera. Raw or poorly cooked (“rare”) meat may be contaminated by different or even more dangerous organisms. Nonpasteurized milk is also dangerous, and it is usually hard to be certain whether local milk is pasteurized or not, especially if it is served already poured.

There are ways to find safe water:

1. Canned or bottled juices or colas are usually safe, as are drinks made with hot water (hot coffee, hot tea).
2. Travelers can buy safe bottled water. The easiest and safest to find is mineral water. Mineral water with carbonation is available everywhere and is safe, because the carbonation does not permit bacteria to grow. However, some persons do not like the taste. Mineral water without carbonation (in Spanish, called “sin gas”) can be purchased in most places. This is generally safe if it comes from a sealed bottle, but it is harder to make certain whether the source of the water is pure. In many countries it is possible to purchase mineral water without gas in liter (quart) bottles in supermarkets (in Mexico, it is sold in pharmacies).
3. Travelers can bring water purification tablets with them. There is a choice of chlorine or iodide; iodide is preferred because it will kill the parasite Giardia lamblia, whereas chlorine may not, if the amount of chlorine is not up to full strength. Both will kill bacteria. (Note: City water supplies in some cities of some countries may be chlorinated but not in sufficient strength.)
4. Travelers may bring water purification filter equipment with them. The equipment should have a filter 0.45 microns or smaller hole size in order to be effective against E. coli. One easily portable, easily usable, and relatively inexpensive filtration system I have personally used is called “First Need Water Purifier.” It has a filter life of 800 pints, the filter can be replaced, and the apparatus including filter costs about $45.00. It can be obtained from REI Inc., P.O. Box C-88125, Seattle, WA 98188-0125, or from the manufacturer: General Ecology, Inc., 151 Sheree Blvd, Lionville, PA 19353.
5. Travelers can boil local water. Three minutes boiling time (3 minutes starting from the time vigorous boiling and many large bubbles appear) is safe against bacteria. For locations at high altitudes, 5 minutes boiling time (or even longer at very high altitudes) is necessary.

Travelers can take certain medicines to prevent infection, or before they get diarrhea (“prophylactic medication”). However, most experts do not recommend prophylactic medication, especially antibiotics, because the medicines may produce side effects in a small number of people.

Travelers can take certain medications to stop diarrhea after it starts. Most cases of diarrhea are not life-threatening and will stop without medication in 2-3 days; therefore, some experts do not advise any treatment of mild or moderate diarrhea for the first 48 hours. However, it is not always possible to predict which cases will stop and which will become worse. The most commonly used medications are antidiarrheal preparations and antibiotics. These should not be used simultaneously. Some experts feel that antibiotics should not be used in cases of nausea and vomiting without diarrhea.

Antidiarrheal medications include the following:

1. Bismuth subsalicylate (trade name “Pepto-Bismol”). The dose is 1 ounce (30 ml) every 30 minutes until the diarrhea stops, but no more than 8 doses (8 ounces) within each 24-hour period. Take for 1-2 days.
2. Loperamide (trade name “Imodium”). More experts prefer this medication than bismuth subsalicylate. Loperamide comes in 2-mg capsules. The usual dose is 2 capsules to begin with, then 1 capsule after each additional loose stool, up to a maximum of 8 capsules within each 24-hour period. At present, this is probably the best overall antidiarrheal medication.

Travelers can take antibiotics to stop diarrhea caused by bacterial infection. Antibiotics would help E. coli infections, but would not cure Giardia infections. The most commonly recommended antibiotics are the following:

1. Doxycycline. It is ordered in 100-mg capsules. The dose is one capsule twice a day for a total of 3-5 days. Doxycycline is a tetracycline antibiotic, and children under age 12 years may get very undesirable side effects.
2. Trimethoprim-sulfamethoxazole (trade names “Bactrim” or “Septra”). It is ordered in double-strength tablets containing 160 mg of trimethoprim. The usual dose is one double-strength tablet twice a day for a total of 3-5 days. A few persons are allergic to the sulfa part of this antibiotic combination.
3. Trimethoprim (without sulfa; trade name “Trimpex”). It is ordered in 100 mg tablets. The usual dose is 2 tablets twice each day for a total of 3-5 days. For persons with poor kidney function the dose is less; a physician should be consulted (the same warning is true for Trimethoprim-sulfa).
4. Ciprofloxacin (trade name “Cipro”). This is ordered in 500 mg capsules. The dose is one capsule twice daily for 5 days. Results are reported to be as good as or better than results of Trimethoprim. Do not use in children or in pregnant or nursing women.

Persons who already have severe disease (lung, heart, kidney, etc.) or who get severe diarrhea should see a physician rather than try to treat themselves.